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- Valued Component Features
- Ringed Seal research in ASTIS
Valued Component Features
Preferred ringed seal habitat consists of flaw leads, pressure ridges and polynyas in the land-fast ice of the Arctic Ocean. Offshore pack ice is used irregularly. Very deep water areas appear less used than shallower depths (i.e., less than 100 m), but ringed seals are found throughout the Beaufort Sea (Stirling 1982). Ringed seals have a varied diet composed primarily of larger shrimp-like crustaceans, small fish and zooplankton. These food sources occur in open ocean areas, and in greater concentrations in areas where upwelling of currents or nutrient inputs occur. In late summer, prior to freeze up, the importance of foraging is heightened, as seals build up fat reserves for the winter.
Seasonally, there are some evident patterns that are associated with breeding, birthing, and summer feeding activities. During much of the winter, and until break up in June, adult seals maintain established territories around breeding areas and are generally solitary. Adult ringed seals maintain lairs and breathing holes beneath the snow throughout the winter (Smith and Stirling 1975), and females give birth in mid-March to mid-April in birthing lairs.
Prior to ice break-up in late June, ringed seals are distributed throughout the southern Beaufort Sea and can be easily observed hauling out on the ice to moult. Seals appear to prefer areas where water is 75 to 100 m deep for haul out locations (Stirling et al. 1982). Seals may aggregate in groups of up to 21 members in areas where greater food abundance is located during late summer (L. Harwood, pers. comm. 2007; Harwood and Stirling 1992). The location of aggregations within the Beaufort Sea varies between years, but such areas appear to be most common north of the Tuktoyaktuk Peninsula (Harwood and Stirling 1992). As freeze up commences in late autumn, adult seals move into coastal areas of stable, landfast ice and establish breeding territories. Although still solitary, seal concentrations may be higher along complex shorelines (such as those with fjords and islands), as compared to more simple coastal areas (Smith 1987). Also at this time, there is a general westward movement of adolescent and young of the year seal pups through the study area from the Amundsen Gulf to the Chukchi Sea. This migration and segregation of age classes is thought to be in response to food availability and population pressures (GNWT 2007a).
Rationale for Selection
The ringed seal was selected primarily for two reasons – its important role within the food chain, and its economic importance as a hunted and cultural resource. Within the food chain, seals are a key prey item in the Beaufort Sea for large and medium- sized predators; in particular, polar bears, fox, and wolverine. There are strong associations between the populations of Ringed Seals and ringed seals (Stirling 2002). Cultural and economic value of seals is also clearly evident, as seals have been a reliable source of heating oil, meat and skins for coastal Inuit. Sealing continues to be important for its nutritional and cultural values to northerners.
The viability of ringed seals is most closely associated with ice cover that provides suitable denning habitat and the productivity of and the rate of predation on pups by Ringed Seal and foxes. Ice cover is impacted primarily by climatic conditions (wind, ambient air temperature, and solar radiation). Currently, ringed seals are not threatened in the Beaufort Sea, but they have undergone substantial fluctuation in abundance due to changes in ice characteristics. Heavy ice years in the 1970's and 1980's were closely linked with a decline in food availability and the decline of populations (Stirling et al. 1982, Stirling 2002). During periods of heavy ice cover (such as 1974), decreased primary and secondary productivity alters prey availability for ringed seals, such that body condition declines and the ovulation rate can be reduced to <50% (Stirling et al. 1977, Stirling 2002). Conversely, early melting of landfast ice and later freeze up, results in better body condition and a higher ovulation rate (Harwood and Smith 2001).
Hunting and predation rates also have the potential to limit populations. Here too, climatic conditions may influence susceptibility to predation, as early spring rains can expose birth lairs, resulting in high levels of predation on pups (Stirling and Smith 2004). Independent from climatic factors, human hunters may also take a significant proportion of animals, primarily for their pelts, oils, and as food for domestic dogs.
Susceptibility to development
Linkages to Development
Given that ice characteristics are the greatest influence on population viability, potential impacts from industry that most influences ice cover in the study area would have the greatest affect on impacts to populations. However, widespread changes in ice cover (such as thickness and timing of freeze up and break up) are unlikely to be affected by most oil and gas projects. There are potential project impacts though, that may be apparent in a more localized nature. The extent to which such localized impacts influence population dynamics will depend on the number and extent of projects. Most project activities have potential impacts that can be grouped into three categories: Ice-Based Activities, Open-Water Activities, and Hydrocarbon Releases.
