by Nathan LaBudde
International Marine Mammal Project
The Bering Sea stretches from Alaska's west coast to the shores of the Russian Far East. Within its frigid waters lie the 800 kilometer, west-central chain of the Aleutian Islands, where scientists have uncovered the chilling truth behind the mystery of the vanishing northern sea otter. Sea otter populations in this part of the Aleutian archipelago, which numbered 53,000 at the beginning of this decade, have dwindled to just 6,000 - an astonishing 90 percent drop in just eight years.
The overtaxed Bering Sea fishery provides half the annual US commercial seafood catch. Substantial increases in trawler fishing over the last three decades have greatly diminished and altered the region's fish stocks - the food supply for many marine mammals. Aggressive commercial overfishing of once-abundant pollock, salmon, Atka mackerel, cod, perch and flatfish species have caused the decline of seal and sea lion populations. In particular, western Steller sea lion populations have dropped 80 percent in 30 years, from a peak of 237,000 in the 1960s to 43,200 in 1994.
Now a recent study published in the October 1998 issue of Science reveals an extraordinary correlation between the decline of Steller sea lions and the extinction-bound northern sea otter.
Of all the awe-inducing marine predators Nature has created, perhaps the greatest is the powerful, intelligent and highly organized transient orca whale (Orcinus orca). A single orca can dispatch a great white shark if need be. In a hunting pack, orcas can attack and kill a full-grown gray whale in a matter of minutes and feast on the unlucky victim's tongue (an Epicurean zenith for transient orcas).
When roaming the Bering Sea, these orcas traditionally subsist on a high-fat diet of Steller sea lions and seals. A single adult male Steller sea lion, with its thick layers of insulating blubber, can weigh up to 2,464 pounds and females can top out at 770 pounds.
But with the recent decline in Steller sea lions and other traditional food sources, transient orcas in the Bering Sea are now attempting to sustain themselves by feeding on small northern sea otters, which average only 50 to 75 pounds.
"This reflects real desperation for the orca," says ecologist Paul Dayon of the Scripps Institution of Oceanography, "They're eating popcorn instead of steaks."
Disney vs. Reality
To many people, furry sea otters are the oceanic equivalent of a bunny. Otters are often characterized as playfully corkspiralling through kelp beds and eating small mollusks while swimming on their backs For centuries, northern sea otters have lived in the Bering Sea without fear of orcas. Now, however, they have a lot to fear. Faced by this super-predator, the otters will be (barring an evolutionary miracle) physically and instinctively ill-equipped to meet the orcas' challenge.
Researchers first witnessed a transient orca attacking and eating a sea otter in Alaskan waters in 1991. A dozen further sightings over the last seven years tell of orcas swallowing otters whole or first plowing into a raft of the otters and stunning them before devouring them.
Scientists have determined that an adult orca feeding exclusively on sea otters would need to consume five per day - 1825 annually - in order to meet its caloric demands. Just four orcas, feeding exclusively on sea otters since the first documented attack in 1991, could account for the entire decrease in northern sea otter populations.
Kelp is on the Way… Down!
Certain species play a central role in maintaining ecosystems in which they lived. These are referred to as "keystone" species. The sea otter is recognized keystone species. The health of coastal kelp forests, which support a range of life from "barnacles to bald eagles," is protected by the sea otters, whose favorite food is sea urchins. With the sea otter's decline, dense coastal kelp forests are being grazed barren by exploding populations of sea urchins.
"Kelp forests, situated in shallow waters and protected coastal zones, nourish and shelter a host of marine life....from crustaceans, mollusks and fish, to marine mammals," notes marine biologist Paul Spong. "They are as vital to marine ecosystems as tidal marshlands are, and as poorly appreciated. Inevitably, as they shrink and disappear, the entire ecosystem which depends on them is stressed… ultimately heading into a disastrous downward spiral."
A simple common-sense (albeit politically difficult) solution rests in scaling back human impacts in the Bering Sea and allowing time and Nature to re-establish the ecosystem's balance.
As the majority of our planet's commercial fisheries approach crisis or collapse, one hears the quick-fix suggestion calling for the culling (slaughter) of cetaceans and pinnipeds. This proposal calls for propping up devastating commercial over-fishing by killing marine mammals that have comparatively minor impacts on diminishing fish stocks.
When faced with such suggestions, it is useful to recall the Domino Effect. Every organism participating in the fabric of the ocean's ecosystem - from phytoplankton on up - is a vital contributor in sustaining aquatic life and ultimately much terrestrial life on Earth.
What You Can Do: The National Marine Fisheries Service is accountable for the management of the Bering Sea. Urge them to reduce the damage from commercial fisheries and to help restore a balanced ecosystem that supports orcas, otters, sea lions and kelp forests. Contact: Rolland Schmitten, Assistant Administrator for Fisheries, [NMFS, 1315 E-W Highway, Silver Springs, MD 20910-3282]. For more information on Steller sea lions contact Laura Seligsohn at IMMP's Pinniped Fisheries Project: [(415) 788-3666 ext. 144, marinemammal@igc.apc.org].
There Otter be a Law