The importance of polynyas, ice edges, and leads to marine mammals and birds

Cmadim

Wildl$e Sewice, 5320 122 Street, Edtmwtm.

Received

I5

Ah.

TM! 3S5, Conada

June 1995: accepted I3 November 1995

Abstract

The correlation between areas of open water in ice-covered seas and increased biological productivity has been noted for some time. To date, most attention has been focused on larger polynyas, such as the Northeast Water and the No&lwater. Although spectacular in their own right, these large polynyas represent only part of a vitally i~~po~a~t continuum of biological productivity that varies significantly between geographic areas and ice habitats, that includes the multi-year pack of the polar ocean and small localized polynyas in annual ice. Surveys of the distribution and abundance of ringed seals in the Canadian Arctic Archipelago have shown differences in density that are correlated with the presence or absence of polynyas. There is also significant variation in the biological productivity of polynya areas of the Canadian High Arctic Archipelago and northern Greenland, all of which receive inflow from the polar basin. Long-term studies of polar bears and ringed seals in western Hudson Bay and the eastern Beaufort Sea show significant but dissimilar patterns of change in condition and reproductive rates between the two regions and suggest that fundamentally different climatic or oceanographic processes may be involved. Prqjections of climate models suggest that, if warming occurs, then the extent of ice cover in Hudson Bay may be among the first things affected. Long-term studies of polar bears and ringed seals in the eastern Beaufort Sea and Hudson Bay would suggest these two species to be suitable indicators of significant climatic or oceanographic changes in the marine ecosystem. K~~wor&polynya; ice edge; polar bear; marine mammals; seabirds; ringed seal

1. Introduction I first wrote about polynyas (areas of open water surrounded by ice) about 15 years ago (Stirling, 1980; Stirling and Cleator, 1981), because I thought they were important to the conservation of the relatively high numbers of marine mammals and birds associated with them. I particularly wished to focus attention on recurring polynyas, that is, those that occur at the same time and place each year, because migrating or overwintering birds and mammals de-

pend on their existence at critical times during the period when the sea is largely ice-covered. A large number of industrial activities were projected to take place in offshore areas in Canada, Alaska, and Greenland, including some of the most important recurring polynya and shore lead systems (Stirling and Calvert, 1983; Stirling, 1990). However, because there were few data on biological processes in and adjacent to polynya areas, it was difficult to evaluate the environmental consequences of anthropogenic activities and make recommendations on how such

0924-7963/97/$17.00 Copyright 0 1997 Elsevier Science B.V. All rights reserved. PII SO924-7963(96)000541

activities might take place with a minimum of detri-

mental effects. By assembling an overview of what was known about polynyas ai that time (Stirling and Cleator, 1981). the late Dr. Max Dunbar and I hoped to help stimulate research that might eventually help facilitate a greater understanding of biological processes common to polynyas as well as the degree of variability that might prevail between polynyas in different areas, That objective has met with mixed success. In a review of priorities for research in arctic marine ecosystems, the Polar Research Board of the United States Academy of Sciences identified research on polynyas as a primary interest (Polar Research Board, 1988). While there have now been two successful expeditions to the Northeast Water (Fig. l), Dr. Dunbar’s dream of an overwintering expedi-

tion to study the Northwater has not been realized to date. Similarly, multidisciplinary proposails to study the Bering Sea polynya have not yet been funde Nevertheless, there have been enough additional smaller scale studies conducted in or adjacent to various polynyas to make it worthwhile to revisit the subject of their biological importance. Recurring polynyas fall into two types: those which are open throughout the winter and those which may be ice covered during the coldest months in some years but which can be relied upon to have at least some open water in early spring, usually by late March or early April, when the first migrating marine mammals and birds arriv& (Stirling, 1980). Polynyas vary in size and shape and may be caused by wind, tidal fluctuations, currents, upwellings, or a combination of these factors. As in earlier discus-

i.DundllElaend 2. Pennyswt

bHetlQat9 s.-sound

80” Fig.

