The Alaska Department of Fish and Game (ADFG) is responsible for managing Alaska’s fish and wildlife resources. Each year, using computer models based on harvest and field data, the department is able to forecast the run strength so that regulations and management practices will allow for the maximum sustainable yield of the resource. That is, we try to figure out how many fish will be returning to our rivers so we can then decide how many we can harvest while not jeopardizing the productivity of future runs and thus maintain the sustainability of the resource.
In 2015, ADFG forecasted a record run of sockeye returning to Cook Inlet in 2016, but the run ended being significantly short of the prediction. While there is some evidence in a recent study that some of the fish bound for the Kenai were intercepted by purse seiners off of Kodiak, we also need be conscious of the fact that these predictions are based on inherently imperfect models. As one famous statistician once said, “all models are wrong, but some are useful.” Therefore we should take these predictions with a grain of salt.
For the 2017 season, ADFG is predicting 2.2 million sockeye to return to Cook Inlet bound specifically for the Kenai River. This forecast for the Kenai is about a million short of the 20 year average. Data incorporated into the model comes from sockeye salmon fry rearing in Kenai and Skilak lakes. In short, ADFG estimates that there were 9.5 million fry that headed out to the ocean in the years 2013 and 2014, so in theory these fish will be headed back to the Kenai this summer. While this might seem like a lot of “baby sockeye,” 17 million fry would be considered a good year.
So why is there such a difference in the number of fry between years? The answer deals with the concept of escapement, the number of adult sockeye that make it back into the river and successfully spawn. Its logical to assume that with the more fish that spawn, the more fish we would see into the future, but its not quite that simple. Sockeye Salmon spawn in a specific size gravel, and the fry that hatch then live in the lake for 1-2 years. Because spawning habitat has spatial limitations (ie fixed area), there is not always enough room for all the fish that enter the river to spawn. In addition, the carrying capacity within the lake systems is also limited. So when it comes to allowing fish into the river to spawn in hope of producing more fish, there is a law of diminishing returns. This is why ADFG sets escapement goals–the sweet spot where we would see a maximum return given the number of spawners. If below the escapement goal, we would see vacancies in the spawning areas, and over escapement would produce crowding of spawning habitat and a lack of food for those fry in the lake. This is why in ADFG would like to see 900,000 to 1.1 million sockeye return to their spawning beds. Anymore than 1.1 would be considered over escapement and anything under 900,000 would be considered under escapement.
While the 2017 Cook Inlet sockeye forecast might be below the 20 year average, don’t write off your trip to Alaska quite yet. The prediction will call for more conservative commercial fishing management until the run is realized. This will limit the time commercial guys are allowed to fish and will likely bode well for our King salmon. And let us not forget that sport fisherman such as ourselves fish the river for sockeye not the inlet. Given the escapement goal put forth, we are almost guaranteed to see at least 900,000 fish pass the lodge during the 2017 season–another reason to not get worked up over this smaller than usual forecast.
2017 Upper Cook Inlet Sockeye Forecast
|Major Age Classes||Total||Escapement|
|Kenai River||Forecast||345||1,299||161||322||2,164||900 – 1,100b|
|Kasilof River||Forecast||282||231||203||81||825||160 – 340|
|Susitna River||Forecast||75||194||12||44||366||See Belowc|
|Fish Creek||Forecast||48||17||1||1||75||See Belowd|