Commercial Salmon Fisheries
Southeast Alaska & Yakutat Research: Chilkat Lake Salmon Research

 

Introduction

Chilkat Lake is one of the most productive sockeye salmon systems in Southeast Alaska and also supports a large run of coho salmon. Chilkat Lake sockeye salmon have been an important contributor to northern Southeast Alaska commercial fisheries for over a century and an important subsistence resource for Alaska Natives. ADF&G has monitored adult salmon escapements at the outlet of Chilkat Lake since 1967, and since 2008 escapement has been estimated with a sonar in tandem with a picket weir. The current biological escapement goal is 70,000–150,000 sockeye salmon and was established in 2009. In addition to salmon counts, biological data have been collected annually at the weir to estimate age, size, and sex composition of sockeye salmon escapements. Basic information about lake productivity has also been collected through limnological sampling to assess potential sockeye salmon production from the lake.

Location

Chilkat Lake is located 30 kilometers northwest of the city of Haines, Alaska (Figures 1 and 2). It is a clear lake approximately 9 kilometers long with a maximum depth of 57 meters. The lake outlet, Clear Creek or Clear Water Slough, flows 0.5 kilometers to the Tsirku River, which then flows for approximately 5 kilometers to meet the Chilkat River. Periodic flow reversals occur when the flow from the Tsirku River overpowers the slough's output. In these events, the Tsirku's glacial waters travel up the slough and into the northern section of Chilkat Lake (Figure 3), and the slough and lake waters become turbid with glacial silt and experience dramatic drops in temperature.

The field camp at the Chilkat Lake weir consists of a main cabin with a kitchen and office, three wall tents, and a tool shed (Figure 4). The three crew members move out to camp in early June to install its many systems and structures and work through mid-October. Generally, a two-person team is on site to keep the project functioning which allows for a rotating schedule with days off. The crew's dedication is the foundation of successfully monitoring Chilkat Lake sockeye salmon, which in turn helps influence management of the District 15 commercial drift gillnet, subsistence, and sport fisheries.

Adult salmon escapement

Since 1967, the main tool for counting adult sockeye salmon returning to Chilkat Lake has been a picket weir, though various other methods have been used in tandem. These included visual weir counts, mark-recapture estimates, and Dual-Frequency Identification Sonar (DIDSON) counts through the weir. The weir is installed to capture the duration of the sockeye salmon run and acts as an indicator for coho salmon run strength. Historically, sockeye salmon returns to Chilkat Lake have averaged 88,234 salmon (range: 23,947–212,757). Sockeye salmon have exceeded the lower bound of the escapement goal 56% of the time since 1976 with low counts from the late 1980s and early 2000s (Figure 5).

The weir is an aluminum and steel bipod structure approximately 33 meters long with a 4.3 meter opening at the center where a removable gate is installed to allow both fish and boat passage (Figures 6 and 7). The weir's unusually deep and wide opening are best monitored in tandem with a DIDSON Sonar placed upriver of the weir. The DIDSON recordings are interpreted daily allowing for inseason monitoring of the sockeye salmon run (Figure 8). The gate is shut at night to prevent fish passage so salmon can be sampled first thing each morning by beach seine (Figure 9 and 10). Age, sex, and length (ASL) data are collected daily to determine the age composition.

In addition to coho and sockeye salmon, resident fish of Chilkat Lake include Dolly Varden, cutthroat trout, Pacific lamprey, threespine stickleback, sculpin species, and round whitefish. Sockeye salmon generally start running mid-June, joined by coho salmon in late August or early September. Since the DIDSON Sonar cannot differentiate between similarly sized salmon species, the crew must use the proportion of coho and sockeye salmon caught in daily beach seines to calculate species apportionment.

Once a month, crew take the jet boat out to 2 anchored buoy locations to collect basic limnological data including zooplankton samples and light and temperature readings. This historical dataset goes back to 1987 and provides a monthly snapshot of temperature and light profiles as well as zooplankton presence and abundance, with samples processed by the the Kodiak Island Limnology Laboratory. These details help track the basic environmental conditions of Chilkat Lake over time and can act as an indicator for salmon health.

Commercial harvest, total run, and harvest rates

The number of Chilkat Lake sockeye salmon harvested in commercial fisheries is estimated using genetic stock identification (GSI) analysis. Sockeye salmon tissue and scale samples are collected from District 15 commercial drift gillnet fishery landings by ADF&G Port Sampling Program staff at fish processing facilities in Haines, Juneau, and Petersburg. Sampling is stratified by statistical week, and sampling efforts cover the first 10 weeks of the fishery when approximately 94% of sockeye salmon harvest occurs. Samples are processed inseason with results quickly available thanks to dedicated staff at the ADF&G Gene Conservation Lab, allowing for the weekly calculation of Chilkat sockeye salmon harvest. The total run is the Chilkat Lake harvest in commercial, sport, and subsistence fisheries plus the escapement count at the weir. Sockeye salmon harvest rates vary from year to year and by week of harvest.

Selected Publications