Fishing For Trout in Warming Waters

Fishing for Trout in Warming Waters - Science-Based Angling Thresholds  

This article was written by Jamie Madden, who recently earned her Master’s degree from Carleton University in Ottawa, Canada, co-advised by Dr. Steven Cooke and Dr. Andy Danylchuk. Her research focuses on recreational fishing and best practices for freshwater fishes.

This is a great example of how we use science to derive best practices for catch-and-release fishing.

Background

It’s that time of year when thermometer graphics show up on social media alerting anglers to be more cautious when targeting trout as water temperatures increase.  Many of the graphics point to 68°F/20°C as a cutoff for when we should stop fishing for trout, but rarely are there details presented as to how that number was derived.  Where is this number coming from, anyway?  Does it cover all species?  How about when a trout is first fought – physiologically stressed - on the end of a line?

Depending on species, fish can have a large or small range of water temperatures that they can generally tolerate.  Science is often conducted to determine optimal temperatures for growth and feeding, and the outcomes can provide insights into changes in fish behavior and their reactions to warming global temperatures.  One major caveat here is that many of these studies test the effects of water temperature without the additional stresses that are related to angling.  So, while the preferred or optimal temperature range of a trout may be appropriate for most of its life, the higher end of that range may present challenges during and in recovery from an angling event.  

Fish undergo exhaustive exercise during angling causing their demand for oxygen to increase.  In warmer temperatures, dissolved oxygen may be harder to come by, which can be one factor increasing mortality if the fish is released.  In addition to exhaustion, air exposure time in warmer temperatures can result in increased lethal and sublethal (i.e. longer recovery times, reflex impairment, higher stress and lactate levels) effects compared to similar times in cool water (see this study and this study).

This brings us back to the 68°F/20°C angling cutoff that gets shared.  Does it fail to take into consideration the activity requirements of a fish being angled?  Where is the scientific evidence behind this number?

With that, I was worried that the information being offered to anglers may be over-generalizing at best, and inaccurate at worst.  Trout anglers should and do care a lot about the wellbeing of the fish they release, and many carry a thermometer to check the water temperature.  State agencies and angling organizations are also starting to promote Hoot Owl regulations to pause trout fishing when water temperatures exceed a certain temperature. 

This growing level of awareness is great, however the decisions we make as anglers should be driven by scientific evidence so that we trust that our actions are indeed making a difference.  It is this uncertainly that prompted my deep dive into the published scientific studies to see how much we know about how different species of trout respond to being angled at warmer water temperatures.  My findings may surprise you.

What I did

Specifically, using Google Scholar I conducted a thorough review of the scientific literature to find research that combined temperature tolerance and exercise for rainbow trout, cutthroat trout, brook trout, brown trout, bull trout, and steelhead. After screening, I extracted all relevant information from each study, including species, location, continuous or constant temperature, type of study (field or lab), angled or exercised, primary variables studied, temperature range, sample size, holding method, mortality percentage, and sublethal effects.

Pooling all the data points from the studies, I produced graphs comparting mortality rates and water temperatures for each species.  When there was enough data, the angling threshold was selected for when mortality began to rise exponentially, usually around 5-10%.  The angling threshold indicates a tipping point for fish — it’s when water temperatures begins to be critical as evidenced by the rapid increase in mortality with every degree increase in water temperature.

The scientific papers are linked here.

What I found

There are varying levels of research done on temperature tolerance during and after angling or exhaustive exercise for the 6 species in this literature review. Notably, research for brown trout and bull trout is severely lacking. I attempted nonetheless to determine an angling threshold from comparisons with similar species, though more research is needed to confirm or adjust this range. Here are the main takeaways from the review:

• Although there are slight differences among thermal tolerances of steelhead, rainbow, brook, and cutthroat trout, the angling thresholds (the temperature that indicates the beginning of an exponential rise in mortality) are lower than the 68°F/20°C commonly shared.

• I found that the angling threshold is around 61°F /16°C for steelhead, rainbow, brook, and cutthroat trout. This number was determined from a combined 24 mortality studies and 9 sublethal impact studies and keeps temperature-based mortality under 5-10%.

• Brown trout are known to withstand slightly warmer temperatures. With the data available (4 mortality studies and 1 sublethal effects study), I suggest an angling threshold of 66°F/ 19°C*.

• Comparatively, bull trout occupy a significantly colder niche than the other species examined. Combining the mortality results from one 2020 study with sublethal data and feeding temperature ranges, I suggest an angling threshold of 54°F/12°C* for bull trout.

*This is our best guess from the limited current literature combined with known life history information of this species. More research is needed to confirm or adjust this number.

Take home message

• Cynically, the temperature stopping point for fishing is a bit like a “choose your own ending” novel with the outcome being “choose your preferred mortality rate”.  Instead, I’ve presented the concept of an angling threshold — a temperature at which mortality begins to increase exponentially (usually going above 5-10% just from temperature) and at which anglers need to start being exceedingly aware of every interaction they have with fish. Some anglers may also decide that this is when they want to stop fishing.   

• The results of my literature review suggest the angling threshold of 68°F/20°C is too high for all the species I researched.

• I encourage anglers to be more conservative and start being aware of the impacts of temperature of fish much earlier, specifically at 61°F /16°C for rainbow, steelhead, cutthroat, and brook trout, 66°F/ 19°C for brown trout, and 54°F/12°C for bull trout.

• While the Keep Fish Wet Principles are always relevant, specific catch-and-release best practices are ever-evolving. Undoubtedly, we need more purposeful research with the aim to determine or confirm species-specific best practices on water temperature, especially for brown trout and bull trout.  There also needs to be much more research on the effects of water temperature, angling induced exercise, and other elements of the angling event, such as air exposure, since the potential impacts from angling are cumulative. For now, I encourage anglers to pay attention to the fish in their hands, be observant, be conservative when the science is behind, and be advocates for the use of current science-based best practices when targeting trout.

Barotrauma in freshwater fishes

­Barotrauma: not just an issue for saltwater fishes

This article was written by Jamie Madden, who recently earned her master’s degree from Carleton University in Ottawa, co-advised by Dr. Steven Cooke and Dr. Andy Danylchuk. Her research focuses on recreational fishing and best practices for retention and barotrauma in freshwater fish.

Have you ever brought a fish up from depth and noticed its eyes bulging, its stomach coming out of its mouth, or it being especially bloated?  These are the tell-tale symptoms of barotrauma, and something we commonly think of happening to marine species like red snapper as they are hauled up from depth.  However, did you know that the same physics can cause barotrauma in freshwater fishes?  Did you also know that sometimes fish may be impacted by barotrauma but not have any of the dramatic tell-tale signs?  Knowing about what causes barotrauma, how to detect it, and how to alleviate the impacts are especially important when releasing fish. ­

From Brown et al. 2009 (https://doi.org/10.1577/T08-122.1)

Barotrauma primarily affects fish that don’t have a connection between their swim bladder and esophagus – these fish are termed physoclistous. Compared with physostomous fish that have a connection (like trout or catfish) and can “burp” out air to empty their swim bladder, physoclistous fish rely on diffusion and resorption of gasses to adjust their buoyancy, which is a much slower process.  When physoclistous fish are caught in relatively deep water and pulled to the surface, the rapid decrease in pressure causes all the air in their body to expand, most notably the air in their swim bladder. In turn, the expansion causes internal displacement, which can be seen through the classic symptoms ofbulging eyes and protruding stomachs.

A fish with barotrauma.

Barotrauma research and media has focused heavily on marine species (see here or here), including research into ways to mitigate the impacts.  Typical mitigation methods include many variations of descending devices, usually containing a weight that attaches to the fish and a secondary line. These devices can be as simple as a weighted hook, or as complicated as a clamp which releases at a preset depth. Many saltwater anglers even keep a simple weighted milk crate on board to lower fish back down to depths. Alternatively, the practice of using a hollow needle to puncture the swim bladder and release air (called venting or fizzing) is a popular, though controversial practice.

Much less research has been done on freshwater systems, species, and mitigation despite that any physoclistous fish that resides in even somewhat deep water can be affected by barotrauma, and widely targeted tournament fish like walleye and smallmouth bass are no exception. Further complicating things is the fact that barotrauma vulnerability can change in a species depending on the time of year, with changing seasons and temperatures prompting fish to move into deeper habitat. Like marine species, freshwater fish are equally subject to bloating and organ protrusion, but may also experience barotrauma with less obvious external cues. Most reliably, the expansion of the swim bladder makes them buoyant, causing them to float on the surface of the water and struggle to descend back to depth after release. Even this symptom, however, may not be obvious. Fish may seemingly swim off into the deep once released, only to pop back up to the surface when they fail to overcome their positive buoyancy a while later.

With little research done on freshwater mitigation techniques, we designed a study to shed light on barotrauma incidences in freshwater and determine how anglers can best deal with these situations. Our study tested the above listed mitigation techniques on walleye with barotrauma in Northern Ontario.

The SeaQualizer descending device in action. From https://seaqualizer.com/technology/

Venting of a fish suffering from barotrauma.

What did we do?

