Spinner dolphins in a remote Hawaiian atoll: social grouping and population structure |
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Authors: | Karczmarski Leszek; Wursig Bernd; Gailey Glenn; Larson Keith W; Vanderlip Cynthia |
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Institution: | a Marine Mammal Research Program, Texas A&M University, 4700 Avenue U, Building 303, Galveston, TX 77551, USA, b Oceanic Society, Fort Mason Center, Building E, San Francisco, CA 94123, USA, and c Midway Atoll National Wildlife Refuge, Pacific Remote Islands NWR Complex, U.S. Fish and Wildlife Service, 300 Ala Moana Boulevard, P.O. Box 50167, Honolulu, HI 96850, USA |
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Abstract: | Spinner dolphins (Stenella longirostris) commonly use inshoreisland and atoll habitats for daytime rest and social interactionsand forage over deep waters at night. In Hawaii, they occurthroughout the archipelago. We applied photoidentification mark-recapturetechniques to study the population structure of spinner dolphinsassociated with remote Midway Atoll, far-western Hawaii. AtMidway, spinner dolphins live in stable bisexually bonded societiesof long-term associates, with strong geographic fidelity, noobvious fission-fusion, and limited contacts with other populations.Their large cohesive groups change little over time and arebehaviorally/socially discrete from other spinner dolphin groups.This social pattern differs considerably from the fluid fission-fusionmodel proposed previously for spinner dolphins associated witha large island habitat in the main Hawaiian Archipelago. Thesedifferences correspond to geographic separation and habitatvariation. While in the main islands there are several daytimeresting places available at each island habitat; in far-westernHawaii, areas of suitable habitat are limited and separatedby large stretches of open pelagic waters with potentially highrisk of shark predation. We hypothesize that with deepwaterfood resources in close proximity and other atolls relativelyfar away for easy (day-to-day) access, it is energetically morebeneficial in the remote Hawaiian atolls to remain "at home"than to travel to other atolls, so there is stability insteadof variability; there is no fission-fusion effect. Thus, thegeographic isolation and small size of remote atolls triggera process in which the fluidity of the fission-fusion spinnerdolphin society is replaced with long-term group fidelity andsocial stability. |
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Keywords: | geographic insularity/connectivity group dynamics Hawaii Midway Atoll social evolution social structure Spinner dolphin Stenella longirostris |
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