Research Document 2024/007

Results of Comparative Fishing Between the CCGS Teleost and CCGS John Cabot in the Estuary and Northern Gulf of St. Lawrence in 2021 and 2022

By Benoît, H.P., Yin, Y., and Bourdages, H.

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 Campelen 1800 bottom-trawl was used for the annual survey of the Estuary and northern Gulf of St. Lawrence (EnGSL). This vessel will soon be retired and is being replaced by the CCGS John Cabot, fishing a slightly modified Campelen 1800 trawl. Paired-trawl comparative fishing experiments involving these two vessels and gear pairs were conducted in August 2021 and August and September 2022 to obtain catch data 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 over 125 fish and invertebrate taxa routinely sampled by the EnGSL 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 (fishes, shrimps and squid) or carapace width (crabs) was evaluated and estimated for 50 taxa, whereas size-aggregated estimates were derived for the others. Given the large similarities between the old and replacement survey vessel and gear, and consequent expected similarity in catchability, and in some cases due to modest sample sizes, estimates of relative catchability were not statistically significant for many taxa. Recommendations for the application of the conversion factors are provided. Use of these conversion factors will maintain the integrity of the over four decade long time series for various northern Gulf marine taxa.

Research Document 2024/007 (PDF, 49,330 KB)

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