Background
Tropical fisheries often are characterised by morphologically-similar co-generic species that are not separated within landed catch. Despite niche overlap, population parameters differ and each species requires separate stock assessment and management responses. Long-term survey series can provide critical seasonal life history and species distribution data that allow spatial allocation of commercial catch to species over the decades.
Methods
In the 1980s, both the juvenile and adult phases of grooved and brown tiger prawns (Penaeus semisulcatus and P. esculentus) were monitored for six years and 18 months (respectively) at Groote Eylandt, western Gulf of Carpentaria (GoC). Since the early 2000s, a 23-year series of annual GoC-wide trawl surveys provide prawn species distribution and abundance indices that confirm the importance of fishery-independent data to inform management.
Results
Both juvenile and adult prawns showed micro-habitat preference and separated spatially within shallow coastal seagrass habitats and on the fishing grounds. Adult grooved and brown tiger prawn distribution data collected in the vicinity of Groote Eylandt during the 1980s provided the impetus to explore rigorous methods to allocate offshore mixed-species catch spatially. The 23-year GoC data series confirmed consistent species distribution that enabled spatial allocation of species’ proportion of commercial catch that provided managers with critical data to estimate species sustainability. The GoC survey series confirmed allopatric distribution for other go-generic species, the blue and red endeavour prawns (Metapenaeus endeavouri and M. ensis).
Conclusion
Mixed-species logbook tropical prawn catch can be apportioned to species based on decadal-consistent spatial distributions of each species. Using these data, species specific stock assessment and targeted management has been applied to this multispecies tropical fishery. Long-term, broad-scale fishery-independent survey data allow the identification of possible spatial distribution shifts among species that can be modelled to ensure the rigor of ongoing fishery assessment.