Forsøksdyr: Validation of the tritiated water method in adult harp seals

Godkjenningsdato 07.02.2020

Godkjenningsperiode 01.04.2020-01.04.2022

The harp seal is a key top predator in the North East Atlantic ecosystem. Thus, this species has been the focus of various research projects concerning energy utilization, daily energy expenditure, diet composition and total population size, in order to allow estimation of the total food consumption of the population and its potential impact on resources and fisheries in the area.
Based on previous studies, we know that harp seals display profound variation in body condition and composition throughout the year. Energy loss and energy deposition resulting in changes in body composition are important processes to take into account when constructing refined yearly total energy budgets for harp seal populations.
The tritiated water method is a commonly used approach to assess the body composition of animals: A bolus of tritiated (i.e., radioactively labelled) water is injected intravenously, and is allowed to equilibrate for 1-2 hours, whereafter a blood sample is collected for determination of the specific activity of tritium in body water. Based on this, total body water can be calculated and based on the water content and distribution between tissues (e.g., muscle, blubber), the body composition may be estimated.
For an accurate calculation of body composition, this method requires validation against an absolute determination of body composition, e.g., through a complete dissection and determination of the water content of various body compartments, which is what we wish to achieve.
Female harp seals arrive to the pack ice of the Greenland Sea in mid-March, to give birth to their offspring. They nurse their pups for a period of 10-12 days and then abandon them, to mate. In the nursing period, the females may be captured alive on the pack ice using hoop nets.
We aim to live-capture 5 adult female harp seals in this way, sedate them (intramuscular injection of Zoletil Forte Vet; 1 mg/kg body mass) and bring them on board the research vessel “Helmer Hanssen”. Here, the sedated seal will be secured on a specially designed board, with straps. A catheter is inserted into their extradural intravertebral vein and a control blood sample is collected. A dose of tritiated water is injected and after ~1 hour a second blood sample is collected. The seal will be maintained lightly sedated by additional i.v. doses of Zoletil Forte Vet, when necessary, and will eventually be euthanized by an i.v. injection of pentobarbital (~30 mg/kg body mass) and frozen, for later detailed dissections to determine the body composition in order to validate the tritiated water method for this species. This part of the study will be conducted in the laboratory facilities at UiT – the Arctic University of Norway. If captured females were still nursing pups at time of capture, these will be euthanized in accordance with Norwegian sealing regulations and used for other research purposes.
The procedures will inflict minimal stress to animals, limited to the minutes from capture until sedation takes action, and could be considered terminal since animals will not regain full consciousness after being sedated.