Commercial Salmon Fisheries
Southeast Alaska & Yakutat Research: Chilkat River Chinook Salmon Research

 

Overview

The Chilkat River is a glacial system located near Haines, Alaska that drains into upper Lynn Canal in northern Southeast Alaska (Figure 1). Over the past 30 years this river has supported runs of Chinook (king) salmon averaging about 3,200 large fish (essentially 28" and greater in length). After leaving freshwater as smolt (approximately 2-3 inches in length and mostly 2 years in age), these fish primarily rear in or near Southeast Alaska. A relatively small terminal U.S. marine sport fishery targets this stock in Lynn Canal, and harvest also occurs in sport and commercial net and troll fisheries in northern Southeast Alaska. Data from research conducted on this stock are combined to estimate full parent (brood) year production, including details on harvest, exploitation rate, marine survival, and smolt abundance.

Abundance of large spawning Chinook salmon is estimated using a mark-recapture study that has been conducted annually since 1991 (Ericksen and McPherson 2004). Prior to 1991, aerial surveys were conducted in two clearwater (non-glacial) tributaries, Stonehouse Creek and Big Boulder Creek. Radio telemetry studies conducted in 1991 and 1992 found that spawning abundance in these two tributaries represented less than 5% of the total escapement, and thus did not represent Chilkat River drainage-wide abundance. Aerial surveys were consequently replaced with a more accurate mark-recapture study.

In 1981, a biological escapement goal was set at 2,000 large fish based on an assumed fraction of the total escapement represented by survey counts. Biological escapement goals are determined by the Alaska Department of Fish and Game (ADF&G) based on the number of salmon that need to escape to spawn to produce sustained yields into the future. Ericksen and McPherson (2004) recommended a revised biological escapement goal range of 1,750 to 3,500 large Chinook salmon based on information gathered from the mark-recapture studies along with limited juvenile tagging results. This goal range was reviewed and adopted by ADF&G in 2003, and subsequently reviewed and accepted by the Chinook Technical Committee of the Pacific Salmon Commission in 2004.

Information on this stock suggests that on average about 20% of the fish are harvested annually. This harvest rate has decreased to about 5% since 2018 due to management actions taken in response to low run sizes. The Chilkat River stock is reasonably healthy and since 1991 annual escapements have been above goal in most years; the management objective was missed in 2007, 2012-2014, 2016-2018, and 2022 (Figure 2). This stock, like most others in Alaska, has experienced a recent decline in productivity.

Adult Spawning Abundance

Mark-recapture studies in the Chilkat River drainage have been conducted by ADF&G every year since 1991. Abundance has ranged from 875 to 8,100 large fish and averaged 3,200 large fish from 1991 to 2023. During June and July, drift gillnets (and fish wheels prior to 2024) are used to capture returning adult Chilkat River Chinook salmon. Drift gillnets are operated consistently in a 3 km (2 mile) stretch of the lower Chilkat River, which also contained the location of two Chilkat River fish wheels prior to 2024 when that project ended. Once captured, the adult salmon are sampled for age, sex, and length information, and they are checked for the presence or absence of an adipose fin. Fish missing their adipose fin are additionally sampled for the presence of coded wire tags that would have been applied to fish during their juvenile life stage (see Juvenile Abundance below). Sampled fish are then tagged with an external spaghetti tag and given two secondary marks to mediate against tag loss (Figure 3).

From August through early September, returning adult Chinook salmon are captured farther upriver using tangle nets and dip nets, or sampled as carcasses where they are inspected for external tags or marks at three principal spawning areas on the Tahini and Kelsall rivers, and Big Boulder and Little Boulder creeks in the Klehini River. During this sampling, fish are again examined for age, sex, and length information, and for the presence of an adipose fin. To learn more about how ADF&G conducts this research, project operational plans that outline project methods, results, and data analyses are available online beginning with the most recent plan, which covers the 2022 Mark-Recapture Project (PDF).

Information gathered during the adult and juvenile work is combined to estimate the total number of Chinook salmon produced by each parent year. Return at age data are also closely analyzed to improve forecasting methods for the Chilkat River stock of Chinook salmon.

Juvenile Abundance

Studies to estimate the abundance of juvenile Chinook salmon in the Chilkat River drainage have been performed by ADF&G annually since 1999. Juvenile Chinook salmon from the same parent year are marked with adipose fin clips and tagged with coded wire tags during September and October, and again April and May as smolt before they emigrate to sea. Tagging in the fall and spring greatly increases the total number of tagged fish leaving the Chilkat River. On average, over 23,000 fall juveniles and 4,000 spring smolt have been tagged each year and smolt abundance has ranged from 60,000 to 290,000 since 1999 (Figure 4).

Freshwater survival (egg-to-smolt) can be estimated by assessing how many smolt are produced from each spawner. In most years freshwater survival has been close to average. The 2012 and 2013 parent years were the lowest in the time series, however, freshwater survival rates have since rebounded (Figure 5). Marine survival (smolt-to-adult) has ranged from 0.8% to 4.6% and averaged 2.5% for the time series, including parent years 1999 to 2017 (Figure 5).

Fall trapping areas include the Tahini, Kelsall, and Chilkat Rivers. Fall work begins in mid-September on the Tahini River, and trapping gradually moves downriver throughout October ending up in the Chilkat River mainstem. Spring work begins in early April and runs through early May, and trapping occurs exclusively in the mainstem.

Fall fingerlings and spring smolt are primarily captured using minnow traps baited with disinfected salmon eggs. After juveniles are captured, they are transported back to camp and anesthetized, marked, tagged, and held for 24 hours to assess retention of coded wire tags and ensure they are healthy prior to release (Figure 7).

Chilkat River Chinook salmon rear at sea from one to five years and information accumulates annually on these parent year releases as returning adults are sampled. The fraction of adult fish having adipose fin clips along with the total number of juveniles released with marks is used to estimate smolt abundance. In addition, the fraction of these fish possessing coded wire tags released in the Chilkat River is used to estimate adult harvests in the various marine sport and commercial fisheries. Data collected from coded wire tag recoveries, when combined with adult spawning abundance estimates, helps researchers estimate complete parent year production, including details on marine harvest, exploitation rate, smolt abundance, and marine survival of Chilkat River Chinook salmon. Sampling and collection of Chilkat River coded wire tags in the various Southeast Alaska marine fisheries facilitates management and are used as inseason predictors of run strength and harvest rates.

To learn more about how ADF&G conducts this research, project operational plans that outline project methods, results, and data analyses are available online beginning with the most recent plan, which covers the 2022 to 2023 field season (PDF).

Selected Publications