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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. [ABSTRACT FROM AUTHOR]

The most recent assessment of NAFO Division 4TVn spring and fall spawning Atlantic herring stocks was conducted in 2018 using Virtual Population Analysis models (VPA) with time-varying catchability. The increase in magnitude of a retrospective pattern in the spawning stock biomass (SSB) of the fall spawning herring models suggested that the model failed to incorporate one or more non-stationary processes in the population dynamics of this stock or in the observation model relating indices of abundance to population abundance. The 2018 spring spawning herring VPA also showed an increase in residual patterns in the catch-per-unit-effort (CPUE) and acoustic indices. Abundances of major predators of herring have changed drastically in the sGSL in the last decades, potentially generating important changes in herring natural mortality. Failure to account for changes in natural mortality due to changes in predator-prey interactions can result in biased estimates of population parameters and vital rates in stock assessments. Hence, estimating natural mortality was another motivation to re-explore 4T herring population models. The objectives of this paper are to perform a comparison of the VPA used in the most recent stock assessment and a series of Statistical Catch-at-Age (SCA) models with different assumptions about temporal variation in population processes (i.e., natural mortality) and/or observation processes (i.e., catchability in the fixed gear fishery). The aim is to determine the best performing model for the 2020 stock assessments. SCA models performed better than VPA models for both herring stocks. For the spring spawning herring stock, the SCA model estimating time-varying natural mortality and catchability to the CPUE index in the gillnet fishery (the qmSCA model) was the best performing model. In the fall spawning stock, the qSCA and the qmSCA models performed best, but the qmSCA was selected as the best model as it provided natural mortality estimates, an important parameter in 4TVn herring stock assessment. Retrospective patterns in SSB from this model must be monitored and the source of the pattern will be investigated using new data sources. Overall, the selected models offered improvements over VPA models used in previous assessments. [ABSTRACT FROM AUTHOR]

Atlantic Herring in 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, 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 regionallydisaggregated (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. [ABSTRACT FROM AUTHOR]

Metamorphosis is a critical developmental stage that presents particular challenges in fish aquaculture. The sharp increase in mortality that accompanies this transformation has often been attributed to nutritional deficiencies. Providing live feed (the rotifer Brachionus plicatilis Müller, 1786 and the brine shrimp Artemiasalina (Linnaeus, 1758)) during the larval stages is costly and labour intensive, which explains why much effort has been put on early weaning. However, previous observations in winter flounder (Pseudopleuronectes americanus (Walbaum, 1792)) indicate that juveniles weaned after settlement had better survival than those weaned at the larval stage. In this study, we tested whether late weaning (at settlement (W0) and groups maintained on co-feeding for 1 month (W1), two months (W2), or 3 months (W3) after settlement) could improve juvenile survival and lipid composition. Our results demonstrated that maintaining co-feeding beyond the larval stage was essential for after-settlement survival. Juveniles co-fed until 90 days after settlement were 32.5% heavier. Analyses of fatty acid trophic markers suggested that juveniles preferentially fed on enriched rotifers rather than inert food. No pigmentation or fin erosion problems were observed in any of the weaning treatments, which indicates good rearing conditions. [ABSTRACT FROM AUTHOR]