Although dolphins are known for their sophisticated social behaviors, scientists studying large communities of dolphins typically find that association patterns are relatively simple. Recently published research by Earthwatch-supported scientists shows, however, that careful sampling methods are critical to revealing the complexity of social patterns in large schools of dolphins.
In a paper in Canadian Journal of Zoology, Drs. Louise Chilvers (University of Canterbury, New Zealand) and Peter Corkeron (Institute of Marine Research, Tromsø, Norway) report on bottlenose dolphin association patterns off Point Lookout, Queensland, Australia. The former principal investigators of the Earthwatch-supported Queensland Dolphins project (1998-2000), Chilvers and Corkeron found that observed social complexity depended on the intensity of sampling.
"Our study suggests that the way data are collected on these larger schools is inherently more likely to produce results that suggest randomness of associations, when dolphins may in fact have definite partners," said Corkeron. "It's a quirk of the math."
Researchers have generally found that when dolphins and other delphinids occur in large schools, numbering in the dozens to hundreds, the composition of each school tends to be fluid. This contrasts with the more stable associations found in some smaller groups, and is consistent with the seeming difficulty of maintaining complex associations among hundreds of individuals.
Earthwatch teams working with Corkeron and Chilvers off Point Lookout sighted 342 groups of bottlenose dolphins, of which 550 animals were individually identified, using photo-identification techniques. This was out of a total estimated population of 700-1,000, characterized by apparently fluid association patterns.
Corkeron and Chilvers found that social patterns in these large schools suggest that the animals associated at random. It was only when they included the 97 dolphins sighted 4 times or more that they detected patterns of association. Corkeron and Chilvers' analysis illustrates the importance of finding the balance between representative data, sampling the maximum number of individuals, and reliable data, acquiring the maximum frequency of sightings.
"It raises a question about some earlier data," said Corkeron. "If researchers aren't careful regarding identifying every animal in a school, they could end up with spurious results from their later analyses. This is part of a current trend to improve the methodological and analytical techniques used by researchers working on dolphin behavior."
The paper also raises some ethical issues around human attitudes toward dolphin management. Related work on the social interactions of smaller groups of bottlenose dolphins show some of the greatest sophistication known in non-human mammals. Corkeron and Chilvers' work raises the question of whether this kind of sophistication may also be found in larger groups of dolphins, if researchers look hard enough.
For more information, see B.L. Chilvers and P.J. Corkeron. "Association patterns of bottlenose dolphins (Tursiops aduncus) off Point Lookout, Queensland, Australia. Canadian Journal of Zoology 80: 973-979 (2002).
For other Earthwatch-supported research on dolphins, see New Zealand Dolphins
Earthwatch Institute is an international nonprofit organization which supports scientific field research worldwide by offering members of the public unique opportunities to work alongside leading field scientists and researchers. The Institute's mission is to engage people worldwide in scientific field research and education to promote the understanding and action necessary for a sustainable environment.