(Figure 1 updated through 2000; addendum added 2003)
There is increasing evidence that salmon populations
in the northeast Pacific are significantly influenced by long-term
climate changes. In the Northwest, temperature and precipitation
data go back about 100 years. During that time there have been
four relatively distinct climatic periods. These are illustrated
in Figure 1, which shows annual precipitation
(departures from the long-term average) for the Oregon Coast.
All stations west of the crest of the Coast Range were averaged
together to get a single value each year, and every year's value
compared with the long-term average. The Water Year (October through
September) was used so that all months from a single winter remained
in the same data set.
The four climatic periods were:
1896-1914 Generally wet (and cool)
1915-1946 Generally dry (and warm)
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1947-1975 Generally wet (and cool)
1976-1994 Generally dry (and warm)
Note that in any given period, not all the years are dry or wet, but that a high percentage follows that pattern. For example, in the 1915-1946 period there were 22 dry years and only 10 wet ones. Consecutive dry years were common (indicating drought periods). The wet period immediately following had 21 wet years versus 7 dry ones, and consecutive dry years never occurred. Droughts were nonexistent during the latter period, although there were several major floods.
Recently, scientists have found that salmon returns
in the Northwest show long-term behavior which closely follows
the climate cycles. Figure 2 was
reproduced from a testimony before the U.S. House of Representatives
by Anderson (1995), who used the "Pacific Northwest Index"
(PNI) to distinguish cool, wet periods from warm, dry ones; note
the similarity of PNI to the graph in Figure 1. Anderson then
compared PNI with Columbia River spring chinook salmon return
going back to 1940 (earlier data are not available). The correlation
between spring chinook and PNI is very strong, as indicates that
salmon return increase during cool, wet periods and decline during
warm, dry ones. While there are undoubtedly human-induced effects
on the fish (including dam construction and habitat destruction),
Figure 2 indicates that natural variability may be a very significant
influence as well, and should be considered in any salmon restoration
plan (such as the Oregon plan currently being implemented).
While stocks in the Northwest have shown low numbers
in recent decades, Alaska salmon have had a tremendous boom period.
Climatologists have known for many years that weather patterns
in Alaska and the Northwest are out-of-phase: wet periods in the
Northwest tend to be dry in Alaska, and vice-versa. The El Nino-Southern
Oscillation appears to be the major reason for this flip-flop.
Interestingly (and perhaps not surprisingly), salmon returns in
the Northwest and Alaska are similarly out of phase. In Figure
3, also from Anderson (1995), the bottom chart shows that
chinook returns in the Rogue and Columbia/Snake behave similarly
over time. The upper figure, however, shows that Columbia and
Alaska salmon are out of phase, with the abundant 1950-1975 period
in the Northwest corresponding with a very poor salmon period
in Alaska. When Northwest stocks declined in the 1970's, Alaska's
were soaring.
An excellent article by Mantua et al (1996) presents a very thorough overview of the Alaska/PNW differences. It is fascinating to see how trends change, and how Alaskan and Northwest fish fortunes have continually been out of phase. The authors quote various issues of Pacific Fisherman:
September 1915 (Pacific Fisherman 1915); wet in Northwest
"Never before have the Bristol Bay [Alaska] salmon packers returned to port after the season's operations so early."
"The spring [chinook salmon] fishing season on the Columbia River [Washington and Oregon] closed at noon on August 25, and proved to be one of the best for some years."
1939 Yearbook (Pacific Fisherman 1939); dry in Northwest
"The Bristol Bay [Alaska] Red [sockeye salmon] run was regarded as the greatest in history."
"The [May, June and July chinook] catch this year is one of the lowest in the history of the Columbia [Washington and Oregon]."
August/September 1972 (Pacific Fisherman 1972); wet in Northwest
"Bristol Bay [Alaska] salmon run a disaster."
"Gillnetters in the Lower Columbia [Washington and Oregon] received an unexpected bonus when the largest run of spring chinook since counting began in 1938 entered the river."
1995 Yearbook (Pacific Fishing 1995); dry in Northwest
"Alaska set a new record for its salmon harvest in 1994, breaking the record set the year before."