1.

60”

40”

Distributionof majorrecurring polynya and shore lead systems in the Canadian and Greenland Arctic in spring.

arger polynyas, sue

observers (e.g., Sniff et al., 1970;

tres in diameter. The correlation between increased biological productivity and an ice edge has be noted in at least basic contexts. First, from present day, as eople approache the polar pack of the Arctic or Antarctic, they have

78” ice normal thickness ice thinner than normal

Fig. 2. Areas of the Canadian High Arctic where the distribution of ringed seals have been surveyed in June, to compare densities in areas south (downstream) of recurring polynyas in Penny Strait-Queens Channel, and Hell Gate with area south of Byam Martin Channelwhere there are no polynyas.

tional aid to migrating species; a place where marine mammals can breathe and seabirds can feed in heavily ice-covered waters; habitat upon which, or into which, to escape from predators; and, possibly most impomf increased productivity near the ice-water interface that results in a greater biomass of invertebmtis and fish for birds and mammals to feed upon. In this paper, I will discuss aspects of the impormce of polynyas, ice edges, and pack ice, with particular reference to seals and polar bears (Ursus mati~imus).Where possible, I will draw biological comparisons between the Northeast Water, the Northwater, the shore lead and polynya systems of the eastern Beaufort Sea and Western Hudson Bay, and some of the smaller polynyas of the Canadian High Arctic (Fig. 1).

2, Mluence of polynyason biologicalproductivity Initially, in the absence of data on primary production or lower trophic levels in or around polynyas, an abundance of marine mammals and seabirds was rcted as being indicative of increased biologiductivity, Historically, for example, in the anadian Arctic, kills of bowhcad whales (&alusna my&etus) between 182Qand 1915 were the vi@inieyof the polynyas of the umberlandSound, and Roes Welcome n adjacent areas as the ice continued to h the summer (Rws, 1993,figs. 13.8 early presence of whales in these a$ probably indicatesa rester availabilityof food there, possibly because of igher primary production, and the fact that many of the whales are still found in these areas later in summer as break-up proceeds SU sts that the availability of food remains high. Similarly, bowhead whales from the north Pacific stack migrate east in springvia the shore leads along theBeaufortSea coast to feed in the vicinity of the Cape BathurstPolynya, and many continueto feed in theatea after the ice breaksup (Moore and Reeves, 1993). Brwn and Nettleship(198 1) showed that all the major colonies of cliff-nestingseabirds in the Canadian Arctic, except one, are located adjacent to recurring polynyas. Kingsley et al. (1985) found &at, in Wellington Channel and Barrow Strait, down-

stream of polynyas in Queens Channel and Penny Strait (Fig. 2), densities of ringed seals (Phocu hispidu) were approximatelydouble what they were in comparable habitat to the west where there were no polynyas. They suggested that primary production was higher in the polynyas of Queens Channel and Penny Strait and under areas of thinner ice with little snow cover adjacent to those polynyas (Fig. 2), resulting in the water flowing south into Barrow Strait being richer in nutrients, which could help support increased overall biological productivity there. In addition, the further mixing with nutrientrich water passing west along the south coast of Devon Island into Barrow Strait from the Northwater (Welch et al., 1992) is probably another major influ-

ence that would support increased biological productivity. Several studies at various scales have now produced data to support the hypothesis that productivity is greater in polynya areas than in adjacent pack ice. In a pioneering study in the flaw lead at Point Barrow, Bursa (1963) noted that primary production began there up to 2 months earlier than under adjacent ice-covered waters. In similar smaller scale studies, Buckley et al. (1979) and Alexander and Niebauer ( 1981) reported wind-driven upwelling at the southern edge of the pack ice near Svalbard and in the Berin Sea, respectively. More recently, important larger scale studies have been carried out in and adjacent to extensive polynya areas. Hirche et al. (1991) demonstrated that; primary production was significantly higher in the Northeast Water polynya than in the surrounding pack ice. Arrigo and McCiain (1994) found that high productivity in the Ross Sea Polynya near Terra Nova Bay in Antarctica was advected to the south by ocean currents, resulting in biological enrichment in the waters of McMurdo Sound. Their data also suggested that the conditions that produce and sustain the Ross Sea polynya facilitate a bloom of such intensity and persistence that estimates of overall productivity in the area should be revised upwards.

