By Schnute, J. & Haigh, R.

Abstract

This paper describes an analytical technique for estimating groundfish biomass from swept area density measurements. Conceptually, the idea is simple. Tows give estimates of biomass density. Bathymetry, locations of fish capture, and other sources of information give estimates of habitat area. Multiplying the density by the area gives an estimated biomass, which might be interpreted as an absolute measure or a relative index. We present a rigorous description of the method, along with a bootstrap technique for assessing uncertainty. Illustrations from Pacific groundfish commercial fisheries and research surveys demonstrate various limitations and advantages to this approach. Our analyses highlight issues of scientific importance, such as the need to obtain better habitat definitions. Comparisons between surveys and commercial fisheries provide some insight into the underlying processes. Despite their limitations, biomass estimation methods play an important role in groundfish stock assessment. Patterns in the analysis of a particular data set may reflect a variety of factors, such as biomass trends, response by fishermen to regulation, and measurement error.