Sex-biased summer association patterns in fin whales indication of male mate competition?

Christian Ramp, Julien Delarue, Anna Schleimer, Richard Sears, Per Palsboll, Martine Bérubé



Baleen whales appear less social compared to odontocetes, particularly outside the breeding season, but remain poorly studied. We analysed 4,915 sightings of 2,608 groups, comprising 292 photo-identified fin whales in the Gulf of St. Lawrence (2004-2010). Skin biopsies were collected from 85 males and 59 females. Solitary females were more common, male sex bias increased with group size. Half-weight association indices confirmed the strong sex bias. Permutation tests showed that the pattern of association was non-random, but did not reveal any long-term (>1day) associations. Based on the weighted non-directed network, males displayed a higher degree of centrality. A directed network analysis using within-group positioning revealed that most males have higher tendency to follow conspecifics, with few males and females leading these groups. These large male-biased fin whale groups resemble humpback whale competitive groups, although they appear to be in the wrong season. We employed skin biopsy samples of the 144 biopsied adults and 29 biopsies from calves observed during the same period to estimate relatedness from the genotypes at 19 microsatellite loci. We identified a total of 34 parent-offspring, 13 full siblings and 1,183 2nd order relations. Five sampled males sired six calves, two calves by the same male. The high proportion of related animals could suggest that these fin whales mate within the Gulf and hence do not constitute a part of a common breeding population in the entire Northwest Atlantic. This could represent a recent development due to the loss of winter ice in the Gulf, thereby opening a new wintering habitat for fin whales. Thus, the strong sex bias observed in the association networks could be related to mating. However, cooperative feeding of large schools of fast preys might also explain the large groups, despite increasing competition among group members. Females’ preference for solitarily might be due to high energetic demands upon reproduction and hence avoidance of intra-specific competition.
Originele taal-2English
StatusPublished - 22-okt-2017
Evenement22nd Biennial Conference on the Biology of Marine Mammals - Halifax, Canada
Duur: 22-okt-201727-okt-2017


Conference22nd Biennial Conference on the Biology of Marine Mammals
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