Survival of graded scallops amusium balloti in Queensland's (Australia) trawl fishery.

In the Queensland, Australia, scallop fishery, the scallop catch is graded at sea using a specially designed grading machine called a "tumbler." Experiments were conducted to determine the effect of repeated trawl capture, grading, and discarding on the survival of sublegal saucer scallops Amusium balloti. Scallops were caught within an area closed to commercial fishing and known to contain dense scallop beds. The trawled scallops were randomly divided into 2 groups, tumbled and control, and subjected to up to 4 tumbles and/or trawls before being caged for 2.5 days adjacent to the trawl grounds. Increased levels of both trawling and tumbling were found to decrease significantly the survival of sublegal scallops. Although 83% of scallops survived repeated intensive trawling (4 consecutive tows), survival fell to 64% when scallops were also graded using a commercial tumbler. Survival was high for both tumbled and control sublegal scallops after 1 trawl (97% and 98%, respectively).

Round scallops and square meshes: a comparison of four codend types on the catch rates of target species and by-catch in the Queensland (Australia) saucer scallop (Amusium balloti) trawl fishery

Concern over the amount of by-catch from benthic trawl fisheries and research into the problem have increased in recent years. The present paper demonstrated that by-catch rates in the Queensland (Australia) saucer scallop (Amusium balloti) trawl fishery can be reduced by 77% (by weight) using nets fitted with a turtle excluder device (TED) and a square-mesh codend, compared with a standard diamond-mesh codend with no TED. This large reduction was achieved with no significant effect on the legal size scallop catch rate and 39% fewer undersize scallops were caught. In total, 382 taxa were recorded in the by-catch, which was dominated by sponges, portunid crabs, small demersal and benthic fish (e.g. leatherjackets, stingerfish, bearded ghouls, nemipterids, longspine emperors, lizard fish, triggerfish, flounders and rabbitfish), elasmobranchs (e.g. mainly rays) and invertebrates (e.g. sea stars, sea urchins, sea cucumbers and bivalve molluscs). Extremely high reductions in catch rate (i.e. ≥85%) were demonstrated for several by-catch species owing to the square-mesh codend. Square-mesh codends show potential as a means of greatly reducing by-catch and lowering the incidental capture and mortality of undersize scallops and Moreton Bay bugs (Thenus australiensis) in this fishery

Marking scallops for release and recapture

Objectives : To develop a method to mark hatchery reared saucer scallops to distinguish them from animals derived from wild populations. Outcomes achieved : Juvenile saucer scallop (Amusium balloti) shells have been successfully marked en masse using 3 chemicals, namely alizarin red S, calcein and oxytetracycline (OTC). Considering spat survival, mark quality and mark duration collectively, the most successful chemical was OTC. Scallop spat immersed for three days in 200 or 300 mg L-1 OTC resulted in good mark incorporation and high survival. Tris was an effective means of buffering pH change during OTC treatment, with no apparent adverse effects to the scallops. The marks from OTC treatment were still visible in live scallops for at least 10 months, even with exposure to natural filtered light during that period. A second discernible shell mark was added 27 days after the first with no evident toxicity to the scallops. A simulated seabed system was designed which provide marked improvements in scallop juvenile survival and growth. Advice on shell marking has been given to QSS by DPI&F, and the first commercial trials have now commenced, with initial results showing successful marking of juvenile scallops at QSS. This research will allow the industry to monitor the survival, growth and movement of specific cohorts of deployed scallops. This will provide valuable feedback to assess the value of the ranching venture, to optimise release strategies, and to develop improved species management plans.

Physical Oceanographic Influences on Queensland Reef Fish and Scallops : Final Report FRDC 2013/020

The project examined coastal and physical oceanographic influences on the catch rates of coral trout (Plectropomus leopardus) and saucer scallops (Amusium balloti) in Queensland. The research was undertaken to explain variation observed in the catches, and to improve quantitative assessment of the stocks and management advice. 3.1 OBJECTIVES 1. Review recent advances in the study of physical oceanographic influences on fisheries catch data, and describe the major physical oceanographic features that are likely to influence Queensland reef fish and saucer scallops. 2. Collate Queensland’s physical oceanographic data and fisheries (i.e. reef fish and saucer scallops) data. 3. Develop stochastic population models for reef fish and saucer scallops, which can link physical oceanographic features (e.g. sea surface temperature anomalies) to catch rates, biological parameters (e.g. growth, reproduction, natural mortality) and ecological aspects (e.g. spatial distribution).