Chinook Salmon Research Initiative
Kuskokwim River Chinook Salmon

Kuskokwim River

Overview

The Kuskokwim River drainage near Bethel and McGrath, Alaska.
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The Kuskokwim River is the second largest river in Alaska, draining an area approximately 130,000 km2, (approximately 50,200 square miles) which represents 11% of the total area of Alaska. Adult Chinook salmon returning to the Kuskokwim River historically supported subsistence, commercial, and sport fisheries, in which annual harvests were 60,000 – 160,000 fish. The Chinook salmon subsistence fishery in the Kuskokwim Area is the largest in the state and remains a fundamental component of local culture (Brazil et al. 2011). The Kuskokwim River also had a lucrative commercial fishery for Chinook salmon through the early 1990s, but directed commercial fishing for Chinook salmon ended in 1987. Total harvest from subsistence, commercial, and sport fisheries has resulted in 25%-60% exploitation of the Kuskokwim River Chinook salmon stock in recent years. Recent declines in abundance have resulted in restriction to fishing opportunity and failure to meet escapement goals.

Current research conducted on Chinook salmon by State and Federal agencies, Native Organizations, and universities contributes to estimates of tributary escapement, total harvest, total return, age-sex-length composition, and an inseason index of run strength. Several projects have been developed that will provide estimates of total abundance and new insight into harvest patterns. The Chinook Salmon Research Initiative is funding five projects in the Kuskokwim River area, to be initiated in 2014, that will address adult abundance, local and traditional knowledge, subsistence harvest patterns, and inseason estimates of subsistence harvest.

Adult Spawning Abundance

Annual estimates of the total number of adult Chinook salmon that return to the Kuskokwim River are important for ensuring the population is managed in ways that promote long-term health and sustain existing fisheries. A time-series of abundance estimates, spanning several Chinook salmon generations, allows fisheries biologists to understand changes in productivity, which is an important first step to investigating the key drivers of Chinook salmon health. Abundance and productivity estimates are also used to establish escapement goals, forecast future run size, and evaluate the number of fish that can be harvested in a given year.

Estimating the total abundance of Chinook salmon that return to the Kuskokwim River each year is a very difficult task. Counting all the Chinook salmon is impractical because the system is very large and remote and the pattern of Chinook salmon migration into numerous large and small tributaries along the river is complex. Instead, total abundance must be estimated for an individual year by combining information from harvest and escapement monitoring projects in selected tributaries.

Efforts to estimate total inriver abundance of Kuskokwim River Chinook salmon was initiated by the Alaska Department of Fish and Game, Division of Sport fish in 2002, by conducting a large-scale mark–recapture study. The study was continued until 2007, with the last year of operations conducted by the Alaska Department of Fish and Game, Division of Commercial Fisheries. The purpose of those efforts was to estimate the annual number of Chinook salmon in the middle and upper portion of the river (i.e., upstream of kilometer 270 or river mile 168). Estimates were successfully completed for years 2003 to 2007.

The completion of the initial mark–recapture studies formed the foundation for a series of subsequent analyses that drastically improved our understanding of Kuskokwim River Chinook salmon productivity. First, Division of Commercial Fisheries was able to estimate total annual abundance of Kuskokwim River Chinook salmon for 2003 to 2007 by combining the mark–recapture estimates with estimates of harvest and escapement downriver. These five years of abundance information were used to scale a statistical model which provided estimates of total run size from 1976 to 2012. The time series of abundance estimates was used to evaluate the productivity of Kuskokwim River Chinook salmon and establish the current formal escapement goal for the entire river of 65,000 to 120,000 fish.

The Chinook Salmon Research Initiative has recommended that Kuskokwim River Chinook salmon run reconstruction model and productivity analyses be periodically recalibrated, particularly during years of low abundance. Towards that goal, the Division of Commercial Fisheries will partner with Kuskokwim Native Association to conduct a three-year mark–recapture study beginning in 2014. The planned mark–recapture project will be similar to the work completed from 2002 to 2007, and will estimate the number of fish returning to the middle and upper portions of the Kuskokwim River. Results will be combined with escapement estimates from the Lower Kuskokwim River tributaries and total harvest, to estimate the total run size for each year 2014 to 2016.

Lower Kuskokwim River tributaries contribute up to 30% of the total return of adult Chinook salmon; however, estimating escapement to this area remains difficult. Chinook Salmon Research Initiative scientists will directly investigate relative escapement, through multiple helicopter flights where individual returning adult Chinook salmon will be counted on the Kisaralik, Kwethluk, and Eek rivers. These are the three most significant spawning tributaries in the lower Kuskokwim River, based on current estimates.

Subsistence

Fish Camp

Local & Traditional Knowledge Study

The Alaska Department of Fish and Game, Subsistence Section will interview selected subsistence harvesters to collect local and traditional knowledge about Chinook salmon. Based on their observations and experience, interviewees will discuss biological and environmental factors important to the freshwater aspects of Chinook salmon migration, spawning, and larvae/juvenile survival. Areas associated with spawning grounds and rearing habitats will be mapped. Information gathered from these interviews will be compared to the results of research projects to estimate annual Chinook returns and to verify if appropriate rivers and streams are listed in the State of Alaska Anadromous Waters Catalog.

Fish Camp

Patterns and Trends in Subsistence Fishing

Information on the patterns and trends in subsistence salmon fishing will also be collected. The goal of this study is to identify variables associated with changing subsistence salmon harvests at the household level in six Kuskokwim River communities. The project will improve managers’ understanding of how Kuskokwim River subsistence fisheries are structured. A formal analysis of post-season household surveys from 1998-2012 will develop household harvest histories and explore patterns and trends in harvest levels. Next, interviews will be conducted in 50% of fishing households selected randomly within three of the study communities, aimed at identifying factors that influence year to year continuity and variation in harvests in the subsistence salmon fishery.

Inseason Estimates of Subsistence HarvestDrying Salmon Eggs

Inseason estimates of subsistence harvest of Chinook salmon in a reach of the lower Kuskokwim River in 2014 will be made to test the efficacy of the study as an estimator of total subsistence harvests. This work will be conducted with selected fishers from three communities who will record their harvests and fishing effort, and then report their data to the Alaska Department of Fish and Game twice a week. Using a weighted average of sample fishers’ harvests, an estimate of the total subsistence Chinook harvest will be developed. At the end of the season, these estimates will be compared with estimates based on post-season household harvest surveys.