Forsøksdyr: Nitrogen excretion and aspects of water balance in fasting hooded seal pups

Godkjenningsdato 10.02.2020

Godkjenningsperiode 20.03.2020-31.12.2021

Hooded seals (Cystophora cristata) display some remarkable biological adaptations that are still poorly understood and deserve study, from a basic research perspective. Pups are born in late March in the pack ice of the Greenland Sea and suckle for 3-4 days, gain weight at incredible rate of 7 kg/day. After weaning, they enter into a voluntary fasting period and passively follow the pack ice for 2-3 weeks before leaving the ice edge to search for food in the Norwegian Sea, probably fasting for another 2 weeks until arrival at feeding grounds (Folkow et al. 2010). During the post-weaning fast, pups have access to potential exogenous water sources in the form of snow and seawater, but it is unclear exactly how these animals maintain energy and water balance while fasting. We will study evolutionary adaptations to this lifestyle, using six hooded seal pups between weaning (age 3 days) and 33 days of age. We wish to 1) quantify the rate of nitrogen excretion in order to determine the rate of protein catabolism, to test the hypothesis that ice-breeding seals-species have a high rate of protein catabolism during post-weaning fast compared to terrestrial breeding seal-species. 2) determine the basal metabolic rate weekly throughout the study period, to test the hypothesis that pups display metabolic depression during the fast, to conserve energy; 3) study the most important mono- and divalent ions of plasma and output in urine, to test the hypothesis that the pups drink sea-water to maintain water balance during their post-weaning fast. The studies will involve limited handling with no minimal impact on animal welfare.
The animals will be captured at the stage of weaning, brought on board FF Helmer Hanssen and kept in specially designed pens with fresh snow continuously available, until arrival at the approved seal holding facilities at the University of Tromsø. Here, they will be maintained in two 40 000 liter seawater pools for the remainder of the study. Once every week, each animal will be sedated and restrained to allow blood sampling from the extradural intravertebral vein. Also, once a week each pup will be placed in a respiratory chamber for a duration of 2-3 hours, for determination of basal metabolic (oxygen uptake) rate by indirect calorimetry. Finally, once a week, pups will be placed in a wooden box, there resting on a metal grid, to allow urine sampling for 24 hours.
Current climate change has led to a dramatic decrease in the extent of the Greenland Sea pack ice. At the same time, the Greenland Sea hooded seal-population has reached a historically low level despite protection for two decades. Less pack ice increases travel distance to feeding grounds and the time spent at open sea. Thus, the current project will contribute to the understanding of the importance of access to snow versus seawater for the health and homeostasis of this species, in face of the current reduction of the pack ice.