• Monitored barotrauma incidence in walleye caught from different depths and after holding them in livewells for 30 minutes

• Tested the effectiveness of four different barotrauma mitigation techniques for returning walleye with barotrauma to depth.

• Mitigation methods included Fishsaverpro weighed hook, SeaQualizer pressure release clamp, weighted milk crate, venting.

• Used biologgers to monitor fish depth and behaviour for 10 minutes after release to see if they recovered from the barotrauma.

What did we find?

• Fish exhibited barotrauma symptoms in water as shallow as 7.5m / 25ft.

• Time spent at surface exacerbated barotrauma symptoms (holding fish in a livewell = more and worse symptoms)

• The SeaQualizer pressure-release clamp was not effective in freshwater, releasing fish much higher than the set depth and failing to alleviate their buoyancy. The simple weighted hook and weighted crate technique equally had 13% failure rates.

• Venting reliably allowed fish to return to depth.

• The orientation of fish once returned to depth was influenced by mitigation technique: fish were found upside down 92% of the time after being descended in the crate, 62% after the weighted hook, 33% of the time after the SeaQualizer, 20% of the time after venting.

 What does all this mean?

Barotrauma happens in freshwater fish. It should be avoided by anglers by 1) limiting deep water fishing when not harvesting, and 2) being prepared with mitigation methods in situations where it can occur. Research is ongoing regarding best practices on venting vs descending, and our study found advantages of venting both in reliability and condition of the fish (orientation) after release. That said, venting should only be attempted by informed anglers. If unsure, descend fish using a simple weighted hook.

Milkfish Myth Busted

We busted the MYTH that milkfish don’t produce lactic acid as the reason why they fight for so long

This post was created in collaboration with the Alphonse Fishing Company, Blue Safari, and Alphonse Foundation and a similar post can be found here.  The study was conducted thanks to a grant from the Alphonse Foundation, Alphonse Fishing Company, and Blue Safari, and in partnership with the Island Conservation Society, University of Massachusetts Amherst, and Carleton University.

Dr. Andy Danylchuk, Dr. Luke Griffin, Dr. Steven Cooke, Dr. Michael Lawrence, and Sascha Clark Danylchuk 

Every few months there is a post in social media remarking that milkfish (Chanos chanos) can fight for so long on the end of a fly rod because they do not produce lactic acid.  Sometimes it’s even attributed to their diet, which mainly consists of algae.  Lactic acid is a byproduct of anerobic muscle activity and is what causes muscles to cramp up after strenuous exercise, ultimately making them harder to use (like when exerting yourself during a long running race).  This is a common physiological response in vertebrates (and has nothing to do with diet), so, as scientists, we were always quite perplexed by the notion that milkfish may somehow be an exception.  In general, understanding how fish physiologically respond to capture and handling is important, and a great step towards developing science-based best practices for catch-and-release.  

Brian Chakanyuka photo

Thanks to the request for us to lead the project and a grant from the Alphonse Foundation, Alphonse Fishing Company, and Blue Safari, we recently partnered up with this team and the Island Conservation Society, University of Massaschusetts Amherst, and Carleton University  in the Seychelles to see if milkfish produce and build up lactic acid as they fight.  Lactic acid ends up in the blood as lactate (as a means to metabolize or get rid of it), and is something that we are able to measure in the field.

Brian Chakanyuka photo

With the weather gods looking out for us and with ample milkfish working the foam lines of the outgoing tides just offshore of the reef crest of St. Francois Atoll, and dropping off the flats inside the lagoon, our collective team of guides and anglers managed to fight and land enough milkfish across a range of fight times to test this hypothesis.  Using non-lethal blood sampling after the milkfish were landed, along with portable blood lactate meters, we tested the blood for the concentration of lactate.

Brian Chakanyuka photo

And, what we can safely say is, the myth is busted.  Milkfish produce lactic acid and blood lactate and the concentrations of it increased with fight time.  However, what we discovered is that for fight times greater than an hour, blood lactate in some fish started to decrease.  This is not something we typically see in other fish species.  Why this happens is still a bit of a mystery, but it could be because of milkfish’s ability to move a TON of water over their gills, helping them begin to recover from the burst swimming earlier in the fight — i.e. these fish might be so efficient at respiring (“breathing”) that they can start to recover while they are still fighting.  

Brian Chakanyuka photo

Final Words

What this short study showed is that milkfish do build up lactic acid and blood lactate as they fight on the end of a fishing line.  Given that it did increase within the first hour, and that higher blood lactate levels can impair muscle activity and the potential for milkfish to get back to feeding on foam lines and avoid predators, we suggest that a species-specific best practices for milkfish would to be to keep fight times to less than 20-30 minutes.  Until the rest of the capture and handling data is analyzed, we also encourage that anglers continue to follow Keep Fish Wet Principles and Tips. 

Barbless Hooks

The Importance of Barbless Hooks

This post was created in collaboration with Fulling Mill and a similar version appears in their blog here.

Barbless hooks have been around for years. However, as catch and release angling has surged in popularity, so too has demand for these hooks. You might be asking yourself, what’s the big deal? After all, you can just crimp the barbs on your other hooks.

 Here’s the thing: when you crimp the barb on a barbed hook you remove the one thing meant to keep the fish on, the barb. Barbless hooks—on the other hand—are engineered to have excellent fish holding power without the barb there in the first place. 

The History of Barbless

So, barbless hooks. Where did it all start? According to Fulling Mill Technical Manager Steve Carew, Fulling Mill has been selling barbless hooks for 25 years or more. He says “the initial designs were introduced due to the increase in catch and release fishing. They were exact barbless copies of the successful barbed hooks that we sold and used in our fly production. I have to say, though, that these hooks were a resounding flop. The initial production batch were quickly discontinued, and it took us many years to sell through the stock.”

 However, the story doesn’t end there. Steve continues, “around 2011 we saw that competition style fly fishing on rivers was really gaining in popularity and the top teams were using manufactured barbless hooks from Eastern Europe. So, we decided to launch a range of barbless flies and initially we used the hooks from Eastern Europe to tie them. We discovered all sorts of quality issues with these hooks, so after a serious sales job on the then owner of Fulling Mill, he was convinced to invest once again in getting barbless hooks manufactured. This time, however, the hooks were not just straight barbless copies of barbed designs. The rest is history. The fly range and the hooks were a huge success, and they continue to be a core part of Fulling Mill’s fly and hook offering.”

What Makes Barbless Hooks Unique?

Barbless hooks are specially engineered to hold hooked fish just as well as their barbed counterparts. According to Fulling Mill Technical Manager Eric Kelley, when you remove the barb on a hook “you need to look elsewhere within the design to see what can add holding power to that hook model.”

As an example of this, he says “a popular method is extending the hook point to give the angler better leverage to hold a fish more securely. You can mess with the angle of the bend as well to increase holding power and leverage applied. Basically, a whole mess of things can be tweaked in the hook shape to get what you’re ultimately after. Its why hook development is so fun.”

The Fulling Mill Barbless Range 

When we introduced our second round of barbless hooks, they were an immediate success. According to Eric, “We released a handful of models all at once to better suit the needs and wants of anglers who kept asking for barbless hooks. The Grab Gape, Jig Force, Heavy Weight Champ and Czech Nymph hooks were the original forerunners. That was a decade ago and immediately after their release, anglers and tyers kept knocking on the door for more.”

While there is still demand for barbed hooks in some applications, with the spotlight being shown on the competition scene, more and more people are now starting to realize that barbless hooks aren’t what they used to be decades ago quality wise. More and more anglers are making the change.

The Benefit of Barbless Hooks for Catch-and-Release

Hooks are one of the more well studied aspects of catch and release angling and the resounding consensus is that barbless hooks are better for fish than barbed hooks.   There are three main reasons why barbless hooks help create better outcomes for each fish you release.  

Less Injury and Bleeding

Barbless hooks cause less injury and bleeding.  Studies on species as wide ranging as trout, bass, and triggerfish have shown the there is less bleeding and injury associated with barbless hooks.  Most of the injury from barbed hooks is a result of the unhooking process.  This study found that barbless hooks significantly reduced moderate or severe injury.  This can become increasingly important when a fish is hooked in sensitive areas (gills, throat, gut, or foul-hooked) where bleeding is more likely to occur.    

Easier and Faster to remove

Second, barbless hooks are easier and faster to remove.  Based on research on a wide range of freshwater and marine fish, using barbless hooks tends to reduce handing time by half.  This is important because the longer your handle a fish the more stressful it is for them (see Principle 3 for more info).  A study on Rock Bass in Lake Erie found that barbless hooks were faster and easier to remove and also reduced the duration of air exposure fish experienced by 50%. 

Less Mortality

There are a number of studies that have shown that barbless hooks reduce mortality of fish after they are released.   In this meta-analysis (a statistical analysis that combines the results of multiple scientific studies), the authors found that in some studies barbless hooks decreased mortality.  Overall, the authors found that in the studies they examined the average mortality rate for barbed hooks was 14.6% and for barbless hooks was 8.2%.  They hypothesized that it was often either or a combination of both of the first two reasons (less injury and bleeding, and faster unhooking) that led to decreased mortality for fish caught with barbless hooks. 

