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    Vladimir Sovyak / The Mainstream

Low numbers of fall chinook: Regional ocean temperature in warm phase

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Numbers have not been impressive for fall chinook this year and chinook anglers are likely to have more frustrating runs to come.

Aiding salmon populations is no linear tasks.  Even programs designed to aid salmon can be harmful to salmon. “If not managed correctly, hatchery fish may detrimentally affect wild populations . . . we are seeing very few hatchery adult chinook at spawning grounds, which is what we want to see,” said Jason Brandt, Roseburg’s ODFW Assistant Biologist. The concern with hatchery fish in spawning grounds is that they can outcompete and alter the genetics of the wild salmon populations.

In addition, Brandt pointed to predation by smallmouth bass and cormorants as threats to young salmon. “We did remove the bag limit and size limit on smallmouth bass. Maybe anglers will be more likely to keep their bass and make some fish tacos,” said Brandt.

These more localized impediments to salmon spawning are overshadowed by the regional issue of ocean temperature. Changes in the Pacific Ocean’s surface temperature are highly influential over the ability of salmon to maintain or grow their populations. The Pacific Ocean’s surface is currently in a strong warmer phase since early 2014, according to the Northwest Fisheries Science Center’s web article “Pacific Decadal Oscillation.”

This climate index is abbreviated as PDO and its effects are becoming observable to the average salmon angler in Oregon. The article explains that Nathan Mantua, PhD., was the first to show the correlation between ocean temperature and numbers of returning salmon: “the cool PDO years of 1947–1976 coincided with high returns of chinook salmon and coho salmon to Oregon rivers. Conversely, during the warm PDO cycle that followed (1977–1998), salmon numbers declined steadily.”

Warm and cold phases have alternated far more frequently since 1998 compared to relatively slow phase changes in the latter half of the 20th century. “The cause of that is debatable,” said Brandt in regard to why warm and cold phases have become shorter. Due to this, returning salmon anglers are liable to see larger runs within years, not a decade or more.

The warm phases of the PDO are about as exciting as tax information to the average angler, and probably most dull among the problems living and future salmon face, but the PDO is highly reliable. The PDO shows yearly averages of slight variations in temperature. It is a climatic pattern that influences salmon populations not just in the Umpqua, not only just in Oregon, but the Northern Pacific and Pacific Northwest.