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NAMMCO 25

Current Abundance and Trends

Ringed seals are the most abundant high arctic seal and although no accurate global estimate is available, the species is thought to number at least a few million animals (Reeves 1998). 

The remoteness and dynamic nature of ringed seal sea‐ice habitat, time spent below the surface, along with their broad distribution and seasonal movements makes surveying ringed seals expensive and logistically challenging, and therefore it is difficult to assess their population size and trend (Kelly et al. 2010b).

 

 02petersen 1053 2 Stephen Petersen Polar Bears International

 Ringed seals hauled out on ice. Photo: Stephen Petersen, Polar Bears Int.

Counting ringed seals

Ringed seals are difficult to count. Other ice breeding seals, such as harp (Phoca groenlandica) and hooded (Cystophora cristata) seals, birth and rear their pups on the surface of the ice. Aerial surveys for these species are conducted to count the pups during breeding season, and pup counts are then converted to total population estimates. Ringed seals give birth in lairs under the snow that are practically invisible from the ice surface. While they commonly haul out on the ice during the moulting period in late spring, it is unlikely that the entire population would be on the ice surface at any given time. Aerial, ground- or ship-based surveys can detect only those seals that are on the ice or at the surface of the water, and this proportion is usually unknown. Therefore, estimates of ringed seal abundance are simply not available for most areas.

Despite these difficulties, aerial surveys of fast-ice areas during the spring have been and are the most widely used method of assessing the abundance of ringed seals, although it is widely recognized that such counts are underestimates (reviewed by Reeves 1998, and more recently e.g. Frost et al. 2004, Moulton et al. 2005, Bengtson et al. 2005, Krafft et al. 2006a). Surveys must be timed to coincide with peak haul-out season and correction factors are still required to account for the number of animals that are not visible at the time of the survey because they are either in the water, or in some cases still in their snow lairs. A variety of methods have been employed to attempt to correct counts to population estimates (Reeves 1998 for review, Bengtson et al. 2005, Kelly et al. 2006, Krafft et al. 2006a) but calibration issues remain (Carlens et al. 2006, Krafft et al. 2006a). Most if not all abundance surveys to date should probably be considered indices of abundance (Kovacs and Lydersen 2006, Kovacs 2014).

 

Counts of breathing holes and/or birth lairs using trained dogs have also proven effective in some areas (Hammill and Smith 1990, Lydersen 1998). Some estimates of abundance have been derived by calculating the number of ringed seals required to support the predation of polar bears and humans in the area. The abundance of polar bears is usually more accurately known than the abundance of ringed seals. For example, Kingsley (1998) used a population estimate for polar bears in Baffin Bay, estimates of their food requirements, and the human harvest by Canada and West Greenland to estimate that there must be at least 1.2 million ringed seals in the area to support this level of predation. Kingsley (1990) used a similar approach to calculate that there must be at least 4 million seals in the Canadian Arctic.

 

ringedseal02Dog sniff University of Alaska Southeast

A dog sniffing out a ringed seal lair during counts of ringed seals in Alaska. Photo: University of Southeast Alaska, read more here 

The NAMMCO Scientific Committee (NAMMCO 1997a) derived a rough estimate of the abundance of ringed seals in NAMMCO Area 1 (Northeastern Canada - Baffin Bay - West Greenland, see 'Distribution') of approximately 1.3 million seals, based on extending existing estimates to areas of similar habitat. This estimate has a large contribution from pack ice areas, where knowledge of ringed seal density is particularly poor. Nevertheless it is similar to the estimate by Kingsley (1998) for roughly the same area.

Abundance and trends

Because of the difficulties in deriving estimates of abundance, there is little information on trends in abundance for most areas. Short-term fluctuations in the numbers of young seals produced have been documented (eg. Kingsley and Byers 1998) and are likely related to annual variations in ice conditions. Seasonal reductions in abundance in the vicinity of hunting communities have also been noted (Reeves 1998). The only areas where population reductions that can definitely be related to over-harvesting have been noted are in the Okotsk Sea and the Baltic Sea. Both these areas were subjected to large-scale commercial harvesting in the past. This harvesting has since been reduced (Okotsk Sea) or has ceased (Baltic Sea), and ringed seal populations are now thought to be recovering in these areas (Reeves 1998). Some small lake populations have also been affected by hunting (Sipilä and Hyvärinen 1998).

The table below gives the most recent abundance estimates for ringed seals in different areas, as well as the conservation status in these areas.

 Ringed seal abundance table