MARINE MAMMAL RESEARCH NEWSLETTER | July 2014 (Issue 10)
Into the Lab
Northern fur seals are only on land on the Pribilof Islands during the summer and fall and then become a true marine mammal once they depart for the wide expanse of the Bering Sea and North Pacific. This transformation to a pelagic existence is particularly extraordinary for young pups.
Young fur seals find themselves suddenly forced to forage and survive alone when just four months old. With winter conditions fast approaching, these youngsters must transfer from relying on milk to fish as they leave the familiar confines of the Pribilof Islands and swim into the unfamiliar expanse of the North Pacific on a journey that will last almost two years.
At first glance, their chances of survival would seem tenuous at best. They are naïve to foraging and may be physiologically underdeveloped for diving. To make matters worse, they are relatively small, and have a thin blubber layer compared to other seals and sea lions. Half of the pups will likely die in their first two years at sea.
The pelagic life of fur seals makes it almost impossible for scientists to study how they survive and whether they are limited by environmental conditions.
UBC Research Associate Dr. David Rosen and MSc student Alex Dalton wanted to understand the potential effects of cold water on the food requirements and migration patterns of young northern fur seals. To that end, they conducted a series of studies that investigated the effect of water temperature on the physiology of six northern fur seals brought to the Vancouver Aquarium from the Pribilof Islands for research. The results of their research have just been published in Marine Mammal Science.
Animals have to expend additional energy to maintain their internal body temperatures when the environment gets too cold or too warm. One aspect of their studies measured the energy the animals used (or more precisely, how much oxygen they consumed) across a range of water and air temperatures over their first four years of life.
Much to their surprise, Rosen and Dalton found that the young fur seals were largely unaffected by cold water temperatures. The juvenile (7-24 months old) fur seals only had to increase their energy expenditure when water temperatures dropped below 6-8°C, which was much colder than previous studies had suggested. The researchers also found the fur seals’ ability to withstand cold water temperatures improved with age. Older fur seals (2.75 to 3.5 yr) had no problem tolerating the coldest water temperatures, except in the summer months (when such cold temperatures are unlikely to be encountered in the wild). Rosen and Dalton also found that fur seals (regardless of age) were largely unaffected by warmer waters, due perhaps to using their large flippers to dump excess heat.
The findings suggest that water temperatures do not play a significant role in the annual migration of the fur seals. They also suggest that fur seal fur is superior for keeping warm than the substantially thicker fur of sea otters. The explanation for this surprising finding may lie in differences in the oils that fur seals and sea otters secrete to maintain the insulative quality of their furs.
Results from these studies help scientists understand the interaction between physiology and behavior of fur seals in the wild, and assist in population conservation plans.