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FINSIGHTS #15 THE POINT OF HOOKS

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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.

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FINSIGHTS- TRANSLATING THE SCIENCE OF FISHERIES REPORTS #12

Finsights #12- 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. 

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.

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.

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.  

 

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FINSIGHTS- TRANSLATING THE SCIENCE OF FISHERIES REPORTS #11

Finsights #11– 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.

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

 

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FINSIGHTS- TRANSLATING THE SCIENCE OF FISHERIES REPORTS #10

 Finsights #10 Lip gripping devices and your catch. Tiger fish. Dave McCoy photo.

Finsights #10 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.

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

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FINSIGHTS- TRANSLATING THE SCIENCE OF FISHERIES REPORTS #9

 Finsights #9– How do you handle fish? Paul Moinester/Keepemwet Fishing photo.

Finsights #9– 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.

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

 

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FINSIGHTS- TRANSLATING THE SCIENCE OF FISHERIES REPORTS #8

By Sascha Clark Danylchuk

 Finsights #8 - Science to help you catch more fish. Bryan Huskey photo.

Finsights #8 - 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." 

"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.

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FINSIGHTS- TRANSLATING THE SCIENCE OF FISHERIES REPORTS #7

Finsights #7 – “I saw the fish swim away so it must be fine” - Part 3

  Finsights #7  Robert Lennox Photo

Finsights #7 Robert Lennox Photo

My last two posts have been about the range of possible lethal and sublethal impacts of catch and release angling on fish, and I want to round out the discussion with one last post. When it comes to sublethal effects, it’s fairly easy to comprehend the direct consequences of angling on an individual fish. What can be more difficult to understand and discern scientifically is how angling could impact an entire population of fish.

One way to get at population level effects is to examine how angling impacts the fitness of fish. Keepemwet Science Ambassador John McMillan recently provided a nice explanation of what fitness means for fish - the ability of an individual to contribute viable offspring to the next generation.  So, a decrease in fitness would be a decrease in the number or the quality of offspring from a given fish.

 Anglers landing an Atlantic salmon. Robert Lennox photo.

Anglers landing an Atlantic salmon. Robert Lennox photo.

 A scientist releasing a studied fish. Robert Lennox photo.

A scientist releasing a studied fish. Robert Lennox photo.

The research paper for this blog post specifically looked at whether catch and release angling impairs fitness. The scientists were able to take advantage of the unique geography of a small river in Quebec, Canada that also contained a fish ladder, which allowed for a complete inventory of Atlantic salmon that entered the river to spawn. Every fish that entered the river was sampled for their genetic makeup. Genetic samples of fish are most frequently obtained by cutting off or punching out a very small piece of fin (it doesn’t bleed and quickly grows back).  

 Atlantic salmon in the river. Robert Lennox photo.

Atlantic salmon in the river. Robert Lennox photo.

What did they do?
    •    All salmon entering the river at a fish ladder were genetically sampled and their length measured.
    •    All anglers on the river were asked to fill out a questionnaire and take a genetic sample of each fish they caught and released.
    •    The following year, fry (baby salmon) were sampled in the river to determine parentage.

What did they find?
    •    20% of the salmon in the river were angled and were the parents of 22% of the offspring. This means that the fish that were caught and released were able to spawn.
    •    Larger angled salmon produced significantly fewer offspring than non-angled salmon, however, there was no difference in number of offspring (in angled vs. non-angled fish) for smaller salmon.
    •    Air exposure decreased the fitness of salmon.  Depending on water temperature, the reproductive success was 2 to 3 times lower for angled salmon that were air exposed versus those that were not.  

Why is this study important to anglers?
    •    Once again, we see that air exposure is bad for fish. In this case, it’s bad for the next generation of fish.  
    •    All fish are not equal – larger fish can be more susceptible to the sublethal effects of angling. This is true when it comes to fitness, as well as when it comes to stress (link to Finsights #4). As anglers, we need to treat the larger fish that we pursue with the utmost care and respect.  Angling can impact large fish in more ways than it does smaller fish and therefore we have an extra duty to Keepemwet.

Link to full research paper.

Happy Fishing!
Sascha Clark Danylchuk

 

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FINSIGHTS- TRANSLATING THE SCIENCE OF FISHERIES REPORTS #6

Finsights #6 – “I saw the fish swim away so it must be fine” - Part 2

 Golden dorado pondering the outcome of it's next meal.  Dave McCoy  photo.

