The Alaska Department of Fish and Game has stopped reporting the number of Kenai River red salmon going past its sonar counter 19 miles upriver from the mouth. The reason? Tens of thousands of pink salmon, also known as humpies, have flooded the river, making it difficult for biologists to differentiate between the two species.
During even years, many Southcentral Alaska rivers and streams see a surge of the less-desirable pink salmon. The DIDSON sonar is used by the Commercial Fisheries Division of Fish and Game to manage the harvest of more than 2 million red salmon that make their way back to Cook Inlet each year. But during the last few weeks, biologists have become concerned that the flood of pinks has skewed their red salmon numbers.
The sonar counter registers each fish that passes in front of its electronic sensors. But it does not differentiate between types of salmon. For that, Fish and Game biologists set up two fish wheels – large, windmill-like devices powered by the current that scoop fish from the river's edge. The fish wheels, placed on both sides of the river near the sonar counter, are checked regularly and the fish inside categorized and counted.
It is the ratio of different salmon species that biologists use to come up with the day's count of red salmon. (If 200 pinks and 200 reds are caught in the fish wheels in a day, it would indicate that only half the total number of fish counted by the sonar that day were red salmon.) But with the surge of pink salmon, biologists began to believe their fish wheel calculations were showing too many red salmon. On Aug. 4, the last day Fish and Game reported red salmon numbers, the sonar had counted 1.1 million fish, but that number could be changed after the season ends.
"The apportion count, based on fish wheel alone, gave us cause for concern because it would indicate that there were a lot of sockeye salmon swimming up the river and other indicators from the commercial catches indicated problems with that count," said Pat Shields, the department's commercial fisheries manager for the Kenai Peninsula.
Shields said his department has installed gillnets on each side of the river and has even experimented with using dipnets to get a more accurate picture of how many salmon -- and what type -- are swimming up the Kenai. But Shields said the final data won't be crunched until the season is over.
"We thought it was prudent to, rather than release information that may get changed or go through a revision, that it would just be better to stop releasing the in-river information," Shields said.
Many sport fishermen use the daily counts from Fish and Game to determine where and how to fish for the prized sockeye salmon. But Shields noted the sonar will be pulled from the river soon. Each August, when biologists record three consecutive days with less than 1 percent of the total number of fish passing the sonar, they remove it. According to Shields, that happened on the nearby Kasilof River on Thursday. Crews pulled the sonar counter from the Kasilof on Friday.
Shields said this is the first time he can remember Fish and Game deciding to keep collecting, but stop publicly reporting, fish count numbers on the Kenai River. Nevertheless, the information remains important. More important, though, Shields said, is getting the numbers right.
"It (the sonar count) helps determine escapement goals, and all kinds of management decisions can be made on them." Shields said.