Find the current biomass at which it would take HZN mean generation times to reach Bfrac x SSBMSY biomass level given zero catches
Blow_opt(lnq, SSBMSYc, MGThorizon, Fc, Perrc, Mc, hc, Mac, Wac, R0c, Vc, nyears,
maxage, movc, Spat_targc, SRrelc, aRc, bRc, Bfrac, mode = 1)number: estimate of log catchability
number: spawning biomass at MSY
number: MGT x HZN
vector nyears long of fishing mortality rate
vector nyears+maxage-1 long of recruitment devitions
matrix maxage by nyears+proyears of natural mortality rate
number: steepness values
vector nages long of maturity at age
vector nages long of weight at age
number: unfished recruitment
matrix of vulnerability maxage x nyears
integer: number of historical years
integer: maximum age
matrix of movement 2 x 2
number: spatial targetting parameters
integer representing recruitmetn dynamics type 1: Bev Holt 2: Ricker
number: recruitment parameter
number: recruitment parameter
fraction of SSBMSY that is the target
1: find Blow 2:report blow 3:plot results