Interactions and Post-Release Survival of Juvenile White Sharks Incidentally Caught in Coastal Southern California Gillnet Fisheries

Of all commercial and recreational fisheries in California, the gillnet fisheries are known to have the highest degree of interaction with white sharks (Carcharias carcharodon), particularly juveniles in southern California.  To evaluate fishery interaction and post-release survival of juvenile white sharks captured in gillnet fisheries, a collaborative research program was established with willing commercial gillnet fishers from 2006-2009.  Incidentally caught sharks were tagged with acoustic or satellite transmitters (PAT and SPOT) to determine post-release survival and subsequent movements relative to annual gillnet fishing effort. Spatial comparison of SPOT tag detections and annual fishing effort indicated a moderate degree of overlap in shark area use and fishing activity.  Incidence of shark capture (CPUE) was not correlated with target catch CPUE.  Post-release survival was high (92.9%); however, annual net mortality varied considerably over years (44±24%). Likelihood of net mortality was higher if net sets were longer than 24 hrs.  Current protections for white sharks appear to be working because of high post-release survival, and mortality rates could be further decreased by reducing net soak times.