Blood-Oxygen Capacity of Ribbon, Spotted, and Bearded Seals
Figure 5. Capture locations of ribbon, spotted, and bearded seals in the Bering and Chukchi Seas in May and June 2009.
Hemoglobin (Hb) concentration and packed cell volume (PCV) are indicators of oxygen storage and transport capacity in the blood. Deep-diving mammals generally have higher PCV and Hb levels than terrestrial mammals, allowing them to store more oxygen, make deep dives, and stay submerged while foraging. The National Marine Fisheries Service has recently been petitioned to list the four species of ice-
associated seals found in Alaska waters (i.e., ribbon, spotted, bearded, and ringed seals) as endangered or threatened under the Endangered Species Act. The petition was primarily based on concerns about global warming and the projected loss of sea-ice habitat. Ice-associated seals give birth and nurse their pups on shore-fast and pack ice; pups use sea ice for resting between foraging bouts. Warming oceans, loss of sea ice, and other environmental perturbations caused by Arctic climate change could affect abundance, distribution, and composition of prey. A loss of suitable sea ice in traditional weaning grounds could isolate seals from important prey communities, requiring longer or more frequent dives. Therefore, information on blood-oxygen capacity may be important for assessing how these seals might be influenced by a changing environment. Existing data on PCVs and Hb levels in these seals are scarce or nonexistent, and information on blood-oxygen capabilities may be important to assess how seals respond to a changing environment.
In May and June 2009, members of the Polar Ecoystems Program sampled ribbon (Histriophoca fasciata) and spotted (Phoca largha) seals from the Bering Sea and bearded seals (Erignathus barbatus) from the Chukchi Sea (Fig. 5). We collected blood samples and measured Hb concentration, PCV, and mean corpuscular hemoglobin concentration (MCHC) in 31 ribbon and 29 spotted seals, including individuals from all age and sex classes. Only three bearded seals were sampled; all three were males, with one adult and two subadults. Mean Hb levels for ribbon, spotted, and bearded seals were 20.80±1.88 grams/deciliter (g/dl), 17.98±3.14 g/dl, and 29.49±2.43 g/dl, respectively. Mean PCVs for ribbon, spotted, and bearded seals were 62.5±3.6%, 56.2±5.3%, and 54.7±1.5%, respectively (Fig. 6).
Figure 6. Mean hemoglobin concentration, packed cell volume, and mean corpuscular hemoglobin concentration (MCHC) for bearded, ribbon, and spotted seals.
In our sample, PCV was highest in ribbon seals for all ages and sexes (Fig. 7). Ribbon seals also had higher Hb values than spotted seals across age groups. These results may be related to the fact that ribbon seals are deeper divers than spotted or bearded seals. Hematology values have been compared in harp (Phoca groenlandica) and hooded (Cystophora cristata) seals; hooded seals, which are deeper divers, had higher PCV levels than harp seals. Hb and PCV levels were very similar between males and females for both ribbon and spotted seals.
We have very limited data for bearded seals (n = 3; all males), but Hb levels were much higher in these three seals than in ribbon or spotted seals (Fig. 7). This raises additional questions because bearded seals are the shallowest divers of the three species and presumably do not need high levels of hemoglobin to assist with deep diving. However, in California sea lions, hemoglobin and MCHC increased with mass, and bearded seals are considerably larger than ribbon and spotted seals.
Figure 7. Hemoglobin concentration, packed cell volume, and mean corpuscular hemoglobin concentration (MCHC) for bearded, ribbon, and spotted seals compared among age classes and between sexes.
A trend in which both Hb and PCV values increased with age from young-of-the-year to subadults and then decreased from subadults to adults has been observed in harbor seals. Our results bear some similarities to this pattern, but larger samples will be required to confirm whether any of the patterns and differences that we found are significant and to relate the patterns to potential responses of these species to a warming climate.
By Heather Ziel, Michael Cameron, Tracey Goldstein, Shawn Johnson,
and Peter Boveng
Additional Reading
Boily, F., S. Beaudoin, and L. N. Measures.
2006. Hematology and serum chemistry of harp (Phoca groenlandica) and hooded seals (Cystophora cristata) during the breeding season, in the Gulf of St. Lawrence, Canada. Journal of Wildlife Diseases 42(1):115-132.
Burns, J. J.
1978. Ice seals. Pp 192-205, In: D. Haley (ed.). Marine Mammals of the Eastern North Pacific and Arctic Waters. Pacific Search Press, Seattle.
Burns, J. M., D. P. Costa, K. Frost, and J. T. Harvey.
2005. Development of body oxygen stores in harbor seals: effects of age, mass, and body composition. Physiological and Biochemical Zoology 78(6):1057-1068.
Weise, M. J., and D. P. Costa.
2007. Total body oxygen stores and physiological diving capacity of California sea lions as a function of sex and age. Journal of Experimental Biology 210(2):278-289.
