Thermal constraints on hauling out by harbour seals ( Phoca vitulina )

• Published in: Canadian Journal of Zoology
• Main Author: Watts, Peter
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1992
• Subjects: Animal Science and Zoology; Ecology, Evolution, Behavior and Systematics; Pacific; Phoca vitulina
• Online Access: http://dx.doi.org/10.1139/z92-083; http://www.nrcresearchpress.com/doi/pdf/10.1139/z92-083

Measurements of the thermal environment were made in conjunction with regular counts of hauled out harbour seals at three sites in the Pacific Northwest. Solar radiation, wind speed, and air temperature were all significantly correlated with numbers of seals on land. These were incorporated into a thermal index of heat flux (expressed in watts per square metre) between the seal and its environment. Numbers of seals hauled out at midday declined sharply as flux increased above 0 W∙m −2 (i.e., when seals theoretically gained net heat from their environment), but remained constant at all measured negative values of flux. This relationship could be described by a nonlinear piecewise regression equation [Formula: see text]. No significant differences in hauling activity were detected between sites throughout most of the year. During the summer, however, one site with significantly higher mean flux than the others also exhibited significantly lower hauling activity. These findings are consistent with the hypothesis that under temperate summer conditions, hauling out can result in overheating. This may be an important constraint on hauling behaviour.