Factors influencing the recovery of Pecten novaezelandiae within Te Whaka ā Te Wera Mātaitai, Rakiura
The New Zealand scallop (Pecten novaezelandiae) is an important customary and recreational species in Whaka ā Te Wera, Rakiura (Paterson Inlet, Stewart Island). Customary management tools such as Mātaitai reserves allow for localised community management of valuable marine resources. P. novaezelandiae populations in Te Whaka ā Te Wera Mātaitai have failed to recover following a fourteen year ban on fishing (rahui) aimed at increasing local population densities after stock collapse. This study examined three potential causes for the lack in recovery of P. novaezelandiae: epibenthic predation, local environmental conditions and recruitment, with an aim to provide recommendations for ongoing local management. Members of the Mātaitai committee and local community raised concern that local densities of the predatory seastar Coscinasterias calamaria, were limiting P. novaezelandiae population recovery. Transect surveys were used to compare the densities and morphology of C. calamaria and P. novaezelandiae between sites. The densities of local C. calamaria were not found to coincide with those of P. novaezelandiae, consistent with previous studies, suggesting that the mobility of both species were likely to lead to variable distribution. This study suggests that predation by C. calamaria is unlikely to explain why P. novaezelandiae have failed to recover. Measurements of temperature, salinity, pH, DO, flow velocity and direction at sites were used to determine spatial and temporal variability in the environmental conditions encountered by P. novaezelandiae within Whaka ā Te Wera. Fine scale sea surface temperature measurements and hydrographic casts throughout the inlet were compared to known tolerances of P. novaezelandiae and related pectinid species and suggest that the temperature and salinity at all sites were not likely to the limit growth and development of P. novaezelandiae post settlement. Monitoring of changes in flow and environmental parameters over a tidal period detected high flows and a potential eddy at a site that contained the densest scallop beds, indicating hydrodynamic features enhance local pediveliger recruitment locally. Comparatively low flows in low-density scallop beds that once held important local fisheries are likely to influence the supply of food and recruits to the sites and recovery of these sites from population decline. Bi-monthly deployment of spat collectors over a year at four sites within Whaka ā Te Wera and one on the open coast outside the inlet in Foveaux Strait were used to monitor P. novaezelandiae pediveliger settlement. Results indicated that P. novaezelandiae settlement within Whaka ā Te Wera peaked in December, and remained high between August-January. Pediveliger recruitment shows strong spatial variability with highest recruitment occurring within Sawdust Bay. Low densities of pediveligers on spat collectors throughout the study suggest that the recovery of P. novaezelandiae is limited by the availability of recruits. Monitoring found low settlement of P. novaezelandiae external to Whaka ā Te Wera suggesting that the population is likely to be limited in its larval connectivity with other scallop populations outside Whaka ā Te Wera The results from this thesis demonstrate that Allee effects induced by the low densities of P. novaezelandiae in Whaka ā Te Wera, in conjunction with the hydrodynamic isolation and local currents are likely to limit the production and retainment of recruits in the inlet. Recovery of P. novaezelandiae in Whaka ā Te Wera requires management intervention to enhance larval recruitment to sites to return the resource to a healthy state.
Advisor: Hepburn, Christopher
Degree Name: Master of Science
Degree Discipline: Marine Science
Publisher: University of Otago
Keywords: New Zealand scallop; Pecten novaezelandiae; Te Whaka ā Te Wera Mātaitai; Paterson Inlet; Customary fisheries; scallop; larval recruitment; predation; community management; local management; Mātaitai; rahui; New Zealand; Stewart Island; Rakiura
Research Type: Thesis