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February 7, 2006

Warming Weather Woes: Seal Pup Drownings

Northern Elephant Seal Cow and Pup

No one wants to see those cute little seal pups drowned, washed up on the beaches. But is this a natural occurrence? Why does it happen?

Dangers of a Dual Life
Seals live a dual life. Seals, sea lions and walruses spend most of their time in the water, feeding. But they all haul out on land for mating and birthing - often in the same place every year. Some seals, like the Gray seal, give birth on the ice floes of the Arctic, while others, like the Northern Elephant seal, colonize great sand dune rookeries along the Pacific coast.

Seal pups are born on land for good reason. Although they are born with their eyes open and grow very quickly, the first few weeks and sometimes months, are a vulnerable time. Seals are not born with the layer of protective blubber. Instead, seal pups start forming a blubbery layer by drinking their mother's rich milk. Without that thick layer of blubber, seal pups are vulnerable to exposure and they don't float well.

Few species can swim from birth and it often takes weeks or months before they can swim on their own. Sometimes they are taught by their mothers, but most often they learn on their own, in tidepools and the shallows, long after their mothers have gone back to the sea.

Swept Away
Severe storms, elevated sea levels, heavy rains and abnormally high tides can have catastrophic effects on seal colonies with youngsters, submerging the rookeries and washing seal pups out to sea before they are ready. Naturally occurring storm trends like El Niño have been known to cause significant increases in pup mortality, which is generally already high. For example, the Northern Elephant seal generally has pup mortality of 50% in the first year, but during the last El Niño in the late 1990's, this rate rose to 80%, with some rookeries like Point Reyes losing an entire generation of pups when storm surge flooded the dunes. Other pinnipeds, like the California Seal Lion, saw their pup mortality rates double during El Niño:

CALIFORNIA SEA LION:
In a typical year, 1 out of every 3 pups dies in their first year
During the 1992 El Niño year, 2 out of every 3 pups died in their first year

More at: El Nino Impacts on Pinnipeds by Species

Human Factors: Global Warming, Erosion, Invasive Species
Lots of other factors make life difficult for seals, not least of which is pollution. But even if we just look at what factors may have some effect on the number of seal drownings, there are quite a few.

Global warming trends and rising sea levels have a direct impact on the frequency of rookery floodings. Unseasonably warm winters make the ice too weak to support seal birthings, forcing seals to give birth in more vulnerable areas like exposed beaches. Just this week, about 75% of the Gray seal pups born so far this season on an island in the Northumberland Strait were swept out to sea and drowned.

Around 1,500 seal pups were swept out to sea and drowned by a tidal surge off Canada’s east coast this week after a lack of ice cover meant their mothers were forced to give birth on a small island, environment officials said Friday.

A resident on the island described how the mother seals had frantically tried to push their tiny pups back on to land as they floundered in the storm-tossed water.

More At: MSNBC: 1,500 seal pups die in tidal surge

The sand dunes themselves , which provide a safe haven for young pups to nurse and learn to swim, are disappearing due to erosion, invasive grasses and plants, development and mismanagement. There are fewer and fewer safe places, away from humans, for seals to birth and raise their pups in peace. As these natural safe havens disappear, more and more seals are forced to use other, more dangerous locations, to raise their pups.

The Northern Elephant seal, which has made a promising recovery from numbers of fewer than 100 seals less than a century ago, recently set up a new rookery along the central coast of California. The rookery is so close to the Route 1 - the famous California Pacific Highway - that at least one elephant seal has been hit by a car after wandering onto the road.

Down coast in San Luis Obispo County, a large colony of elephant seals, numbering up to 5,000, has become established. In 1990 they began to pup on a cove beach near the Piedras Blancas lighthouse, one of the few secluded beaches in that coastal region, and have since spread toward Twin Creeks Beach, beside Highway 1. No docent-led program exists here. People pull off the highway and sometimes get too close, or behave in a foolish manner, courting injury. Some even try to pet the seals. "It's a regular zoo, and it's been a safety problem for some years," says Norman J. Scott Jr., biologist at the Piedras Blancas field station of the National Biological Survey, U.S. Geologic Survey. Elephant seals have wandered onto the coastal highway, and at least one has been hit by a car.

More At: California Coast & Ocean: The Dangerously Attractive Elephant Seals

Do We Interfere?
Conservationalists are mixed as to whether or not people should interfere with what could be considered a natural phenomenon. During the last El Niño, marine mammal refuges all along the Pacific coast were full of distressed animals that had been stranded on beaches or orphaned, but it is also been shown that, for successfully recovering species like the California sea lion, the overall population growth is not adversely affected by these events. Still, there are certainly quite a few endangered seals - like the Hawaiian Monk seal, in which every single pup is vital to the continuation of the species.

Posted by sorsha at February 7, 2006 2:41 PM