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Art and science of counting the Kenai River's precious king salmon

Jenny NeymanRedoubt Reporter
Stephen Nowers photo

New numbers are out, setting the goalposts to which the late run of Kenai River king salmon will be managed. Scientists with the Alaska Department of Fish and Game have released a draft interim escapement goal recommendation calling for 15,000 to 30,000 late-run kings to escape fishing nets and hooks to spawn in the Kenai. The goal is a decrease from the previous range of 17,800 to 37,500 kings.

The decrease doesn’t represent a change in philosophy or priority in what the goal is meant to achieve, said fishery scientist Steve Fleischman, who, along with Tim McKinley, authored the draft report. As with all salmon stocks in Alaska, late-run Kenai kings are managed to provide sustained yield, balancing conservation of the stock — getting enough fish upstream to spawn — and fishermen using the resource. The lower goal range represents a change in data, Fleischman said.

“What’s changed is we feel that we have much better information than we’ve had before,” he said.

New sonar fish counters

The other big change in this goal involves timing. Typically, escapement goals are re-evaluated every three years, but the timeline for the late-run Kenai king goal was sped up following last summer’s disastrous fishing season. Kenai king fishing was restricted, then closed altogether to sport anglers and personal-use dip-netters in July to protect a late run that at first appeared to be drastically low, then unusually late. Commercial set-net fisherman on the east side of Cook Inlet lost their season as they were shut down to prevent kings from getting snagged in the nets they use to target sockeye salmon.

In the ensuing uproar, Fish and Game committed to revising the recommended late-run escapement range ahead of schedule to come up with a goal based on the new sonar technology used to count Kenai kings heading upriver.

Fish and Game has been testing DIDSON sonar technology at its king sonar site at River Mile 9 for several years, growing increasingly confident in its accuracy over the older, split-beam sonar technology, which has been shown to confuse smaller kings with sockeye salmon. The department switched to using DIDSON sonar exclusively for counting Kenai kings this past summer. And while scientists reiterated their confidence in the improved accuracy of DIDSON counts, there was concern about the relevancy of comparing runs based on DIDSON data to counts using the old split-beam technology.

With this report, the department has an escapement goal derived from the DIDSON technology, factored in with the myriad other pieces of information and analyses used to come up with the goal. A newer goal range was needed, biologists said, because the old split-beam sonar method overestimated the number of kings as well as their recent determination that, even with DIDSON, some kings still are being missed.

The sonar site at River Mile 9 is close enough to the mouth that water levels are influenced by the tides. When the tide is in, higher water floods behind the sonar transducers and fish can pass undetected behind the sonar beams. But technicians can’t position the transducers closer to shore or else the equipment would be misaligned or sitting high and dry in lower water when the tide is out.

Moving sonar upriver

The 15,000 to 30,000 escapement goal takes into account the potential for uncounted kings passing behind the transducers at high tide.

“We first detected this in 2011.  This new information is one of the main reasons we are moving the sonar site upriver,” Fleischman said.

The department is working toward moving the sonar counter to a site at river mile 14, far enough upstream to be out of tidal influence. That move still is a year or two away, Fleischman said, but the department didn’t want to wait on setting a new escapement goal.

“Setting an escapement goal is not a one-time thing. It’s a process where we accumulate more and more information over time. We have different experiences, conditions change, we collect more data and we also develop new ways of analyzing the data. So as we improve our understanding of these stocks, we are also able to pick better goals,” he said.

“Given different circumstances, we would have waited for the 2014 Cook Inlet board meeting before we instituted a new goal, but given what’s happened in the last few years, we don’t want to sit on helpful information. So we’re proposing a goal using the best information that we have right now. It is far better than what we’ve had in the past because our assessment information has gotten so much better and because we have a better understanding of the history of the stock,” Fleischman said.

The report states high confidence in the new escapement range being able to produce a good yield from spawning kings.

