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