Interspecific interactions and hybridization in marine mammals
Interspecific interactions, mating attempts and hybridization have been observed in both terrestrial and marine populations (Baird et al. 1998). Hybridization among marine mammals is a little understood, but increasingly observed, phenomenon between unrelated yet overlapping populations (Baird et al. 1998, Dohl et al. 1974, Herzing et al. 1997). This research documents interactions, particularly mating behaviors, between common bottlenose (Tursiops truncatus) and Atlantic spotted (Stenella frontalis) dolphins off Bimini, The Bahamas and examines the possible mechanisms driving these interactions. Understanding these interspecific interactions may have implications for conservation and management efforts directed at these populations and their surrounding environment.
Observations of the Bimini populations will be examined for commonalities between this and other populations (i.e. Dalls (Phocoenoides dalli) and harbor (Phocoena phocoena) porpoises in the northeast Pacific, T. truncatus and S. frontalis in Northern Bahamas). By studying the group of dolphins off Bimini longitudinally, in collaboration with the Dolphin Communication Project (DCP), the subtleties of interspecific interactions will lead to a greater understanding of the potential implications of these behaviors. The methodology of Dudzinski (1998) will be used to record dolphins behaviors and vocalizations simultaneously, under water. Dolphins will be identified by species, sex and age class and will be described for their behaviors according to Dudzinski (1996). Photo-identification tools will be utilized to track individuals; for T. truncatus traditional dorsal fin photographs will be used and for S. frontalis still photographs & underwater video. The factors, both environmental and behavioral, involved in each interspecific interaction will then be analyzed. Specifically, the individuals of each species present, where the interactions occur and frequencies of individual behaviors will be determined. In the absence of DNA evidence, I will look strictly at behavior indicators that suggest hybrids might have been born between S. frontalis and T. truncatus. At this time, no such evidence exists. Because of the lack of known, successful hybrids, two of the most likely hypotheses will be considered. First, the T. truncatus males are being denied mates in their own social group and are therefore seeking out S. frontalis groups for mating and second, there may be an unknown (at this point) environmental stress that is resulting in more range overlap between the two species, which leads to more encounters between the two and finally more opportunity for mating and other interactions.
In addition to analysis of the Bimini populations, a comprehensive literature review will bring a more thorough and more balanced understanding of data that already exist within the research community as related to marine mammal hybridization. This review will be one of the most complete to date, representing known cases of interspecific mating attempts and successful hybridization both in the wild and in captive settings. As more free-ranging dolphin populations are studied, additional observations of interspecies interactions are likely to be observed and documented