At-sea distribution and diet of an endangered top predator: links of white-chinned petrels with commercial longline fisheries

Incidental seabird mortality associated with longline commercial fishing is a worldwide conservation concern. To build conservation strategies it is essential to estimate likelihood of seabird bycatch and amount of overlap between bird’s foraging and commercial fishing areas. We tracked 21 adult white-chinned petrels (Procellaria aequinoctialis) breeding on Kerguelen Island, Southern Indian Ocean, during breeding period in 2006 and 2008. At-sea foraging distribution of white-chinned petrels was mainly confined in Antarctic waters. Commercial longline fisheries targeting toothfish were operating in both French Exclusive Economic Zone (EEZ) and other Commission for the Conservation of Antarctic Marine Living Resources areas during the study. We analysed concurrent data on the position of both birds and vessels to estimate overlap. Static analysis using indices (home range and utilization distribution overlap) revealed that at a large scale spatial and temporal overlap occurred and varied among areas and with breeding stage. Dynamic analysis (detection for each bird location of any operating vessel within a time/space window) revealed few overlap at a small scale. Our study revealed a mismatch between large and small scale overlap estimates, suggesting that birds and vessels occupy the same overall zone with infrequent co-occurrence (19% of birds in the vicinity of vessels). This result was confirmed by the relatively low occurrence of fishery-related items (4 to 22%) in chick food samples. However given the large size of seabirds populations, overall large numbers of birds overlap with vessels and Management Authorities should maintain and promote strict mitigation measures implementation to further reduce bycatch.