Strategies compared and approach taken Western Horse Mackerel - PDF document

Strategies compared and approach taken Western Horse Mackerel Multi- • Constant catch strategies vs slope with a annual Management 50% fixed component. • Final results without spasmodic recruitment. by Beatriz A. Roel • 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 Constant Catch Predicted TAC's under Constant Catch regime • TAC is kept fixed = TARGET YIELD if Target yield of 150 kT Target yield of 200 kT SSB (based on assessment)> SSBref. 250000 – If SSB<SSBref, TAC is reduced linearly. 200000 150000 Tonnes • SLOPE with fixed component (survey 100000 only) 50000 0 TAC y+1 = ½ *FIX + ½ f(slope)* TAC previous 2004 2009 2014 2019 2024 2029 2034 2039 Year Constant Catch? Target Yield Features of the strategies Predicted TAC's under Constant Catch regime • TAC is kept fixed = TARGET YIELD if Target yield of 150 kT Target yield of 200 kT Target yield of 100 kT SSB> SSBref. 250000 – If SSB<SSBref, TAC is reduced linearly. 200000 150000 Tonnes • SLOPE with fixed component (survey 100000 only) 50000 0 TAC y+1 = ½ *FIX + ½ f(slope)* TAC previous 2004 2009 2014 2019 2024 2029 2034 2039 Year 1

Distribution of SSB in the final year of the projections: target yield and slope strategies Slope strategy Standard Catch - Reduction in TAC if SSB<Bref Standard Catch - No reduction in TAC if SSB<Bref Predicted TAC's under Slope Strategy regime frequency in 500 simulations 60 frequency in 500 simulations 60 50 50 300000 40 40 30 30 250000 20 20 10 10 200000 0 0 Tonnes 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 150000 final SSB ('000 tons) final SSB ('000 tons) 100000 Slope strategy ) 50000 frequency in 500 simulations 60 50 0 40 2004 2009 2014 2019 2024 2029 2034 2039 30 20 Year 10 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 final SSB ('000 tons) Comparison of performance between strategies:Target Yield and 6.00E+12 Egg Slope (with a fixed component) 5.00E+12 4.00E+12 3.00E+12 Target Reductio Spasm Median risk SSB % < Median final Cvar Yield n Recruitm Catch < SSBref SSBref SSB SSB 150 No 150 0.37 7.7 0.001 2261.8 2034.2 2.00E+12 No " 169 0.48 11.9 0.002 2138.5 1829.6 170 150 " 150 0.35 5.7 0.008 2294.4 2107.9 1.00E+12 170 Yes " 168 0.45 9.1 0.012 2183.1 1954.4 170 Yes 169 0.24 0.0 0.006 2824.5 2543.6 0.00E+00 152 0.33 6.3 0.036 2266.9 2102.6 No n/a n/a 1982 1986 1990 1994 1998 2002 " 166 0.42 9.2 0.038 2181.8 1961.5 (Slope) " 181 0.51 13.0 0.042 2089.2 1814.3 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. Fishing patterns juvenile areas Fishing patterns adult areas Western horse mackerel - Catch at age JUVENILE AREAS Western horse mackerel - Catch at age ADULT AREAS 13 13 12 12 11 11 10 10 9 9 8 8 7 7 6 6 5 5 4 4 3 3 2 2 1 1 0 0 1997 1998 1999 2000 2001 2002 2003 2004 2005 1997 1998 1999 2000 2001 2002 2003 2004 2005 2

International western horse mackerel catches in adult (left) and juvenile (right) areas tonnes Distribution of SSB in the final year of the 180,000 160,000 projections (no pulse) 140,000 120,000 100,000 Target Yield 180,000 tons 80,000 60,000 60 30% Juv in Catch 40,000 50 60% Juv in Catch 20,000 frequency in 500 0 simulations 40 1998 1999 2000 2001 2002 2003 2004 2005 1998 1999 2000 2001 2002 2003 2004 2005 30 Age Mean age of western horse mackerel in adult (left) and juvenile (right) areas 20 11 10 10 9 8 0 7 0 0 0 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0 0 0 0 5 0 5 0 5 0 5 0 5 0 5 1 1 2 2 3 3 4 4 5 4 SSB final (tons) 3 2 1 0 1998 1999 2000 2001 2002 2003 2004 2005 1998 1999 2000 2001 2002 2003 2004 2005 Distribution of SSB in the final year of the projections (13-15% below Bref; no pulse) Target Yield 180,000 tons 60 30% Juv in Catch 50 60% Juv in Catch frequency in 500 simulations 40 30 20 10 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 5 0 5 0 5 0 5 0 5 0 1 1 2 2 3 3 4 4 5 SSB final (tons) 3