Spawning distribution of North Sea plaice and whiting from 1980 to 2007

Christophe LOOTS, Sandrine VAZ, Benjamin PLANQUE, Philippe KOUBBI

Abstract


The spatial distributions of spawning population of North Sea plaice and whiting were studied using geostatistical analyses. Variograms were computed each year since 1980 on abundance data of spawning adults using the first quarter data from the International Bottom Trawl Survey. Maps of spatial distribution of spawning adults were produced using kriging interpolation. For both species, distributions of spawning adults were in agreement with historical spawning grounds previously described from location of their eggs. This showed that spawning adults’ distribution may be used to infer the distribution of both plaice during its spawning peak and whiting at the beginning of its spawning period. Both species were strongly spatially structured with abundances of spawning adults located in particular areas. Spawning plaice was mainly located in the southern North Sea and along the east coast of the United Kingdom whereas it was virtually absent in the central part of the North Sea. For whiting, recurrent spawning sites were found both to the north and south of the Dogger Bank whereas the central and eastern parts of the North Sea were less suitable for spawning. Although this pattern of distribution remained stable in the last thirty years at the scale of the North Sea, multivariate analysis revealed a shift in the centre of distribution of spawning adults for both species. Changes in the extent of plaice spawning areas may be explained by temporal evolution of its spawning biomass. However, for whiting, the mechanisms responsible for the observed variations remain unclear.

Keywords


spatial distribution; plaice; whiting; North Sea; inter-annual variability; spawning adults

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