Science Advisory Report 2021/049
An Assessment of Northern Shrimp (Pandalus borealis) in Shrimp Fishing Areas 4–6 and of Striped Shrimp (Pandalus montagui) in Shrimp Fishing Area 4 in 2020
- Resource status of Northern Shrimp in SFAs 5 and 6 was assessed based on Fisheries and Oceans Canada (DFO) fall multi-species trawl survey data (1996–2020). Resource status for Northern and Striped Shrimp in SFA 4 were assessed based on Northern Shrimp Research Foundation (NSRF)-DFO summer trawl survey data (2005–20).
- Trawl survey data for SFAs 4–6 provided information on shrimp distribution, length frequencies and biomass. Trends in fisheries performance were inferred from total allowable catch (TAC), commercial catch to date, fisher catch per unit effort (CPUE) and fishing patterns.
- It is recognized that Pandalus borealis are distributed broadly over the Northwest Atlantic Ocean, including SFA 4–6, and that these areas are connected through larval dispersal, but rates of exchange of adults are less understood. These linkages need to be considered to interpret dynamics within and among assessment areas.
- It is recognized that the population of Pandalus montagui spans the area of Eastern Assessment Zone (EAZ), Western Assessment Zone (WAZ) and SFA 4. Currently it is not known what the rates of exchange (export/import) are between these zones, therefore, understanding resource dynamics as a whole requires integrating information from all assessment areas.
- Bottom and sea surface temperatures (SSTs) are important drivers for the development of shrimp eggs and larvae, respectively. In SFAs 4-6, these variables have shown similar trends over the last 40 years, with a cold phase in the mid-1980s and 1990s and a warm period in the late 1990s and early-2010s, but their trends have diverged since 2015. While colder bottom waters prevailed between 2014 and 2017, warmer bottom temperatures led to above average extent of bottom thermal habitat (2–4°C) between 2018 and 2020. In 2020, SSTs were above normal for the first time since 2013.
- Chlorophyll concentrations and zooplankton biomass were below normal in the early and mid-2010s, increasing to values above the long term (1999–2020) average since 2016–17. Additionally, there have been changes in zooplankton community structure over the past decade with fewer large and more smaller copepods although the abundance of large, energy-rich calanoid copepods has increased to above-normal levels in some areas since 2017. Additionally, changes in zooplankton seasonality (weaker spring and stronger summer and fall zooplankton signals) may change the quality and timing of food availability for upper trophic levels.
- Ecosystem conditions in the Newfoundland Shelf and Northern Grand Bank (Northwest Atlantic Fisheries Organization [NAFO] Divs. 2J3KL; SFA 7, 6, and southern part of SFA 5) remain indicative of overall limited productivity of the fish community. While total biomass levels remain much lower than prior to the collapse in the early-1990s, it showed some recovery up to the early mid-2010s, when some declines where observed. Current total biomass remains below the early-2010s level, but with some positive signals in 2020. Since the mid-2000s this fish community has shifted back to a finfish-dominated structure, but has shown small increases in shellfish dominance since 2018.
- The available information for the Labrador Shelf (NAFO Div. 2H, northern part of SFA 5) shows declines in total biomass of the fish community from the levels observed in the early-2010s, but the 2020 survey suggests a potential reversal of this trend. The structure of the fish community is also changing, showing reductions in the dominance of shellfish. This suggests that this ecosystem could be shifting to a finfish-dominated community, as observed in NAFO Divs. 2J3KL (SFA 7, 6, and southern part of SFA 5).
- Consumption analyses indicated that predation is a major driver of the stock. In 2020, the shrimp predation mortality rate in NAFO Divs. 2J3KL (SFA 7, 6, and southern part of SFA 5), which had reached its highest levels on record in 2018-19, declined to levels comparable to the mid-2000s.
- The build-up of shrimp until the mid-2000s occurred during a period of favourable environmental conditions and reduced predation. Shrimp per-capita net production has declined since the mid-2000s, but the trend has shown some signals of reversal in 2019–20. Shrimp per-capita net production is expected to remain around current values, or show modest improvement in the next 1–3 years.
- Predation, fishing pressure, and warm climate conditions remain negatively correlated with subsequent shrimp per-capita net production in NAFO Divs. 2J3KL (SFA 7, 6, and southern part of SFA 5). Fishing in NAFO Divs. 2GH (SFA 4 and northern part of SFA 5) also shows a negative correlation with shrimp per-capita net production in NAFO Divs. 2J3KL, suggesting that shrimp productivity can be impacted by fishing in upstream areas.
- Under current ecosystem conditions (i.e. low shrimp biomass, but potentially declining predation pressure), fishing at the current exploitation rate is unlikely to be a dominant driver for shrimp in NAFO Divs. 2J3KL (SFA 7, 6, and southern part of SFA 5). Fishing pressure could now be more influential on stock trajectories than it may have been when the stock was large. Similar analyses on the relative impacts of predation and fishing for the Labrador Shelf (NAFO Div. 2H, northern part of SFA 5) suggest that fishing could be a more important driver than predation in this area.