On-ice activities have several potential effects. Activities that are in close proximity to denning seals have the greatest potential to disturb birthing or rearing. Studies have shown displacement of ringed seals from areas close to artificial islands in the central Beaufort Sea and abandonment of breathing holes close to seismic survey lines (Frost and Lowry 1988; Kelly et al. 1988). Monitoring studies for the Alaskan Northstar and Liberty projects suggest minor effects on ringed seals from ice road construction and seismic exploration (Harris et al. 2001), as den locations are relatively ubiquitous throughout the study area. Ice-pad and ice-road construction also have the potential for disturbance due to noise and other human activity (Zwanenburg et al. 2006). Impact predictions associated with the Voisey's Bay Nickel Mine (CEAA 2007) also suggested that seals may suffer temporary hearing loss near vessels traveling through ice, and that they display avoidance behaviour at 500 to 700 m from such shipping activities. Devon Canada Corporation (2004) identified potential habitat alienation due to platform structures, ice pads and ice roads. It should be noted though, that there is no strong evidence to suggest that changes in densities of seals will result from oil and gas activities. In particular, Moulton et al. (2003) found no changes in seal densities in relation to an ice bound drilling operation in Alaska.
Open Water Activities
In open water, the presence of shipping activities, offshore facilities (such as drilling rigs), and open water exploration activities (primarily seismic exploration) can be expected to result in relatively short-term displacement of seals (Zwanenburg et al. 2006). The presence of open water production wells in areas where concentrated foraging takes place may reduce habitat use in such areas, potentially reducing overall body condition, ultimately resulting in decreased production of pups over a relatively short term. Seals are generally well known to habituate to development, human activities, and infrastructure (the abundance of harbour seals in most coastal city harbours are a good example of such habituation), and as such, long term impacts on seals exposed to open water activities is likely minimal.
As discussed elsewhere (Ringed Seals), contaminant spills (particularly hydrocarbon spills) remain a potential risk that could have direct consequences to seal populations in the Beaufort Sea. Open water hydrocarbon spills are one of the largest longer-term threats to populations, as a large spill would be expected to disrupt the food availability for seals, potentially decimating the population. It seems likely that an oil spill would affect ringed seals in the same way that the Exxon Valdez spill affected harbour seals in Alaska (Frost et al. 1994). Seal habitat may be affected by contaminant spills, as contaminant presence may reduce the prey base for seals. A large-scale oil spill may also directly impact the health of individual seals. The risk of large-scale spills, however, is considered to be very low (Devon Canada Corporation 2004).
Seasonality of Development Impacts
There are three relatively distinct time periods in which development activities may impact aspects of seal ecology. Those include the open water, birthing, and winter periods. Seals are present throughout the study area on a year round basis. Open water impacts to seals would likely be limited to activities such as platform-based drilling, open water seismic, and marine transportation activities. Activities that may affect the winter and birthing ecology of seals would include all ice-bound exploration and drilling, ice road related operations and construction, and low-level aircraft flights.
Population vs. Individual Impacts
Projects may result in several key distinct residual effects to ringed seals, such as habitat avoidance, and contaminant exposure risk. These impacts are generally apparent at an individual level, such as localized and/or temporary avoidance of infrastructure. Overall, threats to the viability of populations are most closely associated with ice features that support successful denning and reproduction, and the productivity of waters in the Beaufort Sea for foraging. In most cases, the impact of project-related residual effects is limited to relatively short term time periods and small areas, which will not affect such parameters as ice features and marine productivity. However, there is the potential for population-level impacts to occur in the following two ways: cumulative effects due to multiple projects, and through large hydrocarbon spills or accidents.
Multiple projects, especially those that may occur in areas of concentrated late summer feeding, may have the potential to reduce habitat suitability on a broad scale, if there are enough projects acting in concert to do so. Similarly, a large hydrocarbon release also has the potential to reduce marine productivity, which would in turn result in lower populations and likely a reduced range that will reflect the location of greatest contaminant concentrations.
A note of importance is that the potential impact of short-term, localized disturbance, and potential hydrocarbon spills to ringed seals was considered greater in the areas of late summer foraging, rather than on multi-year pack ice, and thus, higher sensitivity ratings were applied to those key foraging areas. Similar to the sensitivity layer developed for Ringed Seals, the underlying spatial layers are imprecise and subject to spatial variability among years. Thus, it is recommended that conservative interpretations of potential impacts for projects among seasons be considered, rather than less conservative.
