AMoveE 2014: Corrie Curtice
Channel: Movebank
Date: 20/05/2014

This talk was presented by Corrie Curtice on 6 May 2014 as part of the Symposium on Animal Movement and the Environment, held at the North Carolina Museum of Natural Sciences in Raleigh.

Curtice C, Friedlaender A, Johnston D, Halpin PN, Gales N, Ducklow H, 2014, "Spatially and temporally dynamic humpback feeding areas in Antarctica"

Abstract: Humpback whales (Megatptera novaeangliae) are the most abundant baleen whale found in the nearshore waters around the Antarctic Peninsula. As a migratory animal, they must acquire enough energy during the summer months in the resource-rich feeding grounds around Antarctica to fuel their migrations to breeding and calving grounds in tropical waters in winter, where resource are limited.
Previous work has shown that the distribution and abundance of humpback whales is best predicted by that of Antarctic krill, the primary component of humpback whale diets in Antarctic waters. Since humpback whales are mobile predators with high energetic demands, it stands to reason that humpback whales will seek out areas with increased prey abundance, changing their distribution to reflect krill distribution changes throughout the feeding season. During summer months, krill are distributed broadly from nearshore to beyond the continental shelf. In autumn, krill are thought to move inshore and toward deep coastal waters in sheltered bays where they coalesce into large aggregations that will be covered by sea ice formation, minimizing predation risk from diving predators, including humpback whales. Given the known distribution of whales in summer months and the ultimate distribution of both whales and krill later in the feeding season, we hypothesized that the movement patterns and home ranges of humpback whales reflect concurrent changes in the distribution of Antarctic krill: home ranges of humpback whales will decrease in size during the austral summer and fall, and the overall distribution of humpback whales will move significantly closer to shore over this time period.
To evaluate these hypotheses, six whales were instrumented with Platform Transmitting Terminals (PTTs) during January of 2012. We applied a new product kernel method over the full date range of location data (162 days). On every fifth day, we calculated the Utilization Density (UD) for each whale whose track existed on that date. The 95% isopleth was used as the extent for the home range. To explore the hypotheses that humpback whale home range area and distance to mainland both decrease during the summer and fall months we used linear mixed effects models to assess humpback home range area and distance from land. Both Julian date and month were used as predictors, and the PTT was used as a random effect to examine individual variation between whales. Home ranges were created for 75 specific days, with between one to five whales having tracks on each day used for the model.
We found that distance to mainland was significant, indicating that with each increase in month there was a corresponding decrease of 41.43 km in the distance to mainland. Home range area was not significantly different over time. This suggests while the distribution of whales changes seasonally with respect to proximity to shore, the lack of a change in home range may indicate that krill is still broadly distributed over a greater area than we thought.