“Stable isotope studies on wild and captive polar bears”
Keith A. Hobson1, Ian Stirling2, and Dennis Andriashek2
1Canadian Wildlife Service, 115 Perimeter Road, Saskatoon, SK., Canada, S7N 0X4
2Canadian Wildlife Service, N.F.R.C., 5320 - 122 Street, Edmonton AB. Canada, T6H 3S5
The measurement of naturally occurring stable isotopes in consumers can provide information on source of feeding as well as trophic level. The period over which this information is integrated depends on the elemental turnover rates of various tissues. These range from periods representing the lifetime of the individual in the case of bone collagen to several hours based on exhaled breath CO2. Moreover, the nutritional pathways involved in tissue and energy synthesis determines how effectively inferences based on recent vs. past diets can be made. Our ongoing isotopic (d15N, d13C) investigations into the nutritional ecology of polar bears of western Hudson Bay has involved an evaluation of the dependence of bears on terrestrial berries during the period they spend on land prior to returning to the sea ice to feed on seals. Consisting primarily of carbohydrates, these berries enter primarily short-term energy pathways whereby most of the ingested carbon is exhaled as CO2. We obtained breath CO2 from wild bears for d13C analysis but required captive bears fed known diets in order to ground-truth our methods. Captive bears raised on marine-based foods showed considerably enriched breath d13C values compared to our wild bears. These data have been used to construct a nutritional pathway model for the bears of western Hudson Bay.
2Canadian Wildlife Service, N.F.R.C., 5320 - 122 Street, Edmonton AB. Canada, T6H 3S5
The measurement of naturally occurring stable isotopes in consumers can provide information on source of feeding as well as trophic level. The period over which this information is integrated depends on the elemental turnover rates of various tissues. These range from periods representing the lifetime of the individual in the case of bone collagen to several hours based on exhaled breath CO2. Moreover, the nutritional pathways involved in tissue and energy synthesis determines how effectively inferences based on recent vs. past diets can be made. Our ongoing isotopic (d15N, d13C) investigations into the nutritional ecology of polar bears of western Hudson Bay has involved an evaluation of the dependence of bears on terrestrial berries during the period they spend on land prior to returning to the sea ice to feed on seals. Consisting primarily of carbohydrates, these berries enter primarily short-term energy pathways whereby most of the ingested carbon is exhaled as CO2. We obtained breath CO2 from wild bears for d13C analysis but required captive bears fed known diets in order to ground-truth our methods. Captive bears raised on marine-based foods showed considerably enriched breath d13C values compared to our wild bears. These data have been used to construct a nutritional pathway model for the bears of western Hudson Bay.