Walruses (Odobenus rosmarus)

Marine mammals 2013
Typography
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Walruses are distributed across the circumpolar Arctic, but their distribution is discontinuous and two subspecies are recognized: one in the Pacific; and the other in the Atlantic. In the northern Barents Sea, they are found from Svalbard through to Franz Josef Land; in the southern Barents Region, they occur in the Pechora Sea and the Kara Sea. Recently, they have been observed regularly in the White Sea as well (Klepikovsky and Lisovsky, 2005; Svetochev and

Svetocheva, 2008; Zyryanov et al., 2008). Walruses also occur in the Laptev Sea, but a recent genetic study confirms that these animals belong to the Pacific subspecies (Lindqvist et al., 2009). Walruses in the northern Barents Sea comprise a single population of Atlantic walruses that occupies the ice between the two archipelagos during the winter mating period (Lowther et al., 2015), although individual animals seem to display considerable fidelity to their respective summering grounds (Freitas et al., 2009). The affinity of animals from the Pechora, Kara and White Seas is currently under investigation. Walruses are generally found in shallow water areas (80 m) with suitable bottom substrate that can support a highly-productive bivalve community within reasonably close proximity to suitable haul-out areas (land or ice). However, they can occasionally be found on ice over very deep areas (NPI Marine Mammal Sighting Data Base; Gorbunov and Belikov, 2008). Walruses were dramatically overharvested in Svalbard in the 1800s and early 1900s, with only a few hundred remaining when they became protected in 1952. Walrus populations were also depressed by hunting in southern parts of the Barents Sea, extirpating them from the Norwegian mainland and reducing them throughout the Pechora and Kara Seas. Franz Josef Land was occasionally visited during this early hunting period, but its isolation meant that it was less impacted than Svalbard. Most walruses in Svalbard are males, but the number of sites occupied by females and calves is increasing (Lydersen et al., 2008; Kovacs et al., 2014). There are approximately 20,000 Atlantic walruses (Stewart et al. 2014), so the Barents Sea represents an important region for this subspecies. Walrus abundance in the Barents Sea has definitely trended upward in recent decades; the rate of increase cannot be accurately assessed however, due to a lack of trend data for Russian sectors, especially Frans Josef Land. Data from only a single aerial survey is available for the Pechora Sea (Lydersen et al., 2012a). However, walruses in southern Russian territories of the Barents Sea are believed to be increasing based on shipping observations (Svetochev and Svetocheva, 2008; Zyryanov et al., 2008; Chernook et al., 2012). There is concern for animals occupying this region due to oil and gas development; available information on the ecology of the Atlantic walruses in the southeastern Barents Sea and adjacent regions is summarized in Boltunov et al. (2010).