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Sustained Yield: Which Numbers Matter Most?

Like your own health, the health of a fishery means monitoring vital statistics. Learn how Alaska manages the sustained yield of its salmon.

by | August 19, 2022

A CIAA fisheries technician tends to a weir at Chelatna Lake in the Susitna watershed. CIAA ran this weir for a number of years to assist with fisheries management. CIAA

Alaskans take sustainability very seriously. In fact, a concept called “sustained yield” is baked right into our Constitution: “​​Fish, forests, wildlife, grasslands, and all other replenishable resources (that) belong to the state shall be utilized, developed, and maintained on the sustained yield principle, subject to preferences among beneficial uses.”

This part of Article 8 gives the state powers to manage Alaska salmon fisheries, as well as other renewable resources.

To produce a sustained yield for Alaska’s salmon fisheries, state managers depend on field reports from weirs, as well as other sources of observation. These are the data points salmon fisheries managers follow closely:

1. Escapement

Throughout their lives at sea, salmon have to escape predators, disease, and scarce food — not to mention the nets and lines of eager Alaska fishermen. Fisheries managers count salmon, which make it past all these hazards and return to freshwater to spawn. This is a number called escapement.

Managers use escapement to set certain goals to meet the standards of sustained yield available to fishermen today and in the future. These escapement  goals include:

  • Biological escapement — This goal is set by ADF&G and based on science. It is based on factors that include productivity — how well salmon can spawn— and the accuracy of the method to estimate escapement. 
  • Optimum escapement — This goal considers the needs of Alaska’s various fisheries: commercial, cost recovery, personal use, sport, and subsistence. It is set by the state’s Board of Fisheries.
  • Sustainable escapement — This goal provides a historical estimate of performance based on five to ten years of data. This estimate can help managers make decisions when they don’t have catch estimates or other data.

When a stock in a specific area doesn’t meet escapement goals, the state classifies it as a stock of management concern. A stock  that repeatedly falls short can be classified as having a “chronic inability” to meet escapement goals.

2. Adult enumeration

ADF&G’s Kasilof River sonar site is one of its longest running sonar sites in Alaska. The sonar cannot identify fish by species so ADF&G uses a fish wheel to separate sonar-detected fish by species to help estimate the sockeye population. ADF&G

Alaska’s area management biologists have crews that collect in-season salmon passage data to manage the fisheries. The main piece of data they collect is the enumeration of adult salmon. Enumeration is the counting of fish. ADF&G and other groups including CIAA report counts from their weirs, which are fences that stretch across a stream or lake to make it easier to get an orderly count.

Weir workers use handheld tally counters and make a click for each new fish they see. In other places, fish counters watch for salmon from tall towers overlooking streams and rivers. On-the-ground weirs generally provide absolute numbers. 

ADF&G also estimates salmon runs from small airplanes and helicopters. They may send crews to count fish by walking alongside streams accessible on foot. These methods provide an indicator, not an absolute number.

Visual counts work well where water is relatively still and clear. In large rivers with silty or turbid water, ADF&G uses sonar count returning salmon. In the Cook Inlet area, the state has sonar sites on the Anchor, Kasilof, and Kenai rivers.

On the Kenai and Kasilof rivers, the sonar counts provide estimates for which ADF&G uses for brood tables. These tables track spawners and returns from those spawners. They form the key statistical foundation that allows ADF&G the ability to forecast returns year after year. 

It’s impossible to count every salmon that returns to their spawning grounds. Together, these enumeration methods provide the state with the best possible data to calculate escapement in season and set future goals.

3. Return projections

ADF&G fisheries managers make two types of projections: preseason and in-season. The preseason projections are helpful to all users for planning the upcoming season, from seafood processors to sport fishing guides. Preseason projections are based upon different methods, some being fairly simple and others more complex depending upon the salmon stock. For example, fishery biologists review historical escapement and total return to build brood tables for Upper Cook Inlet’s major sockeye streams: the Kenai and Kasilof rivers.  

Forecasting returns of a stock are related to various life history abundances such as: sibling relationships from previous years, fry, and smolt abundance information. Researchers use life history abundance values to model and forecast the returns.

Fisheries managers then use in-season forecasting during the fishing season to monitor catch and escapement. They collect information from different sources including commercial fish tickets, number of boats fishing, catch per unit effort, adult enumerations, and test fishing.

This allows ADF&G to adjust harvest opportunity in season. If the number of fish returning is higher than projected, ADF&G may open up more harvest opportunity. If the number of fish returning is lower than projected, ADF&G may limit harvest opportunity until the run meets escapement goals.

Different users groups, such as Upper Cook Inlet commercial fishermen, participate in the harvest. Lisa Ka’aihue, CIAA

4. Harvest

The harvestable surplus means the number of salmon from a stock’s annual run that is more than escapement needs. Managers can can reasonably make this surplus available for harvest. This is where ADF&G takes a backseat, and the Board of Fisheries steps in.

The board’s main function is to set aside harvests for the various user groups including subsistence, commercial, sport, and personal use. The board uses biological and socioeconomic information provided by ADF&G and also public comment when considering fisheries regulations across the state. ADF&G manages the fishery to meet the Board of Fisheries’ allocation plans.

See How It Works

Alaska salmon fisheries management is complex with the goal of sustaining Alaska’s abundant salmon resources. We invite you to learn more from the Alaska Department of Fish and Game.

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