Barbless hooks, in particular those designed as barbless as opposed to barbed hooks that have been crimped, lead to advantages for anglers and fish alike.  Each time you catch a fish, it’s an opportunity to put conservation into action by using best practices — barbless hooks is the perfect place to start.     

Stripers In Our Hands

Words by Kyle Schaefer. Artwork by Bri Dostie.

This piece is part of a collaboration between Confluence Collective, Soulfly Outfitter, and Keep Fish Wet. More info and artwork can be found here and here.

One of the redeemable qualities about striped bass is that, when they are plentiful, these fish are incredibly accessible.  We fish for them on foot in downtown Boston, from quiet beaches in Rhode Island, in the brackish water of the Chesapeake Bay, and by boat all the way from North Carolina to Maine.  In fact, data from 2017 shows that almost 18 million angler fishing trips were taken in pursuit of stripers.  That impressive number represents 9% of the total angler fishing trips taken across the entire country (NOAA - Source).  

If you’re a striped bass angler, you likely know that the population is in trouble.  Striper populations are currently at a 25 year low and the age structure is out of whack.  If our fisheries managers at the Atlantic States Marine Fisheries Commission (ASMFC) don’t correct the trajectory, we all stand to lose this iconic resource.  ASMFC is in the midst of trying to adjust their own mismanagement of the striped bass stock and rebuild the population through a new plan.  Anglers aren’t particularly confident in ASMFC, and with good reason, the commission’s track record is less than stellar.  I share this context to simply set the stage.  I’ll halt right there and shift gears.  This is not an article of doom and gloom but rather, one of hope, and a reminder that: 

STRIPED BASS ARE IN OUR HANDS

This year, the angling community will have millions and millions of chances to care for this species.  Anglers pursue striped bass in myriad ways with a number of goals in mind:  some hope to feed their families, some go fishing to simply catch-and-release, and some to make money in the commercial fishery.  Regardless of how you access and utilize the fishery, it is your right to legally operate within the regulations that your state defines.  

Whether you catch-and-release or catch-and-keep, commercially or recreationally, releasing fish is something that all anglers do.  We are all united by the perfect moments of getting a striped bass to hand, regardless of our ambition and regardless if that fish goes to the cooler or back to the ocean.  

According to the most recent Striped Bass Stock Assessment released in 2019, the number of stripers that unintentionally die from catch-and-release angling actually exceeds the number of bass that are recreationally harvested.  To simply break that down, recreational anglers kill more fish by catching and releasing them than by actually intentionally killing them for food.  That fact might come as a surprise to many but ASMFC estimates that 9% of the fish that are caught-and-released throughout the striped bass season die.  These stripers that die from catch-and-release might be a fish gill hooked in Maine’s cold june water, or a gut hooked striper in New Jersey during the fall migration, or a Maryland bass that just couldn’t survive a summer release in a low oxygen environment, or even a bass that was simply held out of water longer than it could handle after a strenuous fight.   

When we slow down and think about each encounter during the season, it becomes clear that careful handling during every single interaction is not only vital to that individual fish’s survival but to the entire future of the striped bass population.  An encounter with a 14” schoolie and it’s safe release potentially solidifies a future 40” warrior bass that crushes menhaden, eats surface plugs, lives for live mackerel, slurps chunk baits and inhales a well placed fly. ASMFC’s most recent stock assessment, estimated that approximately 3.4 million striped bass died from the practice of catch-and-release, the direct result of our handling and angling practices. That’s an enormous number and one that we have control of through our individual behaviors. Yes, we are individual anglers but together we are the users and stewards of this resource and have an enormous impact.  

Keep Fish Wet is an organization focused on helping recreational anglers improve the outcome for each fish they release.  They do this by taking the best available science on how fish respond to capture and handling, and translate the research into simple techniques that anglers can use to ensure that released fish survive and are healthy.  When doing the math, Sascha Clark Danylchuk, Executive Director of Keep Fish Wet, reminds us that if we decrease release mortality by just one percent (something that is very doable using best practices), then over 250,000 more stripers would remain in the fishery.  Those fish that have been given the best chance at survival will live on to support recovering stocks and be caught again another day.  Whether you fish from a center console, the beach, a rocky shoreline, a skiff, or a downtown piece of city concrete, these principles will help to make sure that your catch is released safely.  

• Minimize Air Exposure.  10 seconds or less is best.

• Eliminate Contact with Dry Surfaces.  Wet your hands before touching fish and avoid bringing them into boats.   

• Reduce Handling Time.  Release fish quickly and only revive fish that cannot swim on their own.

We have high hopes that ASMFC sets the management plan for striped bass on a course to rapid recovery, but in the meantime let’s take this fishery in our own hands and safeguard that each fish we release swims off strong and healthy because:

STRIPED BASS ARE IN OUR HANDS

Winter Fishing

The Forgotten End of the Temperature Spectrum: Winter Fishing

Words by Sascha Clark Danylchuk. Photos by Joe Klementovich.

This post was created in collaboration with Fulling Mill and a similar version appears in their blog here.

Winter Fishing

We often think about what happens to fish as water temperatures heat up in the summer, but neglect to consider the other end of the temperature spectrum. This is true in fisheries science as well — perhaps you could chalk it up to scientists favoring fair weather field work — there are many more studies that examine the impacts of warm water on fish than cold.  The lack of studies, however, does not mean that the subject area is unimportant. Especially in temperate and more northern (or southern) latitudes, fish spend a considerable proportion of their lives contending with cold water temps.  

Below is some biologically relevant information on how fish respond to cold water temperatures, as well as some insights from studies on ice fishing. Combined, these scientific facts provide some considerations and precautions that anglers should take when fishing during the winter months.  

What happens to fish as temperatures decrease

Fish survive between a thermal maximum and minimum, above and below which is fatal. Even within their thermal tolerance range, fish have another smaller range. This is known as their thermal optimum, or the water temperatures at which they thrive and prefer to live in.  The thermal optimum, maximum, and minimum varies by species, but can also vary depending on life stage, size, as well as what temperatures fish are acclimated to.    

Fish are cold-blooded animals so as water temperatures decrease, so do fishes metabolic processes. In fact, water temp is often referred to as the master factor for fish. A fish’s ability to swim, feed, digest food, avoid predators, and defend its location all decrease as water temperatures decrease. This leads to more sluggish, less hungry fish in the winter.  

What to do when fishing in winter

Fish in streams and rivers often move into deeper areas (sometimes forming aggregations) in the winter because there is less optimal habitat as temperatures drop and ice begins to form. Deeper pockets can also be slightly warmer if there are groundwater seeps.  One consideration to make when fishing during the winter is that removing fish from their deep pockets and thermal refuges could be detrimental. Their decreased swimming abilities at low temperatures could make it more challenging for them to return to the preferred spot from which they were caught.  

Recommendation: Consider releasing your fish into the same pool from which you caught it during the winter.  

 Prior to winter, fish in temperate and northern latitudes will pack on the fat that will be later used as energy, especially since feeding tends to decrease during winter months. For some species, prey items are also not as readily available in winter. As winter progresses, energy reserves can become depleted, and if they run out of energy to maintain basic bodily functions, fish can die — essentially from starvation. This is different from winterkill, which mostly occurs in lakes that become completely frozen over when there is not enough dissolved oxygen in the water and fish die of hypoxia (lack of oxygen).     

 Anything that causes the accelerated depletion of energy stores can make the situation worse. Fighting at the end of a fishing line increases the metabolism and muscular activity that is fueled by energy. During the winter when fish haven’t been feeding and are already depending on limited energy stores, long fight times as well as anything else that could require energy, such as healing a hook wound or replacing a slime coat, could impact fish overwinter survival.  

Recommendation: Reduce fight time and use barbless hooks.

Tailwaters

While tailwaters (water below a dam) can be popular spots for winter fishing because they are often free of ice, they can present worse situations for fish. Tailwaters are usually warmer and have an increased flow rate. The increased water temperature raises fish metabolism and fish are able to be more active, but they have to contend with the increased flow rate of the water. Both of these lead to fish needing more food/energy, however, prey availability is usually low — fish are hungrier, but cannot find enough food.  This can result in mortality, especially for smaller fish that have lower energy stores. 

Recommendation: When fishing tailwater in the winter pay attention to the health of the fish.  If they look especially skinny consider fishing further downstream.   

Lessons from science on ice fishing

There have been a handful of studies examining the impacts of ice fishing on fish. Despite the differences between ice fishing and, for instance, fly fishing in open water, there are some parallels we can draw, especially in regard to how fish react to angling at very cold-water temperatures. Two trends that stand out and one aspect that needs to be examined further are:  

1)    During winter, fish have a muted physiological stress response and mortality rates are generally lower. The stress response measured by examining blood concentrations of glucose, lactate, and cortisol (read here for more information) often decreases at lower water temperatures. By holding walleye in a pen, this study was able to show that all fish were still alive 24 hours after angling. This is good news for anglers — fish are less physiologically impacted by angling during the winter.   

