Vital rates of pink abalone Haliotis corrugata ­estimated from mark-recapture data to inform recovery

Abstract

Pink abalone Haliotis corrugata have declined dramatically in southern California despite once being the most important species in the abalone fishery before its closure in 1997. We estimated vital rates using mark-recapture data of pink abalone from San Diego (2003-2007) and Santa Catalina Island (1970-1972), California, and juveniles reared in the laboratory in San Diego (2006-2007). We fit 7 growth functions to annual growth increment data to estimate age at maturity, time to reach the minimum legal size (MLS) in the historic fishery, and the number of reproductive years before reaching the MLS. We used demographic data to construct a growth transition probabil- ity matrix based on the best-fit (Richards) model. We estimated that pink abalone grow slowly (k = 0.07 yr -1 ), reaching a maximum length of 200 mm, and have high adult survivorship (0.77 yr -1 ). We used non-lethal methods to estimate size at maturity, which was 99 mm for males and 103 mm for females (8.2 to 8.7 yr), with 19 yr to reach fishery size. Survival rates in this population did not differ between years or genders, but severe cuts to the foot during handling did decrease survivorship. Despite low population densities, we show evidence of some juvenile recruitment to the region. The slow growth rates suggest that the populations within the southern California abalone fishery closure area could take 30 yr to recover, provided there is successful reproduction and the high survival of adults continues without illegal fishing. Estimating vital rates and demographic characteristics using non-lethal methods provides critical information for investigating the dynamics of low-density populations.