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Witch flounder - Southern Grand Bank
Marine Resource  Fact Sheet
Stocks management recommendations 2015
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: 2014
 
 
Biological State and Trend
State & Trend Descriptors
PartnerFIRMS
Exploitation rateNone-Low Fishing MortalityNo or low fishing mortalityGreen
Abundance levelIntermediate stock sizeIntermediate abundance

The stock size has steadily increased since 1999 and is now at 81% Bmsy. There is very low risk (<1%) of the stock being below Blim or F being above Flim. Recruitment (juveniles < 21 cm) since 2005 has generally been lower than average.
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
 

NAFO reopened a directed fishery in 2015 with a TAC of 1 000 t. Prior to the repoening, witch flounder were previously caught via bottom trawl as bycatch mainly in otter trawl fisheries of skate and Greenland halibut.

Recent catch estimates and TACs are:
  2006 2007 2008 2009 2010 2011 2012 2013 2014 2015
TAC1 ndf* ndf ndf ndf ndf ndf ndf ndf ndf 1.0
STATLANT 21 0.2 0.2 0.2 0.3 0.4 0.4 0.3 0.3 0.3  
STACFIS 0.5 0.2 0.3 0.4 0.4 0.4 0.3 0.3 0.3  

*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 2015 was equal to the TAC of 1,000 t. The probability that F > Flim in 2015 was less than 1%. The probability of F>Flim increases to 26% at an F of 85% FMSY. The population is projected to grow and the probability that the biomass in 2018 is greater than the biomass in 2014 is high under all scenarios. The population is projected to remain below Bmsy for all levels of F examined with a probability of greater than 50%.
  Projections with catch in 2015 = 1 000 t
 

Projected Yield (t)
Median (80% CI)

Projected Relative Biomass (By /Bmsy)

Median (80% CI)

F2015=0.019
2016 1048 (932 - 1175) 0.95 (0.56 - 1.52)
2017 1096 (922 - 1291) 1.00 (0.59 - 1.58)
2018   1.04 (0.65 - 1.63)
75% F2015=0.014
2016 784 (696 - 882) 0.91 (0.56 - 1.52)
2017 822 (696 - 970) 0.96 (0.60 - 1.58)
2018   1.01 (0.63 - 1.64)
125% F2015=0.024
2016 1307 (1163 - 1475) 0.91 (0.57 - 1.51)
2017 1357 (1155 - 1606) 0.95 (0.59 - 1.56)
2018   0.99 (0.61 - 1.60)
Fmsy=0.04
2016 2172 (1384 - 3267) 0.92 (0.56 - 1.53)
2017 2225 (1433 - 3327) 0.94 (0.58 - 1.54)
2018   0.96 (0.60 - 1.57)
75% Fmsy=0.047
2016 2549 (1623 - 3849) 0.91 (0.57 - 1.52)
2017 2602 (1663 - 3888) 0.93 (0.58 - 1.54)
2018   0.94 (0.59 - 1.54)
85% Fmsy=0.054
2016 2936 (1878 - 4429) 0.91 (0.56 - 1.53)
2017 2970 (1893 - 4412) 0.92 (0.57 - 1.52)
2018   0.93 (0.58 - 1.52)






Yield (t) and risk of F> Flim, B<Blim and B<Bmsy for projected F values of F2015, 75% F2015, 125% F2015 2/3 Fmsy 75% Fmsy, and 85% Fmsy.
  Yield P(Fyear > Flim) P(Byear < Blim) P(Byear < Bmsy) P(B2018 > B2014)
  2016 2017 2016 2017 2016 2017 2018 2016 2017 2018  
F2015 (0.019) 1048 1096 <1% <1% <1% <1% <1% 59% 55% 50% 73%
75%F2015 (0.014) 784 822 <1% <1% <1% <1% <1% 60% 55% 50% 74%
125% F2015 (0.024) 1307 1357 <5% <5% <1% <1% <1% 60% 56% 52% 72%
Fmsy (0.04) 2172 2225 3% 3% <1% <1% <1% 60% 57% 57% 69%
75%Fmsy (0.047) 2549 2602 11% 11% <1% <1% <1% 60% 58% 56% 68%
85% Fmsy (0.054) 2936 2970 26% 26% <1% <1% <1% 60% 58% 58% 67%


Assessment Model
Analytical assessment
Results

Previously this stock was assessed using trends in survey indices.

A surplus production model in a Bayesian framework was accepted as the basis for the assessment of this stock. The input data were catch from 1960 - 2014, Canadian spring survey series from 1984 - 1990, Canadian spring survey series from 1991 - 2014 (no 2006) and the Canadian autumn survey series from 1990  2013 (no 2014).

A maximum sustainable yield (MSY) of 3760 (2965 - 4820) tons can be produced by total stock biomass of 59 680 (44 600 - 73 700) tons (Bmsy) at a fishing mortality rate (Fmsy) of 0.06 (0.05 - 0.09). The relative population size (median B/Bmsy) was below Blim (30% Bmsy) from 1993-1998. Biomass has since increased to a level of 81% BMSY in 2014. The probability of being below Blim in 2014 is very low.

Human impact

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

Biological and environmental interactions

Witch flounder is distributed mainly along the southwestern slopes of the Grand Bank.

Fishing Mortality

Recruitment

Biomass
Scientific Advice

Special comments

No special comments.
Management
Management unit: Yes

Management Advice

Recommendation for 2016 and 2017

Scientific Council noted that this is a newly reopened fishery. Acceptable risk levels have not yet been specified, but to allow the stock to continue to increase towards Bmsy, exploitation in 2016 and 2017 should not exceed ⅔ Fmsy, corresponding to catches of 2172 t and 2225 t respectively. Catches at this level will have a 3% risk of exceeding Flim and <1% risk of driving the stock below Blim.


Management Objectives

The NAFO Fisheries Commission reintroduced a 1 000 t quota in 2015. Bycatches in commercial fisheries directed for other species should be kept to a minimum. General convention objectives (GC Doc. 08/3) are applied.

Stock definition for management purposes

The management unit is NAFO Div. 3NO. The stock mainly occurs in Div. 3O along the southwestern slopes of the Grand Bank. In most years the distribution is concentrated toward this slope but in certain years, a higher percentage is distributed in shallower water.
Source of information
 
SCR Docs. 15/37, 38; SCS Docs. 15/04, 05, 06, 07 Click to openhttp://www.nafo.int/publications/frames/sci-docs.html
Report of the Meeting, 29 May-11 June, 2015 - SCS Doc. 15/12 Click to openhttp://www.nafo.int/publications/frames/sci-reports.html
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