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Harriman Expedition Retraced


expedition log



Kathryn Frost

Bering Sea Marine Mammals: Ecology and Conservation

One of the most striking things about the original Harriman Alaska Expedition reports is the absence of an organized report on either terrestrial or marine mammals. There is only brief mention of marine mammals in Expedition narratives. There is a description of the Native sealing camp at Yakutat and a mention of harbor seals, and other brief references to the over hunting of sea otters and fur seals, but no mention is made of harbor seal and sea lion haulouts as the George W. Elder steamed along the coast, nor of the large and small whales they must have seen as they spent many hours at sea without making landfall. As they passed north into the Bering Sea, there were no descriptions of sea otters or walruses at the Pribilof Islands. By the time The Harriman Expedition transited the Bering Sea, the Steller sea cow had been hunted to extinction.

Perhaps part of the reason these animals weren't much mentioned is that already by the turn of the century, many species had already been over hunted and were no longer easy to see. Grey whales were depleted by the 1880s. Bowheads were depleted in the Bering Sea by the mid 1800s, only 10 years after their discovery there. Sea otters and walruses were gone from the Pribilofs by the time the Harriman Expedition arrived there, and sea lions were greatly reduced in number. By 1900, fur seals were close to an all time low.

And so -- where are we today? Grey whales and walruses have recovered. Grey whales are probably as numerous as they ever were … more than 20,000 ply the waters between Baja California and Alaska each year. Walruses -- at least when we last counted them in the mid 1980s -- were thought to be at or near carrying capacity. Sea otters are numerous throughout much of their former range… although recently a large and unexplained decline has been noted in the Aleutian Islands. The thing these species -- grey whales, walruses, sea otters - have in common is a link to benthic food webs. They get their food from the bottom of the sea. They don't feed within the pelagic food web of the Bering Sea -- the world of plankton and forage fish.

And what about the others? The fur seals, sea lions and seals? The species that DO eat pelagic forage fishes. Have they recovered? Are they healthy? A cursory look at the Pribilofs today -- like the one afforded members of the Harriman Expedition Revisited as they visited St. Paul and St. George Islands on their way north through the Bering Sea - initially suggests "yes." The beaches are alive with the bleats of fur seal pups looking for their mothers, and with the jostling of males protecting their harems along the boulder beaches. There is no unregulated commercial hunt for these seals as there was at the turn of the century when the Harriman Expedition visited. Visits to the rookeries -- even by scientists -- are highly controlled. And yet, although almost 800,000 fur seals now come there to have their pups and breed -- up from a few hundred thousand when Harriman was here -- this is a far cry from the 3-4 million that biologists estimate were present 200 years ago -- or the 2 million that were here as recently at the 1950s. And why? Is it entanglement in human debris so common in our oceans today? Competition with commercial fisheries for food? A change in ocean conditions that has altered the availability of the right kind of food for fur seals? As hard as we try, scientists still don't know the answers. Likely there is no one cause … making it even more difficult to determine what might reverse such a decline.

And what of Steller sea lions -- also once so abundant in the western Gulf of Alaska and the Bering Sea? The story there is even more confusing. Until the 1970s, sea lion numbers were high throughout Alaska. Since then, however, there has been a startling decline in sea lion numbers in western Alaska. Counts of pups -- an index of overall abundance and population health -- have dropped along the Alaska Peninsula and the Aleutian Islands, at the Pribilof Islands in the Bering Sea, and in the Kuril Islands of Russia. At Walrus Island in the Pribilofs, only 50 pups were born in 1991 -- a vivid contrast to the 2,800 pups that were once born here each year. In fact, sea lions in western Alaska have declined to such a degree that they are now classified as an endangered species.

As for fur seals, the reasons for the sea lion decline are unclear and may not necessarily be the same now as they were 20 years ago when the decline began. Could it be a change in the ocean? In the late 1970s, ocean temperatures warmed by several degrees, causing quite dramatic changes in the abundance of some of these fishes. Some species, such as pollock, became much more abundant and others such as capelin, a high-fat schooling forage fish, became far less abundant. It may be that the replacement of such high-fat forage species with lower fat pollock may have made it more difficult for sea lions -- especially juveniles -- to get enough calories to make a living.

And yet, that is certainly not the whole story. Killer whales eat sea lions. As the seals and sea lions on which they dine have become less abundant, predation pressure on the remaining marine mammal populations has increased. Sea lions and commercial fisheries compete for the same fish. Commercial fisheries in the Steller sea lion range remove millions of pounds of fish each year. While the fishery itself is considered sustainable, its side effects on other species are unknown. In the not-so-distant past, sea lions have been killed intentionally -- as well as accidentally -- in conjunction with fisheries.

