CATCH-AND-RELEASE IMPACTS ON A FISHERIES GENETIC HEALTH
ENJOYED THE THOUGHT-PROVOKING ARTICLE in Issue 88 about the lasting genetic implications of catch-and-release in headwater fisheries ( An Eye
Towards The Future) and agrees with the sentiment that catch-and-release is an important part of the fishing scene in New Zealand, but not necessarily for the reasons discussed.
Species genetics are developed over a long time and are slow to change, but characteristics change more quickly as they are constantly influenced by their habitat, food, and predation. This explains why, for example, brown trout that travel into the sea can reach huge sizes while high altitude, landlocked lake populations can be stunted, but are still genetically the same. Sub-species, or even new species, are formed when one of these populations develop charactistics best suited to that environment, but are isolated for many millions of years. Our long fin eel is a good example of a new species of eel after being isolated from other eel populations for more than 80 million years.
Trout are a very versatile species that have been moved all around the world, creating many new fisheries, each with its point of difference. But a brown trout is still a BT and rainbow is still a rainbow even when local conditions have started to create observed differences. Add to this the fact that individual trout can vary in length, colour, and condition in response to food supplies and habitat conditions. For example, that typical 4lb fish you see in your local waters could be 3lb after a damaging flood and 8lb during a mice plague. Age varies as well, with a 4lb trout caught in the Mataura catchment aged at 13 years and 32lb caught in the Waiau River aged at four years. Provide lots of food and trout will grow big quickly -- that is why they are farmed.
In terms of trout genetics in headwater fisheries, let us not forget that New Zealand research has confirmed that these large trout did not actually grow large in these waters. They grew in the lower sections of the rivers or lakes and then migrated upstream to breed. Some stay -- mostly males -- to breed again next year and can maintain their size by selecting the larger macroinvertebrates easily spotted in the clear water. So this explains their presence, but does not support an isolated genetic pool of large fish in the headwaters. Instead, it shows how important it is for trout to have full access to a catchment to survive all its variables and take advantage of opportunities to grow and reproduce. Growth for fish, including trout, equates to more productive breeding and survival from predators.
Based on this knowledge, fishery managers spend a lot of anglers’ licence fees on defending waterways from dams and pollution to retain fish passage and habitat throughout a catchment, not just the headwaters. Research into headwater fisheries use has confirmed that the presence of large trout is the key value sought by anglers, so catch-and-release areas were trialed and found to have little influence on trout size and numbers so low bag limits and slot sizes limits were introduced to mainly protect the fishing experience for anglers rather than a population protection measure. Catch-and-release has been frequently voluntarily practiced in headwaters for many decades now and it is proving to be effective at retaining larger trout to the increased numbers of anglers accessing these areas, but will catch-and-release influence genetics in the future?
Given trout come from a very versatile genetic pool, which is constantly mixed by new arrivals from the catchment ( browns even from other catchments) and continues to be shaped by environmental conditions, I think that given these fish represent only a tiny portion of a fishery it is unlikely catch-and-release influences genetics. Perhaps the opposite is true, as catch-and-release allows these trout to continue to breed, limiting new arrivals that may bring with them improved local characteristics that will eventually lead to a fish better adapted to that environment.
My point of view is that voluntary catch-and-release is an important fishery management practice that helps to retain larger trout, which can be caught by increasing numbers of headwater anglers. But if we want to protect the genetics of a fishery, we must protect its whole environment from habitat damage and dams to allow the continuing development of local characteristics that will ultimately dictate the fisheries future.