Tag Archive: pinnipeds


On Thin Ice

Earth Day is coming, Aprill 22nd. And there is yet more evidence that our fragile planet and it inhabitants are in trouble.

As with the Polar Bears which prey on them, marine mammals such as the Ringed Seal are threatened by the changes caused by climate change to the Arctic ice pack. Named for the ring-shaped marks on their coats, the Ringed Seal (Phoca hispida), aka Pusa hipsida, is the most abundant and wide-ranging ice seal in the northern hemisphere: ranging throughout the Arctic Ocean, into the Bering Sea and Okhotsk Sea as far south as the northern coast of Japan in the Pacific, and throughout the North Atlantic coasts of Greenland and Scandinavia as far south as Newfoundland, and include two freshwater subspecies in northern Europe.

Click on image for full-size view.

 

A mother Ringed Seal, her pup, and a plea to be careful with out fragile planet

Fragile Planet

 
Ringed seals are solitary animals commonly associated with ice floes and pack . When hauled out on ice they separate themselves from each other by hundreds of yards.  The ringed seal maintains a breathing hole in the ice thus allowing it to use ice habitat that other seals cannot.

Ringed seals eat a wide variety of small prey that consists of 72 species of fish and invertebrates. Feeding is usually a solitary behavior and their prey of choice includes mysids, shrimp, arctic cod, and herring. While feeding, ringed seals dive to depths of 35 to 150 ft. In the summer ringed seals feed along edge of the sea-ice for polar cod. In shallow water they feed on smaller cod. Ringed seals may also eat herring, smelt, whitefish, sculpin, perch, and crustaceans.

Ringed seals are one of the primary prey of polar bears and have long been an important component of the diet of Arctic indigenous people throughout their range, and continue to be harvested annually by many communities.[ Early Paleoeskimo sites in Arctic Canada revealed signs of harvested ringed seals dating from ca. 4000–3500 B.P., likely captured in frozen cracks and leads in the ice, with a selection for juveniles and young adults.

Marked decreases in Ringed Seal abundance are likely to have cascading effects in Arctic food webs.

The Ringed Seal serves an indicator of ecological change in the Arctic, due to its dependence upon annual sea ice. Ringed seals are  . They are born from mid-March to mid-April and weaned prior to break-up in June. The distribution of Ringed Seals in the world is shown below :

During the lactation period, young seals spend half their time on top of the ice and half underwater, where they are hunted by polar bears. In order to protect themselves from predators and rear their young, ringed seals make snow lairs on the surface of sea ice. Those in the thin snow layers are more susceptible to attack than those in the thick layers. The abundance and the stability of ice is very important for the success of the young seals. If the ice continues to decline due to climate change, young seals will be forced to swim in open water at an early age, causing them to expand more energy and be vulnerable to attack. In addition, the ice is also needed to rest, after the weaning period, which is essential for their development.

Sea ice reduction due to climate change can move the ranges of the Ringed seals further north and would affect their feeding seasons, fertility, and survival. Drift ice created by increasing temperatures can also move up the ranges of harp seals and increase hooded seals off West Greenland, affecting the equilibrium already established between the native populations in that area.

The estimated population size for the Alaska stock of ringed seals is 249,000 animals. Currently, the population trend for this stock is unknown. Ringed seals are listed as a species of “least concern” by the IUCN, and are considered not “threatened” under the Endangered Species Act. Reliable estimates of the minimum population, potential biological removal, and human-caused mortality and serious injury are currently not available. Because the potential biological removal for ringed seals is unknown, the level of annual U.S. commercial fishery-related mortality that can be considered insignificant and approaching zero mortality and serious injury rate is unknown. No information is available on the status of ringed seals.Due to a very low level of interactions between U.S. commercial fisheries and ringed seals, the Alaska stock of ringed seals is not considered a strategic stock.

The decline in the populations of Ringed seals is also affecting the population of their predator – the polar bear. Polar bears prey almost exclusively on ringed seals, and most often kill their pups which depend on sea ice for survival. In addition to polar bears, humans also have been hunting the Ringed seals for centuries. Not only are they a source of food for most coast-dwelling northern people, they are also a source of income. Thousands of Ringed seals are harvested and traded for fur annually by the Inuit and other people of the Arctic Basin.

