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Harriman Expedition Retraced


expedition log



David Policansky

Fisheries and the Bering Sea Ecosystem

As many of you know, some species of marine mammals and birds have been declining in the Bering Sea and some people believe that too much fishing is the cause of the declines. That is the topic of today's discussion. To understand the discussion, we need some basic familiarity with commercial fishing. Also, we've been hearing a lot of comments about fishing and overfishing on this trip and it seemed important to address them. So I begin with a brief description of commercial fishery management.

First, let's define a fishery: It is the fish, the water, the boats, the gear, the fishermen (people), processors, distributors, the markets, and the consumers. Although fishing regulations go back at least to the 14th century, people in general considered the sea to be an inexhaustible supply of fish until about the second decade of the 20th century. Then a fishery biologist pointed out that the sea was exhaustible, that you could deplete a fish population by too much fishing. However, as he warned, it would take an enormously strong scientific case to convince people, especially if their profits were involved. Despite all our opportunities to learn, our approach to managing many ocean fisheries has only recently begun to change much from that of the early 20th century.

Traditionally, we have managed fisheries in two main ways. We can manage the amount of time, money, and effort that go into fishing or we can focus on the amount of fish caught. The first approach is known as input control, because it limits the input in economic terms. As I mentioned in my previous discussion about salmon and halibut, if you don't control input then often the result is an excessive capitalization; in other words, there are more boats and gear being used that are needed for efficient fishing, as a result, landings have to be controlled (known as output controls) and you end up with a crazy race for the fish, and with very short open seasons.

One general kind of approach to solve these problems is to allocate specified percentages of the total allowable catch (quotas) to individuals or to cooperatives or to communities so that they know in advance how many fish they can catch and then they can plan accordingly and fish efficiently, eliminating economic waste as well as physical danger in many cases. This has been happening in many Alaskan fisheries and has contributed both to economic stability and to conservative management of fisheries, i.e., management that does not lead to depletion of the fish stocks. This is the fishery context of the Bering Sea ecosystem, especially for finfish (as opposed to crab species, whose populations are quite low).

In the Bering Sea, the animal that gets most of the attention these days is the Steller sea lion (Eumetopias jubatus), which has been listed as endangered under the Endangered Species Act As a result, many areas have been closed to trawling, mainly for pollock (Theragra chalcogramma), the most important commercial species in the Bering Sea. But we don't really know if the pollock fishery is responsible for or even a contributor to the decline of Steller sea lions. Because of this uncertainty, and quite some time before the fishery restrictions but after the sea lions (and some other mammals and birds) had been declining, the National Research Council (NRC) was asked by the State Department of advice on this problem, and in about 1996 it produced a report called The Bering Sea Ecosystem (see report). That report concluded that many factors were affecting the Bering Sea ecosystem and that it was very difficult to know for sure what was causing the declines, but perhaps the most scenario was the following.

First, it is clear that there have indeed been many changes in the ecosystem, with some species increasing in abundance, others decreasing, and others perhaps not changing much (see Figure 1). Second, we know that there have been significant changes in the atmosphere and the ocean, most notably one in the late 1970s, commonly known as a regime shift. At that time, the Bering Sea became warmer and there was less ice cover than previously; other changes happened as well. (It is possible but not certain that in 2001 the regime is changing again or has recently changed.) Vera Alexander described these changes in detail in her presentation. Third, we know that there was heavy exploitation of the Bering Sea ecosystem from the 1940s or so through the early or mid 1970s. Sperm whales were almost eliminated from the area, and some other whales were heavily exploited as well, and fish were heavily exploited. But whaling has largely ended and since the late 1970s fishing has been quite conservative; the catch of pollock in the eastern Bering Sea (the US-controlled part) has been well below what seems to be available. As a result of all the above factors, now pollock have come to dominate the ecosystem. Finally, we know that sea lions and other mammals and birds seem to need oily fish such as capelin (Mallotus villotus) and sandlance (Ammodytes hexapterus), and they were among the species that declined with the regime shift, as shown in Figure 1. It appears that the weaned pups cannot find enough of those fish (at least, they appear to be short of some kind of food) and so they are not surviving well into adulthood.

temporal change graph

Figure 1. Schematic temporal change in relative abundance of certain marine mammals, seabirds, fish, and shellfish in the Bering Sea. Lower but indicative of changes in sea surface temperature (Committee on the Bering Sea Ecosystem).
Click image for a larger view.

If all the above is true, then reducing pollock fishing will not lead to increases in marine mammals and birds, at least not in the short term. (However, it is possible that localized trawling very near sea-lion rookeries could cause food shortages and so there is a sensible rationale for excluding trawlers from areas close to rookeries, although not even this is certain.)

Although the NRC report is several years old now and new information has been gathered, the overall picture has not changed. There are still lots of pollock in the Bering Sea, sea lions are still declining, although perhaps more slowly than before, and there continue to be restrictions on fishing, especially in the parts of the Bering Sea around Bogoslof and the Aleutian islands, and in the western Gulf of Alaska (not part of the Bering Sea). One still has to wonder what the effects of taking nearly two million metric tons of fish and crabs each year from the Bering Sea might be, even if the fish species are being managed conservatively. Ecosystem effects are hard to understand and they have not been studied very extensively or for very long. For example, we know very little about Bering Sea animals that are not of commercial importance or that are not of special concern for other reasons, such as the Endangered Species Act.

So we have an interesting and difficult policy dilemma. On the one hand, the Endangered Species Act makes it clear that if human activities are jeopardizing an endangered species, they should be stopped or altered. On the other hand, we are still not certain why sea lions are declining. Past or present exploitation of the Bering Sea ecosystem probably have some effect, but the declines could be due mainly to "natural" changes in the ecosystem and they could represent the kinds of population fluctuations often observed in some species. Climates and ocean conditions do change, even when people aren't responsible; they have changed for as long as we know anything about them. And the fishing restrictions could have severe impacts on local economies, especially in places like Kodiak and Dutch Harbor. If fishing is not affecting sea lions, then reducing it might not help them and the economic hardship might not have any compensating benefit.

Although a great deal of money (about $40 million) has been appropriated recently for research on sea lions, it is unlikely that clear scientific answers will be available in the near term. Sea lions, pollock, and some bird species live for many years, and ecosystem changes can be subtle or complex or both. So we will continue to do our best to understand and manage our exploitation of the Bering Sea ecosystem and hope for improvements. But as human numbers and demands of ecosystems everywhere increase, and as climate and other environmental changes -- some natural and some caused by human activities -- continue, difficult problems like that of fishing and declining populations of sea lions in the Bering Sea will continue to arise and challenge us.




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

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