VARIABLE NATURAL MORTALITY-RATE OF JUVENILE NORWEGIAN SPRING-SPAWNINGHERRING (CLUPEA-HARENGUS L.) IN THE BARENTS SEA

Understanding the patterns of mortality rate in the juvenile stages of exploited fish populations is essential for improving current stock a ssessment procedures. Most of the research on ''the recruitment proble m'' has focused on the larval stages, but recent work. indicates that a large part of the variability in year-class strength may be associat ed to variable mortality rates during the juvenile stages. The data on abundance of juvenile Norwegian spring-spawning herring in the Barent s Sea collected by the Bergen Institute of Marine Rest-arch between 19 83 and 1993 was analysed iv test this hypothesis. The results give str ong support to the hypothesis. Survival from the start of the 0-group stage to age 3 years may have varied from 0 to 30% for the cohorts inv estigated. Mortality rate is shown to be strongly age-dependent. and b etween 75% and 99% of the total juvenile mortality occurs during the f irst year of life. (C), 1998 International Council for the Exploration of the Sea.