Demographic consequences of fisheries interaction within a killer whale (Orcinus orca) population
Individual heterogeneity in foraging behavior has been widely documented within predator populations. In highly social apex predators such as killer whales (Orcinus orca), specialization may occur at the matriline level. A small population of killer whales has been documented to occur around the Crozet Islands. These whales feed on a wide range of prey items including seals, penguins and large whales, as well as depredate the local Patagonian toothfish (Dissostichus eleginoides) longline fishery. The level of interactions with fisheries varies greatly between matrilines. Here, we present the results on the effects of such behavioral heterogeneity on the demographic trends of this killer whale population. We used photo-identification data from 1977 to 2011 in a mark–recapture framework to test the effect of varying levels of fisheries interactions on adult survival. We documented significant differences in survival between depredating and non-depredating whales, resulting in divergent intra-population demographic trends. These differences showed low survival, and thus a negative effect, for depredating whales when illegal fishing occurred (poachers used lethal methods to deter killer whales from depredating longlines). After illegal fishing stopped (2003–2011), the survival rates of depredating individuals exceeded the survival rates of non-depredating individuals, suggesting a positive influence of “artificial food provisioning”. This effect was further supported by a higher population growth rate for depredating whales. This study highlights the potential demographic costs and benefits that cetaceans face from depredating fisheries and addresses the demographic consequences of both intra-population feeding specialization and the influence of anthropogenic changes in resource availability.