The sonar only counted 56,000, just over minimum escapement, but biologists think low water and abundance of sockeye hindered the sonar's king counting ability. Post-season aerial surveys found plenty of kings on spawning grounds in all tributaries.
This year the Nushagak king run struggled a bit, at least by the numbers tallied at the Portage Creek sonar site. The kings did make their escapement goal range, but the return was lower than Fish and Game was expecting. Now results from a post-season aerial survey have confirmed what biologists suspected during the season: the king return was probably quite a bit stronger than the sonar accounted for.
On July 12 the Nushagak king count finally eked past 55,000, the lower end of its escapement goal range. It had not been the return that anybody was expecting. But now Fish and Game now says the official escapement count only tells about half the story. Lee Borden is the assistant area management biologist for sport fish in Bristol Bay.
“We ended up putting past the sonar 56,000. Like you said, that number just barely passes our lower goal of 55,000," said Lee Borden, assistant area management biologist for Bristol Bay sport fish. "[But] we have reason to believe now that the run was closer to an average run than that number would indicate.”
In fact, the ADF&G biologists now estimate the 2017 escapement was well above the 55,000 goal, though the sonar count will not be adjusted. The new estimate is based largely on data collected from an extensive post-season aerial survey of all the Nushagak king salmon tributaries (more on that in a moment). To understand why the count was off, Borden points first to the sonar, which was designed to count sockeye, not kings.
"The reason it wasn’t intended to count kings is that kings run farther out in the river, and they run deeper. So if you get a lot of sockeye, they’ll be in closer to the sonar and they’ll block out some of the kings, so you’ll miss some of them on the sonar," he said.
This year the sonar problem was exacerbated by the second highest number of sockeye ever counted in the river, and also a water level that was the lowest many Nushagak veterans say they had ever seen.
"That leads to the water being potentially a little warmer than average," said Borden. "The kings are looking for cold water, so they’ll run a little deeper than they normally would. And having so many sockeye pushes the kings even farther. So you have those two factors working synergistically together [to complicate the count]."
Early on it was difficult to tell if the run was coming in late, or small, or both. But by June 23, the Department reduced the bag limit for sport fish caught Nushagak kings to one per day, two per season. Some sport fish operations complained that the commercial fishery should share the burden and sit out a few tides to let more kings get by.
Based purely on the escapement numbers, Borden says the Department could have put even more tougher restrictions in place to protect the run. But both he and manager Jason Dye suspected there were more kings in the river than the sonar was counting. Dye believed 2017 was shaping up similar to 1997, another very low water year when post-season surveys showed far more kings than were counted as escapement.
Other indicators suggested that was happening. The test fishing at the sonar site was picking up more kings in the nets than the sonar was counting, and the anglers started saying the season was actually going just fine.
"There were days when the sonar would report maybe several hundred fish, and we would have word from fishermen upriver that fishing on that day was good. Which leads us to believe there were more fish than the sonar counted," said Borden.
After the season, Borden was tasked with flying extensive surveys of the spawning grounds. He basically traced every Nushagak tributary by helicopter, carefully counting individual kings in the river and those that had already spawned and died.
"What we found was comparable to historical averages for the surveys. The spawners in the tributaries were about you’d expect for a normal year. If it was a really low year, we would’ve seen less fish in the tributaries.”
The official escapement count of 56,000 will stand, but the Department will note that the number of kings that actually made it upriver was much closer to previous years' average of roughly 90,000. Subsistence and sports fishermen all seemed pleased with the abundance of kings during the season, and the commercial fleet hauled in 32,000, a little more than average, all helping affirm the Nushagak as one of the healthiest king salmon rivers in Alaska.
dave@kdlg.org or 907.842.5281