A Decade of Scuba Effort Reevaluates Approach for Surveying White Abalone (Haliotis sorenseni Bartsch, 1940)

Abstract

Accurate distribution and density data of endangered marine species may be complicated by artifacts from exploitation, survey design, and general difficulty in accessing subtidal habitats. Occasional review of survey data may help restructure survey efforts to improve conservation outcomes. The white abalone (Haliotis sorenseni) is a marine gastropod listed under the Endangered Species Act thought to primarily inhabit depths beyond conventional scientific SCUBA limits (30–60 m) in the southern California Channel Islands. This study reviews surveys at four Channel Islands and four locations along the southern California mainland coast within SCUBA depth ranges and conducts a simulation comparison of the larger survey design used for this study with the standard transect approach presently common in the region. White abalone density was greater along the mainland, particularly in Point Loma and La Jolla, than the Channel Islands, where no live white abalone were recorded. The larger survey approach was found to be more effective at finding simulated white abalone, beyond the expected difference in areal coverage alone. These results show that surveys within SCUBA limits are an effective way to monitor H. sorenseni and that impacts from overfishing on the Channel Islands may make sections of the mainland coast one of the last refuges of white abalone. The greater efficiency of larger surveys can complement standard transect approaches to improve abalone monitoring at sites of interest. Both results can be applied to the immediate conservation of white abalone by improving site selection and monitoring approaches to active restoration efforts.