Overall Status and Threats Assessment of Black Abalone (<i>Haliotis Cracherodii</i>Leach, 1814) Populations in California

Abstract

The black abalone (Haliotis cracherodii Leach, 1814) is a relatively large prosobranch gastropod mollusc ranging from approximately Point Arena in northern California to Bahia Tortugas and Isla Guadalupe, Mexico. In the United States, populations of black abalone on offshore islands, especially those of southern California, were particularly large prior to the mid 1980s. Analysis of long-term fishery-dependent and -independent data revealed that fishing pressure in combination with a lethal disease, withering syndrome, has resulted in mass mortalities of 95% or greater in black abalone populations south of Monterey County, CA. Reduction in local densities below the threshold necessary for successful fertilization (0.34/m2) has been a widespread and pervasive consequence of population reductions by withering syndrome and other factors. The most significant current and future threat that the black abalone faces is that imposed by the spread of withering syndrome, known to be enhanced by periods of ocean warming. Other factors, such as illegal take, ocean pollution, and natural predation, also pose risks to remaining populations and those that may be restored via active management in the future. Without identification, development, and implementation of effective measures to counter the population-level effects of withering syndrome, remaining black abalone populations may experience further declines.