Expedition
Log
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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.
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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.
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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.
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