Sperm whale habitat off Kaikoura, New Zealand : a descriptive study of physical and biological processes influencing sperm whale distribution
Sperm whales (Physeter macrocephalus) are deep-diving marine mammals found in all oceans of the world and occupy a wide range of environmental conditions (Best 1979; Rice 1989). There is no real consensus in describing the perfect sperm whale habitat, yet most of the literature classifies factors affecting their distribution between four distinct but closely linked categories: prey availability, underwater topography, oceanography and biological productivity. Few comprehensive studies aiming to understand the relationships between sperm whale distributions and any of these factors have been performed. Many investigators jump directly into attempting to relate sperm whale distributions to convenient environmental variables, thereby fishing around for significant statistical correlations rather than trying to understand the complex processes and trophic level interactions that control the distributions (Jaquet 1996). The Kaikoura Canyon on the East Coast of New Zealand is an excellent location to study sperm whales and their habitat. In this region, the well-documented male sperm whale population occupies the area year-round (Childerhouse 1995). Although the reasons why sperm whales prefer to spend extended periods of time in the canyon are unknown, extensive use of this region by sperm whales probably indicate a significant level of activity at lower trophic levels and very high biological productivity (Jaquet 1999). Unfortunately, sporadic research conducted in the Kaikoura Canyon during the 1960-70s revealed little about prey distribution, productivity or basic oceanographic processes. Since sperm whales off Kaikoura are the centre of a major whale-watching industry, it is important to describe the sperm whale habitat so we can determine to what extent whales are able to move away from the area if they want to avoid the whale-watching boats. In this study, I used a combination of several techniques including satellite data and in-situ field measurements to describe and develop a general understanding of large and small-scale oceanographic and biological processes off Kaikoura. Results from a literature review and sperm whale prey distribution data showed that sperm whale distribution off Kaikoura can be influenced by prey distribution and availability. However, oceanographic systems in this region may be a determinant factor influencing prey distributions and productivity across many trophic levels. Satellite images of Sea Surface Temperature revealed that mesoscale eddy features offshore might affect the general circulation pattern within the canyon, especially in winter and early spring. Enhanced primary productivity was also associated with these large-scale eddies, as shown by the inspection of SeaWiFS Ocean Color data covering the sampling periods. In-situ CTD measurements across the main axis of the Kaikoura Canyon emphasised the dynamic and variable oceanographic conditions in this area. Downwelling, small-scale eddy locked in place by the bathymetry and evidence of internal waves were also observed. However, no strong and persistent upwelling event was recorded. This study suggests that in-canyon oceanographic features may play a major role in concentrating and retaining production off Kaikoura, although offshore processes may greatly contribute to the enhancement and advection of production in this area. Such a complex combination of processes acting outside and within the canyon may explain why this habitat can sustain many trophic levels, including a semi-permanent sperm whale population.
Advisor: Gibbs, Mark; Slooten, Liz
Degree Name: Master of Science, Environment and Society
Degree Discipline: Environmental Science
Publisher: University of Otago
Research Type: Thesis