A new study indicates that for many species of oceanic sport fish, individual fish that are caught, released and re-fished are more likely than scientists expected. The results raise some interesting questions for policymakers charged with preserving sustainable fisheries.
The study uses data from labeling programs, in which researchers tag the fish and release them into the wild. When these fish are caught, and the tag information is returned to the researchers, they can give scientists information that benefits fisheries policies.
Geoff Buckle, co-author of the study and professor of applied ecology at North Carolina State University, says.
To this end, the researchers examined decades of Atlantic coast marker data sets on four species of fish: black bass (Centropristis striata), gray triggerfish (Balistes capriscus), red grouper (Epinephelus morio) and Warsaw grouper (Hyporthodus nigritus). Using a mathematical model, the researchers determined – for the black sea bass and both species of grouper – that survival was significantly higher after the second, third, and fourth editions compared to the first.
“Think about it this way,” says Brendan Rund, senior author of the study and PhD. A student in North Carolina. Suppose you tag 1,000 fish and recover 100 of them for the first time. After releasing these 100 fish, you only expect to recover 10 of them a second time. But this is not what we see. We see many more fish captured after the second time.
“Our hypothesis is that this increase in catch stems from the selection of powerful individuals,” says Rond.
In other words, since some fish do not survive the first release, and you cannot catch a dead fish, fish that were strong enough to survive were more likely to survive after catch and release events.
The outcome can have a significant impact on stock valuations, which guide fisheries policy.
“One would assume that everything caught and released in recreational fishing is a unique fish,” says Buckle. “So if 5 million black sea bass are caught and released in a given year, that means that there are at least 5 million black sea bass in a fishery. For these three species of fish and probably many others, this is Not true. At least some of these five million people that were caught were the same fish that were caught over and over again. “
“Reliable estimates of the number of unique fish released are essential to accurately assess the health of a population,” says Kyle Schertzer, a study co-author and stock valuation scientist at NOAA Fisheries.
“On the positive side, the study also indicates that for many species, the mortality rate of fish from release appears to be lower than we thought,” says Bacle. “For these species, if a fish survives its first release, it has a better chance of surviving a later release.”
“We believe that the issues raised by our findings are likely to be relevant to the many marine fish stock assessments that rely on catch and release data – although this will vary based on species and details of how each stock assessment is conducted,” he says.
The paper, “Repetitive Fishing of Marine Fish: Implications for Estimating Releases and Deaths,” was published in ICES Journal of Marine Sciences. The paper was co-authored by Paul Rudershausen, a researcher in the North Carolina Department of Applied Ecology. Nate Bashler of NOAA Fisheries; And Beverly Sols of the Florida Institute of Fish and Wildlife Research.
Work performed with support from NOAA, under grants NA14NMF4540061, NA09NMF4720265 and NA09NMF4540140; And from the North Carolina Marine Grant Fisheries Resource Project 07-FEG-01 and 11-FEG-04.