CONSEQUENCES RELATED TO THE CHOICE OF BIOLOGICAL PARAMETERS Stock assessment CONSEQUENCES RELATED TO THE CHOICE OF BIOLOGICAL PARAMETERS A.Abella ARPAT-Livorno, Italy

age Size age N

Biomass T*

FAST GROWING

SLOW GROWING

…what happens when we use different growth parameters and M, but “consistent” among them? Is the perception of the current situation similar? M from Pauly’s equation (1980)

1/2 max 1/8 max 30% SSBo 10% SSBo

Assessment di Merluccius merluccius inTuscany (multigear fishery)

M variabile M costante Lower numbers by size Major proportion removed

variable M costant M Different contribution of each single gear to F by size

variable M costant M

Mortality estimates keeping lenght frequencies separated by sex

Estimation of Z with length converted catch curve

By sex merged

M F Total Data structured by age Simulated data>>>

Males Females

with SURBA the same overestimation will occur...

Size of first maturity