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Abstract

We re-analyze Thorny skate data from two comparative fishing experiments conducted by DFO in 1995 and 1996 using improved and more contemporary methods to estimate the relative efficiency of the Campelen 1800 demersal shrimp trawl survey protocol compared to the Engel 145 otter trawl. We correct possible bias in the method previously applied to these data. We investigate if there are size-based differences and if depth or spatial regions have important effects on results. We also investigate the influence and robustness of the estimation procedures, which was a concern in the original analyses of these data for other groundfish species. We did not find strong evidence that the relative efficiency of the Campelen trawl protocol compared to the Engel was different for smaller-sized Thorny skate compared to larger ones. However, we conclude that there is a potential that size-based differential catchability existed but there is insufficient information to reliably estimate these effects for Thorny skate. We also found evidence of significant differences in relative efficiency among NAFO Divisions and experiments, which is similar to other flatfish species. However, the mechanisms for these differences are unknown and it is not clear if spatial estimates should be used when converting Engel indices to Campelen equivalents. Hence, we do not recommend a different Engel-Campelen conversion factor than the one currently used in stock assessments for Thorny skates on the Grand Banks (NAFO Divisions 3LNOPs).

Cadigan, N., and Simpson, M. 2023. Contemporary analyses of comparative fishing data: a case study of Thorny skate on the Grand Banks (NAFO Divisions 3LNOP). J. Northw. Atl. Fish. Sci. 54: 1–16. https://doi.org/10.2960//J.v54.m739

This forty-fourth issue of NAFO Scientific Council Reports containing reports of Scientific Council Meetings held in 2022, is compiled in five sections: Part A –NAFO Scientific Council Meeting, 03 - 16 June 2022; Part B – NAFO Scientific Council Meeting, 27 July 2022; Part C – NAFO Scientific Council and STACFIS Shrimp Assessment Meeting, 12 – 16 September 2022; Part D – NAFO Scientific Council Meeting, 19 – 23 September 2022; and Part E—the Agendas; Requests; Lists of Research and Summary Documents; List of Representatives, Advisers, Experts and Observers; Merit Awards; and List of Recommendations relevant to Parts A-D.
For the meeting reports of the NAFO Precautionary Approach Working Group (PA-WG), and the NAFO Scientific Council Working Group on Ecosystem Science and Assessment (WG-ESA), visit the NAFO website.

This issue of the Meeting Proceedings of the Commission contains the meeting reports of the Commission (COM) and the joint Commission-Scientific Council (COM-SC), including their subsidiary bodies and working groups held between 1 September 2021 to 31 August 2022. This follows a NAFO cycle of meetings starting with an Annual Meeting rather than by calendar year.