Linking angling catch rates and fish learning under catch-and-release regulations

Many recreational fisheries are subject to varying degrees of catch-and-release fishing through regulations and conservation-minded anglers. Clearly, releasing a proportion of the catch improves conservation of the fishery, yet it is not clear how the released catch contributes to angling quality. If fish change their behavior to lower their individual catchability after they have been caught, then angler catch rates may not be proportional to fish density. Therefore, even catch-and-release fisheries could exhibit poor angling quality if there is sufficiently high angler effort. We tested this idea by experimentally fishing five small lakes that contained rainbow trout Oncorhynchus mykiss in the interior of British Columbia. We found that with sustained effort of 8 angler-hours . d(-1) . ha(-1) and complete release of the catch, catch rates quickly dropped within 7-10 d. Given the individual capture histories of tagged fish, the most parsimonious catchability model incorporated learning and heterogeneity into intrinsic catchability. The best-fit parameter values suggest that the population contained a group of highly catchable fish that were quickly caught and then learned to avoid hooks. There was a seasonal decrease in catchability that was independent of angling; however, it was not sufficient to explain the data. Our results indicate that catch rates may decline because of high angling effort even when the number of fish remains constant. Therefore, management goals that go beyond conservation issues and attempt to maximize angler satisfaction must account for effort density on a recreational fishery.