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Fine-scale habitat selection by coastal bottlenose dolphins: application of a new land-based video-montage technique

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Abstract:

Cetacean distribution and underwater topography are frequently correlated. These patterns are commonly studied on large spatial scales, over tens of kilometres, but very rarely on a fine scale. Sightings of bottlenose dolphins, Tursiops truncatus, within the Moray Firth, Scotland, were previously found to be concentrated within deep, narrow channels. To understand why such areas were selected, more-detailed information on the distribution of dolphins was required. This study describes the development of a video technique to study the spatial distribution and relative abundance of bottlenose dolphins. We then used the methodology to investigate whether water depth and seabed gradient influence the dolphins' distribution patterns. Furthermore, temporal patterns of use were examined with respect to seasonal, tidal, and diurnal cycles. The distribution of dolphins was significantly related to topography: dolphins were sighted most frequently in the deepest regions with the steepest seabed gradients. There was a clear temporal pattern in the use of the area, with sightings peaking during July. However, the presence of dolphins was not significantly related to tidal or diurnal cycles. The topography of the area appears to be a significant influence on its intensive use by dolphins, and patterns of use indicate that topography may facilitate foraging during seasonal migrations of fish.

Il y a souvent une corrélation entre la répartition des cétacés et la topographie sous-marine. Ces patterns sont ordinairement étudiés à de grandes échelles spatiales de dizaines de kilomètres, mais rarement à une échelle fine. Les dauphins à gros nez, Tursiops truncatus, aperçus dans le golfe de Moray, en Écosse, se concentrent dans les chenaux profonds et étroits. Pour comprendre le choix de ces sites, il faut plus de détails sur la répartition des dauphins. Notre étude décrit la mise au point d'une technique vidéo pour étudier la répartition spatiale et l'abondance relative des dauphins. La technique nous a servi à déterminer si la profondeur de l'eau et le gradient du fond influencent les patterns de répartition. De plus, les patterns temporels d'utilisation de l'habitat ont été examinés pour identifier des cycles reliés à la saison, aux marées et à la journée. La répartition des dauphins est reliée de façon significative à la topographie; les dauphins sont vus le plus fréquemment dans les régions les plus profondes avec les fonds de plus forts gradients. L'utilisation de la région suit un net pattern temporel et le maximum de dauphins s'observe en juillet. La présence des dauphins n'est pas, cependant, reliée aux cycles de marée, ni aux cycles journaliers. La topographie de la région semble influer de façon significative l'usage considérable qu'en font les dauphins; les patterns d'utilisation indiquent que la topographie facilite peut-être la recherche de nourriture durant les migrations saisonnières des poissons.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: March 1, 2003

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  • Published since 1929, this monthly journal reports on primary research contributed by respected international scientists in the broad field of zoology, including behaviour, biochemistry and physiology, developmental biology, ecology, genetics, morphology and ultrastructure, parasitology and pathology, and systematics and evolution. It also invites experts to submit review articles on topics of current interest.
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