Bioarchaeological research among prehistoric Pacific Coast populations has shown that external auditory exostoses (EAE) are found in high frequencies. On California's northern Channel Islands archaeological research has demonstrated that there was an intense exploitation of red abalone (Haliotis rufescens), particularly between similar to 8000 and 3500 years ago. If the Island Chumash were free-diving for red abalone in subtidal waters, EAE should be prevalent in prehistoric populations from Santa Rosa Island. We recorded the presence or absence, number, side and severity of EAE growths for 207 adult individuals from three time periods on Santa Rosa Island. Our results show that similar to 11% of the total population was affected, including 22.5% of males and similar to 3.4% of females. The incidence among females increases from 0% in the Early period, to 2.6% in the Middle period, and 6.8% in the Late period. Overall these are lower rates than those reported for other Channel Island and Pacific Coast sites. Given the relatively low percentage of Santa Rosa Islanders affected with EAE, red abalones may have been harvested primarily in shallow waters rather than the deeper subtidal zone. Our data suggest that gender differences in food procurement activities existed on Santa Rosa Island throughout prehistory, congruent with the argument that EAE is an activity-induced pathology that occurs with prolonged exposure to cold water and wind conditions. Copyright (C) 2015 John Wiley & Sons, Ltd.