Golden dorado pondering the outcome of it's next meal. Dave McCoy photo.

My last article aside, we assume that most of the fish that we catch and release actually live. But, does catching and releasing a fish have any impact on it?  Maybe.  Does an angler have any control over what these impacts are?  Sometimes.  

The slew of possible impacts of angling on fish are called sublethal effects. A lot of catch and release angling science has to do with minimizing or explaining the sublethal effects, so it’s important to understand what those can be and how different aspects of angling can have different sublethal effects.  

 Fig. 1. from  the linked paper.  Conceptual diagram outlining the immediate and long-term effects of escape or release from commercial fishing gear and how it relates to each level of biological organization. Question marks (?) denote areas for which no primary literature exists, and present future avenues of research.

Fig. 1. from the linked paper. Conceptual diagram outlining the immediate and long-term effects of escape or release from commercial fishing gear and how it relates to each level of biological
organization. Question marks (?) denote areas for which no primary literature exists, and present future avenues of research.

For this post, I’m focusing on one figure from an article.  Don’t be put off by the fact that this article deals with commercial bycatch and not recreational angling – the issues for released fish are the same, and this paper is widely referenced in the recreational fisheries science literature (not to mention that several of the authors work on recreational fisheries too).  

So, here it is, a rundown of the potential sublethal effects of angling:

Immediate Sublethal Effects
This deals with the acute effects of angling on fish and are most obvious to fishers.  
    •    Physical Injury.  Hooking wounds are what usually come to mind, but don’t leave out blood loss, foul hooking injuries, and injury that occurs during handling and hook removal.
    •    Physiological responses.  Physiology deals with the functions of an organism or it’s systems/parts.  A physiological response occurs when an event (such as angling) causes an animal to function beyond its “normal” activity levels.   This is most often measured via a blood sample in fish (see Finsights #4 for more details).
    •    Reflex impairment.  This is most easily thought of in human terms – when you’ve had one too many and can’t walk a straight line, you have reflex impairment.  For fish, this could include the loss of equilibrium (see Finsights #5), or lack of coordinated movement between the mouth and gills.  

 Testing the reflex impairment of golden dorado on the Rio Juramento, Argentina. Tyler Gagne photo.

Testing the reflex impairment of golden dorado on the Rio Juramento, Argentina. Tyler Gagne photo.

Delayed Sublethal Effects
If the immediate sublethal effects are severe or last long enough a fish could end up with these.
    •    Behavioral impairment.  This could include anything from spawning to swimming behavior.  
    •    Altered foraging efficiency = altered ability to find, compete for, and capture food.
    •    Growth and wound healing.  Animals that must spend energy on wound healing can have decreased growth.
    •    Altered energy allocation has to do with how a fish apportions energy (e.g. energy derived from food) to the life traits of growth, reproduction, and survival.
    •    Immune function and disease development & offspring quality, performance, and survival & reproductive success.  All of these have to do with the point above; when more energy is needed for one of the three life traits, one or both of the others get less energy.  

All of the sublethal effects above only refer to what happens to an individual fish.  It’s possible that these individual level effects can also impact the entire population.  For example, if enough fish experience decreased reproductive success, this could lead to less fish in subsequent generations.  

It’s this step - moving beyond what happens to one fish to the population - that is particularly challenging for the field of catch and release science.  In part, this is because it’s a really hard thing to do - to show, definitively, that sublethal effects at the individual level can have cascading effects on an entire population or community.  In future posts, I will dig into some of the studies that have begun to chart this course.  

As anglers, the more we can do to decrease the sublethal impact of angling on individual fish, the less likely there are to be higher-level effects.

Happy Fishing!
Sascha Clark Danylchuk

 

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Finsights- translating the science of fisheries reports #5

Finsights #5 – “I saw the fish swim away so it must be fine” - Part 1

  The "grey ghost" Alex Filous photo.

The "grey ghost" Alex Filous photo.

I can’t tell you how many times I’ve heard an angler say, “I saw the fish swim away so it must be fine.”  And I’ve certainly hoped for the same on countless occasions; that when I release a fish that’s vigorous and darts out of my hands it will be fine.  The scientist in me, however, knows that this statement can be false for a number of reasons.  

