Abstract
The distribution of animals is the result of habitat selection according to sex, reproductive status and resource availability. Little is known about how marine predators investigate their 3‐dimensional space along both the horizontal and vertical axes and how temporal variation affects space use. In this study, we assessed the spatio‐temporal movement of a sexually dimorphic marine mammal, the grey sealHalichoerus grypusby 1) determining seasonal home range size, 2) testing whether space use of seals was affected by water depth, and 3) investigating the vertical movement of seals according to the maximum depth of each dive. Between 1993 and 2005, we fitted 49 grey seals in the Gulf of St. Lawrence with satellite transmitters. We estimated seasonal 95% fixed‐kernel home ranges for each individual. For each seal, we tested for selectivity and preference for 4 water depth classes at the home range scale and within the home range. We also evaluated the proportional number of dives made in each water depth classes according to the maximum depth of each dive. Home ranges were 10 times larger in winter than in summer. Seals generally selected habitats <50 m deep. They also mainly dove to depths of 40 m or less. At both scales of selection, preference for shallow areas decreased in winter. We also observed that adults used shallow habitats more than juveniles to establish their home range. A spatial segregation based on sex also occurred at the finer scale of selection where females were more concentrated in the shallowest parts of their home range than males. Segregation in space use according to age and sex classes occurred at both the horizontal and vertical scales. Our results emphasise the importance of studying habitat selection of marine predators in 3‐dimensional space, in addition to the temporal scale.
Highlights
Animals are normally not distributed uniformly throughout their range
Few studies have explored the spatio-temporal dynamics of habitat use patterns of marine mammals along both the horizontal and vertical axes, which are linked by water depth, nor have they tested how habitat selection patterns vary according to intra-specific and environmental variability
Since marine mammals exploit a highly dynamic 3-dimensional world, simultaneous information on the diving behaviour and foraging range according to the availability of different water depths is essential to understand their habitat use, because segregation by age or sex at the horizontal scales may not represent segregation in the vertical axes of the water column
Summary
Animals are normally not distributed uniformly throughout their range. Instead, they actively use habitats in response to a combination of factors including resource availability, lifehistory strategies and individual variability (Orians and Wittenberger 1991, Rettie and Messier 2000, McLoughlin et al 2002). Few studies have explored the spatio-temporal dynamics of habitat use patterns of marine mammals along both the horizontal and vertical axes, which are linked by water depth, nor have they tested how habitat selection patterns vary according to intra-specific and environmental variability. Since marine mammals exploit a highly dynamic 3-dimensional world, simultaneous information on the diving behaviour and foraging range according to the availability of different water depths is essential to understand their habitat use, because segregation by age or sex at the horizontal scales may not represent segregation in the vertical axes of the water column. Grey seals are generally associated with shallow depths (Sjoberg and Ball 2000, MacLeod et al 2007), females are known to be shallower divers and exhibit a higher diving effort in smaller and distinctive foraging areas than males (Beck et al 2003a, Austin et al 2004, Breed et al 2006).
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