Research Document 2021/030
Assessment of the NAFO Division 4TVn southern Gulf of St. Lawrence Atlantic Herring (Clupea harengus) in 2018-2019
By Turcotte, F., Swain, D.P., McDermid, J.L., and DeJong, R.A.
Atlantic Herring in the southern Gulf of St. Lawrence (sGSL) consists of two spawning components: (1) spring spawners and (2) 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, and catches in the multi-species bottom trawl survey of the sGSL. The data and indices are reported for the whole-area 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 2020 is estimated to be approximately 26,000 t; 55 % of the limit reference point (LRP = 47,250 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 only slightly reduces the probabilities of SSB decline in projections. By 2029, the probability of exceeding the LRP was 0 % at all catch levels, with SSB values ranging between 160 and 1,198 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 2019 (16,000 t), the probabilities of a 5 % increase in SSB by 2022 are 29 %. Long-term projections show a continuous decline, with SSB in the Critical Zone by 2025. 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. The catch level offering the greatest probabilities of increasing SSB in the short and long term was 2,000 t.
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