Hundreds of orphaned and injured neonatal harbour seals (Phoca vitulina) are brought to wildlife rescue centres every summer. The seals are typically fed artificial milk formulas and formulas based on macerated fish. These formulas are usually fed via gavage to ensure that appropriate volumes are delivered to the animal and to facilitate feeding a large number of animals. This study examined the effects of feeding artificial milk formula and fish-based formula on the survival, health, and growth of orphaned seal pups in captivity.
Pups admitted to the Vancouver Aquarium Marine Mammal Rescue Centre in summer 2007 (n = 113) and 2008 (n = 69) were randomly assigned and fed one of the two formulas until being switched to a diet of whole herring at roughly 20 days of age. Animals were singly housed and fed formula via gavage 4 times per day in 2007 (8% of body weight by volume per day), and 5 times per day in 2008 (11% of body weight by volume per day).
In 2008, pups receiving artificial milk formula gained more (131 g/d ± 14.8, mean ± s.e.m) than those fed fish formula (loss of 4 g/d ± 8.2; p < 0.01). In 2007, with lower daily intake levels, weight gain was very low on both diets (21 g/d ± 13 on artificial milk, 4 g/d ± 3.8 loss on fish formula; non-significant). Survival to weaning was twice as high with the artificial milk formula (40%) compared to the fish formula (21%) in 2007 (p < 0.05 by chi-squared analysis). In 2008, with greater intakes, fewer seals died on either treatment (6/35 on artificial milk, 8/34 on fish formula). The greater weight gains and survival on artificial milk formula may be attributed to the higher caloric intake provided by this diet (7.4 cal/g DM) compared to the fish formula (6.9 cal/g DM), and the improved survival and weight gains on both diets in 2008 were likely due to the increase in feeding level and frequency. Although neither diet achieved the weight gains recorded in mother-raised pups (300-600 g/d),1,2 the artificial milk formula was clearly the more successful of the two. More work is needed on both diet composition and feeding method to achieve higher survival and more natural weight gains.
1. Cottrell, P.E., S. Jeffries, B. Beck, and P.S. Ross. 2002. Growth and development in free- ranging harbor seal (Phoca vitulina) pups from southern British Columbia, Canada. Mar Mamm Sci 18(3): 721-733.
2. Lang, S.L.C., S.J. Iverson, and W.D. Bowen. 2005. Individual variation in milk composition over lactation in harbour seals (Phoca vitulina) and the potential consequences of intermittent attendance. Can J Zool 83: 1525-1531.