Influence of body size and ranging patterns on delphinid sociality: Associations among Commerson's dolphins

COSCARELLA, MARIANO ALBERTO; GOWANS, SHANNON; PEDRAZA, SUSANA NOEMÍ; CRESPO, ENRIQUE ALBERTO

JOURNAL OF MAMMALOGY

ALLIANCE COMMUNICATIONS GROUP DIVISION ALLEN PRESS

Año: 2011 vol. 92 p. 544 - 551

0022-2372

We investigated the association patterns of 48 identifiable Commerson’s dolphins (Cephalorhynchus commersonii) photographed two or more times over a two-year period in Bahía Engaño, Chubut Argentina. The associations among them were not different from random for short time periods (seven days) but were significantly different from random for longer periods. Lagged Identification Rate and Lagged Association Rate models show that dolphins remained in the area on average 15 days and then moved away as the original groups dissolved. Commerson’s dolphins appear to have a fission–fusion society, and the observed strength of their associations is in concordance with the predictions regarding their body size and ranging patterns. The dolphins seem to rely on Bahía Engaño as a core area for most of their activities, but the aggregations are labile and some individuals remain associated in a more stable manner with only a few other individuals.