Assessment of the NAFO Division 4TVn southern Gulf of St. Lawrence Atlantic Herring (Clupea harengus) in 2020-2021

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. Spring spawners were assessed using a statistical catch at age (SCA) model that allowed for time-varying catchability to the gillnet fishery and time-varying natural mortality. The model estimated that spawning stock biomass (SSB) has been in the critical zone of the Precautionary Approach framework since 2002. The SSB median estimate in April 1 2022 is estimated to be 28,835 tons (t); 62% of the limit reference point (LRP = 46,340 t). Under current low recruitment and high natural mortality conditions, this stock is not expected to recover in the short or the long term. Reducing fishing mortality will have marginal effects on the projected SSB trends. By 2027, the probability of exceeding the LRP was not more than 20% at all catch levels, with SSB values ranging between 32,500 and 35,400 t. Fall spawners were assessed as regionally-disaggregated populations using a SCA model that allowed for time-varying catchability to the gillnet fishery and time-varying natural mortality. Estimated SSB has been declining in all three regions in recent years and is currently in the Cautious Zone of the Precautionary Approach framework. At the target catch level in 2021 (~12,000 t), the probabilities of a 5% increase in SSB by 2024 are all under 40%. Long-term projections show a continuous decline of SSB, however the probability of moving into the Critical Zone (under the LRP) by 2027 was 0% at all catch levels. As a consequence of low productivity and high natural mortality, exploitation of this stock should assert caution until high recruitment is observed for consecutive years.