Starting weight most important factor
The results so far have been surprising: growth rates, seasonal fluctuations in body mass, and percent body fat have been generally independent of the seal's diet. Instead, the starting weight has been the critical predictor of whether the seal would add body mass and body fat, Polasek explained.
Seals weighing less than 26 kilos (about 12 pounds) showed little progress in gaining weight and even lost blubber, regardless of which diet they were on. On the other hand, the study's largest seal, which weighed 33kg when she began in 2004, has shown good growth despite being on the low fat diet, Polasek said. A seal that weighed 26kg at the start of the study, on the high-fat diet, has also continued to grow in a similar manner.
These results fit with a recent study by a team from Göteborg University that found wild seal pups smaller than 26 kg when they were weaned were less likely to survive the winter. It seems that mother seals, which produce high fat milk, must impart enough fat to get pups over the 26kg mark, Polasek noted. And once weaned, they must ingest sufficient food to get through the winter when food is less abundant.
Seals rely on blubber both for insulation and as a source of energy. Nutritionally stressed adolescent females may take longer to reach sexual maturation and mature females that are nutritionally stressed may not reproduce, offering clues to why some harbor seal populations are falling, Polasek said.
The seals will continue their low fat and high fat diets as the longitudinal research continues. "We're curious to find if it will take longer for the low fat diet animals to re
Source:American Physiological Society