Combined effects of fisheries and climate on a migratory long-lived marine predator
1 The impact of climate on marine ecosystems is now well documented, but remains complex. Climate change may interact with human activities to effect population dynamics. In addition, in migratory species conditions are different between the breeding and wintering grounds, resulting in more complex dynamics. All these possible effects should be considered to predict the future of endangered species, but very few studies have investigated such combined interactions. 2 As a case study, we assessed the relative impact of fisheries and of oceanographic conditions in breeding and wintering sites on adult survival and breeding success of a population of the endangered black-browed albatross Thalassarche melanophrys in the Kerguelen Islands, Southern Indian Ocean. This study was based on long-term monitoring of individually marked individuals (1979–2005) and identification by tracking studies and band recoveries of the oceanic feeding zones used during breeding and non-breeding seasons. 3 Breeding success was variable until 1997 and then declined gradually, from 0·88 to 0·48 chicks per egg laid. It was favoured by positive sea-surface temperature anomalies (SSTA) and trawl fishery during the breeding period, whereas it was negatively affected by positive SSTA around Tasmania, where the species winters. Adult survival was 0·918 ± 0·004 on average and increased with SSTA during incubation, but decreased significantly with high tuna longlining effort in the wintering zone. 4 Our analyses show that demographic parameters were influenced by both climate and fisheries in both breeding and wintering grounds, but with different effect size. Black-browed albatross breeding success was more favoured by trawlers’ offal and discards than by any of the seasonally/spatially oceanographic conditions, whereas their survival was equally affected by tuna longline fishery through incidental by-catch and spring SSTA. 5 Synthesis and applications. Our work underlines that a comprehensive knowledge of the life history of a species in all the habitats used is important to disentangle the respective roles of environmental conditions and human factors on population dynamics. Identification of these effects is required when proposing effective conservation measures, because the conservation of threatened species may depend on their wintering country's exclusive economic zones.