NOAA Technical Memorandum
NMFS-AFSC-136
Spatial and temporal analysis of eastern Bering Sea echo integration-trawl survey and catch data of walleye pollock, Theragra chalcogramma, for 2001 and 2002
Abstract
The National Marine Fisheries Service (NMFS) is charged with determining whether fisheries for walleye pollock, Theragra chalcogramma, affect ecosystem function, specifically, any adverse impacts on endangered species. Although the spatial and temporal scale of fisheries impacts are an important concern, analyzing fisheries interactions at fine spatial scales is hindered by the resolution of available data. Our study had two goals: to analyze echo integration-trawl (EIT) survey data in association with observer catch records to evaluate the intensity of the walleye pollock fisheries, and to define the spatiotemporal resolution reasonable given the dynamic nature of the resource and the limitations of the data.
In this analysis we used the concept of Observed Catch to Survey Biomass Ratio (OCSBR) as a tool to measure fishery intensity at local levels. The OCSBR is the ratio of observed catch to EIT survey estimated biomass in a given area for a specified period of time. The OCSBR should not necessarily be considered a proxy for the local exploitation rate. This analysis addresses how varying temporal and spatial resolution changes the OCSBR value. A correlation analysis is used to determine the temporal and spatial scale at which OCSBR is a reasonable measure of fishing intensity.
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