Illegal fishing bycatch overshadows climate as a driver of albatross population decline

Effective management of albatrosspopulations requires understanding the impacts of environmental factors on albatrossdemographics. An integrated modelling approach incorporating multiple data sources can further the understanding of albatrossdemographics by incorporating error from all components of modeling, and help distinguish between variability related to one factor (e.g. environment) from that of another factor (e.g. density dependence). We applied such an integrated, spatially-explicit population modelto quantify the impact of environmental conditions (sea surface temperature, SST), fisheries, and density dependenceon a black-browed albatross Thalassarche melanophrispopulation breeding on Kerguelen Island, southern Indian Ocean for the period 1950 to 2011. The model was structured by sex, age-class, and breeding stage, with a 5° × 5° spatial scale and monthly temporal scale. All parameters were estimated within a maximum likelihood framework. This includes estimation of seabird bycatchrates of each of 5 fishing super-fleets, grouped by gear type and reported bycatchrates: (1) Japanese pelagic longline, (2) other pelagic longline, (3) legal demersal longline, (4) trawl, and (5) illegal, unreported, and unregulated (IUU) demersal longline. A decline in the Kerguelen black-browed albatrosspopulation occurred between the mid-1990s through the mid-2000s. Our analysis attributes the majority of modelled bycatchto the IUU demersal longline super-fleet operating near Kerguelen Island 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 as well as illegal and legal fishing activities on vulnerable populations.