The biology, socioeconomics and management of the barramundi fishery in the Fly River and adjacent coast of Papua New Guinea

• National Fisheries Authority, Papua New Guinea
• Department of Environment and Conservation, Papua New Guinea
• Ok Tedi Mining Ltd (Environment Division), Papua New Guinea
• James Cook University, Australia

Barramundi was once the fourth most valuable export commercial fishery in Papua New Guinea, with total catches greater than 200 tonnes per year. But in about 1990 this rather unregulated commercial operation collapsed because of poor catches, and catches plunged to about 4 tonnes/year. But although the commercial fishery virtually ceased, the fish remained important economically for artisanal fishers in PNG's Western Province. Barramundi occur on the coast and inland in all rivers of southern PNG west of Port Moresby, but populations are particularly large in the Fly River. About 200 small-scale fishers worked this area, and barramundi was their most valuable catch. However, these catches were also declining, with figures as low as 10 tonnes per year, of which at least 60% were juvenile fish.
Rehabilitating the barramundi populations in PNG's Western Province therefore became an important issue. ACIAR funded a one-year study of fishing logbook data in 1996, which showed that there were large gaps in knowledge about the biology of barramundi in the area and about the operations of the traditional fishery. In particular, biologists needed to know more about the spawning grounds and the origin of the fish that were being caught. Also unknown was the age structure of the Fly River population and whether it was genetically discrete. Many questions also remained about the socio-economics of the artisanal fishing in the area.

This project aimed to study the biology, socioeconomics and management of the barramundi fishery in order to develop a draft management plan that could revive this important fishery.

The work was divided into two parts. In the first, consisting of three subprojects, the scientists studied barramundi biology. They examined the genetics of the fish, identifying genetically separate stocks and their relative contribution to the spawning population. Scientists determined the seasonality and extent of spawning and gathered vital data such as growth rate and fecundity of the fish. A better understanding of its early life history enabled researchers to accurately describe potential nursery habitats. For the Fly River population, the focus was on understanding the migration of adults between marine spawning grounds and freshwater habitats, which would give an estimate of the potential yield in the Fly River system. Changes in the trace element composition of otoliths (mineral bodies found in the ear of the fish) from coastal and Fly River adults were studied to provide evidence of the habitat history of fish from respective areas.
The second part of the work concentrated on the socio-economics of the barramundi fishery in the region. Researchers analysed the importance of the fishery to the local economy, in the hope of ascertaining the degree of local knowledge about the fish and to find out the ways that artisanal fishers manage it. They were thus able to take local views into account in the two final subprojects - the development of a bio-economic model for the fishery and an overhauled fishery management plan. Both these objectives incorporated cost:benefit analyses of the fishery for coastal communities and provided a range of options for the fishery.
The project was initially designed to complement studies by an AusAID-funded Coastal Zone Management Study into the coastal artisanal fishery in Daru. However, the abandonment of the AusAID project made it necessary to redesign the delivery pathways of this project.

Conclusive genetic and biological evidence was found to demonstrate that there is only one stock of barramundi living in the Fly River and associated coastal waters. The stock extends into West Papua, thereby constituting a cross-border resource, but it differs from barramundi found in the far east of PNG. This finding was unexpected, based on the predictions from studies conducted in Australia.
The biological studies showed no evidence of changes from earlier (1970s) estimates of biological parameters of growth, reproduction and feeding. However, otolith microchemistry data showed conclusively that the migration patterns of Fly River barramundi do not follow a regular set pattern as they do in Australia. Many fish only visit the sea once during their lives, and some individuals remain upriver for extended periods. Analyses of net selectivity for barramundi coupled with reproductive data indicated the importance of conserving large females, i.e. restricting the use of large mesh gill nets.
The socioeconomic study found that the fishing communities along the waterways were unaware that resources, in particular barramundi, are finite and must be managed for sustained yield. No local group had indigenous knowledge of the complex breeding and migratory habits of this species, in waters claimed and fished by a large number of different villages and language groups. Although coastal villages and river clans claimed rights (contested by other groups) to exclude outsiders from waters over which they claimed tenure, no group had traditional resource management practices.
Using the data from all of these studies, the researchers constructed a computer model of the fishery, predicated around searching for a combination of effort controls (size limits, mesh sizes and closed seasons) that would lead to the most efficient use of the available resource. It was used to investigate different management options, such as how the fishery might respond to variations in distribution of fishing effort among the different communities. After appropriate consultation, a Barramundi Fishery Management Plan involving mesh size restrictions as well as closed seasons and areas was accepted by stakeholder representatives then by the National Fisheries Board, and signed into law by the PNG government in April 2003. A Barramundi Management Advisory Committee has been established to oversee implementation of the Plan. The Ok Tedi Foundation and the National Fisheries Authority are continuing to engage in community consultation and education activities in barramundi fishing communities of Western Province.