Calibration of bottom trawl survey vessels : results of comparative fishing between the CCGS Teleost and CCGS John Cabot / CCGS Captain Jacques Cartier on the Scotian Shelf and Bay of Fundy in 2022 and 2023

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. In the Maritimes Region, the Canadian Coast Guard Ship (CCGS) Teleost fishing a Western IIA bottom-trawl conducting the annual Summer Ecosystem Research Vessel Survey of the Scotian Shelf will be replaced by the CCGS John Cabot and CCGS Captain Jacques Cartier fishing the Northeast Fisheries Science Centre Ecosystem Survey Trawl and such a change in protocols required calibration experiments to estimate adjustments for possible changes in catchability. Hence, a comparative fishing experiment was conducted in the summers of 2022 and 2023 involving fishing by paired vessels and gears at a large number of locations 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. This document briefly describes the comparative fishing experiment and the resulting catch data, followed by detailed analyses of the data for 108 fish and invertebrate taxa routinely sampled by the RV survey for which there were sufficient data from the experiment. The analyses employed a suite of contemporary statistical models used previously in comparative fishing analyses in the eastern United States as well as the Atlantic regions in Canada. Recommendations for vessel calibrations of catch numbers based on the results of the analyses were provided for these taxa, where 22 taxa had length-dependent conversion factors using length-disaggregated analysis, 14 taxa had length-independent conversion factors using length-disaggregated analysis, 40 taxa had length-independent conversion factors using length aggregated analysis, and calibration for 21 taxa is recommended as not necessary. Complementary results were also provided for 59 taxa using length-aggregated analysis of catch biomass, of which 42 taxa appear to require a conversion factor, while 15 taxa do not.