リリース後のバスはどこへ向かうのか？

In late August 2021 the North American Journal of Fisheries Management published the long-awaited results of research conducted in Canada on the post-release behavior of smallmouth and  largemouth bass. The research was conducted in Eastern Ontario on Big Rideau Lake during early, mid and late season tournaments. Researchers included Alice E. I. Abrams, A. J. Zolderdo, Elodie J. I. Lédée, Michael J. Lawrence, Peter E. Holder, Steven J. Cooke, and a cohort of willing anglers. An abstract of the research reads as follows, “Black  bass fishing tournaments with conventional weigh-ins tend to displace fish from their capture site and often release fish within close proximity to the weigh-in site. Tournaments often include largemouth bass Micropterus salmoides and smallmouth bass M. dolomieu and occur throughout  fishing seasons; however, there have yet to be any systematic congeneric comparisons across different seasons.” All this to say, the researchers used the latest fish tracking technology to determine what happens to bass after they are released following fishing tournaments. Not just if they survive, but where they go. A total of 88  largemouth and smallmouth bass caught during the three tournaments were fitted with acoustic tags and then released from the same area where the weigh-ins took place. A preseason control group of 30 bass were captured, tagged and also released in the same area. The bass had their geospatial movements tracked using receivers situated around the weigh-in release site, along the passage that led back to the main body of the lake, and throughout the lake itself. The 88 tournament-caught  bass that took part in the research were selected based on the willingness and ability of anglers to share with researchers where each individual bass was caught using a map of the lake. If an angler wasn’t absolutely certain where a specific  fish was caught, or was unwilling to disclose this information, the bass was rejected by the researchers. Data shows that upon being released bass experienced a short-term stockpiling within 300 meters of the release site. All 88 bass eventually left the area – The largemouth taking on average 4.6 days, and the Smallmouth bass left within a day. The distance from the release site to the main body of the lake where all 88 tagged fish were caught is over 10 kilometers. The  Largemouth bass took just under 240 days to return to the main part of the lake, and the smallmouth bass took less than half that time. The smallmouth that took the longest to return (108 days) were caught during the October tournament. Researchers concluded that, “although  fish do survive and eventually return to the main basin, displacement may have broader ecological consequences such as “large-scale displacement of top predators and adverse effects on recruitment”. They conclude that, “there may be merit in tournaments adopting a catch–weigh–release format instead of bringing fish to a central weigh-in location.” There’s plenty of research that has informed how to manage tournament weigh-in processes to mitigate  bass mortality. Many large tournaments also employ boats especially equipped to move bass away from tournament weigh-in sites to facilitate their dispersal. Numerous smaller bass tournaments have adopted these best practices. However, until now, no one has determined where bass go after being released, and just how much time and effort bass expend in the process. I spoke with Dr. Cooke about the research, and he confirmed that each of the bass caught and tagged returned to where they were originally caught. The fact that bass prefer to range within their specific territory should come as no surprise. Even smallmouth  bass known for roving in “wolf packs” routinely visit the same locations. Larger bass will even drive off other bass that are perceived as trespassing. Obviously, just like any animal, bass are creatures of habit. I asked Dr. Cooke how bass manage to navigate their way around a lake, and to find their way back to their home turf. You would be amazed to hear the different tests Dr. Cooke and his team conducted to learn how bass navigate their environment. Dr. Cooke shared with me details of the bass release research along with findings from his research on hook removal techniques and bass mortality. He even had new research to share on how  bass fair when caught through the ice. You can hear my conversation with Dr. Cooke by linking to the below podcast episode of The Blue Fsh Radio Show. https://www.spreaker.com/user/5725616/e347-dr-cooke-on-bass-post-release-behav So, what does all this mean for tournament angling? We know that bass survive post release and that they do eventually return to their preferred range. But what about bass caught during tournaments held on rivers – do they return home if it means swimming up stream? At the very least, we now know bass will have ample opportunity to move away from a weigh-in site before another tournament is held the following weekend, but that doesn’t guarantee they won’t be pressured by anglers who happen upon recently released  bass before they have had sufficient time to clear out. Bringing bass back to a centralised weigh-in location has positive aspects as well. The health of bass can be assessed by tournament officials.  Bass are observed to make sure they are healthy, and anglers are penalised if a fish is judged as mortally wounded. Captured fish can also be examined and samples taken, or tags attached by researchers. Conducting fish health research is challenging as it entails finding and capturing fish. Researchers depend on fishing tournaments to collect samples and attach tags and other tracking devices. Lots and lots of discussion and debate over  fish welfare and tournament rules has already occurred, and without doubt will continue to dominate pre-tournament planning meetings. New innovations, fish handling best practices, rules and penalties are always being adjusted to fit with what we know and what the public expects. Without the trust of the public, the anglers and the sponsors,  bass tournaments would not exist. Bass anglers want to do the right thing, they care about the resource, and they contribute significantly to habitat restoration and research both in terms of money and time. How tournament organizers and anglers respond to the results of the research undertaken by Dr. Cooke and his team will be interesting to track over time as well. Major League  Fishing is a relatively new tournament series that has grown quickly in popularity. It uses a capture, record and release format, but is dependent on 2nd party observers to ensure accurate self reporting. Most amateur bass tournaments involve a team of two  bass anglers. Adding a third observer in each boat poses considerable additional logistical challenges. However, digital real-time measuring and recording technologies could make such human observers redundant. We already pay thousands more for our boats to be equipped with live wells used for keeping fish alive during their transportation back to weigh-in sites. Why not instead allocate this money to pay for secure digital remote reporting equipment that would allow anglers to release bass back into the water where they are caught? Angler apps already on the market possess much of the needed technology to support catch-record-release  fishing tournaments. Their use throughout North America is growing steadily in popularity. In the end though, if an angler is bent on cheating, no rule or technology will stop them from trying their hand.