COS 82-1
Fishery-induced selection: What can be learned from introduced salmonids in sierra Nevada lakes?

Wednesday, August 13, 2014: 1:30 PM
Golden State, Hyatt Regency Hotel
Sebastien Nussle, Environmental Science, Policy, and Management, University of California - Berkeley, CA
Michael T. Bogan, Environmental Science, Policy & Management, University of California, Berkeley, Berkeley, CA
Roland A. Knapp, Sierra Nevada Aquatic Research Laboratory, University of California
Mitch Lockhart, Fisheries Branch, California Department of Fish and Wildlife
Stephanie M. Carlson, Environmental Science, Policy & Management, University of California, Berkeley, Berkeley
Background/Question/Methods
Size-selective fishing is expected to trigger evolutionary changes but the potential for fishery-induced selection to significantly modify population characteristics is controversial and not yet well understood. More research is needed to understand how and when size-selective fishing alters traits and dynamics in harvested populations. In this study, we analyzed data from over 30 populations of non-native brook trout (Salvelinus fontinalis) and rainbow trout (Oncorhynchus mykiss) that were completely removed from lakes in California’s Sierra Nevada during the course of a habitat restoration program. In total, over 45,000 fish were harvested via gill nets and electro-fishing, and length-at-capture and time-at-capture were recorded for nearly every fish. We used these data to estimate fishery selection on body length in replicate populations, and to relate the strength of fishery selection to population- and habitat-specific characteristics.
Results/Conclusions
Even though “non- selective fishing gear” (e.g. variable mesh size gill nets) was used in removal efforts, we found that fishing was more likely to remove larger individuals. Due to this size selectivity, we observed a dramatic decline in the mean and variability of fish length within a few months across populations. The magnitude of this decrease may be linked to population-specific parameters, such as initial size distribution, which could be in turn be driven by local environmental factors (e.g. lake size, elevation). Our study demonstrates that size-selective fishing not only affects population structure by removing the largest individuals, but also that the environment can mediate the impact of fishing. These findings highlight how fishery-induced selection may influence harvested populations and may help inform population-specific management or conservation plans.
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