Harbour seals (Phoca vitulina), Grey seals (Halichoerus grypus), and Harbour porpoise (Phocoena phocoena)

Marine mammals 2013
Typography
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Coastal marine mammal species in the Barents Sea include harbour seals, grey seals, and the harbour porpoise. Larger whales also migrate along the coast on their way north to the take advantage of the summer burst of productivity in the Barents Sea. The harbour seal is a coastal species that is found both in the Atlantic and Pacific Oceans. Harbour seals are gregarious, hauling out to rest on land at low tide every day of the year, in groups ranging from just a few animals up

to a few hundred. The number of individuals hauling out on land is dependent on the tidal phase and height, season, weather conditions, etc. (e.g., Reder et al., 2003; Merkel et al., 2013). Although they commonly shift their favoured haul-out places depending on the season, harbour seals are not truly migratory. For the most-part harbour seals are a temperate species, which occurs as far south as California in the Pacific, Maine in the West Atlantic, and southern Europe in the East Atlantic. But harbour seals also occur, albeit in low numbers in the Barents Sea, along the north Norwegian coast across the border to 39oE, in the region of Ivanovskaya and Saviha Bays. Harbour seals have also been observed in recent years in the White Sea, in both Dvinsky Gulf and Onezhsky Gulf (Vladimir Svetochev, pers. comm.). There is also a small group of harbour seals in Svalbard that is largely restricted to the west coast of Spitsbergen within the Svalbard Archipelago (Blanchet et al., 2014, 2015; Hamilton et al., 2014). The Svalbard stock consists of ~2,000 animals (Merkel et al., 2013); a similar number is found along the Troms and Finnmark coasts (Nilssen et al., 2009). Additionally, some 400-500 animals are found along the Murman Coast (Zyryanov, 2000). Although widely distributed, harbour seals occur at low densities throughout their broad range. The Norwegian coastal stock is hunted in a licensed game hunt; this stock also is subject to mortality via entanglement in gill nets and other fisheries-related mortality. Up until 2010, harbour seals were subjected to unsustainable hunting pressures in many areas along the Norwegian coast including parts of northern Norway. However, surveys conducted in 2011-2014 indicate a small increase in the harbour seal population on the Norwegian mainland, including a small local increase in Troms and Finmark resulting from hunting restrictions. There is still a legal quota-regulated sports hunt for harbour seals, but quotas are now set according to a management plan to ensure that viable harbour seal colonies exist throughout their present areas of distribution. There is concern over potential bycatch levels in some areas; data collected by the Norwegian coastal reference fleet are currently being analysed to estimate the extent of bycatch. Recent observations of killer whale predation on harbour seals along the Norwegian coast also suggest that natural mortality rates may be increasing for this species.

Grey seals occur only in the North Atlantic, south to Maine in the western Atlantic and to the Baltic Sea in the eastern Atlantic. Major population centres are located around the British Isles and on Sable Island off the east coast of Canada. Baltic and Norwegian grey seal populations are genetically different, as are populations in eastern and western Atlantic regions. Subpopulations within the Barents Sea Region also show significant genetic variation (Frie and Kondakov, 2008). Although larger than harbour seals, grey seals share their coastal habitat, but they spend longer periods at sea during parts of the year. This species utilises a wide variety of habitats. Within most of its range, it breeds on land; but it also uses land-fast ice and free-floating pack-ice when accessible — such as in the Gulf of St Lawrence on the east coast of Canada — for hauling out and giving birth during winter (e.g. Tinker et al., 1995). Within the Barents Sea, grey seals occur along the north coast of mainland Norway, and eastward along most of the Murman coast; they are occasionally observed in the White Sea during summer, and have been documented in the Pechora Sea during aerial surveys for walrus (Lydersen et al., 2012a). They have been heavily harvested in the past, being reduced to just 2 breeding locals and very low numbers during the 1950s in northern regions, e.g., only 500-600 animals in Lofoten (Øynes, 1964). Hunting at breeding colonies was prohibited in Norway in 1973. Only 200 pups were produced in Troms and Finnmark in 2003 (Nilssen and Haug, 2007). However, the number of grey seals along the coast of Finmark is likely larger than would be predicted based on the local breeding populations, as Russian seals undertake feeding migrations to Norwegian waters. During 2003-2010, grey seal hunting quotas were set at 25% of regional population abundance; annual removals of around 20% were occurred during this period. Nevertheless, pup production in Troms and Finmark appeared to have increased, suggesting that a large proportion of the removals were not local seals. After 2010, removals have gone down drastically in Northern Norway, due to reductions in quotas and elimination of government bounties. Quotas are now set according to a national management plan for grey seals, which aims to secure viable local populations within their current range. Grey seals were Red Listed in Russia in 1978 and have remained protected since that time. The grey seal colonies on the Murman Coast were last surveyed with pup counts in the early 1990, 1991 and 1994 – the results indicated a minimum population size of 3000-3500 animals (Haug et al., 1994b; Ziryanov and Mishin, 2007).

The harbour porpoise is a small odontocete with a wide geographic range that includes most temperate and boreal waters of the Northern Hemisphere. Two or three morphologically distinct subspecies are known to occur in the Atlantic and Pacific Oceans. It is the smallest cetacean in the Barents Sea, and is largely a coastal species; although sometimes seen in deep areas, harbour porpoises prefer shallow, inshore waters. A single harbour porpoise was sighted repeatedly on the north coast of Spitsbergen over 2005-2007 during summer, often in association with groups of white whales (NPI Marine Mammal Sighting Data Base; Kovacs and Lydersen, 2006). This species normally occurs in small groups and only rarely forms larger aggregations. Onshore-offshore migration is thought to take place regularly, albeit over limited distances. Harbour porpoises live year-round in the southern Barents Sea, and in fjords along the coast of Norway. They tend to be tightly coastal in the western part of their range in the Barents Sea; while in the east they are found along banks sometimes quite far from shore — such as the Kanin and Goose Banks (Skern-Mauritzen et al., 2008). Based on observations made during minke whale surveys, the offshore component of the Barents Sea harbour porpoise population is believed to consist of about ~11,000 individuals (Bjørge and Øien, 1995). No data are available for the nearshore areas where density is expected to be highest. Harbour porpoises are caught accidentally in coastal gill-net fisheries to an extent thought to be unsustainable on a local scale, e.g., the Vestjord area (Bjørge et al., 2013). To sustain current levels of by-catch, immigration of porpoises from adjacent waters is required in this region. The future situation is difficult to predict because migration patterns, population structure, and the general ecology of harbor porpoises in Norwegian coastal waters are not well documented (Bjørge, 2003).