Abstract
Austrovenus stutchburyi is one of the dominant bivalves of New Zealand’s soft shore sheltered habitats (Morton and Miller, 1968; McArdle and Blackwell, 1989). The total inlet biomass level of A. stutchburyi has not differed since the initial survey within Papanui and Waitati Inlets; however, the size class biomass level has differed over time. Most important to the future of the fishery is the juvenile clam biomass that has depleted in both Inlets and remained low with no evidence to predict future recruitment.
The laboratory study showed that the population factors of size class and density of clams affect the clam filtration rates of phytoplankton, with faster clearance rates by large sized clams at high density. The laboratory and field data were combined and showed that the total inlet filter capacity was 20.8 mg per day and 3.0 mg per day of chlorophyll a is filtered by medium and large clams respectively.
This fishery that is harvested by non-commercial and commercial harvesters shows uncertainty in the pattern of recruitment of juvenile clams. The commercial operation needs to consider methods of restocking the population to restore the level of biomass in this fishery. This information provides a baseline assessment for monitoring the health of an inlet, and further monitoring of this dominant species should be continued to ensure the maintenance of its role in this system. Since this current study is based on the latest survey of 2004 and 2007 within Papanui and Waitati Inlet respectively, the improvement in management and the restoration of this population is urgent.