Geostatistical simulations of eastern Bering Sea walleye pollock spatial distributions, to estimate sampling precision

Walline, P. D. 2007. Geostatistical simulations of eastern Bering Sea walleye pollock spatial distributions, to estimate sampling precision. – ICES Journal of Marine Science, 64: 559–569. Sequential Gaussian and sequential indicator geostatistical simulation methods were used to estimate confidence intervals (CIs) for biomass estimates from six echo-integration trawl surveys of eastern Bering Sea walleye pollock (Theragra chalcogramma) biomass. Uncertainty in the acoustic and the length frequency data was combined in the calculation of CIs. Sampling in 2002 provided evidence for isotropy in the spatial distribution. Variogram models were characterized by long ranges (75–122 nautical miles for non-zero acoustic data, for example) compared with the smallest dimension of the survey area (∼100 nautical miles) and small nugget effects (∼20% of the semi-variance in transformed normal space for acoustic data). The 95% CIs obtained for the abundance estimates did not vary greatly between years and were similar to those from a one-dimensional transitive geostatistical analysis, i.e. ± 5–9% of estimated total biomass.