1.0 Introduction

At the direction of the Pacific Salmon Commission, a bilateral committee was assembled to evaluate the feasibility and potential utility of selectively harvesting marked hatchery salmon (PSC Selective Fishery Evaluation Committee 1995). One component of the evaluation utilized a simulation model to address the following questions:

1. Can selective fishery regulations lead to reductions in harvest rates on unmarked stocks and can these reductions be translated into reductions in exploitation rates or increases in spawning escapements? Under what circumstances?

2. Will there be deleterious impacts on the coastwide coded-wire-tag (CWT) program and management tools, such as harvest management planning models? Can deleterious impacts be overcome?

3. If any reductions in harvest rate, exploitation rate, or spawning escapement occur, can they be measured with acceptable levels of accuracy and precision.

4. How would fisheries be affected (e.g., catch level, season length, incidental mortality)?

Specifically, the objectives of the analyses were:

1. Using sensitivity analysis, determine under what conditions a selective fishery could lead to reductions in exploitation rates (or increases in escapement) for natural stocks. Parameters and variables of interest were:

   a) The proportion of fish in the selective fishery which are marked for selective removal;

   b) The mortality rate of fish which are released after capture by fishing gear;

   c) The proportion of a stock's mortality which occurs in the selective fishery;

   d) The probability that an angler misidentifies a marked or an unmarked fish;

   e) The interaction and sequence of selective and nonselective fisheries;

   f) The mortality induced by applying the mark used to identify fish for selective removal.

2. With respect to management regime similar to those currently in place, evaluate how a range of likely selective fisheries scenarios would affect:

   a) The average and range of exploitation rates on natural and hatchery stocks;

   b) The average and range of escapements of natural and hatchery stocks;

   c) The distribution of landed catch and incidental mortality among fisheries;

   d) The catch and length of fishing season.

3. With the same datasets as used in (2), assess the error introduced by selective fisheries into stock assessment tools such as, cohort analysis, harvest management models and stock composition estimators. Determine the extent to which any error that was introduced could be reduced by double tagging (e.g., Group 1 - CWT, adipose clip, ventral clip; Group 2 - CWT, adipose clip) exploitation rate indicator stocks and/or other new stock assessment methods.

Objectives 1 and 2 were addressed by the Modeling and Analysis Workgroup and Objective 3 by the Management Capabilities Workgroup.