Is the problem more deep seated than all of these? People and commercial fisheries change not only the abundance of the species they target, but also ecosystem dynamics of who eats who and how much. Within the past 200 years, people and their fisheries have vastly altered the Bering Sea ecosystem. Species like Pacific ocean perch and yellow fin sole were overfished, the great whales seriously depleted. Removal of these and other species, which were significant consumers of both fish and plankton, has undoubtedly greatly altered the way creatures of the sea interact -- and the aftermath of such changes may also be part of the unexplained and continuing declines we see.

Whatever the cause, it is clear that people must do whatever they can to prevent further human-caused problems. Because there is nothing we can do about cyclic climate change or killer whale predation, we must do what we can -- protect habitat, prevent intentional and accidental killing, minimize competition with commercial fisheries, and minimize emissions that may cause global warming and exacerbate other environmental change.

And what else has changed in the Bering Sea since Harriman's time? What is the status of OTHER marine mammals in this region? One of the unanticipated consequences of the sea lion decline in particular -- which has impacted how a multi-million dollar fishery for pollock is conducted -- is that vast monetary as well as human resources are now directed at solving the "Steller sea lion problem." Because so much attention is being focused here, research on other species is not receiving the attention it deserves.

Spotted seals, the ice-breeding form of harbor seals, eat many of the same small forage fishes that have been implicated in declines of harbor seals, sea lions, and some seabirds. And yet, there is not adequate information on population status or health and condition to know whether this species, too, has been declining. What is the impact of almost two decades of reduced abundance of high-fat forage fish? How do extreme oscillations in the annual extent of sea ice, and particularly years of very light ice coverage, affect feeding and survival of pups which are born and weaned in the ice front?

What of ribbon seals? These seals also inhabit the Bering Sea ice front in spring, where they feed and have their pups. Where do the go in winter? How many are there? Are they abundant and healthy? No one knows. The last studies of ribbon seals were conducted more than 25 years ago. It's hard to believe that we could know so little about a population that probably numbers more than 100,000 seals.

Bearded seals are also largely a mystery. As is the case for ribbon and spotted seals, little research has been conducted since the 1970s and there is no current population estimate. Yet these seals are one of the preferred foods of local Native people throughout western and northern Alaska. They are hunted along the coast in spring when the sea ice first begins to break up -- and again in fall as the ice returns. Bearded seals eat clams and crabs and other benthic creatures. Have they been impacted by snow crab fisheries which harvest that same kinds of crabs that bearded seals eat? What are the interactions between bearded seals and walruses? Are there enough clams and snails to feed them both? Do bearded seals migrate? And if so, to where? There is no ongoing research in Alaska to address these questions.

Scientists are in a little better shape for ringed seals -- the most northern on the ice associated seals. These "polar bear popsicles" inhabit the stable land fast ice along Alaska's northern shorelines. They make and maintain breathing holes through ice that may be 6 ft thick, and the pups are born in snow caves or lairs excavated in snow drifts on the ice. These seals are the major prey of polar bears throughout the Arctic, and are also a source of food for coastal residents. There have been recent surveys of this species, indicating that densities on fast ice are similar to densities in the 1980s. But we still have no current information on reproductive rates, the age at which they mature, and how they use different geographic regions and habitats throughout the year. How will a thinning ice pack across the arctic affect these seals which depend on a stable ice platform on which to bear and nurture their pups?

And walruses? The last usable aerial census of walruses in Alaska was conducted more than 15 years ago. At that time, the population was quite high -- more than 250,000 -- but since then Native hunters and some biologists have noticed changes in walrus condition and age composition. Does this indicate a change in population status? Is the diet the same now as it was the last time walrus food habits were studied more than 15 years ago? Do changes in sediment transport through the Bering Strait affect the clam populations upon which walruses feed?

So where does this lead us? When I first came to Alaska and began to study its many marine mammals, there was a burst of funding -- part of an environmental assessment program associated with leasing of the outer continental shelf - to provide baseline information about Alaska's marine ecosystems. Since then, however, such funding has disappeared - there were "no significant issues" and populations were "healthy, high, and stable." There wasn't enough money to go around, and healthy species with no problems didn't come out on top in funding allocations. Twenty-six years later at least two of these species -- Steller sea lions and harbor seals -- have declined so significantly that we are now spending millions of dollars a year to try to retroactively determine the causes for these declines and determine what, if anything, people can do to improve the situation. What of the other seals for which we have no recent information?

There must be a better way for the next 26 years … to look as we go, to make sure the bases are covered for even those healthy, "non-problematic" species. There must be a way to put our heads together and design research and monitoring programs that will help us to detect changes as they are occurring - not so far down the line that we are trying to figure out how to solve a problem before we even know its cause.




For information on the Harriman Retraced Expedition e-mail: harriman2001@science.smith.edu

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