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 stock's 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

Published in MEPS Vol. 195 (2000) on March 31
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 2000