Fish Numbers May Reflect Down Turn in Ocean Productivity
December 16, 2005
Columbia Basin Bulletin |
|
The
federal agency charged with guarding the health of Columbia River basin
salmon and steelhead populations this week noted 2005s returns have been
relatively strong despite what appears to be reduced ocean productivity to
nourish those fishes to maturity. "Certainly
we didn't expect to see the remarkable, record-breaking numbers of a few
years ago, when highly favorable ocean conditions helped boost
returns," said Bob Lohn, head of the NOAA Fisheries Northwest
regional office in Seattle. "But these numbers are quite
respectable" With the
year nearly ended and fish numbers low, fish counts at Bonneville Dam will
be moderately above average for adult salmon returns in the Columbia Basin
in 2005, with a total of just over 569,000 chinook and 315,000 steelhead
passing the dam by early December. Coho
returns (83,000) are also above average and sockeye returns (73,000) even
stronger, according to a NOAA press release issued this week. The numbers
reported by NOAA were compiled by the U.S. Army Corps of Engineers, which
operates the dam. The
ten-year average for chinook is about 528,000, for steelhead 312,000, coho
81,000 and sockeye 54,000. Summer and fall chinook adult returns were
above average, bringing the total count for the year higher. In a typical
year, about 80 percent of all returning adults are of hatchery origin.
Twelve Columbia Basin salmon and steelhead stocks are listed under the
Endangered Species Act. The lone
species to come in below its 10-year average was the upriver spring
chinook. The run befuddled forecasters by numbering only 74,038 -- about
half the 10-year average for 1995-2004 of 145,297. The
upriver spring chinook salmon return was well below a preseason forecast
that 254,100 adults would return to the mouth of the Those
managers, and NOAA, have suggested that changing ocean conditions are
chief among the factors that affected the upriver spring chinook return
this year and could be a cause of recent years' downward trend for many of
the basin's salmon and steelhead stocks. Government
biologists said that the 2005 numbers -- strong when compared to the
average but down from returns of the earliest 2000s -- reflect
improvements to salmon habitat and to hydropower dams on the Columbia and
Snake rivers on the one hand, and slowly declining ocean conditions on the
other, according to the NOAA press release. "While
it is clear that some sources of mortality have increased relative to
recent years, the available data suggests that no single source (i.e.
Canadian fisheries or sea lions) can be blamed alone," according to a
Nov. 14 preliminary report by TAC that explores possible causes for the
large disparity between the forecast and actual return. The report
explores the potential causes of mortality, as well as the possibility
that flaws in its forecasting methods might have resulted in a
miscalculation. Forecasts
are just that -- based on modeling of fish numbers from current and
previous years -- so are prone to some error. From 1997-2004, the average
forecast error was 32 percent for upriver spring chinook -- sometimes
over-predicting and sometimes under-predicting. But there are few if any
misjudgments on the books as great the 2005 upriver spring chinook
forecast. The report notes that most returns for other spring chinook
stocks were less than predicted. "Because
so many different forecasts in the Columbia River basin were over
forecasts in 2005, it appears that the likely cause of the 2005 return
being so much less than anticipated is not entirely due to forecast
imprecision," the TAC report says. "TAC
believes that the most important factor may be an adverse change in marine
conditions that reduced survival and which likely increased the level of
inherent uncertainty in our ability to forecast the return," the
report says. "The
2005 run points to the desirability to work toward a better understanding
of spring chinook survival in the ocean, but given our limited knowledge
of where spring chinook are at various times in their ocean migration,
this will be difficult problem to address," the report says. The
evidence of changed ocean conditions exists, even though no direct link to
Columbia Basin stocks as been established. "There
were changes noted in the ocean environment in late 2004 and early 2005
such as lack of upwelling and temperatures that are typically associated
with El Nino conditions even though there was not an El Nino at the time.
These changes support theory but do not prove that there could have been
some change in the ocean environment that affected the survival of spring
Chinook," according to the TAC report. The upwelling brings colder
nutrient rich water to the surface which stimulates primary production and
provides food throughout the food web. NOAA
Fisheries earlier tried to unravel the mystery as well, asking its
Northwest Fisheries Science Center scientists to examine variables that
could have caused the lower than expected returns. A May 26 memo from the
Center's director, Usha Varanasi to NOAA Fisheries regional chief, Bob
Lohn, concludes that no single variable is responsible. The memo
noted that "condition in the coastal ocean environment were less
favorable for salmon in 2003 than in recent years." Most of 2005's
returning adults migrating to the ocean in 2003 as yearlings and spend
early times feeding along the coast. Mortality is believed greatest in
that first year in the ocean. A prolonged though weak El Nino persisted in
2003, and that same year a switch began to a Pacific Decadal Oscillation
Index ocean condition reading that is less favorable to salmon. Both the
number of outmigrants and their survival out of the Columbia and its
hydrosystem was good in 2003 and in 2002 when a portion of 2005's
returning adults went to sea. The NOAA
memo also said that a favored salmon foodstuff, northern copepod, were
less numerous in 2003 and piscine predator abundance off the mouth of the
Columbia was up. "These
collectively point to a coastal marine environment for juvenile salmon
that was less favorable than the previous four to five years
(1998-2002)," the memo says. The NOAA
memo also said that, of the five ocean-climate indices it charts that seem
to affect adult salmon, "beginning in 2002, we observed a switch in
three of the indicators toward a negative direction for salmon…."
Those indicators had all been favorable since 1998-1999 and have received
come credit, along with freshwater improvements, for surging salmon
returns during the early 2000s. That surge
has been stemmed to some degree. Following a peak upriver spring chinook
count of 391,367 in 2001, succeeding years' Bonneville counts have
declined to 268,813 to 192,010 to 170,152 and then to 74,038 this year.
Still, TAC notes the 2005 return is the eighth largest since 1980. The latest
TAC forecast is not rosy, however. The 2006 preseason forecast for upriver
spring chinook is pegged at 88,400. The forecast released this week for an
adult return of 49,000 summer chinook to the mouth of the Columbia,
compared to this year's actual adult return of 60,000. TAC's 2005
preseason forecast for summer chinook was 62,400. The 2006
sockeye forecast is 31,100, including 21 endangered Snake River sockeye.
In 2005 TAC predicted a sockeye return of 70,700 and 77,200 return,
including 20 The fall
chinook salmon return to the mouth of the The fall
chinook adult return was 548,900 in 2001 and 733,300 in 2002. The returns
swelled to 893,100 in 2003 and 799,000 in 2004, then dropped off to
561,200 this year, coming in below the preseason forecast of 671,400. Because
ocean conditions are so influential on the rate of adult returns, yet are
essentially beyond human control, government biologists say that the
timing of the arrival of juveniles in the seawater environment may be
crucial, according to NOAA's presss release. A survival advantage is
likely to accrue to young fish that arrive at the mouth of the Columbia
when they are sufficiently mature to adapt to seawater, are big enough to
avoid being eaten and conditions in the river mouth and ocean are optimal
for feeding. Scientists
say they are trying to learn more about this timing and how to take
advantage of it to increase adult returns by adjusting the arrival time of
juveniles in the estuary so that it is not too early and not too late. For more information, visit NOAA Fisheries Service at http://www.nmfs.noaa.gov/
|