Seasonal changes in background levels of deuterium and oxygen- 18 prove water drinking by harp seals, which affects the use of the doubly labelled water method

• Published in: Journal of Experimental Biology
• Main Authors: Nordøy, Erling Sverre, Lager, Anne Regine, Schots, Pauke C.
• Format: Article in Journal/Newspaper
• Language: English
• Published: The Company of Biologists Ltd 2017
• Subjects: VDP::Medisinske Fag: 700::Basale medisinske; odontologiske og veterinærmedisinske fag: 710::Medisinsk biokjemi: 726; VDP::Medical disciplines: 700::Basic medical; dental and veterinary science disciplines: 710::Medical biochemistry: 726; VDP::Matematikk og Naturvitenskap: 400::Zoologiske og botaniske fag: 480::Marinbiologi: 497; VDP::Mathematics and natural science: 400::Zoology and botany: 480::Marine biology: 497; Harp Seal; Phoca groenlandica
• Online Access: https://hdl.handle.net/10037/14143; https://doi.org/10.1242/jeb.161943

Source at https://doi.org/10.1242/jeb.161943 The aim of this study was to monitor seasonal changes in stable isotopes of pool freshwater and harp seal (Phoca groenlandica) body water, and to study whether these potential seasonal changes might bias results obtained using the doubly labelled water (DLW) method when measuring energy expenditure in animals with access to freshwater. Seasonal changes in the background levels of deuterium and oxygen-18 in the body water of four captive harp seals and in the freshwater pool in which they were kept were measured over a time period of 1 year. The seals were offered daily amounts of capelin and kept under a seasonal photoperiod of 69°N. Large seasonal variations of deuterium and oxygen-18 in the pool water were measured, and the isotope abundance in the body water showed similar seasonal changes to the pool water. This shows that the seals were continuously equilibrating with the surrounding water as a result of significant daily water drinking. Variations in background levels of deuterium and oxygen-18 in freshwater sources may be due to seasonal changes in physical processes such as precipitation and evaporation that cause fractionation of isotopes. Rapid and abrupt changes in the background levels of deuterium and oxygen-18 may complicate calculation of energy expenditure by use of the DLW method. It is therefore strongly recommended that analysis of seasonal changes in background levels of isotopes is performed before the DLW method is applied on (free-ranging) animals, and to use a control group in order to correct for changes in background levels.