the edge of the polar ice pack, or Marginal Ice Zone (MIZ), concentrationsof marine mammals and At

convergence was produced at the ice edge. Initially, it was thought that the annual pri production under permanent or seasonal ice cover was negligible (l-5 g C m-‘) because of low light levels and cold water temperatures (English, 1961). However, in a reanalysis of English’s data on dissolved oxygen, Pomeroy ( 1997-this vo~ulne) estimated the annual primary production to be approximately 23 g C mV2. Since then, it has become clear that several groups of algae are capable of growing beneath the ice and that a considerable epontic community can develop (e.g., reviews by Harrison and Cota, 199 1; Legendre et al., 1992). The polar oceans appear to be unique in that a substantial portion of the primary production taking place on both the bottom of the ice as well as within the interstitial cracks may be retained for several months prior to being released into the ocean. Alexander (11974) estimated that sub-ice algae cauld account for 2530% of the annual productivity in shallow coastal waters and Hegseth ( 1994) estimated that 30% of the primary production in the Barents Sea came from the sub-ice algae. Other workers (e.g., Nemoto and Harrison, 198 1) calculated lower values; Welch et al. ( 1992) estimated that ice algae accounted for 10% of the primary production in Barrow Strait in the Canadian High Arctic. Regardless of differences in individual estimates, it is clear that epontic algae are abundant and important. Studies in both the Arctic and Antarctic indicate the presence of a large biomass of sub-ice invertebrates and fish which are sustained by epontic algae (e.g., Andriashev, 1968; Bradstreet, 1982, 1988; Welch et al., 1992). Welch and Bergmann (1989) demonstrated that the depth of the snow cover on the ice was much

ctent

water colu

ngsley et al. (1985) reported densities of ringed seals of 0.06-o. 11 /km’, about ly productive waters of Barrow Strait. In areas of dense multi-year ice in the northeastern Beaufort Sea, I have also seen low, but unquantified, densities o bearded seals (Erignathus barbat ated with leads or annual ice between multi-year floes. These observations, like Pomeroy’s (1996) re-evaluation of prima duction under the multiyear polar pack ice, ore life can be supported in such habitat than was previously thought. Leads in multi-year ice, especially in the flaw zone along the northeastern border of the Canadian High Arctic Archipelago and in the polar basin, can be narrow or up to severltl kilometres wide, depending on winds. Annual ice forms between multi-year floes during winter, providing important areas where seals are able to maintain breathing holes. The thinner annual ice there, and the open leads, also provide areas where additional light can penetrate to stimulate primary production (Bursa, 1963). Recent studies of movements of polar bears, using satellite tracking, show that when they are in multi-year ice they are often associated with leads (Stirling, unpubl. data), which is similar to observations from annual ice areas (Stirling et al., 1993). Such observations may indicate the importance of both: (1) greater local productivity (epontic and pelagic) stimulated by increased sunlight, even in small areas of open

found trace amounts of microbial populations,which they suggested might be enough to support a short food chain.

Kerry (pets. commun.) found that while crabeater seals (L&x&on curccinophagus) were absent in a 550 km margin of pack ice out from the Antarctic continent, they were abundant over and immediately to the north of the edge of the continental shelf, which they suggested was because of higher densities of krill associated with oceanic processes along the shelf break. The importance of the shelf-break in the Arctic appears to have been less studied, although higher densities of marine mammals and birds have been observed in this zone (Ainley and De aster, 1990). In the northeastern Beaufort Sea, densities of ringed seals basking on the sea ice to molt in June declined when depths exceeded 100 m and again at depths of 300-400 m (Stirling et al., 1982). Densities of bearded seals are also greater over relatively shallow waters (e.g., Stirling et al., 1982; Kingsley et al., 1985) but this has not been examined quantitatively over large areas or relative to a wide range of depths.

