Using community science to assess the population dynamics and spatial ecology of the giant sea bass in Southern California

The giant sea bass Stereolepis gigas is the largest marine teleost along the coast of California, USA, 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 heavily overfished across much of their range from Humboldt Bay, California, to Oaxaca, Southern Mexico, and in the Gulf of California. Now listed as Critically Endangered by the IUCN and partially protected by a fishing moratorium in California, there is some evidence that the California population has begun to recover. However, there has never been a direct population assessment of their numbers in California. Using more than 1600 community-sourced photos of S. gigas from the Spotting Giant Sea Bass Project, we identified individuals through unique spot patterns on their flanks by using pattern-matching algorithms. Estimates from a POPAN mark-recapture model suggest a total population of ~1221 adult individuals in Southern California from 2015 to 2022, and a Pradel mark-recapture model indicates an increasing population trend, corroborated by a rise in incidental catch of S. gigas in set gill net landing receipts. 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 creates the capacity to answer critical questions regarding the life history, behavior, and population structure of S. gigas , which will inform future recovery efforts for this at-risk species.