Coastal fronts and upwelling areas utilised by migrating humpback whales, Megaptera Novaeanglia, on the Gold Coast, Australia

Humpback whales, Megaptera novaeangliae, take part in the largest annual migration of any mammal, from polar feeding grounds in summer to tropical breeding grounds in winter. Large scale migration patterns are quite well... [ view full abstract ]

Humpback whales, Megaptera novaeangliae, take part in the largest annual migration of any mammal, from polar feeding grounds in summer to tropical breeding grounds in winter. Large scale migration patterns are quite well known; however, small scale distribution patterns and relationships with environmental conditions have received less attention. Protection from a range of threats, as well as predicting the effects of climate change, requires knowledge of preferred habitat and the reasons behind the preferences.
East Australian humpback whales travel from the Southern Ocean, along the East Coast of Australia, to the Great Barrier Reef (or further) to breed. The East Australian coastal environment is dominated by the East Australian Current, the western boundary current of the South Pacific Ocean, carrying warm water poleward from the tropics. This current, as well as strong northerly winds, is responsible for generating upwelling conditions on the coast and providing the majority of nutrients available for primary production. Sharp temperature changes (fronts) are experienced at the border of the warm current and the cooler coastal and upwelled waters.
This study investigates relationships between humpback whale distribution and environmental conditions on the Gold Coast, Australia. This area is used during both the northern and southern migration, and provides a rest stop for mothers and calves on the return journey. Whale distribution was recorded during boat based and land based surveys. Environmental parameters included bathymetry and remotely sensed sea surface temperature, as well as their gradients. Conductivity and temperature profiles were recorded at the locations of 27 pods. The conditions observed at the whales’ locations were compared with the average across the study area using paired sample t-tests.
Initial outcomes of the study suggest a preference for cooler waters and in areas with a strong temperature gradient. The higher productivity in cooler upwelled water and fronts may provide the whales with a chance of opportunistic feeding, a rare occurrence on their prolonged journey. Following particular hydrodynamic features such as these, which generally run parallel to the shore, may also serve as a tool for navigation.