2)    Although stress responses are often diminished at lower water temps, they can also be prolonged and/or delayed. A study on northern pike, found that it took 45 mins to 4 hours to see changes in blood chemistry following the angling event. As a comparison, in warmer water temperatures we often see these types of changes within minutes. During the winter, this means that fish may not incur the physiological impacts of angling until hours after they are released, and these impacts may last hours longer. We often say that just because you saw your fish swim away does not mean that it’s ok, and this is even more relevant at colder water temperatures.   

3)    While not specifically addressed, several of the studies also point out some of the potential impacts of air exposure during winter fishing. One study noted that fish showed signs of freezing damage to eyes and gills. Very cold air temperatures and windchills could cause damage even during brief air exposures. 

Recommendation: If the guides on your rod are freezing up, consider how delicate gill tissue might respond to air exposure. Just one more reason to Keep Fish Wet.  

Takeaways

Until we have some more conclusive science on the impacts of winter fishing at cold temperatures, it behooves us to employ the precautionary principle and extra careful when fishing during cold temperatures. Returning fish to the same lie where you hooked them, limiting fight time, using barbless hooks, and minimizing air exposure are all important actions that anglers can take to help create better outcomes for fish after release.

NET MESH TYPES

Painting by Diane Michelin

We are pleased to feature this guest blog post from Lenny Tamule.  Lenny is a recent graduate of UMASS Amherst where he majored in Natural Resources Conservation with a concentration in fish ecology.  Lenny also just finished up a season as a guide at Las Pampas Lodge in Argentine Patagonia.  Prior to heading to Patagonia, he had an opportunity to review a recent paper on landing nets, as well as offer a personal reflection on his past use of nets.  

The author Lenny Tamule admiring a stout #keepemwet fish.

It was a calm and cloudy October afternoon and that means brown trout. Within minutes, I was heading to the river. I arrived with my best bud Sully and we got right to it. We made our way down the bank in a spot that had no path. As we approached the river I saw a shadow that isn’t usually there; it was a rather large brown trout. After countless heart racing drifts, my leader stopped, and I was connected. There was a lengthy battle in a heavy rifle and fish was in the nylon net. A combination of being a broke student and new to fly fishing, a cheap, $15 net was all we could really afford at the time. The fish was too big for the small net, and its head almost stuck out. I took a quick photo (regrettably out of water) and put the fish back, but the fish wasn’t swimming and had lost the ability to keep itself upright. I nursed it and tried everything I could to get water passing through its gills but they remained shut. After some time the fish finally swam off. I was relieved. Thirty minutes later we went downstream to fish the next pool. It was then that I saw a sight that made my heart sink deep into my stomach; an upside-down mass on the bottom of the river bed. As someone who prides himself on using best practices for handling fish and getting them back to the river as soon as possible, this was devastating. 

I’ve never shared this story with anyone, perhaps due to embarrassment, but I hope this story will encourage all those who read it to be as smart and kind as possible to the fish they catch (because that day I certainly wasn’t). I don’t know what caused that fish to die — was it the net not supporting it properly, or causing spinal injury, or just myself poorly handling the fish. Whatever the reason, I hope this particular study on nets as well as other catch-and-release studies can help all of us use the best release methods so that no one has to see and experience what I did that day. 

Given the vast number of people who partake in catch-and-release angling, we still do not have as much science on the practice as we would like. This is especially true when it comes net types and how they impact fish health. Many people are under the impression that if the fish swims away it is healthy and ‘okay’. The reality is that we can’t always say for sure once they go back to their world and leave ours. In a study conducted by Teah Lizee and seven other scientists, they assessed the effects of various net mesh types on brook trout in, Quebec, Canada. 

WHAT DID THEY DO?

Here is the skinny on the gear and methods used: 

The Gear

•  Lightweight spinning rods.

•  Barbed treble hooks on size 2 spinners.

  • Angling took place from boat, and 5 proficient anglers were constantly rotating to avoid any potential bias in data.

• Compared large rubber mesh nets, knotless nylon mesh nets, knotted polypropylene mesh nets, rubber coated nylon mesh nets, and bare, wet hands.

  • Bare, wet hands were used to serve as a comparison tool for the 4 net mesh types.

From the above linked and mentioned study by Teah Lizee

The Methods

• The anglers would fish and land 5 fish with each net type and then rotate to the next net type to avoid any potential bias.

• Brook trout were dehooked in the boat with pliers (when necessary) and placed in a holding tank to observe any injury sustained from using the nets.

• They measured mucus (slime) loss, scale loss, fin fraying, handling time, and dehooking time for each net type.

• All brook trout were held in the tank for at least 1 hour for observation.

WHAT DID THEY FIND? Ranking of best to worst net types:

1. Large Rubber Mesh

• Had the lowest amount of scale and mucus loss of any net type.

• Caused some fin fraying (due to large mesh size that allows fins to protrude through the net). 

2. Rubber Coated Nylon Mesh

• Caused some mucus and scale loss. 

• Caused little fin fraying 

3. Knotless Nylon Mesh

• Caused the highest proportion of scale loss.

• Caused the highest proportion of mucus loss. 

• Caused almost no fin fraying 

• Dehooking and handling times were very long because the hook frequently got caught in the mesh of the net. This is the main reason we ranked it lower than the rubber coated nylon mesh.  

4. Knotted Polypropylene Mesh

• Was the only mesh type found to cause significant fin fraying (5.2 times more than bare hands).

• Caused little scale loss, but relatively high amounts of slime loss.

• This net, the rubber coated nylon mesh net, and the large rubber mesh net all had very similar times for dehooking and handling.   

5. Bare, Wet Hands

• Showed high proportion of scale and slimes loss (similar to the rubber coated nylon).

• Caused very little fin fraying.

• Brook trout were dropped much more frequently with bare, wet hands than any net mesh type.

• Dehooking and handling times were the shortest for bare, wet hands.

WHAT DOES IT MEAN? 

• Based on these results, large, rubber mesh nets are the least harmful to brook trout health, and the best available net type.

• Knotted polypropylene mesh was the most harmful net type to brook trout health.

• Although this study focused on brook trout, it also serves as a starting point for assessing net mesh type impacts on other salmonids as well as other species.

• This study begs the question, who will manufacture a better net for fish?

The Nuances of Best Practices in Recreational Fishing

The Nuances of Best Practices in Recreational Fishing

by Dr. Shannon Bower

Lately, I’ve been thinking about a conversation I had a while ago. Partly out of guilt, because I have been a Science Ambassador for Keepemwet for quite some time and have been a fairly silent contributor of late, and partly because the issue of responsible fishing is always on my mind.

When you work in this field for a while, you learn that you can’t be militant about responsible fishing practices. There is simply too much variation in recreational fisheries to know what genuinely good practice is in every single situation. We have some great guidance papers, like Elmer et al. 2017, Brownscombe et al. 2017, and Sims and Danylchuk 2017 (2017 was a good year for best practices research, apparently!) and each of these offers a different take as well as some similar advice. This is a good sign that denotes a lot of agreement among researchers on this issue.

An image from the Brownscombe et al. 2017 paper that shows the different choices that anglers can make and the items they can have handy throughout the process of catching and releasing (or deciding to keep) a fish.

One place where we have some challenges in the field is in the arena associated with individual species. There was a paper by Cooke and Suski in 2005 that asked the question of whether we needed species-specific research to better understand fishes’ responses to catch-and-release. The answer was an emphatic yes, and the authors explored a range of reasons why, including arguing that we see so much variation that it’s difficult to accurately predict how each species will respond in a particular set of circumstances. In terms of variation though, Cooke and Suski pointed out that individual fish respond differently to the same catch-and-release practices, in much the same way that you or I would perform differently if asked to blow bubbles in the water for a full minute, i.e., I would fail miserably and you would probably do fine. As scientists, we’re interested in how the average fish responds to catch-and-release practices like air exposure, but we’re also interested in the range of responses for the whole population that we sample. There are as many potential sources of variation as there are types of responses to catch-and-release, and because of this, Cooke and Suski recommended that we get to work at understanding this variety of responses at the species level.

I think the same can be said for understanding best practices at the scale of individual fisheries, which is where this conversation that I had a few years ago keeps popping into my head. I’d made a post on my Facebook page about using nets when fishing. I had noticed a lot of people using cheap lip gripping devices on fish species with soft mouths that had no teeth. I was seeing photos of anglers in my study area using these devices to hoist the fish vertically out of water, and I wondered just how much pressure these cheaply made devices were putting on the fish’s jaws. I’d turned to the research to see if anyone had asked the question about the effects of lip gripping devices on fish and found a few articles that did nothing to alleviate my concerns (for example, Danylchuk et al. 2008, which was discussed here in an earlier blog. I had suggested that these anglers use nets instead, and to keep those nets in the water while removing hooks and preparing to release the fish. My logic was that the fish would be spared potential damage to the jaw and the air exposure being evidenced by the use of lip grippers. The risk was big though: if you’re using nets, you need to use rubberized nets to avoid damage to the fish’s body. Thrashing in a net that is not rubberized can lead to all kind of badness: major loss of slime that protects fish from infection, and physical damage such as slices and bruising being the two most major that come to mind. So, while I was clear to suggest using rubberized nets, I was also aware that these were not common in the area where I work and that I could be suggesting anglers simply trade one form of potential damage for a form of known damage to fish.

