Red and Black Abalone Studies

We are investigating the processes underlying the persistence and possible recovery of black, Haliotis cracherodii, and red, H. rufescens, abalone populations in central California. Abalone populations have undergone precipitous decline in California starting in the late 1960s, and all commercial and sport fishing south of San Francisco was halted in 1997. White abalone, H. sorenseni, was the first marine invertebrate to be included in the U.S. Endangered Species List, and black abalone is now under evaluation for listing. Intense fishing effort, El Nino events affecting feeding and reproduction, predation by sea otters, and disease all contributed to the decline. A major challenge for ecology, conservation, and management is determining what factors and processes allow marine populations to persist and recover after they have been reduced to low levels through fishing or through natural disturbances. We compared abalone abundances and size structure among eight different areas, protected from 10 to 70 years, and resumed a 30-year study initiated by J. Pearse and colleagues in 1972 within the Hopkins Marine Life Refuge (HMLR). Results to date indicate that abalone populations have remained at low densities despite protection, and that densities and size structure have been remarkably stable over the past 30 years, despite intense predation by sea otters. We are currently investigating the demographic and ecological processes that may underlie these patterns by quantifying recruitment, growth and mortality rates of abalone in the field. The next step will be to combine these empirical data with demographic models and stochastic simulations to examine alternative scenarios for persistence or recovery of these populations.