4. The importanceof the continental shelf

5, Comparisonsof verte

water; and (2) currents carrying additional nutrients from poiynyas or ice edges that make it possible to sustain vertebrate life in extreme areas at high latitudes. For example, at White Island in the Ross Ice Shelf, Antarctica,members of an apparently isolated population of Weddell seals (Leptonychotes weddelli) are not only resident at open cracks formed by passage of the ice shelf around the northeastern tip of the island but are also significantly fatter than conspecifics 25 km away in McMurdo Sound (Stirling, 1972), despite little or no primary production in the immediate vicinity (Knox, 1994). Thus, it appears nutrients to support the food chain in the vicinity of White Island have been carried to the area by currents from McMurdo Sound and the western Ross Sea. Even under the 400-600 m thick Ross Ice Shelf, 450 km from the open sea, Azam et al. (1979)

Besides the greater biological productivity that appears to occur in polynya areas because of the jack of ice, both the depth of the water and the presence of the continental shelf are also important. Satellite photos of spatial distribution of phytaplankton biomass of the Arctic basin end associated seas the markedly ater productivity t over the eontin 1 shelves and in relatively shallow inland seas such as Hudson Bay, as compared to deeper adjacent waters (Smith and Sakshaug, 1990). All the important polynyas and shore lead systems in the Greenland and Canadian Arctic, frromthe Northeast Water Polynya to northern Alaska, lie over the continental shelf (Fig. 1), a feature which probably contributes greatly to their biological productivity. In the Antarctic, the continental shelf-break front appears to influencesignificantlythe distribution and abundanceof seabirdsand seals (Ainley and DeMaster, 1990). Ainley (1985) and Veit and Braun(1984) documented a marked concentration of predators along the shelf break of the Ross Sea. Cline et al. (1969) reported higher concentrationsof seabirds in the pack along the shelf break in the Weddell Sea.

duction adjacent to, or downstrea ent polynya areas In general, water in the Arctic Ocean is low in phytoplanktonbiomass and pelagic nutrients because of lower levels of primary production beneath the multi-year pack ice and physical features that maintain a permanent halocline (Jones et al,, 1990; Smith and Sakshaug, 1990; Legendre et al., 1992). The outflow of water from the polar basin passes through three polynya areas in the Canadian and Greenland Arctic, which vary significantly in: the area and shape of open water areas in different seasons; the extent of continental shelfr the proportions of annual compared to multi-year ice; and the amount of possible upwelling. By comparing the abundance and reproduction of some marine mammals and birds in and adjacent to the Northeast Water, the Northwater, and the shore lead and polynya system in the eastern Beaufort Sea (Fig. I), their relative productivity can be evaluated. Water from the polar basin flows south directly into the Northeast Water Polynya and, after a limited amount of mixing in a localized anticyclonic gyre (Schneider and Bud&s, 1994), flows down the east-

mixing because of strong tidal currents (To

over the continental shelf of west

along the east coast of Baffin Island to the Labrador Sea and the north Atlantic Ocean. One would predict that areas wit primary production would support a higher biomass of benthic and pelagic organisms and? consequently, greater numbers of marine mammals and birds. There are limited data with which to compare primary production in the three polynya areas although those available suggest that the Beaufort Sea is less productive than Lancaster Sound and Baffin Bay (Anderson, 1989). Smith (1995) described primary production in the Northeast water as only moderately productive. In a review of the available data on the distribution and abundance of ringed seals throughout the Canadian Arctic, Stirling and Britsland ( 1995) found that, in comparable habitat types, densities of ringed seals in the Beaufort Sea were lower than in the eastern Canadian Arctic. Smith (1973, Smith, 1987) found that 40% of 4 year old female ringed seals and 60% of 5 year olds taken in western Baffin Bay along the east coast of Baffin Island were sexually mature compared with only 20% and 29% for the same age classes in the Beaufort Sea. Similarly, it has been known for some time that most female polar bears in the Beaufort Sea do not breed for the first time until they reach 5 years of age, a full year later than the age of first breeding in Lancaster Sound, Baffin Bay, or Hudson Bay (Stirling et al., 1976, 1984; Lentfer et al., 1980; Ramsay and Stirling, 1988). There are no quantitative data on the abundance and age-specific reproductive rates of