Other Threats

Warmer ocean temperatures are also more likely to cause an increase in pathogens that affect the Ringed seals. And a migration of Ringed seals to find more stable habitats can increase the spread of these pathogens, which might even lead to an epidemic of a disease. In addition, as temperatures warm, there will be more human presence in the Arctic region, with shipping, fishing, agriculture, and oil extraction. This will further degrade Ringed seal habitats and reduce the availability of their food, such as fish.

In fact, sick and dead ringed seals began to appear in late 2011 on the Beaufort Sea coast near Barrow, the country’s northernmost community. Strandings were reported as far west as Point Lay and Wainwright on the Chukchi Sea.

 
Seal from Alaskan waters showing lesions from an unknown cause

Seal Wth Lesons

The affected animals had lesions on hind flippers and inside their mouths. Some showed patchy hair loss and skin irritation around the nose and eyes. Stricken live seals were lethargic, allowing people to approach. Necropsies on the dead ringed seals found fluid in lungs, white spots on livers and abnormal growth in brains. Symptoms, but no deaths, were also observed in Pacific walrus.

At first it was thought that radiation released from the Fukushima nuuclear reactors in Japan might be the cause. That has been shown not to be the case. Immune system diseases, fungi, man-made and bio-toxins, contaminants and stressors related to sea ice change may be the cause.

Research has combined scientific observations with Canadian Inuit traditional knowledge to how killer whales (Orcinus orca) in the Arctic eat and behave. An increase in hunting territories available to killer whales in the Arctic due to climate change and melting sea ice could “seriously affect the marine ecosystem balance.”

Killer whales have recently started colonizing Hudson Bay They are top predators that affect the behavior of their prey, causing them to run away, dive deep or try to hide among sea ice.  Orcas  eat everything from schools of small fish to large baleen whales, over twice their own size. Smaller mammals seek refuge in shallow waters or on shore, and larger prey run away, dive deep, or attempt to hide among the ice. Even narwhal,  will run to shallow waters and wait until the whales give up.

Sources:

http://www.duke.edu/web/nicholas/bio217/spring2010/kommaraju/casestudy2.htm

http://earthsky.org/biodiversity/fear-of-killer-whales-makes-sea-creatures-run-dive-or-hide

http://www.duke.edu/web/nicholas/bio217/spring2010/kommaraju/casestudy2.htm

http://www.alaskadispatch.com/article/months-later-arctic-ring-seal-deaths-leave-scientists-flummoxed

 

 

Icy Ribbon

Here’s a seldom seen, colorful marine mammal few people have ever heard of – the Ribbon Seal. An Arctic species, one has been vacationing inPuget Sound near Seattle for the last few weeks.

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a ribbon seal resting on an ice floe.

Ribbon Seal

 

The ribbon seal (Histriophoca fasciata) is a medium-sized pinniped from the true seal family (Phocidae).  They are among the most striking and easily recognizable.  They can be identified by the distinctive light-colored bands or “ribbons” that encircle their neck, each foreflipper, and hips.

The contrast is particularly strong with the males,having a dark brown to black pelage with white ribbons, females range from silvery-grey to dark brown with paler ribbons. Newborn ribbon seal pups have white natal fur. After moulting their natal fur, their color changes to blue-grey on their backs and silvery beneath; after some years some portions become darker and others brighter, and only at the age of four years does the typical design show.  Ribbon seals molt their coat of hair annually, beginning in May and finishing in July, with younger individuals molting earliest.

The ribbon seal has a large inflatable air sac that is connected to the trachea and extends on the right side over the ribs. It may function as a buoyancy device, for air storage during diving, or for “phonation.” It is larger in males than in females. The ribbon seal can grow to about 5.2 ft long and weigh up to209 lb in both sexes.

