Larval Abundance in Relation to Stock Size, Spawning Potential and Recruitment in North Sea Herring

Abstract

In recent years the idea that larval abundance estimates provide valid (relative) measures for spawning stock size has become more generally accepted in North Sea herring research (Anon, 1971b, 1972). The application of this stock-size parameter was promoted by increasing difficulties encountered in using catch-effort statistics of the rapidly changing herring fisheries. The use of larval data for this purpose presupposes the absence of major variations in egg and larval mortalities between years and over longer periods. Provided these mortalities do not differ greatly between spawning areas, the estimates would also allow a comparison of the size of local spawning stocks (given length composition and fecundity data) (Zijlstra, 1970; Anon, 1971a, b). As larval abundance is supposed to be related to the size of the spawning stock, it provides finally a useful parameter in stockrecruitment studies (Burd and Holford, 1971). The realization of the probable value of larval abundance as a tool in population studies initiated an international collaboration to improve data collection by coordinated surveys with standardized methods (Boetius and McKay, 1970; Saville, 1970; Wood, 1971; Schnack, 1972; Zijlstra, 1972).