recurrent Beadsand than

birds (Johnson and Ward, 1985) in the eaufort Sea at Cape Bathurst Polynya. Near the No there are .at least six breeding colonies of northern fulmars (Fulmarus glacialis), although population is only a few thousand birds I997-this volume). Similarly, black-l wakes (Rissa tridactyla) are birds would small numbers. Nevertheless, probably not be in northeastern Greenland at all wer it not for the Northeast Water Schledermann f 1980) demonstrated the close correlation between the distribution of reeurrin polynyas in the eastern Canadian igh Arctic and the abundance of archaeological sites from the Thule culture which specialized in hunting marine mammals. Although it is difficult to make quantitative comparisons between areas, Stoker and Krupnik (1993) reported 187 Thule houses with bones from bowhead whales incorporated into them in the Beaufort Sea-Amundsen Gulf area compared with 1197 in the eastern Canadian High Arctic. Andn-easen (1997-this volume) reports there were more Thule sites in the area adjacent to the Northeast Water Polynya than anywhere else in east Greenland (although none contained bones from bowhead whales) but gives no estimate of the number found. Taken together, these superficial comparisons of 1,000

data on marine birds and mammals clearly demonstrate that the Northwater Polynya and adjacent waters are far more biologically productive than either the eastern Beaufort Sea shore lead and polynya system or the Northeast Water Polynya. Consequently, one of the most exciting research opportunities in the study of arctic polynyas is to quantitatively compare oceanographic processes, primary production, energetic pathways, and resultant biomass in these three areas in order to understand what factors determine their overall productivities.

6. A~pxts of the importance of smaller polynyas Although less spectacular in size, the smaller polynyas scattered throughout the Canadian Arctic (Smith and Rigby, 1981) are vitally important on a local scale, especially to seabirds, sea ducks and

marine mammals (Stirling and Cleator, 1981). The overwintering distribution of bearded seals and Atlantic walruses (Odaberrus rusmarus rosmarus) is largely determined by the distribution of recurring polynyas and shore lead systems, including the Northeast Water Polynya (Stirling et al., 1981; Born et al., 1994). Prom the data presented by Schledermann (1980) on the relationship between polynyas and the pattern of prehistoric settlement, it is clear

nce of, and access to, marine-basedlife liable enough to sustain human some interestingdifferences in

been known for some time that male walruses occasionally preyed on ringed seals (Pay, 1960), but in recent years it has also become apparent that walruses prey on a variety of phocid species, inclu bearded seals (Lowry and Fay, 1984) and in some locations may prey to a significant degree on ringed seals (Muir et al., 1995). Thus, it appears that, because of the threat of predation, ringed seals in particular, and to a lesser degree bearded seals, do not occur in abundance in the open water of polynyas inhabited by walruses. During 10 years of observations of the polynya at Dundas Island (Fig. 1) in the spring, we saw only small numbers of polar bears although they were abundant further east where ringed seal numbers were high (Stirling et al., 1978; Kingsley et al., 1985). In this case, it appears that the primary benefit of the polynya area to ringed seals and polar bears is in the stimulation of increased primary and secondary production in adjacent fast ice or pack ice areas. Similarly, in the Northeast Water Polynya, where walruses are present, Born et al. (1997-this volume) showed by satellite tracking that polar bears remained in the pack ice to the southeast and spent little time near the edge of the polynya itself. This probably suggests that numbers of ringed seals actually using the polynya were low. Conversely, at Bellot Strait, where there are no wahuses, numbers of both ringed seals and polar bears are high (Stirling ct al., 1978).

