Spawning grounds of whiting (Merlangius merlangus)

Abstract

Targeted fishing and marine developments can alter the suitability of essential habitat such as spawning areas. Past studies of North Sea whiting (Merlangius merlangus) distribution have led to differing views about the comparative importance of extrinsic and intrinsic constraints on adult distribution in the North Sea. In this study the importance of environmental influences on spawning distribution was examined using GAMs in a two steps approach, after demonstrating from geospatial analyses that there were no confounding density dependent effects on distribution during the period of low stock size investigated. The binomial model (probability of presence) showed a lower predictive power than the negative binomial model (abundance) although the final model (delta model) showed similar performance to previous studies. Whiting showed high plasticity in spawning ground selection with extensive areas of the North Sea appearing suitable across the study period. Nevertheless, a divide between two centres of persistent spawning aggregation was found consistent with the boundary previously suggested from parasite, genetic, otolith chemistry and demographic trends. In addition to aggregations suggested by past egg surveys, another spawning area off the north east Scottish coast was identified. The study identified springtide as a key physical determinant of whiting spawning distribution, which may be linked to the need for larvae to be advected offshore. Contrary to past studies, peak abundance was found around 125m bottom depth, although there may have been differences in physical preferences related to the region of the North Sea studied. The persistence of some spawning aggregations of whiting indicates the need for marine spatial planning to consider the potential impact of marine developments in these areas.