The effects of changing spatial scales on spatial patterns of CPUE for Ommastrephes bartramii in the northwest Pacific Ocean

It has been argued that most of the problems concerning fisheries and aquaculture may be rooted in spatial differentiation, and the spatial patterns of fisheries resources have been widely studied. However, there is a general lack of awareness on how changing spatial scales affect the spatial patterns of fisheries resources. This study explores the scaling relations of spatial patterns of the catch-per-unit-effort (CPUE) for Ommastrephes bartramii in the northwest Pacific Ocean. Several spatial indices commonly used to explore the spatial patterns of fisheries were examined, including the count of valid data points (Count index), global Moran's I, Geary's C, General G, the average nearest neighbor (ANN) ratio and Ripley's K function at different spatial scales. The results show that the Count index and the z-scores of three spatial indices (i.e. Moran's I, General G and ANN) exhibit consistent and robust power law relations, while the z-scores of Geary's C and ANN ratio exhibit consistent and robust logarithmic relations. General G exhibits consistent and robust linear functions in September and October and a quadratic polynomial function in August. The spatial patterns observed from Ripley's K-function become less clustered at coarser spatial scales. Based on the peaks of Moran's I and the nadirs of Geary's C, we identified 25′ × 25′ as the optimum scale for August and October and 20′ × 20′ for September, and 50′ × 50′ as the coarsest allowable spatial scale for August and October and 55′ × 55′ for September, for conducting spatial analysis of O. bartramii in the northwest Pacific Ocean. The methodology presented in this research provides a useful reference to understand the scaling effect and search for the coarsest spatial scale for the survey of fisheries resources.