  This analysis of the variations of brown tiger prawn (Penaeus esculentus)
catch in the Moreton Bay multispecies trawl fishery estimated catchability
using a delay difference model. It integrated several factors responsible for
variations in catchability: targeting of fishing effort, increasing fishing
power and changing availability. An analysis of covariance was used to define
fishing events targeted at brown tiger prawns. A general linear model estimated
inter-annual variations of fishing power. Temperature induced changes in prawn
behaviour played an important role in the dynamic of this fishery. Maximum
likelihood estimates of targeted catchability ($3.92 \pm 0.40 \ 10^{-4}$
boat-days$^{-1}$) were twice as large as non-targeted catchability ($1.91 \pm
0.24 \ 10^{-4}$ boat-days$^{-1}$). The causes of recent decline in fishing
effort in this fishery were discussed.
