Robert Kearney

Accumulation and clearance of the anaesthetics clove oil and AQUI-S™ from the edible tissue of silver perch (Bidyanus bidyanus)

The accumulation and clearance of the main component of the fish anaesthetic clove oil (eugenol), from the edible tissue of silver perch (Bidyanus bidyanus) were examined. Fish were sampled from a commercial silver perch farm to determine the efficiency of commonly employed purging practices in clearing fish treated with this product. After initial exposure to clove oil at harvest, fish were purged for 48 h. This proved sufficient to clear eugenol to below detectable levels. However, following an additional application of clove oil for transport and subsequent purging for 1 week, fish had a mean of 0.32 mg kg−1 of eugenol in their tissues. This indicates that repeated doses of clove oil may lead to fish having a decreased capacity to completely clear their tissue of residue. The effect of temperature and treatment upon the accumulation and clearance of eugenol (or iso-eugenol) was also examined. Fish were exposed to 50 mg L−1 clove oil, 15 mg L−1 clove oil, 15 mg L−1 AQUI-S™, or to no anaesthetic, in water that was either heated or at ambient temperature. At the high dose of clove oil, more eugenol was accumulated in heated water but at the low dose, temperature did not influence the amount of eugenol accumulated. Fish treated with AQUI-S™ accumulated more iso-eugenol at ambient temperature than they did in the heated water. Silver perch were generally able to clear their flesh of residue more rapidly at the higher temperature, although regardless of treatment, residue was cleared to below detectable levels in all fish after 48 h.

Fisheries property rights and recreational/commercial conflict: implications of policy developments in Australia and New Zealand

Commercial fisheries management in Australia and New Zealand is increasingly based on better definition of the rights and responsibilities of resource users. At the same time recreational fishers are claiming a greater share of resources largely based on perceptions of superior economic returns to the community from their activities. The basis of the conflict between traditional, recreational and commercial resource users is moving from physical competition for fish to economic and legal arguments over social priorities. Advantages and disadvantages of increased use of property rights in resource allocation are investigated. It is argued that the recreational sector needs better definition of its claim for priority access to resources.

When is spillover from marine reserves likely to benefit fisheries

The net movement of individuals from marine reserves (also known as no-take marine protected areas) to the remaining fishing grounds is known as spillover and is frequently used to promote reserves to fishers on the grounds that it will benefit fisheries. Here we consider how mismanaged a fishery must be before spillover from a reserve is able to provide a net benefit for a fishery. For our model fishery, density of the species being harvested becomes higher in the reserve than in the fished area but the reduction in the density and yield of the fished area was such that the net effect of the closure was negative, except when the fishery was mismanaged. The extent to which effort had to exceed traditional management targets before reserves led to a spillover benefit varied with rates of growth and movement of the model species. In general, for well-managed fisheries, the loss of yield from the use of reserves was less for species with greater movement and slower growth. The spillover benefit became more pronounced with increasing mis-management of the stocks remaining available to the fishery. This model-based result is consistent with the literature of field-based research where a spillover benefit from reserves has only been detected when the fishery is highly depleted, often where traditional fisheries management controls are absent. We conclude that reserves in jurisdictions with well-managed fisheries are unlikely to provide a net spillover benefit.

The Management of Murray Cod in the Murray-Darling Basin

The Murray cod is the biggest and best known of all Australias freshwater fishes. Unfortunately much of its habitat has been dramatically altered by a wide variety of anthropogenic impacts and it has been excessively targeted by a combination of recreational, commercial and illegal fishing practices. The status of Murray cod throughout the Murray-Darling Basin is reviewed and threats to the survival of the species, the genetic integrity of remaining populations and the ecological systems of which Murray cod are a key component, are analysed. Major knowledge and policy impediments to sustainable use and future management are identified and recommendations for improved management presented.