|Abstract or Summary
- English sole is a major contributor to Oregon and Washington groundfish resources. In accordance with the continued trend of increasing fishing effort, in 1975 Oregon State University Sea Grant
funded an extensive groundfish research program: the Pleuronectid Project. The purpose was to provide information to assist resource management agencies. This thesis is a computer simulation of potential yields of English sole in the International North Pacific Fisheries Commission (INPFC), Columbia and Vancouver Areas, and is one of the steps in the project. To initiate this study, non-linear equations were fit to data on trawl selectivity, catch utilization, seasonal growth, and length at maturity. The computer simulation model, ENGLSH, was used to integrate
these parameter estimates and other valid information. The model was used to examine effects on yields of varying growth and recruitment rates, ogive and knife-edge instantaneous fishing (F) and discard mortality rates, and migration, and estimate maximum sustainable yield (MSY). Model validation suggests that Oregon Department of Fish and Wildlife groundfish surveys overestimate recruitment biomass. The simulation model also indicates that E. A. Best's (1961) 5.5-inch mesh
ogive approximates annual fleet selectivity in Pacific Marine Fisheries Commission Area 3A during years 1969 to 1979. A small amount of ogive discard mortality, less than ten percent of the applied F, reduces optimum F by at least 0.5. Natural variability in growth rate, with half the coefficent of variation of natural variability of recruitment rate, produced double the variation in yield. Most of this difference may be explained by the synchronous effect of varying growth over all cohorts in the event year, versus the recruitment effect being dampened by all other cohorts in the population in that year. On the other hand, when maximum and minimum observed deviations in growth or recruitment were made to persist over years, recruitment produced over a 1000 metric tonnes (t) deviation from mean yield while maximum and minimum growth produced an approximate 75 t deviation. This high yield is consistent with the yields observed in commercial catches off Oregon and Washington from the 1961 year class. MSY is currently estimated at 1850 t and 2500 t for mean cohort analysis and groundfish survey recruitment respectively. Considering
(a) that the model indicates that survey recruitment estimates are too high, and (b) that MSY estimates excluded discard mortality for ages 1-3, 1850 t should be considered the upper limit of potential yield for the INPFC Columbia-Vancouver Areas.