Application of underwater visual census to assessing coral reef fish stocks in the tropical Pacific

Fishing is a major commercial and subsistence enterprise in the southwest Pacific where about 78 000 sq km of shallow coral reefs support a diversity of marine food resources. Islanders rely heavily on coral reef fish for dietary protein and reef fish are a vital component of both subsistence and artisanal fisheries.

In Fiji, the inshore component of the artisanal fishery produced 4700 tonnes in 1988 (value FJ$12 million). In recent years, however, a substantial increase in fishing effort has threatened the sustainability of shallow water coral reef fisheries in the Pacific region.

The need to manage and sustain the productivity of these fisheries is therefore recognised but tropical multi-species assessment techniques are time-consuming, data intensive and beyond the resource capabilities of individual island governments.

In Australia, the Great Barrier Reef supports a commercial line fishery and a recreational fishery. The total commercial catch was estimated at 4000 tonnes in 1988 with a retail value of A$30 million. Estimates for the recreational fishery range from 3500 to 12 000 tonnes for 1990.

As with Pacific island countries, researchers in the Great Barrier Reef have not been able to assess the status of reef fish stocks reliably because of a lack of empirical data and the complexity of the reef fin-fish community.

This project is the second part of a collaborative project between Australia and Fiji. Phase 1 of the project (ACIAR project 8545) determined the viability of an underwater visual census (UVC) method for assessing reef fish population densities and found it to be an effective method for measuring population density and biomass for many fish species.

In this project, which will also include the Solomon Islands, a stock assessment method for coral reef fin-fisheries will be developed based on visual census surveys and the dynamics of stock biomass production.

Scientists will use UVC to quantify reef fish population densities at a range of sites at coral reefs near Ba and Lautoka on the northwest of Viti Levu in Fiji and near Seghe in the Western District of the Solomon Islands.

They will also quantify the catch and effort of the fisheries in the same localities using an array of conventional methods including trial fishing, creel surveys and questionnaires. The data will be analysed to determine the relationships between independent estimates of stock biomass and fishery catch and effort.

The scientists will collect both the biomass and catch and effort data over a range of habitats (e.g. reef slope and lagoon) with varying fish abundance and fishing pressure and during different seasons. At least 10 key species, and up to 50 in total, will be targeted in each fishery. Further evaluation of the UVC method will include the ease with which native observers can learn the technique and the issue of potential error caused by differences between observers.

Over 35 days towards the end of the project the researchers will fish an area of reef intensely using local fishing methods until fish numbers are reduced to near zero. This depletion survey will provide an alternative measure of biomass to compare with the UVC results.

Data analysis and development of stock assessment models will be carried out by fisheries scientists at the Queensland Department of Primary Industries (QDPI) who will use additional biological parameters available from the literature, (e.g. growth, mortality and size at maturity) to determine sustainable yield. QDPI scientists will also work on refinements to UVC technology, especially distributional properties and reproducibility.

Using the relationship between UVC-determined biomass and catch rates, the scientists will estimate sustainable yields, effort and corresponding standing stocks in the fisheries. The stock assessment procedure developed will be compiled into a manual, as a joint production between QDPI and the Australian Maritime College, Tasmania.

If successful, this project will provide Pacific island fisheries personnel with the expertise to use stock assessment surveys in coral reef areas. Such surveys will provide the basic information required to develop national fisheries management plans, including the identification of areas with potential for further fisheries development.

The project will include three training workshops for fisheries staff from Fiji and the Solomon Islands as well as selected participants from other Pacific nations. In Australia, where there is an urgent need to quantify the effects of fishing on the Great Barrier Reef, stock assessment surveys will provide sound data to aid management and development decisions.