Development of an underwater visual census method for assessing shallow water reef fish stocks in the South West Pacific

• Ministry of Primary Industries, Fiji

Reef fish are an important subsistence food in many South West Pacific countries, and also play a major role in small-scale fisheries that yield fish for sale or barter. The value of commercially harvested marine products in South West Pacific Island countries today is on a level with the total value of all other renewable resources. Although the shallow coral reefs cover an estimated 78 000 km2, island population increases and transition from subsistence to cash economies have placed great stress on the shallow water resources. There is growing concern that reef fish stocks are becoming depleted, particularly near centres of dense human population.

One of the priorities of the South Pacific Commission, requested by the Pacific Island countries, is the development and management of small- scale inshore fisheries, for which effective stock assessment is essential. Similarly, promotion of small-scale fisheries through research and development is an increasing area of focus for the Forum Fisheries Agency.

In Australia there is a pressing need to quantify the effects of fishing on the Great Barrier Reef, where fish stocks also seem to be declining. Both commercial and recreational fishing pressure has escalated in recent years, and management and development decisions are being taken with limited information on the status of reef fish stocks.

At present no satisfactory method of assessing the apparent decline in reef fish stocks exists. Models developed for conventional stock assessment require numerous parameter estimates and are inappropriate; and simpler models that explore yields and growth and mortality rates are limited by their assumptions and by the difficulties in collecting the data they require. Although current underwater visual census (UVC) techniques (largely developed in Australia) using scuba divers yield precise, reliable, repeatable estimates of reef fish densities, these estimates must be regarded as relative densities. The scuba diver survey method remains largely unvalidated in terms of actual densities of fish on a reef, and its potential for accurate stock assessment work needs to be assessed.

To this end, the objectives of the project are to:

. develop an appropriate UVC method for estimating stock densities of reef fish exploited in the South West Pacific;

. validate the accuracy of the method using alternative destructive sampling methods such as explosives and poisons;

. carry out preliminary UVC surveys in Fiji and on the Great Barrier Reef to measure stock densities in relation to fishing pressure; and

. provide training in methodology to fisheries officers from collaborating South West Pacific Island countries by involving two officers at all stages of the research.

Visual survey techniques have clear advantages for fish stock assessment in developing countries. They are relatively simple and cheap, provide immediate results, and are non-destructive. An accurate assessment of reef fish stock densities in Australia and in collaborating South West Pacific countries will allow the identification of levels of exploitation in fish stocks, enabling fisheries agencies to manage their renewable resources better and thus increase productivity.

The project has been designed in two stages, each of 18 months duration. The first stage is a pilot study to develop the technique with one South West Pacific country, Fiji. Initial development of the methodology will take place in Australia, because of the destructive sampling required and the additional costs associated with doing such research overseas rather than on the Great Barrier Reef. Then preliminary stock assessment surveys, involving scuba surveys in Australia and Fiji, will be carried out. In Fiji, two Fijian fisheries officers will be involved full time in scuba surveys, data entry and analysis during the two 1-month field trips the Australian team will make to Fiji.

The project will be reviewed at the end of 18 months, and, if the review is successful, will be extended for a further 18 months. This stage will involve extensive reef fish stock assessment in Fiji, in the Great Barrier Reef and in the Cook and Solomon Islands.