  The delay difference model was implemented to fit 21 years of brown tiger
prawn (Penaeus esculentus) catch in Moreton Bay by maximum likelihood to assess
the status of this stock. Monte Carlo simulations testing of the stock
assessment software coded in C++ showed that the model could estimate
simultaneously natural mortality in addition to catchability, recruitment and
initial biomasses. Applied to logbooks data collected from 1990 to 2010, this
implementation of the delay difference provided for the first time an estimate
of natural mortality for brown tiger prawn in Moreton Bay, equal to $0.031 \pm
0.002$ week$^{-1}$. This estimate is approximately 30\% lower than the value of
natural mortality (0.045 week$^{-1}$) used in previous stock assessments of
this species.
