Ringed seals (Phoca hispida), bearded seals Erignathus barbatus), spotted seals (P. largha) and ribbon seals (P. fasciata) are the four species of North Pacific pinnipeds collectively known as the ice seals because of their association with sea ice and their dependence on it for feeding, resting, pupping and mating. All four species, along with the other North Pacific phocine, the harbor seal, are members of the family Phocidae, or true seals. Ringed, spotted and ribbon seals belong to the genus Phoca, and, although each posses distinct coat patterns, are similar in size and gross morphology. They possess the classic streamlined, plump body and round head and large eyes we all associate with seals. The spotted seal is very similar in morphology and coat pattern to harbor seals, so similar in fact that adults are difficult to tell apart in the field. This similarity has led some to suggest that they may be two subspecies of a single species rather than two distinct species. The bearded seal, named for its distinctive long, curling whiskers, is a member of the genus Erignathus and is quite different in size and shape to the other species. Much larger, the bearded seal has a disproportionately smaller head and flippers.
These four species are important members of the marine mammal fauna of the Bering, Chukchi and Beaufort Seas and represent an important subsistence resource for many coastal communities of Alaskan, Canadian and Russian Natives in this region. They are potentially vulnerable to oil development activities and climate change. The species differ in their relationship with sea ice which likely influences many aspects of their biology and ecology, including population abundance and distribution, breeding behavior, association patterns, movement and dispersal (Burns, 1970; Burns et al., 1981). However, little is known about these and other aspects of the biology and ecology of ice seals, and they have received little attention compared to other Bering Sea vertebrate species, some of which are known to be in decline (e.g. sea birds, sea lions, fur seals and possibly harbor seals). Estimates of population abundance and trends, and recent health assessment of ice seals are not available for most species and are confounded by a poor understanding of even the most fundamental information such as population structure, movements and dispersal.
Management objectives are primarily concerned with monitoring the health and status of ice seal populations, determining the possible effects of oil development and global climate change on these populations, and maintaining these species as sustainable resources while ensuring that they remain as functioning elements of their ecosystem. Each of the four species of ice seal are currently managed by the U.S. National Marine Fisheries Service as single stocks in Alaskan waters. These classifications are based solely on their apparent continuous distributions in the Bering, Chukchi and Beaufort Seas. Resolving population structure and describing dispersal patterns is essential to defining meaningful management units and designing effective management strategies.
Molecular genetic techniques are being applied to a number of taxonomic, evolutionary and demographic questions in all four species, including the phylogenetic relationships among the different species and the population structure and dispersal patterns within each species.
We are currently involved in a long-term study with the National Marine Mammal Laboratory and the Alaska Department of Fish and Game (ADF&G) of the population structure within spotted seals and the evolutionary and contemporary relationship of this species to the morphologically similar harbor seal. Analysis of variation within the mitochondrial genome (mtDNA) confirmed that these two seals were indeed separate species (O'Corry-Crowe and Westlake, 1997). More recent research has detected population structure in spotted seals only over very large (>1,000km) distances and has documented a number of individuals that, although identified as harbor seals in the field, turned out to have the spotted seal genetic signature.
We have recently initiated a collaborative research project with the ADF&G to determine whether mtDNA would be informative in resolving questions of population and stock structure in ringed, bearded and ribbon seals. Initial efforts are revealing high levels of genetic variation in all species.
Burns, J.J. (1970) Remarks on the distribution and natural history of pagophilic pinnipeds in the Bering and Chukchi Seas. Journal of Mammalogy 51:445-454.
Burns, J.J., Shapiro, S.H. and Fay, F.H.. (1981) Ice as marine mammal habitat in the Bering Sea. Pp. 781-797, In The eastern Bering Sea shelf: oceanography and resources. vol.2. D.W. Hood and J.A. Calder (eds.) U.S. Dep. Commer., NOAA, Off. Mar. Pollut. Assess., Juneau, Alaska.
O'Corry-Crowe, G.M. and Westlake, R.L. (1997) Molecular Investigations of spotted seals (Phoca larhga) and harbor seals (P. vitulina), and their relationships in areas of sympatry. In Molecular Genetics of Marine Mammals. (A.E. Dizon, S.J. Chivers and W.F. Perrin, eds.). The Society of Marine Mammalogy, Special Publication 3: 291-304.