Foraging behaviour and habitat utilisation of Australasian gannets determined using GPS loggers

Australasian gannets (Morus serrator) breed in the cool temperate waters of south-eastern Australia and also at several localities around New Zealand, where they are a major marine predator feeding on commercially-exploited pelagic fish. This study investigated the foraging behaviour and habitat utilization of gannets at Pope’s Eye Marine Reserve during the 2005-2005 breeding period using GPS-depth-loggers. GPS data were recorded for a total of 45 foraging trips from 20 individuals. Gannets were found to forage at average maximum distances of 52.7 km (± 29.6 km) from the colony, with total foraging path lengths of 177.1 km (± 93.4 km) and foraging trip durations of 16.5 h (± 9.9 h). During foraging trips gannets spent on average 31.5% (± 11.4) of the time flying at an average flight speed of 47.3 km h-1 (± 2.9 km h-1). Gannets made an average of 39.8 (± 35.2) dives per trip and 3.8 (± 5.6) dives per daylight hour. Dives had an average depth of 3.5 m (± 1.1 m) and a mean maximum depth of 7.0 m (± 3.0 m), lasting for a mean dive duration of 5.3 sec (± 1.3 sec). Gannets foraged predominantly in shallow coastal waters and there was some evidence for foraging site fidelity. Considerable individual variation in foraging strategies was also observed. The results highlight the potential of GPS technology to reveal the fine-scale foraging behaviour of marine predators, thereby improving our understanding the interaction between marine predator populations, commercially exploited fish stocks and the marine environment.