Research Document - 2006/008

Standardizing the southern Gulf of St. Lawrence bottom trawl survey time series: Results of the 2004-2005 comparative fishing experiments and other recommendations for the analysis of the survey data

By Benoît, H.P.

Abstract

Bottom-trawl surveys have been conducted annually in the southern Gulf of St. Lawrence during the month of September since 1971. These surveys provide a time series of information on the abundance, size-composition and distribution of more than 70 species of marine and diadromous fish and over 40 marine invertebrate taxa. However, most research activities utilizing these data are contingent on the continuity of the time series for each taxon. This means avoiding or correcting for any systematic changes in catchability of the survey, such as might occur when there is a change in sampling gear, research vessel or the time of day in which scientific fishing takes place. The research vessel CCGS Teleost replaced the CCGS Alfred Needler as the survey vessel for the southern Gulf of St. Lawrence multi-species survey in 2006. The present report contains results from comparative fishing experiments conducted with these vessels that took place in 2004 and 2005. Recommendations for the application of those results, for dealing with issues related to taxonomic identification during the surveys, and for dealing with issues related to survey coverage during the period of 2003-2005 are also included. This report is a follow-up to Benoît and Swain (2003, Can. Tech. Rep. Fish. Aquat. Sci. 2505), which documents the corrections or considerations that should be taken into account when analysing the southern Gulf of St. Lawrence survey data over the period 1971-2002.

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