Strategies compared and approach taken Western Horse Mackerel - - PDF document

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Western Horse Mackerel Multi- annual Management

by Beatriz A. Roel

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Strategies compared and approach taken

• Constant catch strategies vs slope with a

50% fixed component.

• Final results without spasmodic

recruitment.

• Period of the simulations is 40 years
• Fishing patterns as observed in 2003-

2005.

• Biomass reference point (Bref) is SSB

1982.

Features of the strategies

• TAC is kept fixed = TARGET YIELD if

SSB (based on assessment)> SSBref.

– If SSB<SSBref, TAC is reduced linearly.

• SLOPE with fixed component (survey
• nly)

TACy+1 = ½ *FIX + ½ f(slope)* TACprevious

Constant Catch

Predicted TAC's under Constant Catch regime 50000 100000 150000 200000 250000 2004 2009 2014 2019 2024 2029 2034 2039 Year Tonnes

Target yield of 150 kT Target yield of 200 kT

Constant Catch? Target Yield

Predicted TAC's under Constant Catch regime

50000 100000 150000 200000 250000 2004 2009 2014 2019 2024 2029 2034 2039 Year Tonnes Target yield of 150 kT Target yield of 200 kT Target yield of 100 kT

Features of the strategies

• TAC is kept fixed = TARGET YIELD if

SSB> SSBref.

– If SSB<SSBref, TAC is reduced linearly.

• SLOPE with fixed component (survey
• nly)

TACy+1 = ½ *FIX + ½ f(slope)* TACprevious

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Slope strategy

Predicted TAC's under Slope Strategy regime 50000 100000 150000 200000 250000 300000 2004 2009 2014 2019 2024 2029 2034 2039 Year Tonnes

Distribution of SSB in the final year of the projections: target yield and slope strategies

Standard Catch - No reduction in TAC if SSB<Bref 10 20 30 40 50 60 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 final SSB ('000 tons) frequency in 500 simulations Standard Catch - Reduction in TAC if SSB<Bref 10 20 30 40 50 60 5 1 1 5 2 2 5 3 3 5 4 4 5 5 5 5 6 6 5 7 7 5 8 final SSB ('000 tons) frequency in 500 simulations Slope strategy ) 10 20 30 40 50 60 5 1 1 5 2 2 5 3 3 5 4 4 5 5 5 5 6 6 5 7 7 5 8 final SSB ('000 tons) frequency in 500 simulations

Comparison of performance between strategies:Target Yield and Slope (with a fixed component)

Target Yield Reductio n Spasm Recruitm Median Catch risk SSB < SSBref % < SSBref Cvar Median SSB final SSB 150 No 150 0.37 7.7 0.001 2261.8 2034.2 170 " 169 0.48 11.9 0.002 2138.5 1829.6 150 " 150 0.35 5.7 0.008 2294.4 2107.9 170 " 168 0.45 9.1 0.012 2183.1 1954.4 170 Yes 169 0.24 0.0 0.006 2824.5 2543.6 No 152 0.33 6.3 0.036 2266.9 2102.6 " 166 0.42 9.2 0.038 2181.8 1961.5 " 181 0.51 13.0 0.042 2089.2 1814.3 No n/a (Slope) n/a Yes

The assessment does not fit well the initial years of the egg series, which means that the link between eggs and biomass is weak but I took that into account in the model.

0.00E+00 1.00E+12 2.00E+12 3.00E+12 4.00E+12 5.00E+12 6.00E+12 1982 1986 1990 1994 1998 2002 Egg

Fishing patterns juvenile areas

Western horse mackerel - Catch at age JUVENILE AREAS 1 2 3 4 5 6 7 8 9 10 11 12 13 1997 1998 1999 2000 2001 2002 2003 2004 2005

Fishing patterns adult areas

Western horse mackerel - Catch at age ADULT AREAS 1 2 3 4 5 6 7 8 9 10 11 12 13 1997 1998 1999 2000 2001 2002 2003 2004 2005

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International western horse mackerel catches in adult (left) and juvenile (right) areas 20,000 40,000 60,000 80,000 100,000 120,000 140,000 160,000 180,000

1998 1999 2000 2001 2002 2003 2004 2005 1998 1999 2000 2001 2002 2003 2004 2005

tonnes Mean age of western horse mackerel in adult (left) and juvenile (right) areas 1 2 3 4 5 6 7 8 9 10 11

1998 1999 2000 2001 2002 2003 2004 2005 1998 1999 2000 2001 2002 2003 2004 2005 Age

Distribution of SSB in the final year of the projections (no pulse)

Target Yield 180,000 tons 10 20 30 40 50 60 5 1 1 5 2 2 5 3 3 5 4 4 5 5 SSB final (tons) frequency in 500 simulations 30% Juv in Catch 60% Juv in Catch

Distribution of SSB in the final year of the projections (13-15% below Bref; no pulse)

Target Yield 180,000 tons 10 20 30 40 50 60 5 1 1 5 2 2 5 3 3 5 4 4 5 5 SSB final (tons) frequency in 500 simulations 30% Juv in Catch 60% Juv in Catch