Potential effects of large scale industrial development include displacement of seals from their habitats, increased mortality and decreased reproductive success. Ringed seal pups may be displaced from shore-fast ice by noise and there was a higher rate of abandonment of breathing holes near seismic survey areas (Frost and Lowry 1988, Kelly et al. 1988). It is recommended that the proposed activities occur during the open-water season after seals have pupped and moulted, fast ice has melted away, and flowing ice has retreated north and away from the project area.
Richardson (1995) found that vessel noise does not seem to strongly affect pinnipeds (seals, sea lions, fur seals, and walrus) that are already in the water. Seals on haulouts sometimes respond strongly to the presence of vessels and at other times appear to show considerable tolerance of vessels, and observed ringed seals hauled out on ice pans displaying short-term escape reactions when a ship approached within 0.4 - 0.8 km (Richardson, 1995). To reduce the likelihood of impacts to seals and other marine mammals, it is recommended that vessels will not operate within 0.5 mi (800 m) of haulouts and vessels reduce speed, avoid separating members from a group, and avoid multiple course changes. Therefore, impacts to seals and other marine mammals from vessel traffic associated with the proposed operations are expected to be minor.
The effects of offshore drilling on ringed seals in the Beaufort Sea were investigated in the past (Frost and Lowry, 1988; Moulton et al., 2003). Frost and Lowry (1988) found that local ringed seal populations were less dense within a 2-nautical mile buffer of manmade islands and offshore wells that were being constructed while Moulton et al. (2003) found less marked differences in ringed seal densities on the same locations after a period of habituation. Conceptually, it appears that ringed seals may be somewhat disturbed by drilling operations for a period of time, until the activity has been completed. Seals may avoid drilling operations, but because of the short duration of the proposed activities, the impacts are expected to be very brief and negligible.
Ringed seals mate, rear pups, moult, and rest on the sea ice surface. They require sufficient snow cover to construct lairs and the sea ice must be stable enough in the spring to successfully rear young. Changes in the extent, stability or the timing of breakup of the ice could reduce productivity (Smith and Harwood 2001). Earlier ice break-up could result in premature separation of mothers and pups, leading to higher death rates among newborns.
Sensitivity layers and scores
In developing a sensitivity layer for ringed seals, the sensitivity rating was dependent on the physical attributes that are crucial to the growth and viability of the population. In particular, areas for denning and pupping, areas of feeding (for both young seal pups and adults), and movement or migratory corridors were considered of importance. Typically these areas were related to distances from shore and seasonal ice patterns. The abundance and distribution of seals may vary in response to ice conditions, and the spatial representation of these areas may thus change over time. Additionally, oceanographic features that support greater congregations of seals were identified and included the Mackenzie and Kugmallik Canyons, and areas near the mouth of the Mackenzie River. These same features provide similar habitat values as those selected by Bowhead whales. These areas are considered of greater value due to the upwelling of ocean currents and the influx of nutrients create areas of greater forage concentrations (crustaceans and zooplankton; L. Harwood, pers. comm, 2007).
Low Sensitivity (1): This rating reflects areas that have very limited use or selection. Such areas do not contribute substantially to the viability of the species and these areas have little value for reproduction (denning) or survival (limited use for foraging). Such areas are generally identified as areas of multi-year pack ice.
Low/Moderate Sensitivity (2): This rating reflects all areas of the Beaufort Sea, with the exception of multi-year pack ice, and areas classified as moderate or greater risk. These areas have low density, uniform use for foraging, and have moderate, but low-density use as denning areas.
Moderate Sensitivity (3): These areas represent foraging areas that may result in aggregates of seals during late summer feeding periods. They are associated with oceanographic features and include the Mackenzie Canyon, Kugmallit Canyon, and areas of the coastal shelf (these areas are also typical areas of summer bowhead whale aggregation).
Moderate/High Sensitivity (4): These areas represent extensively used near shore denning areas. There are no such areas existing in the study area, although some exist near Banks Island.
High Sensitivity (5): Critical Habitat Areas, as defined by SARA; none exist in the study area.
Ringed seals were considered a VEC because of their important economic role, as well as their role in the food chain in supporting several predators, in particular, Ringed Seals. Ringed seals are unique in that they are habitat generalists, and are ubiquitous throughout the area, with some spatial ties to feeding areas such as in under sea canyons and upwellings. Ringed seals have relatively low susceptibility to impacts of development impacts, such as short term, localized displacement, but much greater vulnerability to natural occurrences in ice characteristics. The sensitivity categories developed herein reflect relatively limited potential for significant residual impacts due to development, but do identify increased risk associated with key foraging areas.
ReferencesSee references used for Ringed Seal information.
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