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Warming Pacific may mean poor salmon runs

6/13/2006

VANCOUVER, British Columbia — The Pacific Ocean off British Columbia's coast was warmer and drier than normal last year, leading to an increased number of exotic species such as tropical squid, and a reduced growth rate in salmon, according to a new study.

The seventh annual State of the Pacific Ocean report, which was compiled by more than 30 scientists from Canada's Department of Fisheries and Oceans, predicts poor salmon runs this summer and fall because of poor ocean conditions dating back three years.

The document holds out a glimmer of hope that the warm-water cycle — which is bad for salmon and herring — might be ending, although it is too early to tell.

"Warm oceanic waters appeared to be cooling to normal temperatures at the end of 2005, but it is unclear if this represents a break in the warm conditions that have persisted since 2003 or a temporary event," the document states.

Among the key findings are that the warm ocean temperatures led to a reduced upwelling of cold water that normally carries a rich supply of microscopic plants (phytoplankton) to the surface, where juvenile salmon feed.

There was also a delay in the spring bloom of plankton, which in cold-water years comes just as young salmon are emerging from spawning rivers, to start their juvenile period of growth in salt water. The result: salmon growth and survival rates were down.

"The biomass of zooplankton (food for many marine fishes) was below normal, and there were unusually high abundances of zooplankton species that normally occur off California; the typical cold-water copepods and euphausiids (krill) in B.C. were proportionally less abundant," the report states.

"The growth of juvenile coho salmon on the west coast of Vancouver Island during spring to fall was the lowest that has been measured since these observations began in 1998. Survival can be low in years of poor ocean growth."

The growth of juvenile coho in southeast Alaskan waters, by contrast, was twice the rate exhibited by salmon off the west coast of Vancouver Island.

While cold-water fish such as salmon had difficulties with the warm conditions, other species were moving in from the south.

Distributed by Scripps Howard News Service.