Elsevier

Animal Behaviour

Volume 80, Issue 4, October 2010, Pages 667-673
Animal Behaviour

To go for a swim or not? Consequences of neonatal aquatic dispersal behaviour for growth in grey seal pups

https://doi.org/10.1016/j.anbehav.2010.06.028Get rights and content

Grey seal, Halichoerus grypus, pups in the breeding colony at Froan, Norway, have a bimodal pattern of early aquatic behaviour. About 40% of the pups spend their time ashore to save energy, which can be allocated to growth or deposition of energy-rich adipose tissue. The other 60% of the pups enter the sea during suckling and the early postweaning period, and disperse to other locations within the breeding colony. Pups may swim distances up to 12 km. Neonatal aquatic dispersal behaviour may lead to increased energy expenditure for thermoregulation and swimming, and thus lead to a low rate of body mass gain during suckling and a high rate of body mass loss after weaning. Thus, we examined relationships between natal aquatic dispersal behaviour and change in body mass (ΔBM) in suckling and weaned pups. Suckling pups that had dispersed >2000 m had a significantly lower ΔBM than suckling pups that dispersed <2000 m or that did not disperse. In weaned pups, there were no effects of aquatic dispersal behaviour on ΔBM. We suggest that the bimodal natal aquatic dispersal behaviour in grey seals at the study site reflects two different strategies for postweaning survival: to stay ashore and get fat, or to take a swim and acquire diving and feeding skills.

Section snippets

Methods

The study was conducted at Froan nature reserve situated north of Frøya Island on the coast of Trøndelag (Fig. 1). A Zodiak rubber boat was used for transport. When pups were located, they were caught using a net, physically restrained, and tagged in the rear flipper with numbered plastic tags (4.5 cm, Rototag, Dalton I.D. Systems, Henley-on-Thames, U.K.). After tagging, they were weighed and classified according to sex and age. The age of the pup was determined on the basis of morphological

Sex comparison

There was no significant difference in ΔBM between suckling male and female pups in any of the three groups (stationary: U = 134.5, Nmale = 16, Nfemale = 19, P = 0.56; <2000 m: U = 88.0, Nmale = 14, Nfemale = 16, P = 0.32; >2000 m: U = 12.0, Nmale = Nfemale = 5, P = 0.92; Table 2). There was no difference between suckling males and females in average dispersal distance (U = 692.5, Nmale = 35, Nfemale = 40, P = 0.933; Table 2). Nor was there any difference between suckling males and females in the dispersal rate, which was 0.54

Discussion

In grey seals, the probability of first-year survival increases with BM and the size of energy reserves at weaning (Hall et al., 2001, Hall et al., 2002). At Froan, suckling pups that showed aquatic behaviour and dispersed >2000 m had a significantly lower ΔBM than suckling pups that dispersed <2000 m or that were stationary (did not disperse; Fig. 3a). However, there were no differences in the BM, or ΔBM, between the weaned pups with aquatic behaviour and those that stayed on land (Table 2). The

Acknowledgments

We thank Arve Gården for assistance in the field, and Mark Silverstone for his highly valued contributions to the study. We thank the referees for valuable comments on the manuscript.

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    1

    M. Ekker is at the Directorate of Nature Management, Tungasletta 2, NO-7055 Trondheim, Norway.

    2

    D. Vongraven is at the Norwegian Polar Institute, Polar Environmental Centre, NO-9013 Tromsø, Norway.

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