Ribbon seals alternate their foreflippers and swing their hindquarters to run across ice, rather than using the caterpillar-like movement typically used by most seals. Ribbon seals are also physiologically and anatomically adapted to make deeper dives (up to about 1950 ft (600 m)) and swim faster than other seals. They have an air sac that Ribbon seals are a seasonally ice-bound species found in the Arctic and Subarctic regions of the North Pacific Ocean, notably in the Bering Sea and Sea of Okhotsk, and adjacent parts of the Arctic Ocean, including the Chukchi Sea, eastern Siberian Sea, and western Beaufort Sea. These seals are relatively solitary, spending most of their time in the open ocean and forming loose aggregations in the pack ice during spring to give birth, nurse pups, and molt.  They are very rarely seen on shorefast ice or land.  This species seems to prefer moderately thick, “clean” ice floes found in the inner zone of the ice front.  From late-March to early-May, ribbon seals in the Bering Sea range from the Pribilof Islands to Gulf of Anadyr, roughly along the continental shelf break, being more abundant in the northwestern ice front.   As the ice recedes during May to mid-July, the seals move farther to the north where they haul out on the receding ice edge and remnant ice, occasionally in dense groups. After the ice has melted, most ribbon seals probably either migrate with the receding sea ice through the Bering Straight into the Chukchi Sea or remain pelagic in the Bering Sea during the rest of the year.

Thus far, there have been only two acknowledged instances where ribbon seals have been found as far south as Seattle, Washington and even further south at Morro Bay, California. There was nothing to suggest that illness was the cause of either seals appearance at either place, as both appeared to be healthy.Ribbon seal mothers give birth to their pups far offshore in the pack ice during April to early-May.  The pups double their weight during nursing and are weaned after three to four weeks.  Mating likely occurs shortly after weaning, though little is known of the breeding system.  Ribbon seals are known to eat a variety of fishes, cephalopods, and crustaceans; however, information about their feeding habits is limited and mostly restricted to the spring when ribbon seals are typically feeding less, as evidenced by their decreased weight and blubber thickness.  Although there is little direct evidence of predation, potential predators of ribbon seals include polar bears, killer whales, sharks, and walruses.  Ribbon seals are relatively unwary while hauled out and can be approached closely by boat.  This behavior suggests that ribbon seals probably do not experience much predation by polar bears, but may also make them especially susceptible to hunting by man.  Siberia and Alaska Natives have hunted the ribbon seal for many generations for subsistence, and the current annual take by Alaska Natives is estimated to be less than 200 seals per year.  Commercial harvests of ribbon seals were conducted by Soviet sealers in the 1960s to 1980s, during which time the Bering Sea population is thought to have declined from 80,000 or 90,000 animals to 60,000.  Surveys during the early and mid-1970s put the worldwide population estimate of ribbon seals between 200,000 and 240,000, with estimates ranging between 60,000 and 100,000 in the Bering Sea.  A more recent and reliable abundance estimate is not currently available.

Predators of the ribbon seal include orca, the Greenland shark and polar bears.

In the 1960s, the population of ribbon seals in the Bering Sea was reduced from about 120,000 to 70,000. The population size increased back to about 130,000 in 1987 after quotas were set to limit harvest to about a fourth of the number of seals hunted previously. In the latest stock assessment (2007), the National Marine Fisheries Service estimated a global population size of 240,000 ribbon seals, 90,000-100,000 of which inhabit the Bering Sea. In the Okhotsk Sea, the average number of ribbon seals was 370,000 between 1968 and 1988. The current population trend is unknown, but recent estimates suggest that no catastrophic declines have occurred in recent decades.

Humans have hunted ribbon seals for generations and are still hunted today by Siberia and Alaska natives for subsistence, but the number of seals harvestedhas always been relatively small (less than 100 in Alaska).

In the early 1950s, the USSR began commercially harvesting ribbon seals in the Sea of Okhotsk ; the fishery quickly intensified in the 1960s,with an average of about 13,000 to 20,000 seals harvested per year. Ribbon seals were also hunted in the Bering Sea beginning in 1961, with an annual harvest of nearly 10,000 individuals. As the ribbon seal population declined, annual harvest also fell, dropping to 3,500 in the Sea of Okhotsk and 3,000 in the Bering Sea in the 1980s (Popov, 1982). Harvest continued to fluctuate in relation to ribbon seals abundance and political and economic unrest. Although the Russian governmentquotas recently put in place would allow large annual harvests (18,000), the annual harvest remains relatively low today.

Other human impacts to ribbon seals include growing oil and gas development in the Okhotsk and Bering Seas, oil spills, and incidental take in commercial fisheries. In addition, global warming may affect the frequency of years with extensive ice, the quality of the ice, and the duration its persistence such that the amount of available sea ice habitat for ribbon seals within their historic range is reduced.