Sometimes the fish we catch and release get injured or die.  There is no getting around that fact and there is only so much that is in an angler’s control.  However, by better understanding the processes that can lead to negative outcomes for fish, we anglers can adjust what is in our control to ensure that more fish live to be caught another day.  

This post is the beginning of a series addressing what can happen once we release a fish.  This particular post addresses post-release predation, and (in full disclosure) a paper authored by me.  Despite the fact that using this paper makes the introvert in me want to hide under the bed, I chose it because it is a fairly straightforward study with results that have a clear application to the catch and release best practices for bonefish.  

What did we do?
    •    Bonefish were caught using fly fishing.
    •    Measured angling time (hooking to landing), handling time (landing to release), air exposure time (cumulative), the presence/absence of blood from hooking, and total length of the fish.
    •    Also noted whether or not the bonefish was able to maintain equilibrium at the time of release.  Having equilibrium = fish that swim away. Lost equilibrium = fish that rolled over or nose-dived and couldn’t readily swim away.
    •    Before release, we attached a small float to the bonefish so that we could follow it (this tracking method was previously tested on bonefish and there was no impact of the float on fish movement and predation)

  Post-release predation on bonefish by a shark,  Robert Lennox photo.

Post-release predation on bonefish by a shark,  Robert Lennox photo.

What did we find?
    •    Bonefish that lost equilibrium were over 6 times more likely to suffer predation, either by sharks or barracuda
    •    Longer air exposure and handling times were the biggest contributors to loss of equilibrium
    •    Predators killed most of the bonefish within 20 minutes of release, but not necessarily close to or within easy viewing of the release location.

Why is this study important to anglers?
    •    Air exposure isn’t good for bonefish
    •    Lots of handling isn’t good for bonefish
    •    Catch and release angling in locations with predators (even if you don’t see the predators) can greatly decrease the chance of survival for fish.

Read the full original report here.


Happy Fishing!
Sascha Clark Danylchuk

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FINSIGHTS- TRANSLATING THE SCIENCE OF FISHERIES REPORTS #4

Finsights #4 – Fish can get stressed too

By Sascha Clark Danylchuk

 Rainbow trout darts back into it's Alaskan stream after release. Bryan Huskey photo via Bristol Bay Lodge.

Rainbow trout darts back into it's Alaskan stream after release. Bryan Huskey photo via Bristol Bay Lodge.

Before we dive into the study (Meka & McCormick 2005), I wanted to start with a brief discussion of stress in fish.  Scientists measure stress in fish to determine how our interactions with fish (e.g. angling) affects their health and welfare. Just like in humans, too much stress in fish can lead to decreased performance, poor health, and even an increase in the likelihood of death.  There are a variety of indicators that can be used to quantify stress, each with advantages and disadvantages. Two of the more common indicators are cortisol and lactate.

Cortisol: a hormone found in all vertebrates and often called “the stress hormone”.  You could think of cortisol as a messenger, and an increase in cortisol can trigger a response in numerous parts of the body.  When scientists measure cortisol level in blood, we assume that a higher level of cortisol is indicative of a higher level of stress.  

Lactate: a byproduct of extreme muscle activity.  For the athletes out there, it’s related to lactic acid buildup in muscles due to anaerobic activity.  In the context of angling, higher levels of blood lactate indicate that a fish has been exercising more in response to being on the fishing line, and is more stressed.  

So, back to the study, this one examines the stress caused by angling for wild rainbow trout in Alaska.  

What did they do?
    •    Used real angling techniques (spin and fly fishing)
    •    Compared rapid capture fish (less than 2 minutes from hooking to hook removal) to extended capture fish (over 2 minutes from hooking to hook removal)
    •    Took blood samples after the hook was removed to measure cortisol and lactate (and a couple of other parameters, which I’m going to ignore for now)
    •    No air exposure to any fish

What did they find?
    •    Extended capture fish had higher levels of cortisol and lactate
    •    Larger fish took longer to land
    •    All else being equal, higher water temperatures can (but don’t always) correspond with higher levels of lactate and cortisol

 Fly fishing the Alaskan backcountry. Bryan Huskey photo via Bristol Bay Lodge.

Fly fishing the Alaskan backcountry. Bryan Huskey photo via Bristol Bay Lodge.

