Migratory timing of 15 sockeye salmon (Oncorhynchus nerka) stocks in the upper Copper River, Alaska, was determined from a tag and recapture project conducted between 1967 and 1972. Time densities and descriptive statistics were used to estimate mean date of migration upstream, variation about the mean, form, and stability of these measures between years within the geographic reference frame of Wood Canyon. The mean calendar dates of migration through the Copper River commercial fishery district of Prince William Sound also were estimated. River level appeared to have a negative correlation with travel rate and was a source of yearly variation in the mean date of migration. Mean dates of migration varied by stock and were grouped by a Student‐Newman‐Keuls test into six time spans that significantly differed from one another. Variation in mean migration date increased through time, with earlier migrating stocks demonstrating greater consistency of timing between years than the later migrating stocks. The majority of migratory time densities were positively skewed, platykurtic forms which were relatively stable between years. Migratory timing of upper river stocks overlapped and harvest control of individual stocks within the Copper River District of Prince William Sound may not be feasible. However, management of groups of stocks according to clusters of time‐density means is feasible. Identification of the upper Copper River stock composition within a commercial fishery period can assist the manager in assessing stock abundance and the probable impact of the fishery on groups of stocks.
The Alaska Department of Fish and Game (ADFG) establishes harvest guidelines for the tanner crab (Chionoecetes bairdi) based in part on the mean catch per pot (CPP) obtained on preseason surveys. Because CPP changes with soak time, it must be adjusted to reflect a standard soak time to avoid biased estimates of mean CPP. We propose a method for doing this based on a model describing the change over time in the number of crabs within a pot. The model can be expressed as R t = (A ‐ B)/(A t ‐ B t); R t is the catch on day 1 divided by the catch on day t; A and B are parameters. After the model is fitted to the daily catches from several pots, the predicted R t values can be used later as correction factors to estimate day‐1 catches from day‐t catches. When the model was fitted to experimental CPP data for tanner crab, the estimated day‐1 catches were closer to the observed values than estimates obtained with two methods currently used by ADFG.
Recreational fisheries management is often compromised by limited information of variable quality from several sources. We develop a form of catch-age analysis to combine uncertain information from creel surveys, age composition, and mark-recapture estimates of abundance. Four systems are used in weighting annual observations: equal, inverse of squared coefficients of variation (CV-2), perceptions of accuracy, and a combination of the latter two. The model is applied to a humpback whitefish (Coregonus pidschian) population in Alaska and evaluated for model fit, parameter uncertainty, conservative forecasts of exploitable abundance, and biological plausibility. The probability of forecasted stock abundance occurring below a threshold level defined by an agency management plan is evaluated for various recruitment and exploitation scenarios. The perception model is judged to be best with the use of the analytic hierarchy process, a decision-making technique. By incorporating perceptions into fisheries decision-making, beliefs in the accuracy of uncertain information are made explicit. In a conservative context, fishery management decisions should include reducing risk to the stock in the setting of harvest policy and in the selection of the assessment model.
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