A Small Foray into the Realm of Giants: Investigating the Movement Ecology of Giant Sea Bass (Stereolepis gigas)

Giant Sea Bass (Stereolepis gigas) faced a steep population decline following severe overfishing in the early twentieth century. In response, the state of California enacted fishing regulations in 1981 that completely closed the recreational fishery, and substantially limited the commercial fishery. Today, Giant Sea Bass populations are apparently recovering, though they are still impacted by incidental catch in the US and the unregulated commercial fishery in Mexico. Understanding the roles of spatially explicit resource management and fisheries on the recovering Giant Sea Bass population requires information on the spatial ecology of individuals. In this study, we used acoustic tag tracking and stable isotope analysis to gain insight regarding habitat use and trophic ecology of the species. We analyzed the stable isotope ratios of carbon and nitrogen from fish collected in the Baja California Peninsula in Mexico and in La Jolla, California. Carbon stable isotope ratios were significantly more enriched in larger individuals than smaller ones, indicating size-dependent trophic specialization. Since November 2018, we have acoustically tagged six Giant Sea Bass in and around the La Jolla Kelp Forest. In general, tagged individuals have remained within close proximity of original tagging locations. Of the three fish that have been tracked for multiple months, one spent almost half its time in marine protected areas adjacent to tagging locations. Our findings, though preliminary, suggest that California’s spatial marine management confers at least some protection to Giant Sea Bass stocks. On the other hand, these protections may vary across the species’ ontogeny based on stable isotope ecology.