Movement and diving of killer whales (Orcinus orca) at a Southern Ocean archipelago

• Published in: Journal of Experimental Marine Biology and Ecology
• Main Authors: Reisinger, Ryan R., Keith, Mark, Andrews, Russel D., de Bruyn, P. J.N.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2015
• Subjects: Southern Ocean; Edwards Islands; Orca; Orcinus orca
• Online Access: https://eprints.soton.ac.uk/455012/

Eleven satellite tags were deployed on 9 killer whales at the Prince Edwards Islands in the Southern Ocean. State-space switching models were used to generate position estimates from Argos location data, while two behavioural modes were estimated from the data.Individuals were tracked for 5.6-53.2days, during which time they moved 416-4470km (mean 82.7kmday -1 ) but 69% of position estimates were within the 1000m depth contour around the islands (<35km from the tagging site). Killer whales showed restricted behaviour close to the islands, particularly inshore where they can effectively hunt seals and penguins, and at seamounts to the north of the islands.Generalised linear mixed effect models were used to explore the relationship between environmental variables and behavioural mode. The best model included depth, sea surface temperature, latitude, sea surface height anomaly and bottom slope, but killer whales did not clearly target features such as fronts and apparent mesoscale eddies. Killer whales showed restricted behaviour in shallow water, at high latitudes and low sea surface temperature - the conditions characterising the archipelago.Dive data from two individuals largely revealed shallow dives (7.5-50. m deep), but deeper dive bouts to around 368. m were also recorded. Dives were significantly deeper during the day and maximum dive depths were 767.5 and 499.5. m, respectively. This suggests that killer whales might also prey on vertically migrating cephalopods and perhaps Patagonian toothfish.Three individuals made rapid and directed long-distance movements northwards of the islands, the reasons for which are speculative.