Burbot research in rivers of the Tanana River drainage and at Fort Knox, 1995

Description

As part of an ongoing stock assessment program, burbot were sampled in two river sections (approximately 25 km in length), one each in the Tanana and Chena rivers, representing the area where most fishing harvest occurs. These sections have been sampled annually since 1986 and 1988, respectively. A systematic sampling design was used, whereby hoop traps were set and moved daily over an eight day period. Estimates of mean catch per unit effort, mean length, length distributions, and proportions of catch for three size categories were calculated. Estimates for each were within the range of observed values from previous sampling years. Seasonal variations in catch rate and composition was cited as a problem in interpreting these annual estimates. Suggestions for improving the study design to alleviate seasonal catch variability are given. Catch-age analysis was used to combine harvest estimates from a statewide mail survey and age composition from catch sampling with auxiliary information in the form of angler effort to estimate exploitable abundance of burbot in the Tanana River drainage. The CAGEAN model results showed a decreasing trend in exploitable abundance from 1987 to 1994, which corresponds to a trend in increased fishing mortality during that time. Catch-age analysis appears to be a promising method for estimating trend in abundance for burbot in the Tanana River drainage, but improvements in the catch sampling program and more accurate estimates of fishing effort are needed to improve accuracy of the estimates. Mark-recapture experiments were conducted in two small settling ponds in the Fort Knox gold mining project to estimate abundance of burbot. The settling pond complex in the Fish Creek drainage was developed into a 67 ha reservoir, and was completed in May, 1996. These estimates represent the total abundance of burbot in the reservoir prior to its completion. Estimated abundance of burbot greater than 120 mm total length was 360 (SE = 90) in Polar #1 Pond, and 486 (SE = 63) in Polar #2 Pond. Total abundance in waters comprising the freshwater reservoir was 846 (SE = 91) burbot. Mean length at age (ages 2-5) and length frequency distributions are presented.

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