The effects of a minimum landings size regulation in the fishery of Norwegian spring-spawning herring

Abstract

Effects of minimum landing size (LC) in the fishery of Norwegian spring-spawning herring have been investigated. The herring is assumed to be a unit stock, in which the growth of immatures differs according to the distribution area. Two immature stock components are distinguished. One distributed in Norwegian coastal waters south of 70 degrees north and one off Northern Norway and in the Barents Sea. Stock and yield per recruit for two corresponding stock components were calculated (ICES standard programmes) using input parameters as observed in the respective areas. The weight in catch by age of immatures is set equal to that observed in autumn catches (expected to be the main fishing season of immatures) whereas the weight in catch of adults is the average over the year. The weight by age in the stock equals observed weight of prespawners. The maturity ogive by component is calculated by using the length dependent maturing scale described by Toresen (1986). The assessment shows that if this stock is managed at Foal, there is little to gain in yield and stock per recruit by introducing a mifimum landing size above 20 cm in Norwegian coastal waters (south of 70 N), whereas some increase in yield may be obtained in the Barents Sea.