Raja PK photo.

Shannon Bower photo.

This advice didn’t sit particularly well with me, despite being the one who’d given it. I sat staring at the screen, thinking about phrasing, and wondering if there was a better avenue of action to suggest, when the telltale ping came through on my phone. It was a friend from Australia, also a recreational fisheries scientist, who disagreed entirely with what I’d written. What was of interest to me though wasn’t the disagreement, it was the reasoning behind it. You see, in his area of Australia, fishing mainly in marine waters, many anglers have learned that using lip grippers can be a very good way of avoiding the use of damaging nets, provided the lip grippers are suitable for the species and used properly. Those two provisos are a big deal: these anglers were using good quality devices that were appropriate for local toothy species and they were trained in how to use them properly. By doing so, the use of lip grippers was actually a best practice in the area. Yet in the area where I worked, using lip grippers was decidedly NOT representing a best practice. Best practices are not always universal. Like the Cooke and Suski paper arguing for species-specific research, I spend a fair amount of time arguing for fishery-specific research. We have a good sense of what many best practices are, but we don’t know how these best practices play out in different fisheries, in different communities, in different cultures and countries around the world.

Dave McCoy photo

All of this means that we have our work cut out for us as scientists. Incidentally, this is also the reason I am such a big fan of Keepemwet and their work. Of all the best practices, arguably the only one that is one hundred percent universal is: keep the fish in the water. When it comes to building local and fishery-specific understanding of responsible fishing practices, that is a great place to start.

THE POINT OF HOOKS

The point of hooks

By Sascha Clark Danylchuk

Hooking damage is the the number one cause of mortality for fish that are caught-and-released. That’s not a surprising statement since hooks are the only commonality for all fish caught by recreational anglers. But what that statement doesn’t address is how and why fish die from hooking damage. If every fish that is landed has a hook wound, what is it that makes some fish die and others live? How much damage do hooks actually cause? Does it matter what type of hook you use? What other factors come in the play to determine if a fish lives or dies after being hooked?

This paper looks at hooks and specifically hooking mortality in many different studies. It’s called a meta-analysis, which is a statistical analysis that combines the results of multiple scientific studies. It’s also a great introduction to Dr. Robert Arlinghaus, our newest science ambassador. Robert’s work is often based a social-ecological systems approach, which means that he looks at fisheries issues through the lens of both fish ecology and social science. You can learn more about Robert here.

What did they do?

Looked at hooking mortality studies for fishes that are important in European freshwater recreational fisheries. All species in a genus were included, even if the species were not found in Europe. Studies conducted anywhere in the world were included in the study.

• 107 studies on 8 European species and an additional 10 species from the same genus.

• Extracted what caused mortality from each study:

Water temperature

Fish length

Hook type (singe vs. treble)

Existence of a barb (barbed vs. barbless)

Type of bait (natural vs. artificial)

What did they find?

Across all studies and species:

• Mean hooking mortality was 15.9%, with a range of 0 to 88.5%.

• Half of the studies reported hooking mortality of less than 10%. Only a few studies reported mortality levels over 50%.

• Factors that are important for hooking mortality:

1. Water temperature (higher water temperatures lead to higher mortality rates).

2. Bait type (average mortality for artificial baits was 11.4%, average mortality for natural bait was 25%)

3. Existence of a barb (average mortality for barbless hook was 8.2%, average mortality for barbed hooks was 14.6%).

For Salmonids:

• Results for trout and salmon species was similar to the overall results.

• Factors that were important for hooking mortality:

1. Water temperature (higher water temperatures lead to higher mortality rates).

2. Bait type (average mortality for artificial baits was 11.6%, average mortality for natural bait was 27%)

3. Existence of a barb (average mortality for barbless hook was 8.6%, average mortality for barbed hooks was 15.1%).

Takeaways:

• The good news is that most of the reported hooking mortality rates were very low (less than 10%).

• High mortality was most often due to deep hooking or when fish were caught at high water temps.

• There are several reasons why barbed hooks could lead to higher mortality rates than barbless hooks: barbed hooks have been known to cause more injury and bleeding, they also take longer to remove which often increases handling time and air exposure (both things known to lead to worse outcomes for fish), and either or both of these could increase stress levels in fish which also leads to poorer outcomes for fish after release.

• Despite the fact that in this study hook type (single vs. treble hooks) did not turn out to be significant, the authors think that hook type is a species specific issue and likely dependent on hook size as well as the mouth morphology of the fish, and the type of fishing. All these factors could not be teased out in the present study, but are likely important on a species by species basis.

Bulkley Steelhead Catch-and-Release Project

Will Twardek photo

Recreational fisheries for steelhead are primarily catch-and-release, including the famed run of the Bulkley River, BC. The success of catch-and-release as a conservation tool is based on the premise that released fish survive and do not suffer any negative consequences. Science has shown, however, that angler behaviour can have dramatic influences on the outcome of catch-and-release angling, and that research is needed that specifically focuses on wild steelhead to identify opportunities for refining handling practices to ensure the best outcome for fish.

Scientists on this project worked alongside volunteer anglers on the Bulkley River to study wild steelhead from Sept 2016 to April 2018.  During this time, 126 wild steelhead were caught and used in one of two studies on the impacts of catch-and-release.  Click here for a full summary of the project.  

Read the published studies here, here, here, and here

What Did They Say? Translating Presentations From the BTT Symposium Part 2

Keepemwet Fishing and Bonefish & Tarpon Trust have teamed up to make the science that was presented at the BTT Symposium last November accessible to a wider audience.  A selection of presentations have been summarized and “translated” into non-technical language that is easily understood by non-scientists.  Several of the translations are below and more are available in the latest issue of the BTT journal.

What is in an angler’s control? Best practices for the catch-and-release of bonefish, tarpon, and permit

Presentation by Dr. Andy J. Danylchuk
UMass Amherst

Catch-and-release is commonly used a conservation tool for fisheries.  Whether it’s mandated or voluntary, it doesn’t take a rocket scientist to know that putting fish back in the water means that there will be more fish to catch tomorrow.  However, catch-and-release is only effective if most fish survive and are left with no permanent impacts.  Using best practices can help anglers achieve this goal.  

Keepemwet Tarpon by Ed Anderson

Best practices are actions that are often simple, and you have probably heard of many of them already, but together they have the potential to create better outcomes for fish that are caught-and-released.   You can think of best practices as catch-and-release version 2.0.  

Often when fisheries scientists study catch-and-release they look at the varying aspects of an angling event and how each contributes to the overall impacts of catch-and-release on an individual fish or a population.   Many parts of an angling event are in the control of an angler (e.g. hook type, duration of air exposure, how a fish is handled), while others anglers have less control over (e.g. water temperature, size of the fish).  The science on catch-and-release has not been conducted for all species and all aspects of angling, so while we can sometimes apply general best practices across species, it’s also important to acknowledge that species specific and location specific difference do occur.  

What do we know and what do we need to know?

While there are over a dozen studies conducted on bonefish (nearly all on Albula vulpes) catch-and-release, there has only ever been one study on tarpon and none conducted on permit catch-and-release.  

Table of the studies that have been conducted on catch-and-release (Sci) for bonefish, tarpon, and permit, elements of the angling event, and their priority for future research (P).  Darker shades represent a higher priority.  Some studies covered multiple elements of the angling event.  De-predation refers to fish being attacked/eaten while on the line during the fight. 

From these studies we are able to form some specific best practice guidelines for bonefish such as:

• Bonefish that roll or nose dive (called loss of equilibrium) are six times more likely be killed by sharks or barracuda after release. Air exposure is the main cause of loss of equilibrium.

• Air exposure is more detrimental to bigger bonefish and at higher water temperatures.

• Multiple studies on bonefish have shown that longer handling times increase stress levels in fish and can lead to poorer outcomes after release.

• Fish barbless hooks. If a bonefish is deeply hooked cut the line instead of trying to remove the hook.

• Don’t use lip grippers on bonefish. A study found that they can cause significant damage.

Until more science can be done on tarpon and permit, it behooves us to use some of what we know from bonefish and other species when fishing for tarpon and permit, such as:

• Reduce/eliminate air exposure

• Minimize handling

• Rethink the “Hero Shot”

Eventually, filling in the gaps in our understanding about how tarpon and permit respond to catch-and-release will enable us to create best practices for all flats fish. 

Acknowledgements

A special thanks to Ed Anderson who donated the artwork accompanying these summaries. Thank you to the presenters and their collaborators for the work that contributed to these presentations, and for allowing us to represent them in these summaries.  Thank you as well to Natasha Viadero, Alora Myers, and Jordan Massie who provided assistance during the symposium.

What Did They Say? Translating presentations from the BTT Symposium Part 1

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Fish reflex tests - a valuable tool for anglers

by Dr. Jake Brownscombe, PhD
Research Associate, Carleton University
Keepemwet Science Ambassador

“Have a seat, Jake” the doctor said as she pulled out a small rubber mallet and proceeded to thump me on the knee with it. My leg kicked outward involuntarily. “Your nervous system is in good condition” she assured me.

