Otolith growth as indicator of herring stock affiliation and survival probability, Dr.grad.stip.

Project summary: Recent studies have demonstrated that daily otolith increments can be identify herring stock affiliation at individual level. In the present project this methodology is used together with acoustic survey data to study the periodical changes in the mixtur e of juvenile herring stocks in Norwegian fjord nurseries from 58-62 grader N It has been hypothesised that sympatric seasonal spawning populations of herring can spread their offspring over both spawning populations, i.e. larvae hatched in spring may end up as autumn and vice versa. In the present project this hypothesis of years -class twinning is tested with daily otolith increment data on NSS herring and neighbour autumn spawners. Small fish are commonly subjected to size-selective mortality with a magnitude and form that changes over time. In the present project data on daily and annual otolith increments are used to test for size selective mortality in NSS herring from the larva l stage until age 3. Most of the NSS herring larvae hatching along the coast from 58-70 grader N drift northwards into the Barents Sea, but a small fraction also end up in fjords along the coast. The present project test for latitudinal differences in dai ly and annual growth (otolith increments) in larvae and juveniles (0-3 group).