Science Advisory Report 2022/021
Assessment of the southern Gulf of St. Lawrence (NAFO Division 4TVn) spring and fall spawner components of Atlantic Herring (Clupea harengus) with advice for the 2022 and 2023 fisheries
- Atlantic Herring in the southern Gulf of St. Lawrence (sGSL) are composed of spring spawning and fall spawning components which are genetically distinct stocks and as such assessed separately.
- The biomass index from a collaborative fishery-independent fall spawning ground acoustic survey has been used for the first time in this assessment.
- For both spring and fall spawning Herring, the trend in natural mortality of ages 7 to 11+ was correlated with the increases in Grey Seal, Atlantic Bluefin Tuna and Northern Gannet abundance over the same time period.
Spring Spawner Component
- Based on the current stock assessment, the median estimates of Spawning Stock Biomass (SSB) have been in the Critical Zone of the Precautionary Approach (PA) Framework since 2002. As of 2020 and 2021, estimated SSB of spring spawning Herring have likely (> 80%) remained in the Critical Zone.
- Under current conditions of high natural mortality, declines in weight-at-age, and low recruitment, the probabilities that SSB will increase by 2024 ranges from 44% at a catch of 0 tonnes (t) to 42% at a catch 1,250 t. Even in the absence of fishery removals, it is likely (> 80%) that the stock will remain in the Critical Zone by 2027.
- Spring spawning Herring are caught in a directed fishery as well as bycatch in the fall Herring fishery for total preliminary landings of 603 t and 403 t in 2020 and 2021, respectively. Fishing mortality in this stock has exceeded the provisional harvest decision rule of the PA Framework since 1999. Total bait removals and discards-at-sea are unknown.
- Recruitment has remained stable at low values since 1993. This low recruitment corresponds with long-term environmental changes including temperature increases and changes in zooplankton abundance and phenology. Given the ongoing trend towards warmer environmental conditions and zooplankton dynamics, it is not expected that recruitment will improve.
- Annual natural mortality estimates for ages 2 to 6 remained stable between 21% and 40% over the time series. However natural mortality for older fish (ages 7-11+) increased since 2010 to reach a maximum of 65% in 2018 before declining to 59% in 2020 and 2021. Based on dynamics in predator abundance, natural mortality is expected to remain high.
Fall Spawner Component
- Based on the current stock assessment, the estimated SSB of fall spawning Herring has been in the Cautious Zone of the PA Framework since 2017, and is virtually certain (100%) to remain there in 2022. The stock has declined over the last decade.
- Under current conditions of high natural mortality, declines in weight-at-age, and low recruitment, the probabilities that SSB will increase by 2024 range from 35 to 40% across all considered catch options (18,000 to 2,000 t). At all catch options, it is exceptionally unlikely (< 1%) that SSB will increase into the Healthy Zone or decline into the Critical Zone by 2027.
- The preliminary landings of the fall spawning Herring component in 2020 and 2021 were 10,065 t and 10,834 t, respectively, from a 12,000 t TAC. Fishing mortality exceeded the provisional harvest decision rule of the PA Framework for most of the 1990s, early 2000s, and 2020-2021.
- Recruitment has been declining since 2006 to reach the lowest levels of the time series in recent years. The synchronicity of events and environmental conditions required to produce strong recruitment, including water temperature and zooplankton abundance, cannot be predicted, and therefore future recruitment is unknown.
- Annual natural mortality estimates for ages 2 to 6 decreased over the time series to very low values in 2021, although the absolute level remains uncertain. For ages 7 to 11+, annual natural mortality increased sharply since 1986 to reach a peak in mid-2010s (63%) before declining to stable values of approximately 49%. Based on dynamics in predator abundance, natural mortality is expected to remain high.
This Science Advisory Report is from the March 22-23, 2022 regional science peer review meeting on the Assessment of the southern Gulf of St. Lawrence (NAFO Division 4T-4Vn) spring and fall spawner components of Atlantic Herring (Clupea harengus) with advice for the 2022 and 2023 fisheries. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.
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