TCCHINOOK (92)-1. January 24, 1992

Joint Chinook Technical Committee. Review of Alaskan Procedures to Estimate Add-On and Predicted Effects of June Fisheries. TCCHINOOK (92)-1. January 24, 1992

Executive Summary

The purpose of this report is to aid the Commission in considering a risk adjustment for the 1992 Southeast Alaska (SEAK) hatchery add-on in accord with the 1991 Letter of Transmittal. Given that the magnitude of estimated SEAK hatchery contributions has increased by ten fold and the uncertainty about the estimate is greater, the adverse consequences on other stocks of over estimating SEAK hatchery contributions are greater now than when the add-on procedure was originally adopted. The CTC recommends that the Commission maintain the risk level of error at 1 in 20.

The report consists of two components: (1) a review of the methods used to estimate the variability associated with estimating the add-on in SEAK and (2) an evaluation of the impact of June fisheries targeted at SEAK hatchery stocks on several other stock groups. The review is based on a draft report prepared by the Alaska Department of Fish and Game (ADF&G) and entitled "Documentation of add-on procedures and estimated impacts of add-on fisheries on chinook salmon stocks in Southeast Alaska" (1991).

The add-on to the SEAK catch is calculated by estimating the total contribution of SEAK hatchery chinook to all fisheries, then subtracting a base-level catch and a risk adjustment. The base-level contribution of 5,000 was set to exceed the level of hatchery production that existed when the ceiling level was established. The risk adjustment, as calculated by ADF&G, is based on the variance of the hatchery contribution estimate. The variance estimate currently used accounts only for the uncertainty associated with tag sampling, the tag decoding process, differences between tagging rates, and, for sport fisheries, estimation of sport catch.

ADF&G uses a variety of statistical procedures to estimate the contributions of SEAK hatchery fish, and the associated variances, to the various SEAK fisheries. Estimation techniques for the non-terminal commercial fisheries, terminal commercial fisheries, and sport fishery are quite different.

- The procedures employed to estimate variance for non-terminal commercial fisheries are considered satisfactory given certain assumptions. Several assumptions, e.g., "knowing the proportion of fish marked without error" need to be validated and evaluated for impacts on estimation error.

- ADF&G assumes that all fish caught in terminal commercial fisheries are of SEAK hatchery origin and, therefore, no variance is used for this portion of the SEAK hatchery contribution. The Chinook Technical Committee (CTC) recommends that this assumption be validated. If the "pure stock" assumption is verified, then catches should be treated as "terminal exclusions" and not be included in the add-on. Otherwise, the contribution and variance should be estimated as for other commercial fisheries.

- Contribution and variance estimates for the sport fishery are less rigorous than those for commercial fisheries. In the past, variances (measured as a coefficient of variation percentage) were assumed and not calculated from the sampled data. ADF&G currently is revising procedures for the sport fish sampling program to improve the contribution estimate; in addition, variances will be calculated from the sampled data. The CTC cannot comment on these now procedures until we receive more detailed operational plans.

- Unsampled fishing strata for the commercial fisheries are ignored in add-on computations (i.e., no contributions are calculated for these areas). Contribution estimates for unsampled fishing strata for the sport fishery have been calculated in the past. The CTC recommends that contribution estimates not be made for the unsampled strata. Apparently the new sport sampling procedure is expected to substantially eliminate unsampled strata in the future.

Given documented reduction in marking rates and the associated increase in uncertainty of mark rate estimates, the rapid increase in recreational catch (which has a larger variability about estimates of hatchery contributions compared to the commercial sampling program), and unaccounted for sources of potential uncertainty, the CTC concluded that the hatchery add-on is estimated with less certainty now than it was when the add-on procedure was established.

In an effort to increase the harvest of SEAK hatchery chinook, three new fisheries have been initiated during June in Alaskan inside waters: "experimental" (troll), "hatchery access" (troll), and "terminal" (troll, gillnet, seine, and sport) fisheries. The proportion of the catch comprised of SEAK hatchery chinook is much higher in the June fisheries than in the summer troll season. If the June fisheries were eliminated, there would be a resulting loss of SEAK hatchery catch by the troll fleet. However, allocation of chinook to June fisheries results in an increase in the number of chinook non-retention days in the general summer troll season. Examples of the numbers of fish involved are given in this report.

The change in fishing mortality from instituting June fisheries to increase access to SEAK hatchery production differs between stocks considered. Comparing the June to general summer fisheries, the concentrations of SEAK hatchery fish, North/Central B.C., Upper and Lower Georgia Strait, and West Coast Vancouver Island Stocks are higher, while concentrations of other stocks like the Harrison, Upper Fraser, Washington, and Oregon are lower.