7. Monitoring polar bears and seals in polynya

areas as possible tndkators of climatic and phic variability Bathurst Polynya and in the shore lead system in the stem Beaufort Sea and near the Bellot Strait et al,, 1981, 1982)but present only Pdynya Wrlin at low densities n the areas around the Penny Strait, Queens Channel, or Hell Gate polynyas (Kingsley et

In western Hudson Bay and the eastern Beaufort Sea there are well defined shore lead polynya systems (Fig. 1) which influence the distribution of seals and the polar bears that prey upon them (Smith, 1975; Stirling et al., 1982, 1993; Stirling and Derocher, 1993; Lunn and Stirling, unpubl. data). In Western Hudson Bay, population studies of polar

al,, 1985). Similarly, although bearded seals and wa1Nlsesfeed on bottom fauna in some of the same nerd pdynya areas, such as Penny Strait and

bears have been ongoing from 1966 through 1994,

ns Channel, they appear to segregate from each other to some degree. Cleator and Stirling (1990) reported that, in years when walruses were abundant in the plynya at Dundas Island (Fig. 1). vocalization rates of bearded seals were low and vice versa, It has

and in the eastern Beaufort Sea studies of ringed seals and polar bears have continued intermittently from 1970 to 1994 (Stirling et al., 1977; Derocher and Stirling, 1992; Stirling and Lunn, 1996). Polar bears in Western Hudson Bay are unique in

ave severe co

where in polar bear range, an

is even more remarkable considzri~g ljnat Bay is the only area in w bears must fast for 8 months, during which time they produce cubs and nurse them from a birth weight of about 0.6 kg to about 1I kg in 3-4 months. It ic not known how natality has been sustained at a level so much higher than other polar bear populations, but it suggests that overall biological productivity in Hudson Bay is very high. Hudson Bay is fairly shallow, has the largest shore lead polynya system in the Canadian Arctic (Dunbar, 198I ), and contains leads throughout the annual ice cover, all of which suggest a potential for significant primary production. Perhaps not surprisingly, satellite imagery also suggests overall productivity of phytoplankton is high in comparison to other Arctic marine areas (Smith and Sakshaug, 1990, fig. 9.2). However, to date, there are few other quantitative comparative data. In western Hudson Bay, beginning in the late 1970s or early 198Os,through to the late 198Os, the condition of polar bears of all age and sex classes, including adult females declined, as did survival of their cubs (Derocher and Stirling, 1992). This decline did not constitute a threat to the population because, even when natality was at its lowest in the late 198Os, the rates were still higher than the upper range of values for bears elsewhere in the Arctic (e.g., Stirling et al., 1976, 1984) and estimates of population size have remained relatively constant for the last 12 years (Derocher and Stirling, 1995; Stirling and Lunn, 1996). Because there are so few long-term biological

cant global cooling in 1992, particularly in the northe ere, and continue to a lesser degree through 1993 ( cCormick et al., 1995). Catchpole anuta (1989) noted a similar association between severe ice conditions in previous volcanic eruptions. The temperatures in Hudson Bay in 1992 was that breakup was 3 or more weeks later than it was in 1991. Thus the polar bears were heavier when they came ashore in 1992, probably because they had been able to feed on seals for longer and store more fat prior to their annual fast during the open water season (Stirerocher, I993) and, consequently, natality rose in 1993. In 1993 and 1994, the timing of break-up appeared to be more normal, although this has not been analysed quantitatively. Although the condition of the bears declined slightly from their 1992 levels, they did not decline to what tiiey were in 1991 (Stirling and Lunn, 1996) suggesting that the effects of atmospheric cooling were still present and detectable in the condition and reproductive parameters of the bears. In contrast to the long-term unidirectional change in condition and natality of polar bears in Hudson Bay, the ovulation rates of ringed seals and natality rates of polar bears in the eastern Beaufort Sea fluctuated widely between the mid 1960s and the mid 199Os, on an approximately decadal scale, with the maximum recorded rates being double the minimum (Stirling and Lunn, 1996).