Why is this study important to anglers?
    •    Choosing tackle that reduces the amount of time a fish is on the line and the time it takes to handle the fish and remove the hook is important to reducing stress.  
    •    Bigger fish that fight longer are likely more stressed

See the full report: Physiological response of wild rainbow trout to angling: impact of
angling duration, fish size, body condition, and temperature
Julie M. Mekaa,∗, Stephen D. McCormickb

Happy Fishing!
Sascha Clark Danylchuk

 

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FINSIGHTS- TRANSLATING THE SCIENCE OF FISHERIES REPORTS #3

Finsights #3 – A classic air exposure paper

by Sascha Clark Danylchuk

 Rainbow trout resting before release. Bryan Huskey photo.

Rainbow trout resting before release. Bryan Huskey photo.

Please note that we have updated this post because the study discussed has been misinterpreted and taken out of context.   The importance of the Ferguson and Tufts 1992 study is that it was the first to demonstrate the potential magnitude of impact that air exposure can have on fish.  HOWEVER, the numbers from that study are NOT meant to be representative of what happens in real fishing situations!!!!  I cannot emphasize this point enough!

Happy Fishing!
Sascha Clark Danylchuk

 

For the first Finsights translation I wanted to start with a classic manuscript about air exposure and fish, and arguably, the paper that started it all.  The paper (linked here and at the bottom of this page) is titled “Physiological effects of brief air exposure in exhaustively exercised rainbow trout (Oncorhynchus mykiss): Implications for ‘catch and release’ fisheries” and was published in the Canadian Journal of Fisheries and Aquatic Sciences in 1992 by Ralph Ferguson and Bruce Tufts.

What did they do?
In this study, the scientists compared three groups of rainbow trout:
    •    Fish that were exercised
    •    Fish that were exercised and air exposed (for 60 seconds)
    •    A control group of fish that were neither exercised nor air exposed
Because this experiment was performed in a lab, chasing trout around the tank was used as a proxy for exercise, which is how scientists think of angling or fighting a fish.  

They then measured a bunch of different blood parameters that are used as indicators of stress.  I don’t want to go into the details of blood chemistry here – it can be confusing and I don’t think necessary to understanding the main points of this study – but I do want to point out that this is a very common way to look at the effects of angling on fish.  

Lastly, the scientists looked at the survival of fish in each of the three groups and also added another group that was exercised and air exposed for 30 seconds, but where no blood samples were taken.  

What did they find?
    •    Air exposure made a big difference!  
    •    Rainbow trout that were air exposed were more stressed and exhausted than any of the other fish.
    •    More fish that were air exposed died compared to those that were just exercised.

Why didn’t the air-exposed trout survive? The scientists argue that the trout that were air-exposed died because fish gills don’t work in air.  Gills consist of tiny, delicate structures, called lamellae, where oxygen exchange occurs.  Water flow across the lamellae is essential for proper functioning and for a fish to breathe (oxygen in, carbon dioxide out…just like us).  When fish are lifted out of the water, the lamellae collapse and stick together and the fish can’t get any oxygen.  

Imagine running a marathon and then being forced to hold your breath – your body (and likewise that of an angled fish) would be deprived of oxygen at the precise moment that you needed it the most.

 Rainbow trout lifted slightly as it's released. Bryan Huskey photo.

Rainbow trout lifted slightly as it's released. Bryan Huskey photo.

Why is this study important to anglers?
The authors end this paper by making a very important point: Because this study was performed in a lab, with hatchery rainbow trout, and with exercise as a proxy for angling their results are not intended to be predictive of what would happen in an actual angling event. BUT, their results do clearly indicate that air exposure is important and can have a big impact on the well-being and survival of angled fish.

This paper got the scientific community to begin to start thinking about the different parts of an angling event (air exposure, hook type, fight time, etc), and how each might influence the stress and survival of fish.  Since this paper, the scientific community has done much more on stress related to angling, and with many more species, especially wild fish being angled in natural settings.

Lastly, I just listened to an excellent interview titled “Why should we believe in science?”  If you are still curious about the scientific process I enthusiastically recommend this eloquent interview with Naomi Oreskes, as well as her TED talk on the same subject.  

Happy fishing!
Sascha Clark Danylchuk


 Click here to view "Physiological effects of brief air exposure in exhaustively exercised rainbow trout (Oncorhynchus mykiss): Implications for ‘catch and release’ fisheries”

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