Rare and threatened species - marine mammals

Rare and threatened species
Typography
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The Barents Sea is inhabited by 21 species of sea mammals. Among these, 11 species are threatened according to the IUCN Red List, 13 are included in the Red Book of the Russian Federation (2001) and 8 extant species are on the endangered species list of Norway (Table 4.3.6) (plus the recently extinct northern right whale stock). Anthropogenic factors thought to be most harmful for marine mammals are fisheries interactions, pollution, and climate warming; the

latter is a particularly acute problem in the Arctic, and a serious threat for all ice-associated marine mammals. Increasing levels of tourism in Svalbard might also pose additional risk to polar bears in that region. Polar bears were severely overharvested in the Barents Sea Region, but became protected in 1973. The first population survey, in 2004, estimated that 2,650 bears reside in the northern Barents Sea; current population trends are unknown.

Walruses were dramatically overharvested in Svalbard during the 1800s and early 1900s; only a few hundred animals remained 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. Numbers of walruses in the Barents Sea have definitely trended positively in recent decades, though the rate of increase cannot be accurately assessed due to insufficient data. Walruses in the southern areas of the Russian zone are also thought to be increasing. Total population size of the entire northern Barents Sea is unknown; Russian areas have never been surveyed.

Little is known about narwhals in the Barents Sea. They do enter fjords north of Svalbard in summer and can be seen at the southern edge polar ice across the northern Barents Sea during summer, being most numerous near Franz Josef Land (Gjertz, 1991; Gorbunov and Belikov, 2008; NPI Marine Mammal Sighting Data Base).There is no abundance estimate for narwhals in the Barents Sea. They are believed to be less numerous than white whales in this area. Extreme overharvesting in the Barents Region during the 1600s-1700s came close to exterminating the Spitsbergen stock of bowhead whales. The present number of bowheads belonging to the Svalbard stock is not known, but is presumably only in the tens (Christensen et al., 1992) or at most, in the low hundreds.

White-beaked dolphins are the only dolphin to remain in the Barents Region on a year-round basis. They are the most numerous dolphin species in the Barents Sea, with a population size of 60,000-70,000 individuals. The abundance trend for this species within the Barents Sea is not known. Grey seals occur along the north coast of mainland Norway, east to about Murmansk. They have been heavily harvested in the past, being reduced to just 2 breeding locals and very low numbers in the 1950s in northern regions, with some 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). Despite low numbers of grey seals, hunting bounties were instituted in 2003 to reduce numbers further. Grey seals were Red Listed in Russia in 1975 and have remained protected since then.

Harbour porpoises live year-round in the southern Barents Sea and in fjords along the coast of Norway. The Barents Sea population is believed to consist of about ~11 000 individuals (Bjørge and Øien, 1995). They are caught accidentally in coastal gillnet fisheries to an extent that may be unsustainable locally (Bjørge & Godøy, 2009); however, the population structure of porpoises in the Barents Sea and Northern Norway is not well described.

The northern bottlenose whale has a distribution similar to that of the sperm whale; being concentrated south of the Barents Sea, with only large males migrating as far north as Spitsbergen. There is no recent information about the distribution of this species in the Barents Sea. Fin whales and humpback whales are the second and third most abundant baleen whales in the Barents Sea, respectively. Although heavily depleted by earlier commercial whaling, they have shown strong recoveries both in the Pacific and Atlantic Oceans. The North Atlantic stock is thought to have increased considerably during the past 10-15 years. Blue whales are also seen in the Barents Sea, but they are so rarely spotted during sighting surveys of the region that a meaningful population estimate cannot be given for this species. Other small cetaceans that frequent the Barents Sea include bottlenose dolphins, common dolphins and white-sided dolphins, all of which can be seen in the southern Barents Sea. Assessment of the population size of these small cetaceans in this region is complicated by the fact that dolphins are often difficult to identify; and tend to be grouped into “springers” during sighting efforts.

Most species of marine mammals in the Barents Sea region are currently protected. There is, however, a risk to small coastal seal populations the south because of policies aimed to reduce these populations to avoid conflicts with inshore fisheries and aquaculture. Cruise-ship tourism, which is particularly intense in Svalbard, poses potential risks to marine mammal populations; however little is known regarding its consequences. Industrial development including oil drilling and transport as well as other types of shipping pose risks to some marine mammals, particularly near the coast. On a broader scale, regional pollution and projected climate change are perhaps the most serious threats to marine mammals in the Barents Sea. Although the Barents Sea is by no means heavily polluted, some animals living there (e.g. polar bears) exhibit high concentration of certain contaminants, in particular persistent organic substances such as polychlorinated biphenyls (PCBs). Other ecosystem changes that can affect marine mammals include changes in food webs. The winter/spring harp seal invasions to coastal areas of northern Norway — resulting from shortages of capelin, polar cod, and herring — serve as useful examples. In addition to consuming fish, migrating seals may cause substantial damage to gill-net catches and the nets themselves. They probably also cause emigration of commercial fish species from traditional fishing grounds to deeper waters which are much less suitable for fishing. From the perspective of the seals, reduced recruitment prevailed during most of the seal invasion period.

