Wandering whales? Relationship between whales and the sea ice environment in the Southern Ocean

Each austral summer large baleen whales migrate into the Southern Ocean to feed on krill. The melting of sea ice leads to algal blooms which allow rapid growth and development of krill. In order to predict how baleen whales will respond to long-term changes in the physical environment, we need to understand the relationships between baleen whales, their prey and the physical environment. The spatial models in this thesis are based on visual observations by whale observers onboard ships in open waters. The model analyses suggest that Antarctic minke whales are more often found close to the sea ice edge, continental shelf and frontal systems. Estimates show higher numbers of minke whales in regions that experienced more sea ice melting during austral spring and summer. These findings strongly suggest that the amount of sea ice cover, and especially its seasonal change, affects populations of minke whales at the regional scale. For the Scotia Sea, different species of baleen whales may target different types of krill. Minke whales and humpback whales were more often found in waters inhabited by juvenile krill, while fin whales were more often found in deeper waters, inhabited by adult krill. Improved understanding of whale behaviour will help us to better predict how baleen whales will respond to environmental change. We hardly know how far away baleen whales can detect krill swarms and how they forage in a three-dimensional environment. Recent advances in infrared detection and acoustic research are promising techniques to remedy this knowledge gap

Generalised additive models to investigate environmental drivers of Antarctic minke whale (Balaenoptera bonaerensis) spatial density in austral summer

There is a need to characterise the physical environment associated with Antarctic minke whale density in order to understand long-term changes in minke whale distribution and density in open waters of the Southern Ocean during austral summer months. To investigate environmental drivers of Antarctic minke whales density, generalised additive models (GAMs) were developed, based on line transect data collected for the International Decade of Cetacean Research (IDCR) and Southern Ocean Whale Ecosystem Research (SOWER) programmes. The GAMS were fitted independently by survey year. Explained deviances ranged from 14.9% to 35.1%. Most models included covariates related to transition zones, such as distance to the continental shelf break and sea ice edge, both of which showed a predominantly negative relationship with whale density. This study suggests high variability in the relationships between Antarctic minke whale density and the environment. None of the selected covariates had a consistent qualitative relationship with density at either the circumantarctic or the regional scale. This in part may be explained by the changing ice-related boundaries of the surveys between years and hence differences in survey region. Another possible reason is that in absence of better data most of the covariates considered were derived from remote sensing data. More localised surveys with comparable survey area conducted across the Southern Ocean, where whale sightings data are collected simultaneously with in situ non-biotic and prey data, are likely to provide a better assessment of the environmental determinants of whale density