Sex bias in biopsy samples collected from free-ranging dolphins

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Querouil, Sophie
Freitas, Luis
Dinis, Ana
Alves, Filipe
Cascao, Irma
Prieto, Rui
Silva, Monica A.
Magalhaes, Sara
Matos, Jose A.
Santos, Ricardo S.
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Bottlenose dolphin
Common dolphin
Spotted dolphin
Biological samples
Sex ratio
NE Atlantic
Biological samples of free-ranging dolphins are increasingly used to gain information on population structure and ecology. In small cetaceans, the gender of individuals usually cannot be determined at sea, and population sex ratio has to be inferred indirectly. We used molecular sexing to determine the gender of 340 biopsy samples of bottlenose dolphins, Tursiops truncatus, spotted dolphins, Stenella frontalis, and common dolphins, Delphinus delphis, collected around the Azores and Madeira. Sex ratio was globally skewed in favor of males, and differed between species and archipelagos. Skew was probably influenced by the selectivity of biopsy collectors and seasonal or year-round predominance of males in natural populations. Skew was also influenced by sampling duration and intensity. In the Azores, when several samples were successively collected within the same group, the proportion of female samples decreased as a function of sample order. This trend indicated a tendency for females to increasingly avoid the boat while samples were being collected. It showed that males and females reacted differently to the perturbation caused by the biopsy sampling process (i.e. sample collection and driving style).
Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in European Journal of Wildlife Research 56 (2010): 151-158, doi:10.1007/s10344-009-0299-7.
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