Pecten novaezealandiae at its southern limit: habitat dynamics and ecology within Paterson Inlet, Stewart Island
Twist, Brenton A.
The New Zealand scallop (Pecten novaezealandiae) is a species of high commercial, recreational and customary value. Productivity within scallop fisheries is highly variable due to sporadic recruitment, high mortality and predation. Customary fisheries practices can provide an alternative way of managing local marine environments. In the Te Whaka ā Te Wera Mātaitai (customary fisheries area) within Paterson Inlet, Stewart Island, there is currently a harvesting ban on P. novaezealandiae due to a recreational fisheries collapse. In the present study factors influencing the current distribution of P. novaezealandiae and aspects of their ecology that potentially explain this distribution, including food supply, growth rates and movement, were examined within Paterson Inlet. A better understanding of the habitat preferences and the ecology of the scallop within this area could improve local management of the fishery. Logistic and linear statistical model averaging techniques identified distance from inlet entrance, macroalgae cover, presence of benthic microalgae, and harvest pressure as factors highly correlated with scallop distribution and density. P. novaezealandiae was more likely to be present and at higher densities as distance from the inlet entrance increased. The observed gradient could be due to larval recruitment patterns, or historic fishing pressure. P. novaezealandiae were also negatively associated with mats of benthic microalgae suggesting scallops could be removing or preventing settlement of microalgal mats through feeding. Alternatively, these mats could be indicative of unfavourable scallop habitat. Stable isotope analysis demonstrated an enrichment of 13C and 15N in δ13C and δ15N with increasing distance from the inlet entrance. The difference was potentially linked to greater utilisation of detrital matter compared to phytoplankton within the inner inlet. Scallops were more likely to be present in the Mātaitai, possibly due to the lack of harvesting pressure. However, they were less likely to be present in the Ulva Island Marine Reserve, which was attributed to its position within the inlet. A negative relationship between scallops and percentage of macroalgae cover was also observed. Tracking movements of tagged P. novaezealandiae revealed average movement of 1.82 metres per month and a maximum movement of 16.75 metres after two months. The limited amount of movement and the negative relationship with macroalgae cover could be explained by the behaviour of P. novaezealandiae burying itself beneath the sediment as seen throughout this study and demonstrated in a closely related scallop species. Any spatial refuge created through management intervention is only likely to have positive effects through enhanced larval recruitment due to protection of breeding aggregations, not through movement of adults. A tag recapture study on the scallop population within Paterson Inlet indicated slower growth than estimated by previous studies, with P. novaezealandiae taking 3-3.5years to reach 100mm in length. This study demonstrated some of the important factors and ecology of P. novaezealandiae controlling the observed distribution in Paterson Inlet and provides valuable information to help better manage this fishery.
Advisor: Hepburn, Christopher D.; Rayment, William J.
Degree Name: Master of Science
Degree Discipline: Marine Science
Publisher: University of Otago
Keywords: New Zealand; Scallop; Movement; Growth; Indigenous Fisheries; Customary fisheries; Pecten novaezealandiae; Isotope
Research Type: Thesis