Field Notes
U.S. Fish & Wildlife Service
Field Notes Entry   
ALASKA FISHERIES: Video Weirs, Windows into the World of Alaska's Migrating Fish
Alaska Region, May 5, 2014
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Killey River weir.
Killey River weir. - Photo Credit: USFWS/Lucas Young
Salmon passing through a video weir.
Salmon passing through a video weir. - Photo Credit: USFWS
Kuskokwim River in Western Alaska
Kuskokwim River in Western Alaska - Photo Credit: USFWS/Palma Ingles

In Alaska, the Service uses fish weirs to monitor salmon returning to tributaries that flow through National Wildlife Refuges and feed three incredibly important salmon systems: the Kuskokwim, Kenai, and Yukon rivers. While the Kenai River is known worldwide for its sport fisheries, the Kuskokwim and Yukon are significant in that they provide a key source of food for Alaska Native peoples and rural residents that still practice a subsistence way of living.


For over a decade, our Kenai Office fisheries biologists have been pioneering innovative underwater video technology at Kenai and Kuskokwim weirs, allowing them to provide more accurate counts of abundance with less manpower. For example, artificial lighting and a sealed camera box filled with clear water can record passing fish 24 hours a day even when the water is cloudy. Motion detection software only records motion events, saving staff many hours during review. This year, our Fairbanks Office is integrating video technology into the remote Yukon tributary weirs. These weirs provide a platform to gather key pieces of information (e.g. escapement) needed to conserve Alaska’s salmon populations and manage associated fisheries.

How do they work? Our weirs consist of evenly spaced PVC pickets aligned parallel to the direction of flow. The upstream end of each panel is anchored to the river bottom and the downstream end is lifted above the surface by a resistance board that planes upward in flowing water. Standard video components include a sealed box to house the video camera, pond lights and a digital video recorder (DVR) equipped with motion detection software. Migrating fish enter a narrow chute on their way upstream and pass in front of the video box. The analog video signal is routed to the DVR and converted to digital format instantaneously. The DVR removes blank footage and only reports motion events. We also incorporate fish traps to collect samples (e.g., scales for ageing or a small fin clip for genetic analyses) and use microwave technology to monitor remote sites. We power our remote video systems with a combination of solar and thermoelectric energy. After passing through the weir, fish continue their migration upstream to their spawning grounds.

In the Kuskokwim region, fisheries biologists from our Kenai Office use weirs as their primary platform to monitor the salmon that return to two Kuskokwim River tributaries—the Kwethluk and Tuluksak rivers. Daily escapement numbers are relayed to managers charged with in-season (realtime) management of fisheries in the lower reaches of the river. Both tributaries flow through the Yukon Delta National Wildlife Refuge and support Chinook runs that make an important contribution to the overall natural diversity of the Kuskokwim’s run.

These two tributary populations experience heavy fishing pressure as they pass through the lower reaches of the Kuskokwim. As a result of low escapement, sport and subsistence fisheries have been restricted in both systems, as well as in the mainstem Kuskokwim River near the villages of Kwethluk and Tuluksak, to help protect these spawning populations.

Our Kenai fish biologists have used underwater video technology at these two weirs since 2010 to get an even clearer picture of the runs in real time. For example, clear footage lets them determine sex ratios for each species without handling the fish. This information is helpful in understanding changes in, for example, the size of Chinook salmon and the ratio of males to females over time.

In the Kenai region, recreational salmon fishing throughout the Kenai River watershed overlaps with a uniquely Alaska “personal use” dipnet fishery for Alaska residents in the lower river, marine recreational fisheries, and set and drift gillnet commercial fisheries in Cook Inlet. These fisheries intercept migrating salmon at different points along their migration through Cook Inlet and up the Kenai River—from the beginning of the earliest run to the end of the latest.

While 2013 was a bumper year for Kenai River sockeye salmon, the total number of Chinook returning to the Kenai is declining, with 2012 and 2013 returns being the lowest on record. Based on when they migrate (“run”) upstream and where they spawn, Kenai River Chinook fall into two main groups: early- and late-run. Most early-run Chinook spawn in Kenai River’s tributaries within the Kenai National Wildlife Refuge and tend to begin migrating up the Kenai between late April and early July. Late-run Chinook return between mid-June and mid-August to spawn in the Kenai’s mainstem.