"Columbia [Washington and Oregon] spring chinook fishery shut down; west coast troll coho fishing banned."
There are indications that global ocean and atmosphere
conditions are the cause of the long-term climate variations shown
in Figure 1. There is also evidence that a switch in regimes occurred
in late 1994, and that we have returned to the conditions which
tend to yield wet, cool winters in the Northwest (see Conveyor
Belt article). If so, it would appear that environmental conditions
may be very favorable for a resurgence of Northwest salmon stocks
(and unfavorable in Alaska). While I do not disagree with the
emphasis in the Oregon Salmon Plan on restoring salmon habitat,
it appears clear that natural variations play an important role
in fish survival and reproduction, and that these variations should
be considered in drafting the Plan.
Recent evidence suggests that a rebound may already
be occurring. On April 28, 1997, Oregon Department of Fish &
Wildlife issued a statement that the number of chinook salmon
redds in the Upper John Day River last summer were the second
highest since 1959. Jim Myron of Oregon Trout said "It's
good news for everybody concerned, whether it's rancher, environmentalist
or state employee - and it's especially good news for the fish."
Maybe there IS a silver lining in all those gray rain clouds!
The last several years have seen tremendous increases in salmon returning to rivers in the Northwest. Most scientists acknowledge that changing ocean conditions are responsible. Figure 4 shows spring chinook salmon at Bonneville Dam from 1938-1998, quite similar to Anderson's figures. Following the 1997-98 El Niño event, salmon returns soared. Figure 5 shows the same Bonneville Dam counts, but updated through 2002. Early reports suggest that 2003 is another big year for Pacific Northwest salmon.
Anderson, J.J. 1995. Decline and Recovery of Snake River Salmon. Information based on the CRiSP research project. Testimony before the U.S. House of Representatitives Subcommittee on Power and Water, June 3.
Beamish, R. J. 1993. Climate and exceptional fish production off the west coast of North America. Canadian Journal of Fisheries and Aquatic Sciences. 50:2270-2291.
Beamish, R. J. and D. R. Bouillon. 1993. Pacific salmon production trends in relation to climate. Canadian Journal of Fisheries and Aquatic Sciences 50:1002-1016.
Bumgartner, T. R., A. Soutar and V.Ferreira-Bartrina. 1992. Reconstruction of the history of Pacific sardine and northern anchovy populations over the past two millennia from sediments of the Santa Barbara Basin, California. CalCOFI Report 33:24-40.
Ebbesmeyer, C. C., D. R. Cayan, D. R. McLain, F. H. Nichols, D. H. Peterson and K. T. Redmond. 1991. 1976 step in the Pacific climate: forty environmental changes between 1968-1975 and 1977-1984. Pages 120-141 in J.L. Betancourt and V.L. Sharp, editors. Proceedings Seventh Annual Pacific climate (PACLIM) Workshop, April 1990. California Dept. of Water Resources. Interagency Ecological Studies Program Technical Report 26.
Ebbesmeyer, C.C. and R.M. Strickland. 1995. Oyster Condition and Climate: Evidence from Willapa Bay. Publication WSG-MR 95-02, Washington Sea Grant Program, University of Washington, Seattle, WA. 11p.
Francis, R.C. 1993. Climate change and salmon production in the North Pacific Ocean. Pages 33-43 in K.T. Redmond and V.J. Tharp, editors. Proceedings of the Ninth Annual Pacific Climate (PACLIM) Workshop, April 21-24, 1992. California Dept. of Water Resources. Interagency Ecological Study Program Technical Report 34. Francis, R.C. and S. R. Hare. 1994. Decadal-scale regime shifts in the large marine ecosystems of the Northeast Pacific: a case for historical science. Fisheries Oceanography 3(4):279-291.
Pearcy, W.G. 1992. Ocean Ecology of North Pacific Salmon. University of Washington Press, Seattle. 179 p.
Ware, D. M. and R. E. Thompson. 1991. Link between long-term variability in upwelling and fish production in the northeast Pacific Ocean. Canadian Journal of Fisheries Aquatic Sciences. 48(12):2296-2306.
Ware, D. M. 1995. A century and a half of change in the climate of the NE Pacific. Fisheries Oceanography. 4(4):267-277.
