UC Santa Barbara

The giant sea bass, Stereolepis gigas, is the largest marine teleost found along the California, USA coast and is an important apex predator in kelp forests and rocky reef ecosystems. Due to their slow-growing nature and tendency to form predictable, seasonal aggregations, S. gigas were fished to near-extinction throughout their entire range: Humboldt Bay, California to Oaxaca, Southern Mexico, and in the Gulf of California. Now listed as Critically Endangered by the International Union for the Conservation of Nature and partially protected by a fishing moratorium in California, there is some evidence that the California S. gigas population has begun to recover. However, there has never been a direct population assessment of their numbers in California. Using more than 1,600 community-sourced photos of S. gigas via the Spotting Giant Sea Bass Project, we identified unique individuals through their spot patterns using machine learning algorithms, as S. gigas have idiosyncratic markings on their flanks. Estimates from a POPAN mark-recapture model suggest an approximate total population of 1,221 adult individuals in Southern California from 2015 to 2022. Additionally, a Pradel mark-recapture model indicates an increasing population trend, corroborated by an increase in incidental catch of S. gigas documented in set gill net incidental landing receipt data. We also found evidence of minimal population connectivity throughout Southern California with high site fidelity amongst resighted individuals. The contribution of this open and living resource of photo-identification data further creates the capacity to answer critical questions regarding the life history, behavior, and population structure of S. gigas, to inform future recovery efforts for this at-risk species.