“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