If you grew up on this planet, you know the doctor was checking my knee-jerk reflex. Perhaps lesser known, the speed and intensity of this reaction can indicate internal nerve damage or the presence of disease. It’s a simple external test that indicates what is going on inside of the human body.

Fish have reflexes too. And they can tell us a lot about their internal condition, such as their level of stress, ability swim or to perceive predators. This is particularly useful for anglers because fish cannot tell us how they are feeling. If you ask a fish “If I let you go, can you swim well enough to survive?” its response will be inconclusive. Trust me, I’ve tried… more times than I’d care to admit.

The idea behind catch-and-release fishing is that the fish will survive, grow bigger to be caught again, and continue to contribute to the population. Yet, we know this isn’t always the case. Fish sometimes suffer mortality after release due to stress or injuries associated with angling (but the odds of this can be minimized substantially by using best practices - see this paper for an overview). Whether or not a fish survives depends on its condition, which can be hard to assess as an angler without any fancy medical or veterinary tools.

That is, until recent research developed a set of reflex tests that can be applied to fish, by anglers, to assess their condition. These are the four most effective reflex tests, how to do them, and what they tell you:

1. Escape response

How to do it:  With the fish in the water in a net or livewell (scientific holding pen shown here), approach the fish from behind and grab at its tail. Observe if the fish attempts to escape.

What it means: If a fish doesn’t try to swim away it fails this test, has at least some level of impairment and could be at risk of mortality - other tests will provide further insights.

2. Righting response

How to do it: Flip the fish upside down (belly up) in the water and let go. Observe if the fish rights itself within 5 seconds.

What it means:  If a fish cannot right itself within five seconds it fails this test, and is in poor condition and at risk for mortality.

Pro tip: Count the amount of time until the fish rights itself and note whether it struggled to do so. If a fish rights itself quickly and with ease, it is in good condition to swim away immediately.

3. Regular ventilation

How to do it: Holding the fish in the water, observe for regular, consistent ventilation (opening and closing) of the operculum (gill plates).

What it means: If a fish isn’t ventilating at regular intervals, it fails this test, and is highly impaired and at high risk for mortality.

4. Eye tracking

How to do it: Holding the fish in water, roll the fish side-to-side, observing whether its eye(s) remain level (passes test), or roll with the body (fails test).

What it means: If a fish fails this test, it is highly impaired and at very high risk of mortality

While these aren’t true reflexes by strict definition, they are responses that are always present in fish unless impaired due to stress. The above tests are presented in order of operation, starting with escape response. If a fish fails this test, proceed with the righting response test, and so on. If a fish has no reflex impairment, the best course of action is to release the fish immediately to reduce handling time. However, if there is reflex impairment, particularly loss of righting response, anglers can hold fish in a net or livewell until its condition improves. Further, on any given fishing day, if captured fish are repeatedly in poor condition, anglers can consider altering their fishing practices (e.g., use different lures or fish in different locations) to minimize their impact on fish.

The Science:

The concept of using reflex tests as an indicator of fish condition was first developed and applied in the context of commercial and aboriginal seine net fisheries for Pacific salmon (see these two articles for reference) 1, 2. Based on the success of multiple studies in predicting salmon survival using reflex tests, scientists began apply these tests to recreational fisheries. This study found bonefish with impaired righting response are six times more likely to suffer predation post release (see Finsights #5). Another study later showed that reflex impairment indicates that bonefish have reduced swimming and decision-making capabilities post release, which is why they are more vulnerable to predators. Reflex tests are now used widely as measures of fish condition for diverse species such as sharks, great barracuda, largemouth bass, and fat snook. As science continues to develop the relationship between reflex tests, fish condition, and survival, these tools will become increasingly useful for anglers to assess the condition of their fish and make informed decisions about how to treat the fish prior to release.

THE IMPORTANCE OF WATER TEMPERATURE

Brian O'Keefe photo

Why is water temperature so important?

by Sascha Clark Danylchuk

It’s been a particularly warm autumn here in New England. Usually we would be at peak fall foliage about now, but I still see mostly green out my window. As someone who would take heat over cold any day you won’t catch me complaining about our delayed progression towards winter, but it has gotten me thinking about temperature and, in particular, the importance of water temperature for fish.  

Google fish and water temperature and you’ll find a plethora of pieces on the optimal water temperature for different species of fish. There are graphs, tables, and lengthy articles written on the subject. Many anglers are aware that high water temperatures are not good for fish (think of hoot owl restrictions, daily closures between 2pm and midnight, and fish kills in the summer) and it’s all related to the role water temperature plays on fish biology.  

Almost all fish are cold blooded, with rare exceptions such as tuna and opah. They are ectotherms, which means that their body temperature is a direct result of the temperature of the environment (water), and poikilotherms meaning that water temperature varies and thus so does their body temperature. Each species of fish has an optimal water temperature (an ideal temperature for living and proper functioning) as well as a critical thermal maximum and minimum (temperature beyond which vital bodily functions break down and that can lead to death).  

Being poikilothermic ectotherms means that many of a fish’s body systems are influenced by water temperature. In fact, water temperature is often referred to as the “master factor” when it come to fish. The rate of metabolism, the chemical process that converts food to energy, is highly dependent on temperature. In general, for every 10 degrees Celsius that water temperature increases, a fish’s metabolic rate doubles. This means that at warmer water temperatures, fish have a faster metabolism and need more food. It also means that at warmer water temperatures fish need more oxygen, a critical component of the metabolic process. However, all else being equal, warmer water holds less oxygen than colder water.  

A number of studies have demonstrated that water temperature impacts the survival and recovery of fish from angling, but most of the time those studies didn’t directly consider water temperature. This study specifically examines the effect of water temperature on angled fish.

What did they do?
    •    They used bluegill in this study because they were easy to catch and typically live in water with dramatic temperature variations.
    •    Fished at three different water temperatures (low = 18.3°C/64.9F, medium = 22.8°C/73F, high = 27.4°C/81.3F)
    •    At each temperature, after angling they air exposed fish for different durations from 0 seconds to 16 minutes (yes, 16 minutes is a very long time and not very realistic, but most of the times were less than 2 minutes and they wanted to see what happened at an extreme).  
    •    Time to recover, immediate and delayed mortality (up to 48 hours after angling) was measured for each fish.

What they found:
    •    Time to recover increased significantly as water temperature increased.
    •    Almost no immediate mortality at any temperature.
    •    Delayed mortality was highest (nearly 40% of fish died) for the high water temperature. Also, more fish died and died faster with more air exposure at the high water temperature.  
    •    No fish died at any water temperature with 0 seconds of air exposure.  

Why is this study important for anglers?
    •    This study underscores that stressors to fish (caused by angling or otherwise) are interactive and/or cumulative, especially when it comes to water temperature.
    •    At higher water temperatures remember that fish need more oxygen (but the water might actually contain less oxygen) and fish take longer to recover from angling.
    •    Food for thought, how might climate change affect fish and fishing? Will fish be able to adapt to warmer water temperatures? Will we see more fishing closures as summers get hotter? Are you already starting to see climate change impacts on your home water?  

Happy fishing!
Sascha Clark Danylchuk

CAN YOU REVIVE FISH?

Can you revive fish?

by Sascha Clark Danylchuk

FINSIGHTS #13 Can You Revive Fish?

I would guess that most anglers have heard of, if not performed, revival techniques for fish. If you haven’t, it’s the practice of holding fish into the current or moving them in the water before letting them go to help them get more oxygen and recover from the exhaustion of angling. When I first heard about this I was encouraged to move fish forward and backward in the water. This technique was soon replaced with an “only forward” or “figure-eight” method. But why and how have these techniques become part of our catch-and-release tool kit?

Just like us fish need oxygen, but unlike us they get it from water. On each side of the back of their throat most fish have four gill arches, which are curved, bony structures. Attached to each gill arch are two rows of filaments. Each filament has thousands of lamellae, which are like tiny plates and provide the surface for gas exchange. While water flows one way past the lamellae, blood flows in the opposite direction and this countercurrent exchange allows fish to absorb oxygen and expel carbon dioxide.  

The important part of this to remember is that water needs to flow in one direction for fish to respire effectively: water goes in the mouth, over the gills, and out the operculum (gill cover).  

Copyright © 2009 Pearson Education

If my description and the diagram still leave you confused check out this video:
https://www.youtube.com/watch?v=XEIRlw5rCUk

Based on this explanation of gill function, it seems completely logical that you could revive a fish after angling and help it get more oxygen by increasing the amount of water that flows over the gills, right? You wouldn’t be alone if you said yes; many websites, guides, anglers, and fishing organizations encourage anglers to revive fish like this prior to release.

But, how well do these techniques actually work?  A couple of scientific studies give us insights into the effectiveness (or lack thereof) of such revival techniques.  

Salmon in Rivers:
The first study was performed in a lab, but because labs aren’t always realistic enough the scientists also did a similar study in a natural setting, and it’s the latter study that I’m going to focus on here. Using Fraser River sockeye salmon caught with a seine net (a large, soft net that is commonly used as a non-angling way to capture fish) and via angling, the scientist examined whether assisted ventilation (facing fish into the current for one minute) after air exposure had any effect on the survival, movement, and ability of the fish to reach natal spawning grounds.  

