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Optimizing Fishery Values

March 29th, 2016

Cook Inlet salmon fisheries are complex. King, sockeye, and silver salmon all return to multiple watersheds, swimming through gillnets, dipnets and hooks, seeking to return to natal streams to spawn. All that effort yields important economic, social, cultural and recreational gains, and the next generation of returning salmon if all goes according to plan.

The plan hopefully optimizes the values generated from these various salmon fisheries. Combined, the salmon fisheries in Cook Inlet support a $1 billion economic engine. And the Kenai River is central to all this activity, home to both the largest sport and personal use salmon fisheries in Alaska and the largest commercial salmon fishery in the Inlet.

The current statewide king salmon crisis has not spared Cook Inlet salmon fisheries. As evidenced by the 2012 Cook Inlet King Salmon Emergency Disaster Declaration, it has been difficult for users, creating tension and hardship for many. With every crisis, though, there is also opportunity to look at things anew – to reevaluate if there is a better way to do things.

Research on salmon in Cook Inlet hints that there may indeed be a better way to manage our fisheries, with a win-win for all user groups and the salmon. Fishery research published by Dr. David Welch, Migration behavior of maturing sockeye and Chinook salmon in Cook Inlet, Alaska, and implications for management, provides important clues to fish behavior in Cook Inlet.

The research showed clear differences in the median depth of marine migration of Chinook (15.75 feet) and sockeye (5.9 feet) in Cook Inlet. Is it possible to take advantage of the fact that Chinook in Cook Inlet tend to migrate at deeper depths in the marine waters than sockeye? Could set gillnets, now severely limited because of Chinook bycatch, be configured in a new manner to allow them to fish more often in the lucrative sockeye commercial salmon fishery while minimizing intercepts of migrating Chinook to the rivers for escapement and the lucrative in-river sport fisheries?

A follow up study last summer by Welch on how various sized set gillnets behave through the extreme tide cycles of Cook Inlet sheds further light on an opportunity to craft new strategies for a win-win solution. He teamed up with east side set netters to study the behavior of various lengths of set gillnets: 45 mesh, 36 mesh, and 29 mesh gear. The nets were instrumented with depth receivers at the lead line, ¼ net, ½ net and ¾ net; the results can be seen in an animation here.

The animated results show that for 75 percent of the time, all nets, regardless of mesh depth, hung at 6 feet or less in depth, primarily in the sockeye rich zone. During the strongest parts of the tide cycle, the lead lines for all gear were often at depths of two to three feet, just under the surface of the water, stretched flat like a piece of paper.

The various sized nets only fell to deeper depths during slack water; 45 mesh gear, in slack water, hung about 17 feet; 36 mesh hung about 14 feet; and 29 mesh gear hung about 11 feet. 29 mesh was the only gear that did not hang at or below the median depth for Chinook (15 feet) anytime during the tide cycle. This research corroborates the anecdotal evidence of those set netters who have voluntary switched from 45 mesh to 29 mesh gear, who say that the shallower gear still allows for good harvests of sockeye while reducing the number of Chinook in their nets.

Two areas of further research are indicated:

1) Would gear designed to fish more perpendicular in the top six feet of the water column (such as 15 mesh gear with a heavier lead line) be even more efficient in targeting sockeye while minimizing harvest of Chinook?

2) What is the drop out mortality on larger size (greater than 30 inches) Chinook salmon associated with various mesh size set gillnets?

In the past decade, fishing primarily with 45 mesh gear, the east side set net fishery has been the largest harvester of Chinook salmon heading back to the Kenai and Kasilof Rivers. Due to this harvest capacity, set netters on the east side of Cook Inlet have sat on the beach more often than not during these times of historic low returns of Chinook. Research indicates that set nets fishing no deeper than seven feet will access 2/3 of available sockeye and reduce Chinook harvest by more than 75 percent.

Maybe there is a way to build a better mousetrap, one that profits set netters, in-river sport anglers and salmon escapements, so that fishery values are optimized to the benefit of all.

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