Hunting and scavenging on the coasts: The arctic fox
The adaptations of the arctic fox (Alopex lagopus) to life in the cold enable it to survive and remain active year round, despite a body weight of a mere 3-4 kg (Prestrud 1991; Fuglei and Øritsland 1999; Fuglei 2000). The arctic fox has historically been a valued game species due to its thick winter fur. Although the species is found both in coastal and inland regions, population densities tend to be higher and the production of kits more stable in coastal areas. The most likely reason for this discrepancy is that inland populations rely on more fluctuating food sources (small mammals, ungulate carcasses from natural deaths and predation by large predators).
The arctic fox can be described as a terrestrial predator and scavenger. Nevertheless, its survival depends on the marine environment in many parts of the Arctic. First, marine resources (seals, tidal invertebrates, seabirds, eggs) constitute 50-100% of arctic fox diet in coastal areas (Frafjord 1993; Angerbjörn et al. 1994; Hersteinsson and Macdonald 1996; Eide et al. in press). Foxes regularly follow polar bears out on the ice and scavenge on the carcasses of marine mammals killed by bears. Second, the availability of marine resources has been shown to directly affect the population dynamics of arctic foxes (Roth 2003), acting as a stabilizing alternative resource in years of low densities of small mammals. This suggests that - at least in the more extreme parts of the species range - a source-sink system may exist where inflow of individuals from coastal populations acts to stabilize or even maintain low productivity of inland populations. The arctic fox is an important agent in the transfer of energy from sea to land (Carlton and Hodder 2003) and the maintenance of complete ecosystems comprising the marine, coastal and terrestrial environments vital to its survival.
Breeding on the coasts, living in the pack ice: The polar bear
Although the polar bear (Ursus maritimus) is described as a marine mammal, depending almost entirely on marine food sources (Ramsay and Hobson 1991), this species is a classic example of the intimate connection that exists between land and sea in arctic environments. Polar bears rely on fast ice or pack ice for hunting and spend most of their time on the sea ice, roaming over several hundred thousand square kilometres (e.g. Born et al. 1997; Mauritzen et al. 2001; Wiig et al. 2003). In addition, female bears are entirely dependent on undisturbed coastal areas for denning (Larsen 1985; Stirling and Andriashek 1992; Amstrup 1993; Amstrup and Gardner 1994; Messier et al. 1994; Clark et al. 1997; Van de Velde 2003). A breeding female bear spends as much as 6 months on land from entering the maternity den in late October/ November, until the cubs are old enough to follow her out on the ice. Individual bears regularly become stranded on land when the ice retreats in summer. At the southern edge of its range polar bears are routinely forced to deal with long periods without ice. This is the case for instance in Hudson Bay, Canada where the bear population spends close to 4 months on land during the ice free period (Stirling et al. 2004), surviving on stored fat.
Since the essential resources for polar bears include both undisturbed coastal land areas and fiord- and pack ice for hunting seals, the polar bear is faced with both terrestrial and marine threats. Increased infrastructure development and exploitation along arctic coastlines pose a direct threat to important polar bear denning areas (e.g. Amstrup 1993), as well as deteriorating the adjacent marine habitat and increasing the chance of human-bear conflicts. As the permanent ice cover retreats, new coastal areas become available for development. The retreating ice also means a loss of polar bear foraging habitat, forcing bears on land more often and for longer periods. This will affect the physical condition, reproduction and survival of the bears and potentially extirpate local polar bear populations altogether (Stirling and Derocher 1993; Stirling 1997).