Impact of additional small-scale survey data on the geostatistical analyses of demersal fish species in the North Sea

Abstract

Geostatistical tools have been used to study the impact of additional small scale catch data (star survey design) on the spatial analysis of fish, regarding different biological groups of dab, Limanda limanda and whiting, Merlangius merlangus. A standard survey carried out in January (2001-2003) in a meso-scale area in the German Bight was modified by additional small-scale sampling in 2002 and 2003. Adopting the star survey reduced the small-scale variability for medium-sized and male dab, as indicated by lower values of the nugget effect and an increased resolution of the spatial dependency. For whiting no reduction in the small scale variability could be detected; a significant difference in the spatial structuring was only found for two different size groups of whiting. Uncertainty of mean catches of dab and whiting was reduced in 2002, while in 2003 the effect of the star survey was less pronounced due to the high local density of the nearby stations. We conclude that the star survey design can be an inexpensive and effective procedure — depending on the species studied and/or the positioning of the nearby stations — when a minimised small-scale variability and a reduction of uncertainty in mean biomass of fish are the focus of interest.