Final Report - 2008-019-DLD - Biological and economic harvest evaluations of the eastern king prawn fishery
Stock assessment of the eastern king prawn (EKP) fishery, and the subsequent advice to management and
industry, could be improved by addressing a number of issues.
The recruitment dynamics of EKP in the northern (i.e., North Reef to the Swain
Reefs) parts of the fishery need to be clarified. Fishers report that the size of the
prawns from these areas when they recruit to the fishing grounds is resulting in suboptimal
sizes/ages at first capture, and therefore localised growth overfishing.
There is a need to assess alternative harvest strategies of the EKP fishery, via
computer simulations, particularly seasonal and monthly or lunar-based closures to
identify scenarios that improve the value of the catch, decrease costs and reduce the
risk of overfishing, prior to implementing new management measures.
Principal Investigator: Tony Courtney
Key Words: eastern king prawn, Melicertus plebejus, recruitment, tag-recapture, fishery economics, maximum sustainable yield, MSY, maximum economic yield, MEY, EMSY, harvest strategy evaluations, fishing power, generalised linear model, GLM, linear mixed models.
Summary: To date, these are the main outcomes achieved by this project:
- Eastern king prawns (EKP, Melicertus plebejus) are a valuable commercially-fished stock
in Queensland and New South Wales, with a total annual landed value of about $45
million. An important outcome of the project was that it initiated a series of steering
committee meetings that were made up of commercial fishers, GBRMPA, fishery
economists, fishery managers and scientists from both states to focus on the fishery’s
performance, stock assessment and management. The project promoted collaborative
research, assessment and management of the fishery.
- In its northern distribution (i.e., 22–24oS) the fishery is located over 100 km from the
coast and the source of prawns caught in this area has been unknown. The study
concluded the prawns most likely recruit from offshore reefs associated with the
Capricorn-Bunker Islands. As a result, fishers and managers are now in a stronger
position to develop and implement management measures, including closures, in this part
of the fishery.
- Fishing power in the EKP fishery was found to have increased by 52% from 1989 to
2010, highlighting the need to take fishing power changes into account when reporting
long-term trends in catch rates, assessing the stock and forecasting catch rates and
- The project derived a new quantitative description of growth for M. plebejus by utilizing
all available tag-recapture data from Queensland and New South Wales. Latitudinal and
seasonal effects on growth were quantified. Growth rate falls to a minimum in winter,
peaks in summer and declines with increasing latitude. This new description improves
the accuracy of stock assessment and modeling of harvest strategies.
- An economic survey of the Queensland EKP fishery provided information on fixed and
variable costs, total invested capital, gross value of product, average boat gross margin
and total vessel costs. The data are used to comment on the profitability and economic
viability of the fishery.
- The project evaluated 18 management scenarios put forward by fishers and managers
from both states. These included one-monthly trawl closures, a cap on total fishing effort,
and within-year catch rate control rules, as well as assumptions about annual increases in
operational costs and fishing power.
- The project identified how profitability and sustainability of the EKP fishery could be
improved by deriving estimates of MEY and EMEY. The results were presented to
industry and managers at steering committee meetings. If current fishing costs remain
steady or increase, total effort levels between 7000 and 20,000 boat-days will produce