Foraging ecology of grey-headed mollymawks at Marion Island, southern Indian Ocean, in relation to longline fishing activity

• Published in: Biological conservation 2000-12, Vol.96 (2), p.219-231
• Main Authors: Nel, Deon C., Nel, Jeanne L., Ryan, Peter G., Klages, Norbert T.W., Wilson, Rory P., Robertson, Graham
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Animals; Autoecology; Aves; Biological and medical sciences; Dissostichus eleginoides; Foraging ecology; Fundamental and applied biological sciences. Psychology; Grey-headed mollymawks; Incidental mortality; Indian Ocean; Longline fishing; Marine; Thalassarche chrysostoma; Thunnus maccoyii; Tracking; Vertebrata
• ISSN: 0006-3207; 1873-2917
• DOI: 10.1016/S0006-3207(00)00072-0

Incidental mortality due to longline fishing has been implicated as the main cause for the global population decline in grey-headed mollymawks ( Thalassarche chrysostoma). Two of these fisheries, within the potential foraging range of grey-headed mollymawks breeding on Marion Island, have increased drastically over the past 5–10 years. In order to understand the impacts of these fisheries on the grey-headed mollymawk population breeding on Marion Island, we studied their foraging ecology by tracking their foraging trips and sampling their diets. During the incubation stage, birds made long foraging trips, mostly towards the subtropical convergence and sub-Antarctic zones, bringing them into contact with areas of intense southern blue-fin tuna ( Thunnus maccoyii) longline fishing. Females spent a higher proportion of their time within these areas than males, thus exposing themselves to a higher risk of incidental mortality from this fishery. During the early chick-rearing stage, foraging trips were shorter and to the southwest of the island in the Polar frontal and Antarctic zones, thus avoiding any contact with the southern blue-fin tuna industry. However, short foraging trips (