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Hydrography and larval fish distribution in the northeastern North Sea were studied during a research programme carried out during the period from 1991 to 1994. The aim was to examine the connection between frontal zone formation and nursery characteristics of gadoid larvae at the shelf break. Emphasis was placed on the year-to-year variation in frontal characteristics and distributional patterns of larvae An area of about 67000 km2 covering the northeastern North Sea, the Skagerrak and the Kattegat was surveyed by grid or transect sampling. At each sampling station the hydrography was studied by CTD casts, and the abundance of fish larvae was measured by depth integrating tows of a 2 m ring net. Five species of gadoid larvae and small luveniles were found in the area. cod Gadus rnorhua, whiting Merlangjus merlangus, haddock Melanogrammus aeglefinus, Norway pout Trisopterus esmarki and saithe Pollachius virens. Larval abundance differed markedly between species and years. The abundance of all species was the highest in 1992 and declined during the follo~ving 2 years. In 1994, cod and whiting were the only gadoid species observed. Peak abundance of all gadoids was found in the vicinity of the frontal zone; however, the relationship between larval distribution and hydrography differed among species. Correspondence between spatial and interannual variation in characteristics of frontal zones and larval distributions suggests that frontal zone variability is a central element in the early hfe of gadoid larvae from the area.

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As with most teleosts, the life cycle of the cod (Gadus morhua) is characterized by high productivity of eggs leading to high concentration of larvae. These stages are known to be associated with high mortality rates. Mortality of older stages (juveniles and adults) has been relatively poorly studied. We use capture-mark-recapture (CMR) methodology to estimate time and age variation of natural mortality and fishing mortality in a coastal cod population within the Norwegian Skagerrak coast. A total of 36 728 reared 6-mo-old, and 2415 wild-caught mostly 18-mo-old, individually tagged cod were released in four consecutive years, leading to 4155 recaptures by fishermen. Tag loss and mortality due to tagging appeared negligible for reared young fish, but up to 60% of the wild-caught tagged fish disappeared just after release. Tag return by fishermen was ϳ50-60%. Natural mortality was found to be high in the 6-12 mo range, but subsequently it decreased rapidly and was no longer age-dependent. Fishing mortality was negligible for fish younger than 1-yr-old, intermediate for 1-yr-old fish, and high for older fish. The seasonal pattern of fishing varied much between age classes, with 2-yr-old fish mostly taken by recreational fishermen in summer, and older fish mostly taken by professional fishermen in winter. Because it is directed toward relatively young fish, recreational fishing may have a strong impact on the population; we specifically point out the coincidence between the increase of tourism and the decrease of the cod stock in the Risør area during the last 20 yr. Total mortality varied little between years, except during ϳ5 mo after a major algae bloom in May 1988, when fish disappeared at a high rate whatever their age (no emigration was observed in connection with the algae bloom). We conclude that mortality of adult fish may be an important determinant of the stock size.