Afognak Lake Sockeye Salmon Monitoring Project (2020–2022)
Data files
Aug 09, 2023 version files 21.82 KB
Abstract
The Afognak River (Litnik) has historically supported one of the largest sockeye salmon subsistence fisheries for Kodiak Archipelago residents. In the 2000s, the number of sockeye salmon returning to Afognak River had diminished substantially resulting in closures to commercial, sport, and subsistence fishing in Afognak Bay. Local subsistence users, represented by the Kodiak-Aleutians Regional Advisory Council, Kodiak Fish and Game Advisory Committee, and Kodiak Tribal Council, stressed the importance of the Afognak River system to local subsistence users and contended that continued closures would make it more difficult for local residents to meet their sockeye salmon needs and shift fishing efforts to small nearby sockeye salmon runs. The Afognak Lake Sockeye Salmon Stock Monitoring Project enumerates adult sockeye salmon into Afognak Lake through a weir located on the Afognak River, describes run-timing, or proportional daily passage, of sockeye salmon through the weir, estimates the age and sex composition of adult sockeye salmon returns, and estimates the average length (mm) by age and sex of sockeye salmon passing through the weir. Data collected from this project provide salmon management biologists the ability to make in-season decisions to execute commercial and sport fisheries. In addition, the information that is gathered from these projects refines the escapement goals and improves preseason run forecasts to allow for maximum sustainable yield and prevent unnecessary restrictions of federal and state subsistence fisheries.
Methods
Weir Installation and Adult Salmon Enumeration
A 27 m long weir was installed perpendicular to the stream flow and consisted of 10 wooden tripods (each tripod consisting of three 4″ x 4″ x 8′ spruce timbers and 2″ x 6″ x 6′ horizontal cat-walk supports), 33 aluminum pipes (2″ x 10′), 44 picketed aluminum panels (1″ aluminum pipe with 1″ spacing totaling 30″ x 6′), and 2 framed panel gates. All materials were secured with sandbags and lashed together to create a fish-tight structure that conformed to the contour of the stream channel.
Two counting gates were placed between panels in the two deepest channels of the river enabling fish to be counted as they pass through the weir. A white flash panel was placed on the substrate beneath each gate to enhance visibility and species identification. Fish were counted by field technicians using hand tally denominators as fish migrated upstream through the gates. The counting gates remained closed until staff were present to count fish through the weir for escapement enumeration or when fish were being collected into the live trap for age, sex, and length sampling (ASL).
Age, Sex, and Length Sampling
An upstream “Scott live trap” (local name for a modified trap capable of capturing steelhead) was installed in front of the east bank gate, which acted as a sampling trap as well as a downstream steelhead trap. The trap consisted of 6 weir panels placed horizontally in the river in the form of a diamond.
Adult sockeye salmon were sampled at the weir site throughout the adult escapement. Details and procedures for adult sampling are outlined in the Kodiak Management Area Sockeye Salmon Catch and Escapement Sampling Operational Plan, 2022. All scales, when possible, were collected from the preferred area of each fish. Scales were mounted on scale “gum” cards and returned to the Kodiak ADF&G office where impressions were made on cellulose acetate. Fish ages were determined by examining scale impressions for annual growth increments using a microfiche reader fitted with a 60X lens following designation criteria established by Mosher 1968. Ages were recorded using European notation, where a decimal separates the number of winters spent in fresh water (after emergence) from the number of winters spent in salt water (e.g., 2.3). The total age of the fish includes an additional year representing the time between egg deposition and emergence of fry. Length measurements were taken from mid-eye to tail fork to nearest 1 mm and sex was determined from external morphological characteristics.
On days where escapement occurred but no samples were collected, proportions were estimated by linear interpolation between sampling events. The sample size was selected so that the proportion of each major age group (by stratum) was estimated within at least α=0.07 of its true value 95% of the time. Standard error of the age proportions was calculated as the square root of estimated variance of a proportion. Average length (unweighted) was calculated by age and sex.