Polovina et al. (1994) showed similar long-term unidirectional declines in productivity of three marine species, including Hawaiian monk seats (fbf~~~ktcs sckartinsfandi), beginning in the early 1980s and continuing to the present, which they attributed to a large-scale and long-term climate event (a change in the location of the Aleutian low)

that altered deep-level oceanic mixing, with consequent effects on ecosystem productivity. In contrast, Testa et al. (1991) demonstrated that the reproduction of three Antarctic phocids, over periods of 20-40 yr, fluctuated at 4-6 yr intervals, and suggested the possibility that they were influenced by the El Niiio-Southern Oscillation. Similarly, in the

Scotia Sea region of the Southern Ocean, decreases in the reproductive performance of albatrosses. penguins, and fur seals that last 3-4 yr have been documented (Croxall et al., 1988) and have been suggested to be a consequence of redistributionof krill outside of the normal foraging range of these predators and, indirectly, a result of changes in oceanographicand atmosphericforces @riddle et al., 1988). Taken together, the data on polar bears and ringed seals from the eastern Beaufort Sea and polar bears from western Hudson Bay indicate that significant variation occurs in both natality and body condition, but with markedly different patterns. Stirling and 6) suggested that the fluctuations in Huday are a consequence of climatic change s thusa in the eastern euufort Sea are caused term oceanographic factors. However, even if the causes are not yet understood, it is clear

that lsng-term changes are occurring in arctic marine ecosystems and one effective way of detecting their effects is by monitoring species at the top of the ecological pyramid.

which would take place through polynyas and shore leads (Stirling and Calvert, 1983). For example, if all the proposals made in the 1980s had been approved, Lancaster Sound and the southern portion of the Northwater (one of the richest areas for marine birds and mammals in the Canadian Arctic) could have had offshore drilling for and production of hydrocarbons, year-round shipment of natural gas from Melville Island and oil from the Beaufort Sea in specially built ice-breaking tankers, extended-season shipments of ore from at least two mines, and extensive shipping to provide the logistic support for all these projects. Partly because of environmental concerns and partly because of cost, none of these projects went forward, but changes in world economic conditions could make any or all these projects viable at some time in the future. Similar proposals exist for other biologically productive areas of continental shelf in the Arctic, such as the Barents and Bering Seas. We cannot predict all the possible ecological consequences of such disruptions, although some, such as the disastrous effects

on seabirds of an oil spill in a polynya in spring, for example, are self evident. However, it now seems clear that the large polynyas and edges of the polar pack, particularly where they are over the continental shelf, are vital to the overall biological productivity of polar oceans and 10 all trophic levels of the associated ecosystems, Consequently, the development of appropriate conservation measures should be an additional product of ecosystem-based research and management in these areas.

Acknowledgements I

am particularly grateful to the Canadian Wildlife

8* Environmental concerns

Service, Polar Continental Shelf Project, Natural Sciences and Engineering Research Council, and World Wildlife Fund (Canada), for their long-term support

In the Arctic there is a significant degree of overlap between biologically important ureas with polynyas ami shore leads, and the continental shelf where considerablereserves of hydrocarbonsare ais0 believed to exist (Stirling, 1990). Similarly, yearhas been proposed from several areas round shipping in the Canadian and Greenland Arctic, some of

of my research on polar bears and seals in the Arctic. The following organizations provided significant support to individual projects over the years which helped make it possible to write this paper: Beaufort Sea Project, Arctic Islands Pipeline Project, Arctic Petroleum Operators Association, Northern Oil and Gas Assessment Project, Dome Petroleum, and the Governments of Manitoba and the Northwest Terri-

ar. Syst., 10: 67-P.

cism of earlier drafts.

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