Population Dynamics of the New Zealand Geoduck, Panopea zelandica, in Golden Bay, New Zealand
Geoduck (genus Panopea) are a large and commercially significant marine clam in the phylum Mollusca, which are distributed throughout the world with Panopea zelandica being found in New Zealand (Quoy & Gaimard, 1835). Aquaculture NZ set a target of $1 billion by the year 2025 (Aquaculture NZ, 2005) and Panopea zelandica is one of two species identified to achieve this goal. Advancement and expansion of the existing geoduck fishery are obviously instrumental in achieving this target and hence there must be a more thorough understanding of population dynamics, stock structure, and potential effects of harvesting upon a population (Gribben & Heasman, 2015) to create a sustainable growth in the P. zelandica fishery. Despite the comparatively large amount of literature available on farmed and hatchery-raised geoduck in NZ, information and studies performed on wild Panopea zelandica remain relatively sparse. It was the goal of this thesis to investigate stock structure, harvesting efficiency and components of productivity of Panopea zelandica in the Collingwood area of FMA7. Water depth was the strongest predictor of geoduck density as well as a highly significant association (p-value = 0.00038) between grain size and density. We found a normally distributed group of size classes and our ages ranged from 4 to 33 years old. We found an estimated instantaneous mortality (Z) of 0.209 with an Linf of 127.5mm and a growth rate (k) of 0.110. We found a total [effectively virgin] parent biomass of 1,334kg with an average density of 0.062km/m2 and a CV of 0.205 and found show-factors of 15.9 to 30.8% sensu Gribben, Helson & Millar (2004). Our results were broadly comparable with previous studies. Future research could investigate sex ratios and the effect of protandric development on population harvesting as well as the effect of sediment type on siphon colour, the implementation of crossdating and perhaps investigating the viability of SONAR technology into biomass surveys. This thesis has contributed to the overall understanding of population dynamics, stock structure and other components of the P. zelandica identified by previous publications as being important focal points for research as well as outlining possibilities for future work.