National Assessment of
Alaskan and Bering Sea marine ecosystems show strong signals of climate-driven changes. Further climate change is likely to bring large changes in marine ecosystems including stocks important for both the commercial and subsistence catch. However, definitive information on which organisms will be affected in what way from changes in climate is very limited.
Fisheries of the Bering Sea Impact Study (BESIS) region (N. Pacific Ocean, Bering Sea, Sea of Okhotsk, Chukchi Sea, and Gulf of Alaska) are among the most productive in the world and are the largest in our nation. This region accounts for over 28% of recent total worldwide landings of fish, mollusks, and crustaceans. In addition to supporting commercial, subsistence, and recreational harvests of marine and freshwater fisheries (some 450 species), the BESIS region also supports 25 species of mammals and the largest and most diverse populations of seabirds in any similar sized region in the Northern Hemisphere.
In 1990, Alaska's 54-billion pound seafood harvest, which consisted mostly of salmon, king crab, halibut, shrimp, and scallops, was greater than that of any other state and equaled half of all the seafood harvested in the entire nation. By 1995, the value of Alaska's commercial fisheries exceeded $1.4 billion. In addition to their role in supporting the region's economy, BESIS region fisheries, largely harvested by distant-water fleets, also serve an important role in international commerce.
The BESIS region is one of the least industrialized in the world, and its fisheries are essential to many of the region's native cultures. Traditional cultures, many of which rely on subsistence harvest and consumption, depend on the healthy functioning of the entire ecosystem, which includes fisheries, marine mammals, and waterfowl.
Various sources have provided evidence that this region experiences climate-driven changes at many different time-scales -- e.g., daily, seasonally, for decades. This region has experienced a few decade-long climate variations (sometimes referred to as a regime shift) during this century that have apparently caused rapid and extreme changes in the region's marine ecosystems. The most recent of these regime shifts (a regime shift can include: changes in water and air temperature, in sea ice cover, in air pressure, and in wind direction for example) occurred in 1977. Previous shifts occurred in 1924 and 1946 and some data suggest that another could have occurred in the early 1990s.
There was a strong climatic change from 1977 through 1988 that resulted in warmer sea-surface and deeper water temperatures, a lowered percentage of ice cover, reduced average pressure, and changes from normal in air temperature and in wind direction. Oceanographic (e.g., water temperature, ice cover, air temperature, wind direction and speed) and biological (e.g., available food) processes directly and indirectly control the productivity of fisheries, with some changes being good for some populations and bad for other populations. Salmon runs soared after the last regime shift and have largely remained high since then. Other fishery populations crashed.
The discussion that follows considers environmental, social, and economic impacts of present and future climate change on Alaska's fisheries. Possible strategies to address these impacts complete this discussion.
Various factors influence fish population sizes and distribution, including environmental conditions such as water temperature. Some species have responded negatively to the most recent regime shift (to warmer conditions) in the BESIS region, even as this shift has produced better conditions for many other fish stocks. For example, even though crab stocks, numbers of some forage fishes, and the number of Greenland turbot have declined significantly, many groundfish stocks and salmon are flourishing -- the stocks increasing with warming air temperatures.
The quantity of Pacific cod has increased 600% to 1.1 million tons and rock sole increased 350% in the 20 years since the regime shift of the late 1970s. Other varieties that have shown improvement include Pacific halibut, yellowfin sole, flathead sole, Alaska plaice, arrowtooth flounder, Atka mackerel, walleye pollock, mixed skate species, Pacific herring, Pacific ocean perch, and sablefish. As pollock and other predatory fish increased in numbers, several species of forage fish with high nutritional value, such as capelin and herring, declined sharply.
Pacific salmon off the coast of Alaska clearly have benefited by recent freshwater and marine environmental changes because portions of their life cycles occur in both marine and freshwater environments. Beneficial freshwater factors include increased stream temperature, stream flow rates, and air temperature. Marine conditions that have benefited Pacific salmon include increased air and sea-surface temperatures and reduced Bering Sea ice cover. These marine changes from average conditions occur with El Niño events (about 1 year in duration) and with some decade-long cycles as well. Changes in precipitation and temperature expected with increased climate change could therefore enhance salmon productivity much more regularly.
However, one of the species that has suffered in recent years is the red king crab. Stocks have declined sharply since the early 1980s, possibly as a result of changes in fishing patterns as well as changes in the environment. Humans have over-fished this species, which reduced stock size to critically low levels. In addition, environmental changes, such as temperature increases in air and water; changes in the direction and strength of marine currents; and reduced food availability also have contributed to the plummeting red king crab population.
