On the road to extinction? Population declines of the endangered white abalone, Haliotis sorenseni

In 2001, the white abalone (Haliotis sorenseni) became the first marine invertebrate to be listed as endangered under the Endangered Species Act (ESA). Low densities and recruitment failure due to Allee effects were identified as being the major threats to the species’ long-term viability. Visual transect surveys conducted using a remotely operated vehicle (ROV) since 2002 indicate a dramatic and continued decline in white abalone total abundance (∼78% decrease) and density (33–100% decrease, depending on depth and year) between 2002 and 2010 at Tanner Bank, an area of historically high abundance (>1/m2). An increase in the size distribution over this same time period suggests individuals in the white abalone population are growing larger (and aging) with little or no indication of adequate recruitment success. The vast majority (between 77% and 89%, depending on the year) of white abalone were observed alone, which suggests that the likelihood of reproductive success within this population remains very low. The continuing decline 30 years after the last major commercial harvest demonstrates that the strategy of benign neglect, or allowing the population to recover without intervention, has clearly failed. We recommend immediate proactive conservation through population enhancement by out-planting healthy, captive-bred white abalone in areas where populations have reached or are approaching local extinction.

► White abalone, Haliotis sorenseni, was listed as endangered in 2001. ► Low densities are thought to inhibit recovery through poor reproductive success. ► A 75% decline was observed in an isolated population between 2002 and 2010. ► Remaining adult abalone are growing older and new recruitment appears to be minimal. ► More proactive conservation measures, such as population enhancement, are recommended.