Abstract:
The Greenshell™ mussel (Perna canaliculus) is the most valuable aquaculture species in New Zealand. A review of the aquaculture development of P. canaliculus identified several areas where information was lacking, particularly for the factors that influence the growth, condition and retention, which are critical for effective management of its aquaculture. Over a two year period, both juvenile settlement and adult growth and condition were measured in the Hauraki Gulf to assess the potential addition of Hauraki Gulf-sourced spat to the industry. In order to focus spat collection efforts, settlement rates at two sites were measured and no difference found, although settlement at 11 m depth was consistently higher than at 4 m. Seasonal spat settlement was also consistent between the sites, with considerably higher rates in spring and summer months. Mussels have traditionally been sourced from Ninety Mile Beach, which spawned a month earlier than Hauraki Gulf mussels, and had significant differences in condition during October and November, therefore allowing greater harvesting yield. There was no difference in mussel growth between the two sources. Retention and attachment rates increase our understanding of how it may be possible to selectively seed spat of a certain size range onto farm lines to ensure greater retention rates, and these were found to vary among spat collected from the five locations examined. Attachment rates were found to decrease at a shell length of 5 mm and upwards, whereas retention rates decreased in juvenile mussels from 0.8 to 5 mm in shell length and then increased again from 5 mm upwards. Finally, this research examined how underwater sound affects the growth and retention of spat, with 50 - 500 Hz of white noise resulting in the highest growth and retention rates and lowest mortality for both static and flow-through experiments. Collectively, the results from this study improve our understanding of the biology of P. canaliculus in relation to aquaculture conditions. The results also provide a number of avenues for greatly improving the efficiency and commercial production from Greenshell™ aquaculture, not only in the Hauraki Gulf, but potentially in other key growing areas.