Effects of survey scale and water depth on the assessment of spatial distribution patterns of selected fish in the northern North Sea showing different levels of aggregation

Abstract

Geostatistics was employed to investigate spatial structuring of herring, cod, dab, haddock and whiting at different spatial scales in the northern North Sea. Additionally, a structural analysis of the maximum water depth was carried out to assess habitat associations of fish. Linear, spherical, exponential and Gaussian models were fitted to the semivariograms, showing clear spatial autocorrelations. At the smaller scale, spatial structuring was weak for haddock, herring and dab, increasing at the greater spatial scale, with the exception of whiting. Mean catch rates, estimated classically and geostatistically, were in good agreement. Corresponding variances were clearly reduced at both spatial scales, when accounting for spatial distribution of the fish. At the greater survey scale a high level of habitat association was detected for haddock and whiting, while a poor habitat association was found for cod, dab and herring. The smaller scale seems to be the threshold at which spatial structuring of “cpue” could have marked influence on estimation error. Thus, survey scale is important when analysing spatial patterns and estimating mean biomass indices, and a sound analysis of relations in spatial structuring of fish and habitat conditions is essential to derive more precise estimates.

Keywords:

• Clupea harengus
• depth associations
• Gadus morhua
• Limanda limanda
• Merlangius merlangus
• Melanogrammus aeglelfinus
• North Sea
• spatial analysis
• universal kriging
• variogram models

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Acknowledgments

This work is part of the PhD thesis of V. S. at the Carl von Ossietzky Universität, Oldenburg, Germany, supported by the Scholarship Program of the German Federal Environmental Foundation (Deutsche Bundesstifung Umwelt, Osnabrück; No. 20002/290).

Notes

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark