In the Gulf of Carpentaria, banana prawns
(Penaeus merguiensis) form dense aggregations that are
targeted by trawl vessels with the help of small aeroplanes and colour
sounders. Such aggregating behaviour is rare in penaeids and may lead to a
change in catchability when stock abundance changes. Commercial logbook data
containing trawl-tow records have been used to identify the location, time of
capture and biomass of over 600 banana prawn aggregations during
1991–92. The number of aggregations decreased by 83% in the first
three weeks of the fishing season. The average biomass of an aggregation
decreased even more rapidly than the number of aggregations and, after three
weeks of fishing, it had been reduced by 93%. The apparent decrease in
the biomass of aggregating prawns during the first three weeks of the season
is, therefore, in the order of 99%. This is considerably greater than
the 66% decrease that can be estimated from catch per unit of effort
data. It also suggests that catchability is directly related to stock
abundance. Assessment models that assume that catchability is independent of
stock size may not be appropriate for the assessment of the status of common
banana prawns in this fishery.
The Cost of Co-viability in the Australian Northern Prawn Fishery
