Monitoring the Prey-Field of Marine Predators: Combining Digital Imaging With Datalogging Tags

Authors

Sascha Hooker, British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 OET, United Kingdom
Ian L. Boyd, British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 OET, United Kingdom
Mark Jessop, British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 OET, United Kingdom
Oliver Cox, Wild Insight Ltd, 5 Cambridge Road, Ely CB7 4HJ, United Kingdom
John Blackwell, Wild Insight Ltd, 5 Cambridge Road, Ely CB7 4HJ, United Kingdom
Peter Boveng, National Marine Mammal Laboratory, Alaska Fisheries Science Center, National Marine Fisheries Service
John Bengston, National Marine Mammal Laboratory, Alaska Fisheries Science Center, National Marine Fisheries Service

Date of this Version

7-2002

Comments

Published in MARINE MAMMAL SCIENCE, 18(3):680-697 (July 2002).

Abstract

There is increasing interest in the diving behavior of marine mammals. However, identifying foraging among recorded dives often requires several assumptions. The simultaneous acquisition of images of the prey encountered, together with records of diving behavior will allow researchers to more fully investigate the nature of subsurface behavior. We tested a novel digital camera linked to a time-depth recorder on Antarctic fur seals (Arctocephalus gazella). During the austral summer 2000-2001, this system was deployed on six lactating female fur seals at Bird Island, South Georgia, each for a single foraging trip. The camera was triggered at depths greater than 10 m. Five deployments recorded still images (640 x 480 pixels) at 3-sec intervals (total 8,288 images), the other recorded movie images at 0.2-sec intervals (total 7,598 frames). Memory limitation (64 MB) restricted sampling to approximately 1.5 d of 5-7 d foraging trips. An average of 8.5% of still pictures (2.4%-11.6%) showed krill (Euphausia superba) distinctly, while at least half the images in each deployment were empty, the remainder containing blurred or indistinct prey. In one deployment krill images were recorded within 2.5 h (16 km, assuming 1.8 m/sec travel speed) of leaving the beach. Five of the six deployments also showed other fur seals foraging in conjunction with the study animal. This system is likely to generate exciting new avenues for interpretation of diving behavior.