Characterizing the spatial distribution of a semi-demersal gadoid

No abstracts are to be cited without prior reference to the author.

High-resolution, two-dimensional measurements of density are collected routinely during echo- integration trawl surveys. Echo-trace classification (ETC), the detection of aggregations within echograms, is used to describe and analyze spatial distributions of pelagic organisms. This approach is appropriate for species that form well-defined schools, but is limited when used for species that form demersal layers or diffuse pelagic shoals. As an alternative to ETC metrics, we used landscape indices to quantify and characterize spatial heterogeneity walleye pollock (Theragra chalcogramma) density distributions. Survey transects were divided into segments of equal length and a series of landscape metrics were calculated to measure occupancy, fragmentation, acoustic density structure, and vertical distribution. Ordination and classification techniques were used to examine relationships among metrics and to develop a classification typology for spatial patterns. The resulting classification consisted of six echogram types. Visual inspection revealed that spatial patterns of segments assigned to each type were consistent, but considerable overlap existed among types. Spatial analysis revealed that types were spatially autocorrelated and that the location among types within the survey area differed.