The early life-history dynamics of Northeast Arctic cod: levels of natural mortality and abundance during the first 3 years of life

摘要

Recruitment at age 3 of the Northeast Arctic cod (Gadus morhua) is highly variable. It has generally been believed that year-class strength for this stock is determined prior to settlement to the bottom after about 6 months. However, newer observations indicate that year-class strength may change considerably between settlement and recruitment at age 3. Our analyses cover the 1983-2009 year classes where comprehensive data from total egg production (TEP), surveys, and stock assessments were available for a thorough examination of these cohorts. On average, only 6 out of 1 million of a new generation at the TEP stage reaches the age of recruitment to the fishery. The between-cohort variability in abundance is greatest at the ages 0-1 stage. Although the mortality is highest during the first months of life, the year-class strength can also be affected considerably by processes taking place between the 0-group stage (similar to 6 months) and age 3. The mortality in this period of life seems to be strongly density-dependent, and cannibalism is an important source of mortality.