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

“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.

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.

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.

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

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

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

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.

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 study here.

Happy Fishing!
Sascha Clark Danylchuk

Fish Can get Stressed Too

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.

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.

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 study: 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

A classic air exposure paper

A classic air exposure paper

by Sascha Clark Danylchuk

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.

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

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

Parts of a Scientific Paper

By Sascha Clark Danylchuk

Taking a non-lethal blood sample from a bluefin trevally in French Polynesia. Photo provided by author.

Read post #1 Introduction to Finsights here.

The writing style of scientific manuscripts makes many people cringe. The use of the passive voice (scientists rarely use “I” or “we”) and the density of the writing can make scientific papers difficult to follow. Similarly, discerning the important aspect of the study can be tricky because scientists go to extremes to avoid adjectives and subjectivity and almost everything written is given equal credence. I’ve put together a brief description of the major parts of a scientific manuscript and what to look for in each section for improved comprehension.

Abstract: brief summary of the study and its findings. This is the place to start to see if a paper might be relevant and interesting.

Introduction: background of pertinent previous studies, and goals and hypothesis for the present study. From the introduction you should understand the motivation for the study.  It’s also a great place to find references to other studies that might be of interest.

Methods: a description of the study process, with enough detail so that another person or research team could replicate it. This can be very dry, and it’s supposed to be that way.  

Results: a description of the findings and the results of statistical analyses. This can be confusing unless you have a good grasp of statistics. Look for terms like “statistically significant” to recognize what is important. The figures and tables (graphs, maps, and diagrams) will also highlight notable trends and findings, however there is a definite skill to figuring out what is scientifically meaningful.

Discussion: an objective interpretation of the results and statistics, and how the findings add to our understanding of the subject matter. A good discussion should key in on the results that are the most meaningful. The discussion also often covers the limitations of the study, which are important for understanding how broadly the findings can be applied (e.g. does this apply to all trout, only brook trout, or only brook trout in New York?).

Keepemwet Fishing Science Advisor Andy Danylchuk and field assistant Kim Ovitz doing work on Golden Dorado in Northern Argentina. Tyler Gagne photo.

When I read a manuscript, I usually spend most of my time on the abstract, introduction and discussion.  It’s these sections that get to the core of the subject matter and provide most of the type of information that an angler would find interesting.  

Lastly, it’s important to remember that each study and corresponding manuscript is an incremental step in addressing a large subject matter. Rarely can any one study tackle all questions, but put together, over time, scientists strive to find complete answers to complex problems.

Happy fishing!
Sascha Clark Danylchuk

Introduction to Finsights

By Sasha Clark Danlychuk

I have been seeking water for as long as I can remember. As a child, it was the beach or a mountain stream in which to play. Eventually, I began to search for the creatures living in the water and it was no great surprise that this led me to become a fisheries scientist. I still love to play in the water, and more often than not, that involves fly fishing.

The author Sascha Clark Danylchuk cradling perfection in the form of a bonefish.

More and more, however, I find the intersection between my work as a fisheries scientist and my passion as a recreational angler to be messy and convoluted. I admire that innate conservation ethic exhibited by many anglers, but find the lack of scientific backing to their practices frustrating. Likewise, I appreciate my colleagues’ quests to solve issues and find sustainable solutions, but I am aggravated that their ideas rarely make it past esoteric scientific publications.

In my quest to clarify fisheries science to recreational anglers, and to encourage scientists to make their work accessible to a wider audience I have teamed up with Keepemwet Fishing for a blog series I am calling Finsights in which I will “translate” some of the most important scientific studies on recreational angling so that they can be understood by more people.

But, let’s begin with the scientific publications process and why scientists write in such a complex, dense, and let’s face it, dull style. Scientific publications were developed as a means for scientists to make their work known and judged objectively. The process of publication requires a scientist (or, more often than not, the group of scientists) involved in a study to write a manuscript, which follows a very specific format, and to submit the manuscript to a journal of their choosing. There are hundreds of journals, and they vary in subject matter as well as quality. Once a manuscript is submitted it is read by an editor or associate editor who then must find 2-3 anonymous peers to also review the manuscript and decide if it is worthy of publication. Publications are reviewed based on the quality and merit of the study as well as quality of writing. If the manuscript is accepted (usually after some revisions are made) it is published. If it is rejected, the authors can submit it to another journal and try again. Throughout this entire writing process the goal is precision; the writing has to be absolutely accurate and the wording extremely precise, making the journal articles both dense and generally dull (no flowery adjectives or subjectivity allowed!).  There is also a limit to how much the authors can extrapolate their results.

Almost too scenic to fish. Sascha stream side in Patagonia.

The advantages of this process is that there is an ongoing body of literature which has been judged as sound and provides the basis of further study for any given scientific subject. The number and quality of peer-reviewed publications has also become the standard by which scientists are evaluated.

The disadvantages are that the whole process (from submission to publication) can take months to years, meaning that by the time one study is published the scientist is often working on the next study. Also, you cannot publish a study in more than one journal, and authors of manuscripts are not paid for their publications, if anything they pay the journal to publish their work.

The realities of the peer-review process can also hinder publication. Not only is it often difficult for editors to find reviewers for a manuscript (reviewers volunteer their time and it can take many hours to properly review a single manuscript), but I have also heard many stories of manuscripts that were rejected because an editor failed to find a peer-reviewer who was a true peer and adequately understood the subject matter of the manuscript.  The manuscript can also be rejected based on the challenge to adequately communicate the science, or that the science simply wasn’t ‘up to snuff’.

Submerged brown trout. Bryan Huskey photo.

Next time I’ll go through the major sections of a scientific paper and provide some hints for discerning the important bits and finding the ‘highlights’ that are important to anglers interested learning more about the fish they are after.

Happy fishing!
Sascha Clark Danylchuk