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The early llfe of cod was studied dunng a survey programme covenng the northeastern North Sea, the Skagerrak and the Kattegat In May 1992 Our aim was to asses the interrelated effects of physical and biolog~cal factors on d~stnbutlon, growth and surv~val of larval cod In the present paper we descnbe the ~d e n t~f i e d nursery areas of larvae/juveniles and analyse the connect~on between the distribution of cod and hydrograph~cal (frontal) charactenstics of the areas A total area of 67000 km2 was covered by statlons in a 10 X 10 nautlcal mile grid Sahn~ty, temperature, N 0 3 + N 0 2 and chlorophyll concentrat~on were proflled through the water column Zooplankton were sampled by a submers~ble pump and abundance of fish larvae/juveniles were estlrnated by depth-integrating tows of a 2 m nng net The hydrographlcal measurements indicated a shelf break front posit~oned along the shelf slope In the southern part of the lnvestigatlon area, and w i t h~n the zone of the front we observed enhanced prunary product~on and abundance of both phyto-and zooplankton The distnbut~on of larval and juvenlle cod was also related to the hydrography, the abundance of cod peaked wlthln a restricted zone and the aggregat~ons extended as a cont~nuous band along the front We suggest that the observed concurrence between a hydrograph~c front and cod larvae/juvenlles is a general and recurrent phenomenon based on the spawning h a b~t s of cod and aggregation due to flow convergence at the front

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Folkvord A, Johannessen A, Moksness E. 2004. Temperature-dependent otolith growth in Norwegian spring-spawning herring (Clupea harengus L.) larvae. Sarsia 89:297-310. SARSIANorwegian spring-spawning herring larvae (Clupea harengus L.) were reared at different temperature combinations in the laboratory, and marked twice with a fluorescent dye, alizarin complexone, to estimate otolith growth and increment deposition rate. A daily increment deposition rate was confirmed in the sagittae of larvae reared at 12°C from day 16 (first marking age), while the apparent rate of increment formation of larvae reared at 4°C was clearly less than one per day. A reduction in rearing temperature from 12 to 8°C between days 16 and 30 (second marking age), significantly affected sagitta growth during the inter-mark period compared with those reared at 12°C throughout. Similar somatic growth rates were observed in both groups temporarily reared at 8°C between markings (about 6% day À1 ), but the otolith growth rate was more than four times higher in the group originating from 12°C compared with the one originating from 4°C. The body size versus otolith size relationship was temperature dependent, and larvae originating from different temperature regimes could be distinguished based on the differences in otolith growth pattern, but not based on differences in body size alone. The temperature-dependent otolith growth in herring larvae is expected to be of major importance for the observed differences in otolith microstructure patterns of herring stocks from different environments and regions in the field. However, this may be difficult to document in situations when larvae have low otolith growth and clear increment patterns are not present.

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Standard length, dry mass and RNA : DNA ratio measurements of 3876 Atlantic cod Gadus morhua larvae and juveniles from 26 families of recruit (fish during their first year of spawning) and repeat spawners (fish which were in their subsequent spawning season) reared in two mesocosms (2500 and 4400 m3) under semi‐natural conditions were analysed over a period of 10 weeks using microsatellites. Larvae from recruit spawners were significantly longer and heavier at hatch and throughout the 10 weeks. RNA : DNA ratios from recruit spawner offspring were only significantly higher at week 1. The smaller (2500 m3) mesocosm was characterized by low plankton density during the transition from endogenous to exogenous feeding followed by a higher density during the metamorphosis period (weeks 4 and 5), with the reverse pattern evident in the 4400 m3 mesocosm. Patterns of larval growth followed patterns of zooplankton density. Significant differences in RNA : DNA ratios between the mesocosms at all comparable sampling dates were found and within each mesocosm individual fish exhibited a wide range of growth and condition responses under the same environmental conditions. RNA : DNA ratios as a function of size differed in the amount of variability between mesocosms, indicating that the higher food density led to a higher proportion of well‐conditioned larvae in the first 3 weeks. Food availability probably has a major role in determining offspring growth and condition, with limited effects due to maternal effects in cases where the broodstock females are approximately of similar size and condition.

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.