MEPS 177:221-233 (1999)  -  doi:10.3354/meps177221

Variability in frontal zone formation and distribution of gadoid fish larvae at the shelf break in the northeastern North Sea

Peter Munk1,*, Per Olov Larsson2, Didrik S. Danielssen3, Erlend Moksness3

1Danish Institute for Fisheries Research, Charlottenlund Castle, DK-2920 Charlottenlund, Denmark
2Institute of Marine Research, PO Box 4, S-45300 Lysekil, Sweden
3Institute of Marine Research, Biological Station Floedevigen, N-4817 His, Norway

ABSTRACT: 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 juveniles were found in the area: cod Gadus morhua, whiting Merlangius 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 following 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 life of gadoid larvae from the area.

KEY WORDS: Gadoid larvae · Distributional characteristics · Interannual variability · Hydrographic fronts · Plankton assemblages

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