Distribution and habitat associations of the California moray (Gymnothorax mordax) within Two Harbors, Santa Catalina Island, California

While kelp forests are some of the best-surveyed ecosystems in California, information on cryptic inhabitants and their role within the community are lacking. Kelp itself provides overall structure to the habitat; however the rocky reef to which the kelp attaches is known to provide additional structure for cryptic species. Gymnothorax mordax, the California moray, is an elusive predatory species that is considered abundant in the waters around Catalina Island. However, no life history data exists for this species. We examined habitat composition, relative abundance, size pattern distributions, and biomass of G. mordax within Two Harbors, Catalina Island. Habitats were sampled using a combination of baited trap collection and transect surveys using SCUBA. A total of 462 G. mordax were captured, primarily in shallow (< 10 m) waters. Individuals of G. mordax were associated with mostly boulder and cobble substrates. Measurements of relative abundance and density indicate that G. mordax is more prevalent than reported in previous studies. We also discovered that the 6 trapping sites from which all morays were collected, differed in size structuring and density while the relatively high biomass did not change across sites. In general, southern facing sites exhibited higher densities of morays, while northern facing sites showed more size structuring. We show how the structural complexity of the rocky reef habitat in an already diverse kelp forest ecosystem, can support a high biomass of a cryptic elongate predatory fish.