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Witch flounder - Southern Grand Bank
Marine Resource  Fact Sheet
Stocks management recommendations 2018
Witch flounder - Southern Grand Bank
Fact Sheet Citation  
Witch flounder in Div. 3NO
Owned byNorthwest Atlantic Fisheries Organization (NAFO) – More
Related observationsLocate in inventorydisplay tree map
 
Species:
FAO Names: en - Witch flounder, fr - Plie cynoglosse, es - Mendo, ru - Камбала длинная (красная) атлантическая
Geographic extent of Witch flounder - Southern Grand Bank
Main Descriptors
Considered a single stock: Yes        Spatial Scale: Regional
Management unit: Yes        Reference year: 2017
 
 
Biological State and Trend
State & Trend Descriptors
PartnerFIRMS
Exploitation rateNone-Low Fishing MortalityNo or low fishing mortalityGreen
Abundance levelsmall stock sizeLow abundance

The stock size increased since 1999 to about 2010 and then declined after 2013 and is now at 37% Bmsy. (Bmsy = 60 000 t). There is presently a 29% risk of the stock being below Blim and a 4% risk of F being above Flim. Recruitment in 2017 surveys increased in the fall to a value just above the time series mean while those in the spring increased to a value approaching the time series mean.
Habitat and Biology
Climatic zone: Temperate.   Bottom type: Unspecified.   Depth zone: Slope - Deepslope (500 m - 1000 m).   Horizontal distribution: Neritic.   Vertical distribution: Demersal/Benthic.  

Geographical Distribution
Jurisdictional distribution: Straddling between High Seas and EEZ

Water Area Overview
Spatial Scale: Regional

Geo References
Resource Structure
Considered a single stock: Yes
Exploitation
 

The fishery was reopened to directed fishing in 2015 and is exploited by otter trawl. Prior to the reopening, witch flounder were caught as bycatch in bottom otter trawl fisheries for yellowtail flounder, redfish, skate and Greenland halibut.

Recent catch estimates and TACs are:
  2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018
TAC ndf ndf Ndf ndf ndf ndf ndf 1.0 2.2 2.2 1.1
STATLANT 21 0.2 0.1 0.4 0.4 0.3 0.3 0.3 0.4 1.0 0.6  
STACFIS 0.3 0.4 0.4 0.4 0.3 0.3 0.3 0.4 1.1 0.7  

*ndf = no directed fishing



Effects of the fishery on the ecosystem

No specific information available. General impacts of bottom trawl gear on the ecosystem should be considered.
Assessment
 
Overall Assessment Results
Reference Point
 

Reference points were estimated from the surplus production model. Scientific Council considers that 30% Bmsy is a suitable biomass limit reference point (Blim) and Fmsy a suitable fishing mortality limit reference point.
Projection

Projections and risk analyses.

All projections assumed that the catch in 2018 was equal to the TAC of 1,116 t (which produces F2018). This assumption was based on reported catches to the end of April 2018 of almost 600 t. The probability that F > Flim in 2018 is 30% at a catch of 1 116 t. The probability of F>Flim ranged from 7 to 50% for the catch scenarios tested. The population is projected to grow under all scenarios and the probability that the biomass in 2021 is greater than the biomass in 2018 is greater than 60% in all scenarios. The population is projected to remain below BMSY for all levels of F examined with a probability of greater than 90%. The probability of projected biomass being below Blim by 2021 was 19 to 24% in all catch scenarios examined and was 15% by 2021 in the F=0 scenario.
  Projections with catch in 2018 = 1 116 t
  Median Median (90% CI)
F=0 Projected Yield (t) Projected Relative Biomass (By /Bmsy)
2019 0 0.39 (0.19, 0.91)
2020 0 0.43 (0.21, 1.02)
2021   0.48 (0.23, 1.12)
F2017=0.03 Projected Yield (t) Projected Relative Biomass (By /Bmsy)
2019 740 0.39 (0.19, 0.91)
2020 792 0.42 (0.20, 1.00)
2021   0.45 (0.20, 1.09)
2/3 Fmsy=0.04 Projected Yield (t) Projected Relative Biomass (By /Bmsy)
2019 979 0.39 (0.19, 0.91)
2020 1035 0.42 (0.19, 0.99)
2021   0.44 (0.19, 1.08)
85% Fmsy=0.05 Projected Yield (t) Projected Relative Biomass (By /Bmsy)
2019 1248 0.39 (0.19, 0.91)
2020 1306 0.41 (0.19, 0.99)
2021   0.43 (0.19, 1.06)
Fmsy=0.06 Projected Yield (t) Projected Relative Biomass (By /Bmsy)
2019 1468 0.39 (0.19, 0.91)
2020 1522 0.41 (0.19, 0.98)
2021   0.42 (0.18, 1.05)



Projected yield (t) and the risk of F> Flim, B<Blim and B<BMSY and probability of stock growth (B2021>B2018) under projected F values of F=0, F2017, 2/3 FMSY, 85% FMSY, and FMSY.
  Yield 2019 Yield 2020 P(F>Flim) P(B<Blim) P(B<BMSY) P(B2021>B2018)
      2019 2020 2019 2020 2021 2019 2020 2021  
F=0 0 0 0 0 26% 20% 15% 96% 95% 93% 72%
F2017=0.03 740 792 7% 8% 26% 22% 19% 96% 95% 93% 67%
2/3 Fmsy=0.04 979 1035 19% 20% 26% 23% 21% 96% 95% 94% 65%
85%Fmsy=0.05 1248 1306 36% 37% 26% 24% 23% 96% 95% 94% 63%
Fmsy=0.06 1468 1522 50% 50% 26% 25% 24% 96% 95% 94% 61%


Assessment Model
Analytical assessment
Results

This stock is assessed utilizing a surplus production model in a Bayesian framework. A full assessment was conducted in 2017 and 2018.

The input data were catch from 1960-2017, Canadian spring survey series from 1984-1990, Canadian spring survey series from 1991-2017 (no 2006) and the Canadian autumn survey series from 1990-2017 (no 2014).

The next assessment is planned for 2020.

Human impact

Mainly fishery related mortality. Other sources (e.g. pollution, shipping, oil-industry) are undocumented.

Biological and environmental interactions

Witch flounder in NAFO Divs 3NO are distributed mainly along the tail and southwestern slopes of the Grand Bank. The Southern Grand Bank (3NO) EPU is currently experiencing low productivity conditions and biomass has declined across multiple trophic levels and stocks since 2014.

Fishing Mortality

Recruitment

Biomass
Scientific Advice

Special comments

This advice is given by SC on its own accord in light of the special comment in 2017 (Because of the uncertainty and proximity to limit reference points the next full assessment is rescheduled for 2018).
Management
Management unit: Yes

Management Advice

Recommendation for 2019 and 2020

The probability of being below Blim in 2021 ranges from 15% to 24% amongst the tested scenarios. The NAFO PA framework specifies that there should be a very low probability of being below Blim.
Management Objectives

The Commission adopted a total allowable catch (TAC) of 1,116 t in 2018. General convention objectives (GC Doc. 08/3) are applied.

The management unit is NAFO Divisions 3NO. The stock mainly occurs in Div. 3O along the southwestern slopes of the Grand Bank. In most years the distribution is concentrated toward the slopes but in certain years, a higher percentage may be distributed in shallower water.
Source of information
 
SCR Docs 18/14, 18/03, 18/05, 18/25; SCS Docs. 18/05, 18/06, 18/07, 18/08 ; NAFO/GC Doc 08/3.
Report of the Meeting, 01 -14 June, 2018 - SCS Doc. 18/19.
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