The impacts of proposed climate change scenarios on marine mammals in Arctic regions are likely to be profound for endemic species. If increases in temperature and retraction of ice continue as predicted by many models, and suggested by current data trends, marine ecosystems would be expected to shift polewards; if the loss of sea ice is as dramatic as expected, profound negative consequences could ensue for Arctic animals that depend on sea ice as their breeding or foraging habitat. The predicted worst-case reductions in sea-ice extent, duration, thickness, and concentration from now until 2020, threaten the existence of whole mammal populations and, depending on their adaptability, could result in extinctions of some species.

Physical changes in the marine environment are likely to have impacts first and foremost on the animals that depend on sea-ice habitats. Any alteration to the distribution of sea ice and its characteristics will affect polar bears. To a large extent, the impact will be mediated via effects the physical changes will have on ringed seals and other ice-associated seals, which are the primary prey of polar bears. But, polar bears also need the ice directly as a corridor to move from one area to another. Reduced ice cover, particularly in the early spring and delayed formation in the autumn could have very negative long-term consequences for polar bears. For example, pregnant females build their birth dens in thick snow on land or on sea ice in some areas, and require good spring ice conditions when they emerge with their cubs after many months without eating. And, should the sea ice vanish, the only option left to polar bears would be the terrestrial summer life-style of brown bears (from which they evolved). Increased levels of human interaction would probably put this species’ survival at risk.

Like the polar bears, ice-living seals are highly dependent on the nature and extent of sea ice, whether for pupping, moulting, or resting; some species also forage on ice fauna. Walruses have specific ice requirements. If the ice extent in winter is reduced in years to come, the polar pack might retract to water too deep for walruses. Additionally, crowded haul outs that favour epizootic conditions, and local pressure on food resources, pose additional risks for walruses unable to utilize their normal rotation of ice and land. A further concern for walruses is that a decline in sympagic ice flora and fauna could result in a decrease in the flux of carbon to benthic communities upon which walruses are dependent. The species do haul out on land during summer in some areas and might therefore adjust more readily to land breeding than the other ice-breeding Arctic pinnipeds. This could however restrict their distribution quite dramatically — to areas where high-productive benthic communities are located close to suitable haul-out areas during ice-free months. Hooded seals and harp seal suffer high pup mortality in years with little sea ice. It is impossible to predict whether harp and hooded seals will adjust to new locations for breeding and moulting if the spring-ice distribution changes dramatically over a relatively short time frame. The current situation for West Ice hooded seals — with declines of 85-90% in recent decades, in addition to 50% declines in White Sea harp seal pup production — does not bode well for flexibility in adjusting to changing conditions.

Harbour seals and grey seals are land breeders in the Barents Region. Sea ice actually limits the distribution of harbour seals, though grey seals use this habitat readily for breeding in other parts of their range. For these species, most climate change impacts are likely to be mediated through changes in their prey populations and via human interventions. Harbour seals in Svalbard are heavily dependent on polar cod, similar to ringed seals, so it is likely they will be required to shift prey. Productivity is likely to be higher overall in the Barents Sea with less ice and warmer temperatures, but it is difficult to predict what will happen to the intricate linkages throughout the region’s foodweb. However, coastal population sizes of these two species in the Barents Region are currently largely determined by management decisions regarding hunting and culling levels within Norwegian territories.

The response of whales to climate-induced change is uncertain, but climate change is likely to have negative implications for species which are endemic to the High Arctic. The uncertainty of cetacean responses is linked primarily to uncertainty in future prey availability, in combination with our current lack of understanding of their linkages with sea ice. At very least the ice-associated cetaceans would be likely to face increased competition from migratory species in a warmer Arctic. Bowhead whales are the most ice-adapted cetaceans, having evolved as ice-whales. Their low numerical status in the Barents Sea makes them particularly vulnerable. They are dependent on calanoid copepods and euphausiids for food; changes in sea-ice conditions are likely to have large impacts on their foraging. It is not known whether this species could survive in ice-free waters. Currently, narwhal and beluga also spend much of their time in association with sea ice, and are known to forage at the ice edge and in ice cracks. But, these two species also live far south of the ice edge in summer. Narwhal are thought to feed on cephalopods at this time of the year, so the impact of climate change on this species is likely to be mediated through changes in the distribution of sea ice and its effect on key prey species.

Table 4.3.6b. Species on the 2010 Norwegian Red List considered threatened due to negative population trends by category: critically endangered; endangered; or vulnerable. From Meld.St.10 (2010-2011) —Norwegian Ministry of the Environment (NMD, 2012).

Other cetaceans which regularly frequent Svalbard waters avoid ice-covered areas. Pilot whales, white-beaked dolphins, northern bottle-nosed whales, fin whales, humpback whales, and blue whales all feed in open water areas and cover a wide range; their distribution is predominantly determined by prey availability. The impact of climate change on these species will likely also occur via changes to their prey base. If Arctic marine productivity increases as the seasonal ice cover diminishes, which is likely, it can be expected that more cetacean species will spread northward from temperate waters toward Svalbard and the northern Barents Sea.

Other threats posed by climate change to Arctic marine mammals include: increased risk of disease in a warmer climate; potential for increased pollution in the Barents Sea as a consequence of more precipitation and river-borne pollution; increased competition from temperate species that expand northward; stronger impacts of shipping along the Northeast Passage; and development (particularly petroleum development) in previously inaccessible areas. Complexities arising from alterations to the density, distribution, or abundance of keystone species such as polar bears could have significant and rapid consequences for the structure of the ecosystems they currently occupy.

 
 
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