Supporting material for stock assessment of NAFO division 4TVn Southern Gulf of St. Lawrence Atlantic Herring (Clupea harengus) in 2022-2023

Abstract

Atlantic Herring (Clupea harengus) in Northwest Atlantic Fisheries Organization (NAFO) Division 4T, referred to as the southern Gulf of St. Lawrence (sGSL), consists of two spawning components, spring spawners and fall spawners. This document presents the most recent information on trends in abundance, distribution, and harvest for the spring and fall spawning Herring components in NAFO Division 4T. This includes catch-at-age and catch-per-unit-effort (CPUE) indices, fisheries-independent acoustic indices, experimental gillnet survey indices, mesh selectivity, fishery-dependent acoustic indices and catches in the multi-species bottom trawl survey of the sGSL. The data and indices are reported for the sGSL for the spring spawners, and regionally-disaggregated (North, Middle, and South regions) for the fall spawners where applicable. This information is the basis of the assessment of spring and fall spawning 4TVn Atlantic Herring. Since the last assessment in 2022, we continued collecting data from our various data sources including commercial landings, telephone survey, port sampling, fishery independent acoustic survey, industry acoustic survey of spawning grounds, experimental variable mesh size net and multispecies bottom-trawl survey. From these data sources, the calculations of catch-at-age matrices were improved by translating calculations from Statistical Analysis Software and Excel into R language. The translation process facilitates the future reproduction of calculations, and was an opportunity to address issues in the calculation of past biomass estimates. While the trends remained after this process, yearly estimates shifted slightly higher or lower depending on the region and the spawning component. In addition, the process fixed the abnormal retrospective pattern observed in the previous assessment which means a more accurate biomass estimates. The spring and fall populations still face a lot of uncertainties, especially regarding rising sea temperature, which may change spatial distribution of Atlantic Herring and affect other demographic metrics (i.e., recruitment). This document is meant to support the stock assessment of Atlantic Herring in 4TVn by presenting data sources and data changes between the 2022 and 2024 assessment, but does not include details on model methodology.