The basic limiting factors for fish production in polar and subpolar regions
are light and temperature. Warming in high latitudes should lead to longer growing
periods, increased growth rates, and ultimately, perhaps, increases in the general
productivity of these regions (IPCC 1996, WG II, Section 220.127.116.11). On the other
hand, the probability of nutrient loss resulting from reduced deep-water exchange
could result in reduced productivity in the long term. Again, this complexity
highlights the importance of changes in temperature for patterns of circulation.
Global warming could have especially strong impacts on the regions of oceanic
subpolar fronts, where temperature increases in deep water could lead to a substantial
redistribution of pelagic and benthic communities, including commercially important
fish species (IPCC 1996, WG II, Section 8.3.2).
In polar regions, the number of dominant fish species is small; many species
of low abundance are typical of tropical regions, with the exception of upwelling
areas. Only 15-20 commercially important species in the Arctic or Antarctic
Oceans are recorded, whereas the numbers increase to about 50 and 16-450 in
the boreal and tropic areas, respectively (Laevastu, et al., 1996). The poleward
distribution of fish due to climate warming generally expands fishing areas.
This expansion might produce better yields of fish production. In the higher
latitudes, however, spawning grounds of cold-water species that are very sensitive
to the temperature change might be destroyed by changes in water properties.
In some cases, fisheries on the margin of profitability could prosper or decline.
For example, if there is a retreat of sea ice in Antarctica, the krill fishery-which
is regulated by the current ice-free period-could become more attractive to
nations not already involved (IPCC 1996, WG II, Section 18.104.22.168). Fishery statistics
may be more valuable for the analyses of interannual and long-term fluctuations
of marine populations than was previously thought. Time series of catch-per-unit-effort
(CPUE) statistics from the commercial krill fishery operating around South Georgia
during 1973-1993 have been used for considering the hypothesis that fluctuations
in the abundance of krill in the Scotia Sea area are related to environmental
changes. A consistent correlation has been found between the various CPUE indices
and ice-edge positions: The further south the ice-edge occurred during the winter-spring
season, the lower the CPUE values in the following fishing season. The most
extreme expression of this relationship was the lack of a krill fishery in 1978
and 1984, when the ice did not extend far north during the previous winter.
By contrast, in 1978 and 1984 the March ice-edge reached its northern limit
at 50ŮS, preceding high CPUE values in 1979 and 1985. A consistent relationship
also exists between CPUE and water temperature. Warm-water temperature in the
South Georgia shelf area in January-February corresponded to lower CPUE values
in the same year. There also is significant correlation between air transport
in late spring and CPUE in the next year. For example, a prevalence of southerly
meridional air transport precedes high CPUE values (Fedoulov et al., 1996).
It must be emphasized, however, that the physical regimes of the sub-Antarctic
region in the vicinity of South Georgia are very complicated, and this model
may not be applicable to the entire Antarctic.
Fedoulov et al. (1996) proposed the following mechanism as a hypothesis to
explain how ice, ocean, and atmospheric components of the Southern Ocean affect
krill distribution. Krill usually are more abundant in the southern Scotia Sea
along the Weddell Scotia Confluence (WSC), so it is likely that the currents
play a key role in krill transport to South Georgia from the Antarctic Peninsula.
The WSC zone extends northward in the eastern Scotia Sea, and this colder water
penetrates along the southeastern shelf of South Georgia. The position of the
WSC is thought to be determined by the intensity of the Weddell gyre, which
in turn is driven by the formation of dense and cold Weddell water. The main
factor in the creation of the cold Weddell water is increased salinity resulting
from ice formation. Hence, the dominance of a warm or cold year reflects the
intensity of the Weddell gyre and consequently the general position of the WSC.
It is reasonable to suppose that ice can start to influence krill distribution
when it is close to or covers the area of the WSC. Ice cover modifies the mechanism
of drift current formation and creates favorable (northern ice-edge position)
or unfavorable (southern ice-edge position) conditions for krill transport to
In a recent study, Loeb et al. (1997) are documenting a more complex relationship
between krill and salpa, a pelagic tunicate. In essence, extensive seasonal
ice cover promotes early krill spawning, inhibits population blooms of pelagic
salps, and favors the survival of krill larvae through their first winter. Salpa
blooms affect adult krill reproduction and the survival of krill larvae. If
a decrease in the frequency of winters with extensive sea-ice development accompanies
the warming trend in the Antarctic Peninsula area, the frequency of krill recruitment
failures would be expected to increase, and the krill population would decline.
An increase in salpa blooms would further depress krill numbers. This codependency
of competing species on changing climate variables has implications for the
management of the krill fishery and for populations of vertebrate predators
such as penguins, fish, and whales, which depend on krill.
Agriculture in polar lands is severely limited by the harsh climate. Although
agriculture is not practiced in Antarctica, some agriculture currently takes place
in the Arctic. If temperature were to increase and result in earlier last-freeze
dates and later first-frost dates, conditions for Arctic agriculture should become
more favorable, although climate conditions will still make agriculture in the
Arctic extremely difficult. There already are indications in Alaska, based on
the last 70 years, for an increase in the length of the growing season (Sharratt,
1992). Although considerably more land will be available for farming if temperatures
increase, moisture and nutrient problems will limit the productivity of these
areas (Mills, 1994). The more immediate effects are likely to be on plants such
as cotton grass that are important to caribou and reindeer populations (Kuropat,