White abalone at San Clemente Island : population estimates and management recommendations

White abalone (Haliotis sorenseni), a marine mollusk indigenous to southern California, was listed as endangered in 2001. In 2004, underwater surveys using a remotely operated vehicle (ROV) identified several remnant populations of white abalone, including one along the west and south shores of San Clemente Island (SCI). In 2012, another survey of white abalone habitats was conducted at SCI to examine potential changes in that population. White abalone are sparse at SCI; only five white abalone (mean shell length of 17.2 cm (standard deviation (SD) = 2.2 cm and 17.7 cm (SD = 1.8 cm) in 2004 and 2012, respectively) were observed in each of the two surveys. Average densities were 0-1.24 abalone per hectare (ha-1) in 2004 and 0.27-1.44 abalone ha-1 in 2012, which resulted in a slight increase in the population from 353 (standard error (SE) = 62) to 565 (SE = 136) white abalone during that time. However, the low density and patchy distribution of white abalone at SCI resulted in high coefficients of variation (CVs) for population estimates in all years and depths (CV = 0.70-0.96). In order to slow down or halt the progression towards local extinction at SCI, NMFS recommends the following steps be taken: 1) the U.S. Navy (Navy) should continue to support research and monitoring efforts that focus on learning more about the movements, growth and spawning behavior of its small but persistent population; 2) the Navy should continue its outreach and education mission in order to discourage illegal take of all abalone species at SCI; and 3) the Navy should consider the locations of the observed animals when planning operations that may impact white abalone or its habitat at SCI. These recommendations are provided at the request of the Navy as stipulated in the funding agreement.