The impact of spatial scale on local Moran’s I clustering of annual fi shing effort for Dosidicus gigas offshore Peru

摘要

The spatial scale(fishing grid)of fisheries research affects the observed spatial patterns of fisheries resources such as catch-per-unit-effort(CPUE)and fishing effort.We examined the scale impact of high value(HH)clusters of the annual fishing effort for Dosidicus gigas offshore Peru from 2009 to 2012.For a multi-scale analysis,the original commercial fishery data were tessellated to twelve spatial scales from 6′to 72′with an interval of 6′.Under these spatial scales,D.gigas clusters were identified using the Anselin Local Moran’s I.Statistics including the number of points,mean CPUE,standard deviation(SD),skewness,kurtosis,area and centroid were calculated for these HH clusters.We found that the z-score of global Moran’s I and the number of points for HH clusters follow a power law scaling relationship from 2009 to 2012.The mean effort and its SD also follow a power law scaling relationship from 2009 to 2012.The skewness follows a linear scaling relationship in 2010 and 2011 but fluctuates with spatial scale in 2009 and 2012;kurtosis follows a logarithmic scale relationship in 2009,2011 and 2012 but a linear scale relationship in 2010.Cluster area follows a power law scaling relationship in 2010 and 2012,a linear scaling relationship in 2009,and a quadratic scaling relationship in 2011.Based on the peaks of Moran’s I indices and the multi-scale analysis,we conclude that the optimum scales are 12′in 2009?2011 and 6′in 2012,while the coarsest allowable scales are 48′in 2009,2010 and 2012,and 60′in 2011.Our research provides the best spatial scales for conducting spatial analysis of this pelagic species,and provides a better understanding of scaling behavior for the fishing effort of D.gigas in the offshore Peruvian waters.