The scientists found no benefit of reviving fish when looking at movement and survival following release.

Bass and Trout in Lakes:
Here’s a pair of good sciencey words: lentic refers to still, fresh water such as a lake or pond. Whereas lotic refers to moving, fresh water as in a stream or river.

The third study examined largemouth bass and brook trout in lentic systems. The scientists compared three groups of angled and air exposed fish: group 1 fish were immediately released, group 2 fish were moved back and forth in the water for revival, and group 3 fish were moved in a circular or figure-eight motion for revival.  

Jake Brownscombe photo.

As with the previous studies in lotic systems, the scientist found no benefit of either methods of revival for fish in lentic systems; neither form of assisted ventilation led to faster revival for largemouth bass and brook trout.  

Why can’t you revive fish using these methods?
Despite the intuitiveness of revival techniques, these studies showed that they didn’t help fish. Why not? Here are a couple educated guesses from the authors and other experts:
    •    Holding fish causes them some stress regardless of what you are doing to them. Therefore, holding fish longer by trying to revive them counteracts any benefits they might receive.
    •    Most species of fish, including sockeye salmon, largemouth bass, and brook trout, can respire on their own by opening and closing their mouth and opercula. After angling, they typically do this and are already maximizing oxygen uptake. Anything we as anglers try to do to help them get more oxygen doesn’t actually make enough of a difference.

Why is this important for anglers?
Despite our best intentions, letting fish go as soon as possible is probably the best thing we can do for them. Any fish that can swim away should be released and doesn’t need to be revived. We probably are not harming fish by trying to revive them (none of the studies showed any detriment to fish that were revived), but we likely aren’t doing them any favors either.  

Of course as with any rule of thumb, there could be a few caveats to this recommendation depending on the species of fish, situation, and location. For example, if a fish cannot swim away, reviving it could be beneficial. Similarly, in an area with predators it is possible that holding fish longer and reviving them gives them a better chance of escaping post-release predation attempts. But, more studies need to be done to assess these situations.

For now, the research suggests that there is no benefit to reviving fish, that we shouldn’t hold fish longer than necessary, and that letting them go when they are ready to go is ideal.

Happy Fishing!
Sascha Clark Danylchuk

An Interview with Sascha Clark Danylchuk

An interview with Sascha Clark Danylchuck

No better way to start a day than with coffee and a rod on your home water. Andy Danylchuk photo.

KWF- Give us a brief bio, background including why you are focused on fish, fish habitat and conservation.
SCD- I grew up in a family where my parents were in constant disagreement about the ideal vacation spot – one preferred the mountains, the other the beach.  We were lucky enough to spend time in each setting and it was mostly through those experiences that water, and nature in general, became deeply ingrained in my identity.  

I didn’t really start fishing until after college when I moved to the Turks and Caicos Islands to work as a research assistant at a marine science field station.  My brother built me a fly rod, and I taught myself to cast with flies I tied myself.  Needless to say it was many months before I caught anything, but wading flats gave me a whole new perspective and appreciation for the ocean, and I was smitten.  

While I knew that I wanted to pursue a career focused around science and water early on, my focus has shifted within those boundaries over the years.  I’ve come to realize that a multidisciplinary, multipronged approach is necessary to make a significant difference when it comes to helping recreational fishing become more sustainable.  

KWF- What's your favorite fishing memory?
SCD- Watching my daughter out-fish her older brother, my husband, and myself on the Madison.  She claims it was due to her “good luck shorts” (which have fish on them), but she’s developing into a badass little angler.   

KWF- How about your bucket list trip or fish species to catch?
SCD- Arctic grayling.  I recently spent time in a remote corner of Argentine Patagonia and it renewed my excitement about salmonids.  I’d love to head to the other end of the Americas to fish for grayling.  

Sascha and kiddos in Argentina on their recent Fish Mission. Andy Danylchuk photo.

KWF- Tell us about your most recent fishing trip.
SCD- I just returned from seven months of traveling.  My husband had a sabbatical so we pulled our kids out of school and took off on a three-part Fish Mission.  We started in Argentina living in a 400 square foot cabin for two months.  We spent time hanging out with the phenomenal crew from Las Pampas Lodge and fished some of the most beautiful water I’ve ever seen.  I landed my personal best rainbow, a 24-inch beauty, on a day so windy that downwind was the only direction I could cast (not that I’ve ever been skilled at casting into the wind).  

Next we were in the Florida Keys for a couple months.  I lived there almost 10 years ago and it was fun to visit old haunts and see friends.  I still, however, have yet to land a permit…

The final part of our Fish Mission was a three-month camping trip from Florida to Massachusetts the long way – first heading west to CA, then north to British Columbia, and finally east back to New England).  I designed and my husband and I built a trailer that had a kitchen, but we tented it the whole time – even in 19oF thundersnow (yes, it exists) at the Grand Canyon, which is not an experience I feel the need to repeat anytime soon!  We had planned to do a lot of fishing along the way, but the huge snowpack in the west last winter meant that many of the rivers were still too high to fish well.  Getting to spend so much time outdoors, however, made up for the fishing we missed.   

Sascha fishing in the Bahamas. Andy Danylchuk photo.

KWF- Why volunteer with KWF? Hopes for the future of the movement?
SCD- There is a fracture between science and conservation in recreational angling, especially when it comes to best practices.  I believe that anglers want to do the right thing, but I don’t think that they always get a clear message from scientists about what exactly the right thing is.  KeepEmWet is the much-needed link that can engage anglers and scientists directly, create information flow in both directions, and move all of us towards being better stewards of our finned natural resources.  

KWF- If you were a fish, what species would you be and where would you live?
A bonefish on the flats, of course.  My happy place is wading a tropical flat, it makes no difference whether it’s in the Caribbean or the Pacific –  it’s always where I would rather be.  

When scientists get together to talk fish

When scientists get together to talk fish

A couple weeks ago I attended the 8th World Recreational Fishing Conference in Victoria, BC, Canada. This gathering of 380 people from 22 countries included fisheries scientists, managers, students, and other fishy folk. We spent three and a half days giving and listening to presentations on topics such as citizen science, monitoring and assessment of recreational fisheries, understanding angler behavior, use and challenges of catch-and-release, and engagement of fishers in the management process.

While there was a lot of talk of scientific methodology, statistics, and other topics that could put most anglers to sleep (and has even been known to put fellow scientists to sleep), there were also a number of issues discussed that are relevant and valuable for anglers, especially for those of us that strive to follow KeepEmWet Principles and stay informed about fisheries issues.

Rick Hansen (Man In Motion) gives an inspirational opening address at the 8th World Recreational Fishing Conference about the impacts of fishing on his life. Andy Danylchuk photo.

Catch-and-Release
There were 33 presentations given in a symposium squarely focused on the use and challenges of catch-and-release in recreational fisheries.  A few of the highlights are:
    •    Deep hooking is the single most important factor influencing the survival of fish. If a fish is deeply hooked, it’s better to cut the line than try to remove the hook.
    •    The type of net you use matters – size of the mesh as well as the material can influence slime and scale loss, and fin fraying, but there still isn’t a comprehensive review and comparison of net types across a wide range of species.  
    •    Landing steelhead using either a net or tail grab is fine
    •    Everything we do to fish is magnified at higher water temperatures.  For example, while 10 seconds of air exposure may not significantly impact fish when water temps are low, 10 seconds of air exposure at higher water temperatures may be enough to temporarily impair swimming ability.  

Angler Engagement and Involvement
Starting with the keynote speakers there was a lot of emphasis on finding ways to interact with and involve anglers in the science and management of recreational fisheries.  Ideas ranged from creating interactive apps that provide data to scientists to having anglers guide research needs and creating partnerships where anglers help manage fisheries.  

It was encouraging to hear so many different people echoing this sentiment. Stay tuned for the roll out of several new KeepEmWet Science Ambassadors in the coming weeks; scientists who also fish and understand the passion and importance of anglers in making fishing sustainable. With this in mind, our goal is for KeepEmWet Fishing to be a platform for anglers and scientists to connect more directly.  

Finally, KeepEmWet Fishing was mentioned in at least eight different presentations (only one of which was by yours truly).  It seems that even scientists are starting to pay attention to social media and recognize the value in the KeepEmWet movement ;)

Happy Fishing!
Sascha Clark Danylchuk

Lip Grippers

Lip gripping devices and your catch. Tiger fish. Dave McCoy photo.

Sport Fishing Magazine recently published an article on A Guide to Lip Grippers. The very last paragraph of the article touches on how lip gripping devices can impact fish and the author states “Many of the lip-grip manufacturers interviewed independently stated that they believe their weight scales do not cause physical damage to fish or inhibit future feeding ability — when the fish is hung vertically”.  I decided to dig through the scientific literature to see if anyone had looked at this at this and found only three studies that focused on lip gripping devices, each on different species.

