Prehistoric Predation on Black Abalone by Chumash Indians and Sea Otters

Present populations of black abalone (Haliotis cracherodii Leach) at Santa Cruz Island, California are presently dense, up to 90/m^2. Examination of shell middens created by Chumash Indians suggests that such high present-day densities may have developed recently after the elimination of the black abalone's two cardinal predators: Chumash Indians and sea otters (Enhydra lutris). The size distribution of abalone in existing populations is skewed towards large individuals (>100 mm) whereas shells from midden populations are smaller (<80 mm). A difference in predation intensity may account for the disparity in population characteristics between historic populations and contemporary populations of black abalone. Intense intraspecific competition among black abalone, as well as certain behaviors, may be recent developments following reduction in predation intensity. If so, black abalone may be experiencing relatively new selection regimes.