Evaluation of anti-foulants on over-catch, other forms of biofouling and mud worm in Sydney Rock Oysters

Project number: 1998-314

Project Status:

Completed

Budget expenditure: $294,781.00

Principal Investigator: Rocky de Nys

Organisation: UNSW Sydney

Project start/end date: 7 Oct 1998 - 25 Mar 2003

Contact:

FRDC

Need

Over the past 20 years oyster production in NSW has steadily declined by more than 40%. Two major problems exacerbating the industry's continuing decline are:

1) escalating costs of production associated with slow growth and high mortality rates suffered by Sydney Rock Oysters due especially to QX disease and winter mortality and mud worm infestation .
2) severe overcatch and other biofouling problems generated by both Sydney rock oysters (SRO's) and Pacific oysters(PO’s).

The problem of combating overcatch and fouling is compounded by the protracted 3 to 4 year turn-off times for Sydney rock oysters. These problems are currently being addressed by periodic manual cleaning and hot water dips in conjunction with the use of elevated intertidal growing heights. The latter exposes overcatch oysters and other biofouling organisms and mudworms, to lethal levels of heat stress and desiccation. The hidden costs of elevated growing height is reduced feeding and growth rates.
Direct costs of combating overcatch and other forms of biofouling has been estimated as high as 30% of total operating costs. These have contributed considerably to the progressive decline of many formerly productive leases. This has been of major concern to both government and community based conservation groups. Derelect leases in Port Stephens alone total almost 900ha and will cost an estimated $8million dollars to clean up and rehabilitate.

Development of a cost effective antifoulant coating technique has the potential to significantly arrest the decline of the oyster industry in NSW, and to reduce costs of production inTasmania and South Australia. In a recent postal survey of farming practises and attitudes of NSW oyster farmers to such a development (conducted by the Aquaculture CRC), approximately half of the respondents expressed a high level of enthusiasm and support for this project proposal which has also gained highest priority ranking from ORAC (NSW Oyster Industry Research Advisory Committee) and ACFR(Advisory Council on Fisheries Research) the NSW state FRAB.

Objectives

1. To evaluate the effectiveness and commercial practicality of one application per overcatch season on antifoulant coatings in providing intertidal tray cultured oysters protection from overcatch of both Sydney Rock and Pacific Oyster spat and from other common forms of biofouling commonly encountered in Port Stephens.

2. To assess and improve the cost effectiveness and commercial practicability of these treaments: a) in relation to other forms of farming single seed oysters within Port Stephens (especially intertidal basket and subtidal raft farming) and b) to enable a lowering of usual growing height of oysters thereby accelerating their growth without jeopardising survival or market quality.

3. To determine whether benefits attached to objectives 1 and 2 can be achieved when extended to a representative array of commercial oyster farming areas and techniques used throughout the rest of NSW

4. To assess whether successful types of antifoulant coating techniques pose signficant risks to the environment, to the oysters themselves or to consumers.