Variation in growth and seasonal condition of ringed seal, Phoca hispida, from the Canadian Arctic

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Goodyear, Michael A.
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Ringed seal (Phoca hispida) morphometric data from three locations in the eastern Canadian Arctic were compared to examine geographic variation in aspects of growth, life-history, and condition. Seals from Eureka (80$\sp\circ$ N) reached an asymptotic length of 150.9 cm, 14.0 cm greater than individuals from Arctic Bay (73$\sp\circ$ N) and 22.7 cm greater than those from Pangnirtung (66$\sp\circ$ N). Seals may reach sexual maturity sooner in Arctic Bay than Eureka or Pangnirtung. Statistically significant sexual dimorphism was evident in Pangnirtung were males were 6.7% longer than females. Condition, expressed as blubber content (% of total mass) was estimated using three published indices of condition: blubber thickness, axillary girth/length $\bullet$ 100, and the 'LMD' index. These indices did not adequately describe changes in condition for this data and did not provide a meaningful measure of the absolute amount of fat present. A new method of estimating absolute sculp (skin and blubber) mass from sculp volume calculated by a prolate spheroid model was developed. Regressions of mass in relation to length for various seasons demonstrated that spring and summer mass loss averaged 14 kg for an adult seal with an asymptotic length of 128 cm. Prior to sexual maturity, juveniles lost proportionally less mass than adults. Observed differences in growth and condition may reflect variation in life-history strategies related to primary productivity and predation pressure by polar bear (Ursus maritimus) and Inuit.