Various marine mammals and seabirds that feed on species such as capelin and herring have had to change their diets to other less fatty species and have in turn declined sharply. Populations of many species of seabirds, including kittiwakes, murres, cormorants, larus gulls, guillemots, puffins, and murrelets, have declined by 50 to 90% since the 1970s. Marine mammals show similar signs of food stress. In the Gulf of Alaska, both stellar sea lions and harbor seals have declined by more than 80%. The extreme decline of stellar sea lions has prompted significant restrictions on the pollock fishery since 1998, to increase the sea lions' food supply.
Northern fur seals declined by about 35% from 1970 to 1986, then rebounded somewhat through 1990. Sea otters have declined as much as 80% since 1990 over much of the west coast, but this decline has been attributed to predation rather than food shortage. The loss of sea otters could likely be accounted for by a few Orca whales, perhaps only a single pod, beginning to prey on sea otters following a decline in their usual prey. While climatic effects on marine mammals through changes in food supply are most pronounced at longer time-scales, shorter-term changes can affect them in other ways, such as changes in the extent of sea ice that provides habitat for some species and excludes others.
Increasing numbers of fish species, and those dependent on them, could suffer as the extent of sea ice coverage over the winter in the Bering Sea continues to decline, a phenomenon that began several decades ago and is discussed in the previous section. This decline, combined with changes in sea-surface temperatures, affects the availability of nutrients, which in turn effects the productivity of Alaska's fisheries by limiting the growth of phytoplankton and zooplankton. Phytoplankton and zooplankton populations, food sources for fish and other aquatic organisms, can also be reduced as a result of loss of stratospheric ozone, the atmospheric shield that protects our planet from the sun's harmful rays (UV-B). High levels of UV-B can impact the growth and reproductive ability of the plankton. Threats to these food sources are very real, as total stratospheric ozone over the north polar region was 40% lower in March 1997 than in the Northern Hemisphere winters of 1979 and the early 1980s.
While it is possible that the responses of these ecosystems to future climate change will be large, whether the possible changes will be positive or negative is highly uncertain at this time. One preliminary study conjectured that 21st century climate change could increase or decrease particular Alaskan fisheries by as much as a factor of two.
Changes in Alaska's climate and its impact on the state's fisheries would significantly affect its people, many of whom depend on Alaska's fisheries for their food and livelihood. Residents of the 56 communities that border the Eastern Bering Sea depend on hunting and fishing as a food source and on commercial fishing for millions of dollars of revenue each year. Inland and distant communities also have strong ties to the BESIS region's commercial fishing industry through kinship, trade, employment, reliance on salmon, and participation in commercial fisheries.
Subsistence hunting of marine mammals occurs directly from shorefast ice in spring. Thus, a retreat or melting of ice in winter and spring would affect the migration patterns of marine mammals, such as the bowhead whale, and could put them beyond the reach of subsistence hunters.
Subsistence harvest not only serves as an important food source for Alaska's rural residents, it supports a unique set of behaviors, ethics, and beliefs, which provide a moral foundation for rural communities and a sense of continuity between generations. Thus, climate change, in addition to compromising sources of food and livelihood, would threaten the cultural fabric of rural Alaska.
Having captured 23% of the state's workforce, Alaska's seafood industry is the largest private sector employer in the state. Moreover, many residents rely heavily on subsistence foods, much of it fish and marine mammals, consisting of an estimated annual wild and subsistence harvest of 10.5 million pounds per year.
According to recent studies, the replacement cost of this wild food harvest ranges from 13% to 77% of the total income for communities that depend on subsistence foods. Estimating a replacement cost of $3 to $5 per pound of meat, families would need an additional $5,000 to $14,000 per year to buy the food they can provide for themselves by fishing, hunting, and trapping.
Climate-change impacts on revenue from commercial fisheries would depend on whether the demand for a specific fish is elastic (when increased catch results in increased revenues) or inelastic (when increased catch results in decreased revenues). Unless total demand increases, higher catches of Pacific halibut and Pacific salmon, two species that have benefited from recent climate changes, will not produce greater revenues. Moreover, modest increases in walleye pollock populations would cause the demand to become inelastic. Exceptions to the inelastic demand for most groundfish stocks are likely to be highly valued species with depressed harvests, such as sablefish and commercially targeted crabs.
If climate change reduces the extent of sea ice coverage, then fishers could have improved access to stocks that come together seasonally and improve their catch-per-unit effort (e.g., increase the volume of catch per trip) without an increase in stock abundance. However, this same reduction in sea ice coverage could result in marine mammals congregating and migrating beyond the reach of subsistence hunters.
Strategies to Address Potential Impacts on Fisheries
In the face of extreme uncertainty about the positive or negative impacts of future climate effects on specific fisheries, the most useful adaptation options will be those that increase the ability of human activities and communities to shift their exploitation to abundant species. Some examples of issues for consideration include:
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