Final Anchovy TAC and Sardine TAB for 2011, Using OMP-08

Transcription

1 FIHERIE//WG-PEL/43 Final nchovy TC and ardine T for, Using OMP-08 Carryn L de Moor Correspondence carryn.demoor@uct.ac.za Following the recent recruit survey, the revised and final outh frican anchovy TC and sardine T are to be recommended. The following data have been used: 1) November 2010 survey sardine 1+ biomass: t. 2) November 2010 survey anchovy 1+ biomass: t. 3) May survey anchovy recruitment: billion. 4) Time after 1 May that the survey commenced: (survey commenced on 27 th May) 5) nchovy recruit catch from 1 st November to 26 th May, using monthly cut-off lengths from Cunningham et al. 2007: billion 6) nchovy adult catch from 1 st November to 26 th May, using monthly cut-off lengths from Cunningham et al. 2007: billion 7) Juvenile sardine : anchovy ratio (by mass) observed in the May recruitment survey: ) Juvenile sardine : anchovy ratio (by mass) observed in the May commercial catches: ) Directed sardine TC for 2010: t. 10) Directed anchovy normal season TC for 2010: t 1. Using the above data, the final TC and T recommendations are calculated by OMP-08 to be: Directed sardine TC: t Initial normal season anchovy TC: Revised normal season anchovy TC: dditional season anchovy TC: Total anchovy TC: t t t t Initial normal season sardine T: t Revised normal season sardine T: t dditional season sardine T: t Total sardine T: t The equations used to calculate these TC/s are given in the ppendix. MRM (Marine Resource ssessment and Management Group), Department of Mathematics and pplied Mathematics, University of Cape Town, Rondebosch, 7701, outh frica. 1 The total anchovy TC for 2010 was t, comprising of t for the normal season and t for the additional season. 1

2 FIHERIE//WG-PEL/43 Comments on the TCs s no Exceptional Circumstances were declared for sardine in December 2010, there is no update to the directed sardine TC. The additional season anchovy TC was constrained by the maximum of t. cknowledgements Janet Coetzee and Jan van der Westhuizen are thanked for providing the input data for these computations. References Cunningham, C.L., van der Westhuizen, J.J., Durholtz D. and Coetzee, J Record of the Generation of Data Used in the ardine and nchovy ssessments. Unpublished MCM Document MCM/2007/EPT/WG-PEL/03. 28pp. de Moor, C.L. and D.. utterworth OMP-08. MCM document, MCM/2008/WG-PEL/23. 15pp. 2

3 FIHERIE//WG-PEL/43 ppendix: ummary of revised and final anchovy TC and sardine T equations of OMP-08 (from de Moor and utterworth 2008). Revised TC / T The revised anchovy TC is initially calculated as: N 2, = TC α ns q p + 1 N rec0 ( p) 2010, N Nov This results in 2, 2010 = TC t. s the normal season anchovy TC in 2010 was above the 2-tier threshold of t, this TC is subject to the following constraints: which results in 1, 2, 1, ns, { TC ; ( 1 c ) c } TC min{ c TC c } max + TC 2, 2010 = mxdn tier mxtac ; t. The anchovy biomass projected for November 2010 is above the Exceptional Circumstances threshold and thus no Exceptional Circumstances provisions were invoked. 2010,Nov - the estimate of anchovy abundance (in thousands of tons) from the hydroacoustic spawner biomass survey in November Nov - the historic average index of anchovy abundance from the spawner biomass surveys N rec = ( N from November 1984 to November 1999, of thousand tons., r e 0.5(6+ t ) 0.9 /12 ) + C,0 bs e [0.5(6+ t )]0.9 /12 - the simulated estimate of anchovy recruitment from the recruitment survey in, obs N,,r, back-calculated to 1 November 2010 by taking natural and fishing mortality into account. N 0 = the average 1985 to 1999 observed anchovy recruitment (in billions) in May, backcalculated to November of the previous year. α = a control parameter which scales the anchovy TC to meet target risk levels for sardine ns and anchovy. p = the weight given to the recruit survey component compared to the spawner biomass survey component in setting the anchovy TC. q = reflects the average annual TC expected under OMP99 under average conditions if mxdn α = 1. ns c = the maximum proportional amount by which the normal season directed anchovy TC mxtac can be reduced from one year to the next (note that the additional season anchovy TC is not taken into consideration in this constraint). c = the maximum directed TC that may be set for anchovy (in thousands tons). 3

4 ns, FIHERIE//WG-PEL/43 c = the maximum amount by which the anchovy TC is allowed to be increased within the,0bs = normal season (in thousand tons). C the observed juvenile anchovy landed by number (in billions) from the 1 st of November 2010 to the day before the recruit survey commences in. t = the timing of the anchovy recruit survey in (number of months) relative to the 1 st of May. The revised sardine T is calculated using: 2, λ 1, 2, 1, T = TC + r ( TC TC ) + T 2, = This gives T t, where λ = γ, r } Trh max{ = = 3500t- the fixed tonnage of adult sardine bycatch set aside for the round herring fishery each year. γ = a conservative allowance for the ratio of juvenile sardine to juvenile anchovy in subsequent catches. 1 r = r + r ) = ( 2, sur, com - the ratio of juvenile sardine to anchovy in the sea during May, calculated from the recruit survey and the sardine bycatch to anchovy ratio in the commercial catches 2 during May. rh Final TC / T (the anchovy additional sub-season from 1 st eptember) The final anchovy TC is initially calculated as: TC N q p N 3, = α + 1 rec0 ( p) 2010, N Nov This gives TC result in TC 3, = t. The constraints: 2, 3, 2,, { TC ; c } TC min{ c TC c } max + 3, = mntac mxtac ; t. The anchovy biomass projected for November is above the Exceptional Circumstances threshold and thus no Exceptional Circumstances provisions were invoked. α = a control parameter which scales the anchovy TC to meet target risk levels for sardine, and anchovy. c = the maximum amount by which the anchovy TC is allowed to be increased within the additional sub-season (in thousand tons). 2 Only commercial catches comprising at least 50% anchovy with sardine bycatch are considered. 4

5 FIHERIE//WG-PEL/43 The final sardine T is calculated as: T which gives T 3, 3, = 2, = T + min γ t. Here: 3, 2, { T ; ( TC TC ) } T = 2 - the maximum fixed tonnage of juvenile sardine bycatch set aside for the anchovy additional sub-season each year (in thousand tons). 5