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Let’s Jump Carefully to Conclusions from New King Salmon Genetic Data

June 24th, 2013

Over the winter, the Alaska Department of Fish and Game (ADFG) gave us our first glimpse of new genetic data on the stock composition of king salmon harvested in the Upper Cook Inlet (UCI) commercial fishery. Tremendous advances in genetic stock identification capabilities over the last decade and a progressive initiative by ADFG to employ these tools is revolutionizing our ability to manage mixed stock fisheries.

This analysis suggested that Kenai late-run kings accounted for a smaller proportion of the East Side Set Net (ESSN) harvest than previously thought.

  • Just 64-72 percent in 2010-2011 rather than the nearly 100 percent previously assumed.
  • Most of the rest were of Kasilof River origin.
  • The new numbers equate to a commercial harvest rate of only about 13 percent of the Kenai late-run kings on average (virtually all of it in the ESSN fishery).

Confronted with the prospect of another record low king return and an abundance of sockeye, commercial fishers are now asking whether restrictions for kings are even necessary given this new information. However, close inspection of the data shows the new numbers need to be weighed with an abundance of caution.

First, we have yet to hear a coherent explanation how the ESSN fishery is able to exploit 50 percent or more of the Kenai sockeye while taking only 13 percent of the kings which return with virtually the identical run timing. When the ESSN fishery is operating at full intensity, it harvests more than 90 percent of the sockeye moving along the beaches at that time judging by the corresponding drop in sonar counts. It is difficult to believe that this disparity is due to species selectivity of mesh size or big kings breaking through the mesh. While the big kings are less likely to be gilled in the sockeye mesh, kings are readily tangled by the mouth. Depth of travel might be a partial explanation but this possibility has been roundly panned by commercial fishery proponents. Exploitation rate analyses need to be validated with a comprehensive analysis of net species and size selectivity.

Estimates of commercial exploitation rates are also potentially confounded by the same questions with the model-based historical king run reconstruction that plague interpretations of the Didson sonar correction factor. Run size estimate that might be biased high in the complicated model analysis would cause commercial exploitation rates to be substantially underestimated.

It is also important to remember that commercial exploitation rates are minimum estimates based only on mortalities that are counted. Actual mortality would be greater by an unknown amount due to any unreported harvest and net drop-out. While sport catch and release mortality is estimated and accounted on the sport side, no estimate of commercial drop-out is made. The high incidences of net-marked fish in the river following commercial fishing periods suggest that significant drop-out mortality cannot be discounted.

Genetic data are available only for 2010 and 2011. It is unclear whether fishery patterns in these years are representative of fishing patterns in other years. Fishing was heavy in the Kasilof section in both years, particularly in the front of the season. Fishing of Kenai beaches in 2010 was limited early out of concern for a low Kenai sockeye forecast while strong early Kasilof sockeye counts led to substantial Emergency Order (EO) time. In 2011, Kenai sockeye were slow to show but the Kasilof was fished early and often.

It is also unclear how effectively the 2010 and 2011 fishery samples represented the actual commercial harvest in those years. The new genetic information is preliminary data from an internal memo that was attached to the late-run Kenai River king salmon assessment report. A complete report has not yet been published. We don’t know how fishery sampling and analyses were stratified relative to fishery times and areas. Nor were sample sizes reported by fishery time and area. A complete accounting of methods and discussion of assumptions is necessary to effectively qualify this new data for management application.

Even if new numbers are accurate, the commercial harvest share of Kenai late-run kings continues to be substantial. The average ESSN harvest share is nearly 40 percent but it has been as high as 72 percent (in 2012). This is despite a sport fishery priority for kings. A much smaller harvest share of commercial-priority sockeye in the personal use and sport fisheries has led to great consternation in the commercial fishery.

There is no discounting the fact that the ESSN fishery can have a disproportionate impact on the delivery of kings to the inriver fisheries during much of July and it is typically concentrated around two or three weeks when the peaks of the sockeye and king runs overlap. The Kenai River king sonar counts often drop precipitously in response to extended periods of commercial fishing.

Lastly, the new genetic data, if accurate, will have significant implications to the management of Kasilof kings. The current data suggests there are significant numbers of late-run Kasilof kings being harvested. Escapement of this stock is unmonitored, productivity is unknown, and no management plan exists for this stock. New numbers indicate it is high time to take another look at late-run Kasilof king status and management.

Genetic analysis tools promise tremendous utility in future management. It’s just conveniently premature to take a limited preview of preliminary data to the bank in order to justify unrestricted fisheries on a very poor king salmon return, particularly in light of well-documented problems and corresponding low credibility of historical king stock assessment efforts.

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