To better monitor the early-runners, our Kenai Office operates weirs fitted with underwater video technology on three Kenai River tributaries that flow through the Refuge: the Funny River (operated since 2006), the Killey River (operated since 2012), and, in 2013, Quartz Creek—a smaller tributary that provides another important spawning area for early-run Chinook. It’s important that early-run Chinook reach these tributaries—over half of the Kenai’s early-run Chinook are thought to spawn in the Killey and approximately 20% are thought to spawn in the Funny River, although the latter number has been less in recent years (10-11%).

The information gathered from the weirs on the Killey and Funny Rivers, and most recently Quartz Creek, is being used in combination with radiotelemetry data, genetic data, and harvest information to generate population abundance estimates for comparison with information being gathered by ADF&G with new sonar technology. Ultimately, a better understanding of the Kenai’s different populations can help ensure their conservation.

Last but not least, the massive Yukon River and its tributaries drain a remote and still-wild swath of land in Alaska and Canada that’s the size of Texas and Louisiana combined. Fewer than two dozen of the world’s rivers are longer—in the U.S., only the Missouri and Mississippi surpass it in length. Yukon River salmon are equally impressive, with some Chinook and fall chum salmon undertaking a Herculean journey up the entirety of its length (~2,000 miles)—those that spawn in its headwaters in British Columbia have one of the longest freshwater migrations on Earth.

Because Yukon River Chinook and, increasingly, fall chum (as Chinook numbers decline statewide) have such importance, the U.S. and Canada established a long-term commitment to manage and conserve these two species as a shared resource and give priority to subsistence uses via the Yukon River Salmon Agreement of 2001. To help meet the obligations of this agreement and the ecological and subsistence mandates of ANILCA, our Fairbanks Office has a Subsistence Fisheries Branch with a permanent staff of six biologists. They monitor and work jointly with the State of Alaska to manage the in-season harvest of salmon on federal public lands and determine if subsistence needs are being met in Yukon River communities.

The Service coordinates with ADF&G and numerous other agency and non-agency partners to piece together a greater understanding of the salmon’s part in the ecology of the Yukon River for the benefit of the people who rely upon this important resource in their everyday lives.

For 20 years, the Service has annually collected data on salmon abundance, run-timing, age, sex and length as Chinook, chum, and other species that move upstream through weirs located on several key Yukon River tributaries that flow through Refuge lands, including the Andreafsky and Gisasa Rivers.

The 120-mile long Andreafsky River and its East Fork flow through the Yukon Delta National Wildlife Refuge and converge near the village of St. Mary’s (population ~500). This highly productive river supports some of the Yukon’s largest runs of Chinook, chum, coho, and pink salmon. The Gisasa River, located within the Koyukuk National Wildlife Refuge, is a tributary of the Koyukuk River. The Koyukuk is a major Yukon River tributary, entering the mainstem downstream of the community of Galena (population ~470). It hosts one of the Yukon’s largest summer chum runs. The Service uses the Gisasa River weir to help monitor the effectiveness of various conservation actions aimed at ensuring enough Chinook and summer chum salmon escape the downstream fisheries and reach their spawning grounds.

The two decades of consistent data that have been collected at weirs like these is rare, given the complicated and costly logistics associated with such a large river system flowing through a remote and largely roadless area. The data is thus very important, both in terms of 1) monitoring escapement and run-timing (key pieces of information needed to inform the decision-making process for setting subsistence and commercial fishing periods in real time), and also 2) tracking how fish populations originating from Refuge lands are changing over time (e.g., number of spawners, their size, age, and the ratio of males to females).

The information collected at these weirs is being used to review population trends throughout the Yukon’s basin and to create models to help reconstruct the numbers of salmon that entered the mouth of the Yukon River historically. These efforts will help improve understanding of escapement needs and ultimately aim to ensure there are healthy and diverse fish for the future.

Contact Info: Katrina Mueller, 907-786-3637, katrina_mueller@fws.gov
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