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