Spatial variability in responses to environmental conditions in Southern Hemisphere long-finned pilot whales

Investigating past responses to variations in the marine environment can provide insights into how species might respond to future change. Using long-finned pilot whales Globicephala melas stranded in New Zealand (2011) and Australia (2012), we investigated relationships between tooth growth chronologies, as a proxy for energy budgets (which underpin population state), and interannual variations in broad-scale climate indices (Southern Oscillation Index [SOI], Indian Ocean Dipole [IOD]) and spatially explicit, seasonally averaged sea surface temperature (SST). Tooth chronologies from pilot whales that stranded in Australia had a positive relationship with the SOI and a negative relationship with the IOD. Those from New Zealand had a positive relationship with the SOI, but at a 1 yr lag. Positive SOI and negative IOD conditions are associated with increased storm activity across the southern Australian/New Zealand region. The resulting changes in regional SST, currents and frontal activity likely influences the distribution of prey resources and associated high-order predators such as pilot whales. Correlation maps between tooth growth chronologies and SSTs suggest differences in habitat utilisation between the 2 regional groups, with pilot whales stranded in Australia associating with the subtropical and subantarctic fronts south of Tasmania, and those stranded in New Zealand associating with a number of regions of seasonally enhanced productivity close to New Zealand. This study greatly enhances our understanding of the environmental conditions influencing populations of an insufficiently studied species in the region.