- TAC was increased from 8,730 t in 2018/19 to 8,960 in 2019/20 and reduced, by 8%, to 8,290 t in 2020/21.
- The annual commercial CPUE declined considerably between 2015/16 and 2017/18 to the lowest levels in two decades and has remained low since.
- Over 1996 to 2020 the fishable biomass index averaged 370,000 t. It was 118,000 t in 2020, an increase from 2019, but still near the lowest levels in the survey time series.
- Over 1996 to 2020 the female spawning stock biomass (SSB) index averaged 232,000 t. It was 74,800 t in 2020, an increase from 2019, but still near the lowest levels in the survey time series.
- The exploitation rate index ranged between 5.5% and 21.5% from 1997 to 2020/21 and was 5.6% in 2020/21. If the TAC is fully taken in 2020/21 then the exploitation rate index will be 10%.
- The female SSB index is currently in the critical zone of the integrated Fisheries Management Plan (IFMP) Precautionary Approach (PA) Framework with a 35% probability of being in the cautious zone.
- The rebuilding plan states a maximum exploitation rate of 10% while the female SSB index is in the critical zone. If the 2020/21 TAC of 8,290 t is maintained and taken in 2021/22, the exploitation rate index would be 7%.
- TAC was reduced from 25,630 t in 2018/19 to 22,100 t in 2019/20 and further reduced, by 35%, to 14,450 t in 2020/21.
- Standardized large-vessel CPUE had varied without trend at relatively high levels for more than a decade before falling below the long-term mean beginning in 2017/18. Commercial catch rates may have been partly influenced by ice coverage.
- The number of stations sampled by the DFO multi-species survey in 2020 was reduced due to several factors. Retrospective time-series simulations suggest that the biomass estimates may slightly underestimate the stock status in SFA 5 in 2020.
- Over 1996 to 2020 the fishable biomass index averaged 127,000 t. It was 80,400 t in 2020, an increase from 2019, but still near the lowest levels in the survey time series.
- Over 1996 to 2020 the female SSB index averaged 63,000 t. It was 51,300 t in 2020, an increase from 2019, but still near the lowest levels in the survey time series.
- The exploitation rate index varied without trend with a median value of 15% from 1997–2020/21 and was 16.4% in 2020/21. If the TAC is fully taken in 2020/21 then the exploitation rate index will be 22.4%.
- Female SSB index is in the healthy zone within the IFMP PA Framework with 19% probability of being in the cautious zone. If the 14,500 t TAC is maintained and taken in 2021/22, then the exploitation rate index will be 18%.
- TAC was reduced from 15,725 t in 2018/19 to 10,845 t in 2019/20 and further reduced by 20%, to 8,658 t, in 2020/21.
- Large-vessel standardized CPUE varied without trend near the long-term mean (1989–2019/20).
- Over 2005 to 2020 the fishable biomass index averaged 97,200 t. It was 58,900 t in 2020, a 9% increase from 2019 and the third lowest level in the time series.
- Over 2005 to 2020 the female SSB index averaged 60,900 t. It was 43,100 t in 2020, a 9% increase from 2019 and amongst the lowest levels in the time series.
- The exploitation rate index ranged between 7% and 37.3% from 2005/06 to 2019/20 and was 12.8% in 2020/21. If the TAC had been taken, the exploitation rate index would have been 14.7%.
- Female SSB index in 2020 was in the cautious zone within the IFMP PA Framework, for the third consecutive year, with a 6% probability of having been in the critical zone and a 36% probability of having been in the healthy zone.
- The by-catch limit of 4,033 t has not been taken in the past eight years, with the commercial catch ranging between 1,113 t and 3,035 t.
- Over 2005 to 2020 the fishable biomass index averaged 28,800 t. It was 25,500 t in 2020, a 35% decrease from 2019.
- Over 2005 to 2020 the female biomass index averaged 22,100 t. It was 18,700 t in 2020, a 43% decrease from 2019.
- The exploitation rate index was 9.7% in 2020/21. If the by-catch limit had been taken, the exploitation rate index would have been 15.8% in 2020/21.
- There was no limit reference point (LRP) established for this resource during this meeting. Subsequently, there is no IFMP PA Framework for this resource.
SFA 6 Pandalus borealis
SFA 5 Pandalus borealis
SFA 4 Pandalus borealis
SFA 4 Pandalus montagui
This Science Advisory Report is from the February 22-26, 2021 Zonal Advisory Meeting on Assessment of Northern Shrimp in Shrimp Fishing Areas (SFAs) 4–6, Eastern Assessment Zone (EAZ), and Western Assessment Zone (WAZ); and of Striped Shrimp in SFA 4, EAZ and WAZ. 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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