Research Document 2023/083

Results of Comparative Fishing Between the CCGS Teleost Fishing the Western IIA Trawl and CCGS Capt. Jacques Cartier Fishing the NEST Trawl in the Southern Gulf of St. Lawrence in 2021 and 2022

By Benoît, H.P., and Yin, Y.

Abstract

Bottom-trawl surveys provide key inputs to stock assessments for groundfish stocks and other taxa, for ecosystem monitoring and reporting, and for research. These surveys can produce annual indices of abundance that are proportional to stock size, provided that the proportionality constant, typically called catchability, does not change over time. This is typically achieved through the use of standardized survey design and procedures. Periodically it becomes necessary or desirable to change one or more aspects of the protocol, and calibration experiments are typically required to estimate adjustments for possible changes in catchability. From 2004 to 2022, the CCGS Teleost fishing a Western IIA bottom-trawl was used for the annual survey of the southern Gulf of St. Lawrence (sGSL). This vessel will soon be retired and is being replaced by the CCGS Capt. Jacques Cartier, fishing a different trawl. Paired-trawl comparative fishing experiments involving these two vessels and gear pairs were conducted in September in 2021 and 2022 to obtain data for catch required to estimate their relative fishing efficiency for a large number of fish and invertebrate taxa that are routinely sampled in this survey. In this document we briefly describe these comparative fishing experiments and report on analyses of the resulting data for 116 fish and invertebrate taxa routinely sampled by the sGSL survey. The analyses employed a suite of contemporary statistical models used previously in extended comparative fishing analyses in the eastern United States and which were recently extensively tested using simulations. Relative catchability as a function of individual lengths (fish, lobster and squid) or carapace width (crabs) was evaluated and estimated for 38 taxa, whereas size-aggregated estimates were derived for the others. Given considerable differences between the old and replacement survey protocols, which include a substantial change in the fishing gear and tow length, important differences in length-dependent and independent relative catchability were expected for this comparative fishing experiment and were estimated for a number of taxa. Recommendations for the application of the conversion factors are provided. Use of these conversion factors will maintain the integrity of the over five decade long time series for various southern Gulf marine taxa.

Research Document 2023/083 (PDF, 33,116 KB)

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