Male harassment of female New Zealand sea lions, Phocarctos hookeri:: mortality, injury, and harassment avoidance

Sexual aggression by male pinnipeds during breeding can lead to female injury and death, affecting reproductive success, fecundity, and increasing the cost of mating for females. Thus, females that employ strategies to minimize the probability of being injured will be at an advantage. Here we investigate the extent of injuries and the number of deaths attributed to male harassment, and test the hypothesis of whether the arrival and departure behaviour of female New Zealand sea lions (Phocarctos hookeri (Gray, 1844); NZSL) at Sandy Bay, Enderby Island, the Auckland Islands, is adapted to reduce the chance of injury or death from encounters with male NZSLs. During the breeding season, harassment by non-territorial male NZSLs causes mortality in adult female NZSLs, approximately 5 in every 1000 females breeding each year. Permanent scars from male bites are observed on 84% of adult females. This mortality and visible injury rate only represents the direct impacts on female NZSL from male harassment. Indirect impacts, such as the time and energy cost of avoidance behaviour, pup separation, and pup injury and death, can have as significant long-term effects on individuals and the population. We find that male harassment can influence the behaviour of individuals in NZSL breeding harems.