Identifying Sexually Mature, Male Short-Beaked Common Dolphins (Delphinus Delphis) at Sea, Based on the Presence of a Postanal Hump
Aquatic Mammals 2002, 28.2, 181–187 Identifying sexually mature, male short-beaked common dolphins (Delphinus delphis) at sea, based on the presence of a postanal hump Dirk R. Neumann1, Kirsty Russell2, Mark B. Orams1, C. Scott Baker2, and Padraig Duignan3 1Coastal Marine Research Group, Massey University, Auckland, New Zealand 2Department of Biology, University of Auckland, New Zealand 3Department of Veterinary Science, Massey University, Palmerston North, New Zealand Abstract Introduction For detailed studies on the behaviour and social To fully comprehend the behaviour and social organization of a species, it is important to organization of a species, it is necessary to distinguish males and females. Many delphinid distinguish males and females. Long-term studies species show little sexual dimorphism. However, in of bottlenose dolphins (Tursiops truncatus, T. mature male spinner dolphins, Stenella longirostris aduncus), which tracked focal individuals of known (Perrin & Gilpatrick, 1994) and Fraser’s dolphins, sex, revealed sexual segregation of mature males Lagenodelphis hosei (Jefferson et al., 1997), tissue from females (Wells, 1991), the formation of male between the anus and the flukes forms a so-called coalitions (Wells, 1991; Connor et al., 1992), and peduncle keel, or postanal hump. We discovered an differences in the activity budgets of males and analogous feature in free-ranging short-beaked females (Waples et al., 1998). Many delphinid common dolphins, Delphinus delphis,offthe species show little sexual dimorphism, which makes north-eastern coast of New Zealand’s North Island. it exceedingly difficult to sex individuals at sea. For Genetic analysis of skin samples obtained from many species, the only individuals that can be sexed bow-riding individuals revealed that dolphins without capture are those that are consistently with a postanal hump were indeed always male.
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