Small Bivalve Fishery assessment

Tasmania has small fisheries for venus clams (Venerupis largillierti) and flat oysters (Ostrea angasi).

IMAS scientists survey the fished stocks every two or three years, which allows the biomass to be estimated.  Information on biomass, plus other information such as the abundance of undersize, is then used for setting the total allowable catch (or quota).

The study found the flat oyster fishery to be assessed as ‘sustainable’ with low risk of overfishing and the venus clam fishery to be ‘environmentally limited’. No estimate of biomass was made for the venus clam fishery in 2016 because fishers had observed sharp declines in stock.

A large reduction in the catch per unit effort (CPUE; an indirect measure of the abundance of a species) in 2015 and 2016, along with the associated catch being significantly lower than the available TACC, suggeststhat biomass has been depleted to the point that recruitment could become affected.

Since 2013, venus clam catches have been < 8% of the estimated fishable biomass. It is worth noting that fishing mortality is likely less than indicated by this percentage because venus clams also occur outside the defined beds within the Georges Bay Northern Zone.

Previous assessment on length frequency distribution in 2014 indicated that a settlement pulse had occurred but this has failed to translate to significant recruitment to the fishery. On the basis of the low rate of fishing mortality, the reduction in biomass is most likely attributable to environmental causes. For fishing year September 2016 – August 2017, the two Georges Bay Northern Zone licensees took a voluntary reduction in TACC to 3 tonnes (< 1% of estimated biomass of 2014) and may allow recovery in this fishery.

The full report can be found here.