 
Bonefish The first study looked at if lip-gripping devices caused injury to bonefish.  They compared bonefish held vertically in the air with a lip gripper to those held horizontally in the water with a lip gripper, all compared against a ‘control group’ where bonefish were handled only with bare hands   Bonefish held with a lip-griping device either vertically or horizontally were prone to injury – 90% of fish had at least minor injuries (which included holes through the tissue of the lower jaw where the lip gripping device was placed) and 35% of fish had major injuries (including broken mandible and separated tongue).  Conversely, only one of the fish held by hand had a minor injury and none had major injuries.  All fish survived for 48 hours after being handled, but the authors did not monitor for long-term survival or feeding ability.  

Injuries sustained to bonefish using a mechanical lip-gripping device. Link to report.

Barramundi In 2009, a different group of scientists looked at how lip grippers compared to nets for holding barramundi (an Australian sportfish).  They compared barramundi held in a net with those held vertically by a lip gripper, as well as those held horizontally with a lip gripper and one hand supporting the midsection of the fish.  They found that all fish held vertically and 81% of fish held horizontally had holes in their lower jaws.  However, no fish had severe injuries as was seen with bonefish.  Furthermore, all fish resumed feeding within 3-5 days and all holes healed within three weeks.  The scientists also took x-rays of some of the barramundi to see if holding them with lip grippers had any effect on their vertebral alignment.  They found that holding barramundi vertically, and to a lesser extent holding them horizontally with the lip gripper causes vertebral separation.  None of the vertebrae separations recovered after three weeks. Being water dwellers where the water supports much of their body weight, holding fish in the air has the possibility of causing damage or separation to vertebrae.

Florida Largemouth Bass The most recent study on lip grippers was conducted on Florida largemouth bass and examined the differences between holding largemouth bass vertically with a lip gripper, by hand on the lower jaw using a tilted grip, and using a two-handed hold.  They found no difference in feeding behavior, survivorship, or rates of injury between any of the three methods of holding bass.  They did, however, find that largemouth bass that were held with the lip-gripping device took longer to recovery than other fish.

Why are these studies important to anglers?
    •    These three studies constitute a start to the much-needed research on lip-gripping devices, and given the diversity of these devises and the species they are used on, clearly there is more work to be done.
    •    What these studies do show is that there is a wide variation in how lip-gripping devices affect the incidence of injury on different fish species.
    •    What I could not find are any studies that examine repeated use of lip grippers, long-term affects on fish, or compare injuries from lip grippers to those caused by nets.  
    •    If tackle manufactures want to make claims that their lip grippers and other fish handling products do not harm fish, they should consider independent testing.

Happy Fishing!
Sascha Clark Danylchuk

Fish Slime

How do you handle fish? Paul Moinester/Keepemwet Fishing photo.

You’ve hooked up on a fish.  You fight it, reel it in, and get ready to land it.  Do you reach for a net? A lip gripping device? Or just stick your hands in the water?  And what do you do once you have ahold of the fish?  Does it stay in the water? Does it go in a boat or a livewell?  

How we choose to handle the fish we catch and release can have a huge impact on the health of those fish.  Some of the negative effects of handling on fish we can actually see (such as the loss of scales or equilibrium) but many we cannot, either because they are invisible to the naked eye, are internal, or occur after we release the fish.  

This study uses a clever way to examine some of the invisible injuries to fish and how different handling techniques impact the skin of fish. All fish are covered with an epithelial layer, which is on top of the scales and provides a barrier to pathogens, UV light, and desiccation (drying out). There is also mucus on fish, but the amount varies among species. Unlike with humans, the outer layer of cells on fish are living and a disruption to the epithelial layer creates a susceptibility to infection.

Fluorescein is a non-toxic dye that can be used to examine epithelial damage on fish (it is some of the same stuff used by detectives to look for blood at crime scenes). After being dipped in a solution containing fluorescein, areas on a fish with damaged epithelium with glow green under a UV light.   

What did they do?
    •    Used fluorescein dye to examine how different handling methods damage the epithelial layer on largemouth bass and northern pike.
    •    Handling techniques included different types of nets, a lip gripping device, and placing a fish on a variety of boat surfaces.
    •    Largemouth bass from a semi-professional live-release tournament were also measured for epithelial damage.
    •    After being subjected to the fluorescein dye, fish were photographed under a UV light and damaged area (seen as green on the photos) was measured using computer software.

A northern pike photographed under UV light after being exposed to fluorescein dye. The green areas indicated epithelial damage from handling. Image from linked report.

What did they find?
    •    Northern pike had more epithelial damage than largemouth bass across all handling methods
    •    Largemouth bass from the tournament had the most epithelial damage. This isn’t surprising as they were often subjected to multiple handling methods, where the experimental fish were only subjected to one handling method.  
    •    Rubber, non-knotted landing nets caused less damage than nylon, knotted nets for pike. For bass, there wasn’t a difference between net types.  
    •    All fish placed on a boat surface had epithelial damage and those placed on indoor/outdoor carpet had more damage than those placed on a bare metal surface.

Why is this study important to anglers?
This study shows that different species can have different reactions to the same type of handling. This is one of the reasons the science of catch-and-release is so interesting and can be confusing, and why ‘one size fits all’ rules may not apply. Nevertheless, here are two generalities that we can uphold because they are supported by this study (and others) and follow the precautionary principle – the idea behind “better safe than sorry”.  

    •    This study confirms what many anglers have thought for a long time; that softer, rubber, non-knotted nets are better for fish.  
    •    Likewise, contact with boat surfaces (carpet or smooth metal) causes damage to fish and rough surfaces cause the most damage. I would argue that placing fish on any hard surface (rocks, logs, boats) either wet or dry has the potential to cause epithelial and internal damage to fish. Whenever possible, fish should be held over water deep enough for them to swim in. But remember, we also need to #KeepEmWet.

See the complete study here.

Happy Fishing!
Sascha Clark Danylchuk

The Science of Catching more Fish

By Sascha Clark Danylchuk

Science to help you catch more fish. Bryan Huskey photo.

I want to introduce a new type of scientific paper, called a review paper.  So far, the literature I have used has been based on single studies.  Every once in a while, however, scientists will gather together much of the literature about a given topic, summarize it, and be able to draw new or stronger conclusions due to the support of multiple studies.  While review papers often lack the detail of papers based on individual studies, they are very helpful in advancing a discipline or subject area.  

Just a couple months ago there was a review paper published on what makes fish vulnerable to capture by hooks.  Because fishing is not a random process, some species or individuals within a species are more likely to be caught by anglers than others.  Likewise, at any given moment some fish may be in a vulnerable state while others are less vulnerable.  There are many, many factors that influence fish vulnerability and as anglers we know that what worked yesterday to catch a fish may not work today. The authors of the review paper have used a three-part framework to discuss the various aspects of vulnerability - represented by the yellow triangle in Figure 1.  There is also a video accompanying this paper.

"Vulnerability of fish conceptualized as a dynamic state-switching process in which fish transition into states of vulnerability as a function of the internal state, the encounter with the predator (i.e., fisher), and the selectivity of the gear. We also show how vulnerability is modified across axes of life history and environments and how it can be modulated by management actions such as fishing restrictions. Fish vulnerability is only observable insofar as the fish is captured, making it difficult to empirically quantify. Nevertheless, these concepts are the foundational mechanisms driving vulnerability."

Internal state
What is going on inside an individual fish and the factors that influence a fish to eat and strike comprise its internal state.  While the need to eat in fish is controlled by metabolism (just like in humans) there are many environmental factors that play into this, especially as fish are cold blooded.  The abiotic factors are those that are non-living such as physical (temperature, light, lunar phase) and chemical (dissolved oxygen, pH, salinity) properties of the environment.  The biotic environmental factors are the other living organisms including other fish of the same species, as well as predators and prey.  

Predatory encounter
When a fish is hungry or motivated to feed, you can think of it as a predator looking for prey.  The chance that the prey will be the hook on the end of your fishing line is the “predatory” encounter.  The probability of hooking a fish depends where a hungry fish is as well as where your fishing gear is – you will never catch a fish if there aren’t fish close to you to be caught.  Predatory encounter relates to the spatial components of vulnerability including fish and human movement patterns.  

Gear selectivity
The type of fishing gear we use, either by choice or regulation, ultimately determines whether you will catch a fish that is hungry and in the right place at the right time.  Fishing gear is selective, meaning it works better on certain (sized, shaped, or species of) fish.  Incorrectly selected gear (e.g. the wrong species of fly) can turn a vulnerable fish back to the invulnerable state.  Similarly, the ability of fish to learn in catch and release situations also influences gear selectivity.  

Why is this important for anglers?
As anglers, we talk and think about fish vulnerability constantly.  We talk about the bite being on or off, which flies or lures work, what moon phase is best for fishing, where the secret spots are, and on and on and on. There are books and magazines and blogs devoted to the topic.  Likewise, there are at least as many fishing theories out there as there are anglers.  While some of the factors that influence fish vulnerability are in an angler’s control, many are not.  Thinking systematically and using this mechanistic approach to vulnerability just might help you have more success the next time you are on the water.  

Read the entire review paper here.

Happy Fishing!
Sascha Clark Danylchuk

Fish vulnerability by Robert Lennox.