MEPS 334:225-235 (2007)  -  doi:10.3354/meps334225

Cross-frontal variation in growth rate and prey availability of larval North Sea cod Gadus morhua

Peter Munk*

Department of Marine Ecology and Aquaculture, Danish Institute for Fisheries Research, Charlottenlund Castle, 2920 Charlottenlund, Denmark

ABSTRACT: Fish larvae are often concentrated in areas of hydrographic fronts and frontal processes are likely to affect larval growth and survival. The potential influence could be direct through impact from specific physical parameters, or it could be indirect through enhancement of prey availability in the frontal zone. The present paper examines the physical–biological linkages for cod larvae distributed across hydrographic fronts in the NE North Sea, hypothesising that larval growth rate and prey availability are promoted in the central frontal zone. Cod larvae and zooplankton were sampled along a series of cross-frontal transects in May of 1992, 1993 and 1994. Growth rate was ascertained from age-at-length, using otolith examination, while prey availability was estimated from copepod abundance and prey preference curves. Larval growth rate was significantly promoted at the front, and significant along-frontal and interannual differences were also found. Prey availability was enhanced in the frontal areas, but there was no significant relationship between availability and corresponding estimates of larval growth rate. The findings stress the need to consider environmental variability when ascertaining growth rates of larval fishes and point to the influence of hydrographic fronts in the survival and recruitment processes of fishes.

KEY WORDS: North Sea · Hydrographic fronts · Cod larvae · Prey availability · Otolithmicrostructure · Specific growth rate · Differential mortality · Recruitment

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