productivity of the Pacific Ocean, requiring adjustments in the food webs. It has
been predicted that under current emission rates of greenhouse gases temperature
increases would be large enough to shift the position of the thermal limits of
sockeye salmon (Oncorhynchus nerka) by 2050. Such a shift may exclude
sockeye salmon from the entire Pacific Ocean, and severely restrict the overall
area of the marine environment that would support growth. The impacts of such
changes on the dynamics of the entire North Pacific Ocean and on the
ecosystem’s ability to adapt to natural PDO cycles remain to be seen.
3 Anthropogenic Effects
Climate/Fish Cycles and Industrial Fisheries
As we have noted through the case studies presented, basin-scale environmental
conditions can vary substantially on decadal to multi-decadal timescales,
regardless of observed long-term warming trends. At the global scale we also
observed decadal cycles that may not be linked to global warming (Figure 2b).
Global temperature oscillations with a period of 65—70 years, mainly in the
Northern Hemisphere, have been observed. Supported by results from
600-yr-long simulations of atmosphere—ocean general circulation models it
has been concluded that this oscillation arises from internal variability of the
ocean—atmosphere system. Similar periodic oscillations have been observed in
other atmospheric indices such as the length of day (reflecting the rate of spin of
the Earth) and net air mass transport in the N/S and E/W directions (reflecting air
pressure differences).
Interestingly, multidecadal fluctuations in fish abundance have also been
observed for several centuries, both during the pre-industrial and industrial
periods. Figure 16 shows synchronized fluctuations in the catch trends
of 10 of the most important commercial fish species in the 20th century. The
author concluded that most sardine (anchovy) species increase in phase with
increases (decreases) in global temperature, suggesting that each species may
favour particular climatic conditions. The relevance of these observations to
global change research is that it suggests that fish fluctuations reflect changes in
the biological productivity of the ocean, which may be atmospherically steered. If
this is true then one should question the assumption of many global change
models that the ocean is in a biological steady state.
D. W. Welch, B. R. Ward, B. D. Smith and J. P. Eveson, Fish. Oceanogr., 2000, 9, 17—32.
M. E. Schlesinger and N. Ramankutty, Nature, 1994, 367, 723—726.
T. Delworth, S. Manabe and R. J. Stouffer, J. Clim., 1993, 6, 1993—2011.
L. B. Klyashtorin, Fish. Res., 1998, 37, 115—125.
T. R. Baumgartner, A. Soutar and V. Ferreira-Bartrina, CALCOFI Rep., 1992, 33, 24—40.
D. H. Cushing, in B. J. Rothschild (ed.), Toward a Theory on Biological Physical Interactions in the
World Ocean, Kluwer Academic Press, 1988, pp. 235—244.
R. A. Schwartzlose, J. Alheit, A. Bakun, T. R. Baumgartner, R. Cloete, R. J. M. Crawford, W. J.
Fletcher, Y. Green-Ruiz, E. Hagen, T. Kawasaki, D. Lluch-Belda, S. E. Lluch-Cota, A. D.
MacCall, Y. Matsuura, M. O. Nevarez-Martinez, R. H. Parrish, C. Roy, R. Serra, K. V. Shust,
M. N. Ward and J. Z. Zuzunaga, S. Afr. J. Mar Sci., 1999, 21, 289—347.
B. J. Rothschild, in Climate Change and Northern Fish Populations, Can. Sp. Publ. Fish. Aquat.
Sci., 1995, 121, 201—209.
M. Barange
76
been predicted that under current emission rates of greenhouse gases temperature
increases would be large enough to shift the position of the thermal limits of
sockeye salmon (Oncorhynchus nerka) by 2050. Such a shift may exclude
sockeye salmon from the entire Pacific Ocean, and severely restrict the overall
area of the marine environment that would support growth. The impacts of such
changes on the dynamics of the entire North Pacific Ocean and on the
ecosystem’s ability to adapt to natural PDO cycles remain to be seen.
3 Anthropogenic Effects
Climate/Fish Cycles and Industrial Fisheries
As we have noted through the case studies presented, basin-scale environmental
conditions can vary substantially on decadal to multi-decadal timescales,
regardless of observed long-term warming trends. At the global scale we also
observed decadal cycles that may not be linked to global warming (Figure 2b).
Global temperature oscillations with a period of 65—70 years, mainly in the
Northern Hemisphere, have been observed. Supported by results from
600-yr-long simulations of atmosphere—ocean general circulation models it
has been concluded that this oscillation arises from internal variability of the
ocean—atmosphere system. Similar periodic oscillations have been observed in
other atmospheric indices such as the length of day (reflecting the rate of spin of
the Earth) and net air mass transport in the N/S and E/W directions (reflecting air
pressure differences).
Interestingly, multidecadal fluctuations in fish abundance have also been
observed for several centuries, both during the pre-industrial and industrial
periods. Figure 16 shows synchronized fluctuations in the catch trends
of 10 of the most important commercial fish species in the 20th century. The
author concluded that most sardine (anchovy) species increase in phase with
increases (decreases) in global temperature, suggesting that each species may
favour particular climatic conditions. The relevance of these observations to
global change research is that it suggests that fish fluctuations reflect changes in
the biological productivity of the ocean, which may be atmospherically steered. If
this is true then one should question the assumption of many global change
models that the ocean is in a biological steady state.
D. W. Welch, B. R. Ward, B. D. Smith and J. P. Eveson, Fish. Oceanogr., 2000, 9, 17—32.
M. E. Schlesinger and N. Ramankutty, Nature, 1994, 367, 723—726.
T. Delworth, S. Manabe and R. J. Stouffer, J. Clim., 1993, 6, 1993—2011.
L. B. Klyashtorin, Fish. Res., 1998, 37, 115—125.
T. R. Baumgartner, A. Soutar and V. Ferreira-Bartrina, CALCOFI Rep., 1992, 33, 24—40.
D. H. Cushing, in B. J. Rothschild (ed.), Toward a Theory on Biological Physical Interactions in the
World Ocean, Kluwer Academic Press, 1988, pp. 235—244.
R. A. Schwartzlose, J. Alheit, A. Bakun, T. R. Baumgartner, R. Cloete, R. J. M. Crawford, W. J.
Fletcher, Y. Green-Ruiz, E. Hagen, T. Kawasaki, D. Lluch-Belda, S. E. Lluch-Cota, A. D.
MacCall, Y. Matsuura, M. O. Nevarez-Martinez, R. H. Parrish, C. Roy, R. Serra, K. V. Shust,
M. N. Ward and J. Z. Zuzunaga, S. Afr. J. Mar Sci., 1999, 21, 289—347.
B. J. Rothschild, in Climate Change and Northern Fish Populations, Can. Sp. Publ. Fish. Aquat.
Sci., 1995, 121, 201—209.
M. Barange
76