MEPS 195:249-259 (2000)  -  doi:10.3354/meps195249

ABSTRACT: The distribution of a pelagic species, the North Sea herring Clupea harengus L., derived from acoustic surveys during the summer and prior to spawning is shown to have a strong relationship to seabed substrate and water depth. Substrate information was derived from a remote acoustic classification technique (RoxAnn). Herring were shown to aggregate in areas characterised by a seabed of sand and gravel. This type of substrate is similar to that on which they spawn, yet the surveys were carried out 2 to 3 mo prior to spawning. The herring also showed a preference for zooplankton-rich waters with depths between approximately 100 and 150 m. These relationships were examined during 3 years (1992, 1994, 1995) using Generalized Additive Models (GAMs) and were found to be stable between the years examined. Results indicate a robust relationship between spatial distribution patterns and these environmental factors, despite substantial changes in the stock level and age structure of the population. A multiyear GAM analysis confirmed the stability of this relationship and the stock¹s reduction. Herring preferences for specific substrate types, water depth zones and zooplankton conditions are hypothesized to modulate the prespawning spatial aggregation of the species to potentially suitable spawning grounds.

KEY WORDS: Generalized Additive Models (GAM) · Acoustics · Seabed · Substrate · Pelagic · Depth · Zooplankton · Herring · Distribution · RoxAnn