Illegal fishing bycatch overshadows climate as a driver of albatross population decline
Résumé
Effective management of albatross populations requires understanding the impacts of environmental factors on albatross demographics. An integrated modeling approach, incorporating multiple data sources, can further the understanding of albatross demographics by incorporating error from all components of modeling and distinguishing between variability related to one factor (e.g. environment) from that of another factor (e.g. density-dependence). We apply such an integrated, spatially-explicit population model to quantify the impact of environmental conditions (sea-surface temperature: SST), fisheries, and density-dependence on a black-browed albatross (Thalassarche melanophris) population breeding on Kerguelen Island, southern Indian Ocean for the period 1950-2011. The model is structured by sex, age-class, and breeding stage, with a 5 × 5 spatial scale and monthly temporal scale. All parameters are estimated within a maximum-likelihood framework. This includes estimation of the seabird bycatch rates of each of five fishing super-fleets, grouped by gear-type and reported bycatch rates: (i) Japanese pelagic longline, (ii) other pelagic longline, (iii) legal demersal longline, (iv) trawl, and (iv) illegal, unreported and unregulated (IUU) demersal longline. A decline in the Kerguelen black-browed albatross population occurred between the mid-1990s through the mid-2000s. Our analysis attributes the majority of modelled bycatch to the IUU demersal longline super-fleet operating near Kerguelen for this period. Including SST during the incubation period indicated that warm SST favors high breeding success. These results indicate that effective management requires an integrated understanding of the impacts of the environment, illegal, and legal fishing activities on vulnerable populations