Science Advisory Report 2020/029

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 2020 and 2021 fisheries

Summary

• 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.
• Statistical Catch at Age models that incorporated time varying changes in catchability in the fixed gear fishery and changes in natural mortality have been used for the first time in this assessment.
• For both spring and fall spawners, the increasing trend in natural mortality of ages 7 to 11+ was correlated with the increase in indices of Grey Seal and Atlantic Bluefin Tuna abundance over the same time period.

Spring Spawner Component

• Based on the current stock assessment, the 2018 and 2019 estimate of Spawning Stock Biomass (SSB) of spring spawning herring has likely (>80%) remained in the Critical Zone of the Precautionary Approach Framework. The stock has been below the limit reference point (LRP) since 2002.
• Under current conditions of high natural mortality, declines in weight-at-age, and low recruitment, it is unlikely that SSB will increase in the short term (2021 and 2022) or the long term (2029) at all catch options between 0 and 1,250 t. Even in the absence of any fishery removals, it is very likely (> 90%) that the stock will remain in the Critical Zone.
• A directed fishery targets spring spawning herring with landings of 798 t and 1,047 t in 2018 and 2019, respectively. Fishing mortality in this stock has exceeded the provisional harvest decision rule of the Precautionary Approach Framework since 1999.
• Recruitment has remained stable at low values since 1994. This low recruitment corresponds with long-term environmental changes including temperature increases and changes in zooplankton abundance. Given the ongoing trend towards warmer environmental conditions, it is not expected that recruitment will improve in future years.
• Natural mortality estimates for ages 2 to 6 varied between 21% and 41% over the time series, however natural mortality for older fish (ages 7-11+) increased since 2011 to an estimated value of 64% in 2018 and 2019.

Fall Spawner Component

• The SSB of fall spawning herring in 2020 is virtually certain (100%) to be in the Cautious Zone of the Precautionary Approach Framework.
• Under current conditions of high natural mortality, constant fishing mortality, declines in weight-at-age, and low recruitment, it is unlikely that SSB will increase in the short term (2021 and 2022) or the long term (2029). Reducing fishing mortality will slightly reduce the probabilities of declines in the short and long term projections. It is unlikely (0-33%) that SSB will increase by 2022 at any catch option.
• The preliminary estimated landings of the fall spawning herring component were 16,742 t from a 25,000 t TAC in 2018 and 15,544 t from a 22,500 t TAC in 2019. Average fishing mortality exceeded the provisional harvest decision rule of the Precautionary Approach Framework for most of the 1990s and 2000s but is currently below the provisional harvest decision rule at stable levels.
• Recruitment has been declining since 2006 and reached the lowest levels of the time series in recent years. Environmental conditions that promote high recruitment require the synchronicity of temperature, zooplankton abundance, and timing of the release of herring larvae. The occurrence of future environmental conditions for successful fall spawning herring recruitment cannot be predicted.
• Natural mortality estimates for ages 2 to 6 decreased over the time series, with trends that matched the declines seen in the abundance of Atlantic Cod in the sGSL. For ages 7 to 11+, annual natural mortality estimates increased sharply in 2004 to reach a peak in the mid-2010s and has since stabilized at values of approximately 55%.

This Science Advisory Report is from the March 12-13, 2020 regional science peer review meeting on the Assessment of stock status of Atlantic Herring (Clupea harengus) from the southern Gulf of St. Lawrence (NAFO Div. 4T-4Vn) to 2019 and advice for the 2020 and 2021 fisheries. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

Science Advisory Report 2020/029 (PDF, 3,132 KB)

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