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Hand-rearing harbour seal pups (Phoca vitulina) : the effect of diet and supplementary heat on growth and survival MacRae, Amelia


Hundreds of stranded harbour seals pups (Phoca vitulina) are brought to wildlife rescue centres every year, often unweaned and in poor body condition. Typical hand-rearing diets include artificial milk-replacers and diets based on macerated fish, both normally fed via gavage. Mortality rates for these animals can be high and weight gains on artificial formulas are low. This study was designed to determine the effect of the following treatments on the growth and survival of captive orphaned seals: (1) feeding pups an artificial milk-replacer versus a fish-based formula; and (2) the provision of supplementary heat. Pups admitted to the facility in summer 2007 (n=145) and 2008 (n=98) were randomly assigned to one of two diets and fed until weaning at roughly 20 days of age. In 2008, 25 pups were also provided with a supplementary heat source. Diet and heat treatments were compared using average daily gain (ADG) and mortality rates. In 2007, with pups fed formulas at 8% of body weight per day, pups fed milk-replacer gained more (43 g/d ± 12, mean ± SEM) than those fed fish-formula (loss of 13 g/d ± 6; p<0.01) and their survival to weaning was twice as high (p<0.05, chi-squared analysis). In 2008, with daily intake increased to 11% of body weight per day, weight gain was improved for both diets but remained higher on milk-replacer (123 g/d ± 12, loss of 6 g/day ± 8; p<0.01) and fewer seals died on either treatment (6/35 on milk replacer, 8/34 on fish formula.) Pups provided with heat did not show any differences in ADG (p>0.05) or survival rate (p>0.05) but did show increased heat-seeking behaviour at ambient temperatures below 16°C (p<0.001). I conclude: (1) although neither diet achieved the weight gains recorded in mother-raised pups (400 – 800 g/d), the artificial milk formula was clearly more successful; (2) supplementary heat can be safely used for unweaned pups in poor body condition at ambient temperatures <16°C; and (3) more work is needed on both diet composition and feeding method to achieve higher survival and more natural weight gains.

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