Nearshore habitat use by Hector’s dolphins at Banks Peninsula

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1. Abstract

Knowledge of the dynamic use of habitat by marine top-predators increases our understanding of the role these species play in marine ecosystems and enhances our ability to establish effective habitat-based species management. Such information is particularly important for threatened species that inhabit coastal environments where anthropogenic effects on habitat quality can be significant. Hector’s dolphin is an endangered, endemic cetacean that is found year-round at Banks Peninsula. This study aimed to assess how ‘hotspots’ in the dolphins’ near shore distribution vary among seasons and over time. Visual sightings data from standardised surveys of the Banks Peninsula coast were analysed using fixed kernel density estimation (KDE). Twenty-five years of data were available and were pooled into four seasonal categories and three time periods. Separate KDE analyses were undertaken for each category. To further assess habitat use, passive acoustic monitoring devices (TPODs) were deployed at ten locations around the Peninsula. KDE of visual sightings demonstrated variation in the use of hotspots among seasons. Mean summer hotspot density ranged between 3.5 and 6.4 dolphins/km2 (SE = 0.02<0.08), mean winter density was between 0.13 and 0.92 dolphins/km2 (SE = 0.01<0.03). KDE analysis also suggested variation in the importance of some locations over time, with a recent decrease in dolphin density at several hotspots. Acoustic data showed little difference in habitat use among monitoring locations during winter and spring. In summer, variation in relative dolphin density among sites was evident, however these differences did not always correspond to the density values calculated using KDE analysis. This study illustrates the patchy nature of Hector’s dolphin distribution at Banks Peninsula and suggests analyses of distribution may be sensitive to the monitoring method. 

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