A Quarter Century of Monitoring the Fish Assemblages of San Diego Bay, California from 1995 to 2019

Abstract. A time series of 22 samples collected in April and July were taken of the fish assemblages of San Diego Bay over 11 non-consecutive years from 1995 to 2019. Each sample consisted of four ecoregions using a variety of collection methods designed to assess all components of the ichthyofauna. These samples yielded a total of 525,288 fishes belonging to 90 species and weighing 3,507 kg over the 25-year period. Northern anchovy was the most abundant fish species comprising 41% of the total catch despite its virtual absence near the end of the survey period, followed by topsmelt, slough anchovy, shiner perch, and Pacific sardine. Round stingrays dominated in weight constituting more than 27% of the total biomass taken followed by spotted sand bass, and northern anchovy. Approximately 64% of all individual fish captured in San Diego Bay during this study were juveniles. In a canonical correlation analysis, temperature, distance from the mouth of the bay, and salinity accounted for nearly 93% of the variance in individual species abundances. In the time series analyses, we found all three potential temporal patterns of fish species abundance, biomass, and diversity, namely: 1) significant decreases over time, 2) significant increases over time, and 3) no significant change over time. Abundance of eight of the top 35 species (including northern anchovy, topsmelt, slough anchovy, and shiner perch) and all forage species combined decreased over the study. Two species increased significantly in abundance, spotted sand bass and dwarf perch. Whereas, total abundance, total biomass, species richness, Shannon diversity, and the majority (71%) of species abundances did not change over the 25-year period. Despite various environmental perturbations and the general trends of decreases in larval and fish abundance indices over the Southern California Bight in recent years, the stability in species richness and composition over time reflects the generally resilient nature of the fish assemblage structure of San Diego Bay that has been maintained by active management including restoration practices.