“At the lower bound of the recommended range there is a high probability of achieving near optimal yields, with greater than 95 percent probability of achieving greater than 70 percent of (maximum sustained yield), greater than 90 percent probability of achieving greater than 80 percent of (maximum sustained yield), and greater than 70 percent probability of achieving greater than 90 percent of (maximum sustained yield) on average. At the upper bound of the recommended goal range these probabilities are reduced, but still relatively high.”

'Kenai not overharvested'

Setting the escapement range is a balance between giving fishermen harvest opportunity while protecting conservation of the stock.

“We’re always faced a trade-off — a lower goal carries some increased risk to the fish stock, in the sense that there is less of a buffer. A higher goal allows more fish to spawn but increases risk to the fishery because there may be more restrictions. This is true whenever we set an escapement goal, although the particulars vary from one stock to the next,” Fleischman said. “Happily, our analysis shows that the Kenai has not been over-harvested and the new goal reflects that. At the same time it provides better protection to the stock because our assessment technology allows us to detect small runs much more reliably.”

“This goal was hammered out at weekly meetings over the course of several months. We looked at the analyses several different ways,” he said.

The escapement goal range sets a target for which fishery managers can shoot, liberalizing or restricting fisheries in accordance with rules set by the Alaska Board of Fisheries. The nuts and bolts of how escapement is met through fishery management are hashed out through the board process. Currently, the Upper Cook Inlet Board of Fisheries Task Force, formed in the fall, is meeting throughout the winter and will bring recommendations to the Board of Fish this spring. The task force next meets Monday at the Challenger Learning Center of Alaska in Kenai.

How to manage fisheries to achieve the escapement goal range is beyond the purview of the scientists tasked with coming up with the goal recommendation. Fleischman and his colleagues’ part in the puzzle is to determine how many spawners are needed to create an optimum yield, in order to restart the salmon life cycle on an abundant note.

An abundant start to a brood, however, doesn’t necessarily mean there will be a robust return of kings when those fish are due to come back to spawn. Habitat conditions, food availability, predation and fishing pressure — both in river, in Cook Inlet and in the ocean — can turn what began as an optimal yield from spawners into a lousy return.

“How many fish can we expect back if we do use this new escapement goal? This is one of those things that you just can’t answer accurately because it involves predicting the future. However, we can say that the range of escapements in the goal would provide a near-optimal amount of yield,” Fleischman said.

The report states that the expectations of yield performance upon which the escapement goal is based are developed from stock dynamics of brood years 1979 to 2008. But the more recent brood years, 2004-08, showed about a 29 percent decline in productivity. If the lower-than-average conditions persist, it could result in a reduction in yield of nearly 50 percent from the 1979-2008 average conditions, the report states.

Fleischman said that it’s important to note that this is a draft report, still in the comment and revision process. The text is likely to change, though Fleischman said that the escapement goal numbers likely will not — at least not immediately.

If or when there is a change in the late-run Kenai king escapement goal resulting from new data, it will be an apples-to-apples update, rather than an oranges-to-apples reconfiguring, like this revision from a goal based on the old split-beam technology to the new one based on DIDSON sonar.

An 'evolving' goal

“Normally we wouldn’t be changing a goal out of cycle in the Board of Fish process. We’re also still in the process of transitioning to new assessment tools.  The new assessment will involve a sonar site up at Mile 14. And that won’t be complete for another year or two.

“This goal is an interim goal, in that sense. The analyses that we’ve done so far are the very best that we can do at this point. But as new information comes in and our understanding changes it may very well result in some change in the goal. This is not unusual — every escapement goal in the state is subject to review on a rotating three-year cycle,” Fleischman said.

He stressed that interim doesn’t mean inferior or ill-informed,  just means evolving.
“The bottom line is that the new goal will be a large improvement and we’re instituting it ‘out of cycle’ because it would be helpful to have it right now,” he said.

To view the draft interim escapement goal report, as well as other information for the Upper Cook Inlet Board of Fisheries Task Force here.

Jenny Neyman is editor of the , an online news site covering the Kenai Peninsula. Used with permission.