Assessing the use of remote underwater video (RUV) to identify fish and their feeding behaviour in New Zealand's Greenshell™ mussel (Perna canaliculus) farms

Fish predation poses a significant and escalating challenge for the global mussel aquaculture industry. In New Zealand, Greenshell™ mussel farms experience crop losses of up to 100 % that are anecdotally attributed to fish predation, although the fish species responsible have not been confirmed. In this study, remote underwater video (RUV) was used to observe fish activity within four mussel farms at different stages of production in the Firth of Thames, New Zealand. The RUV enabled the identification of the fish species inhabiting mussel farms, including those responsible for predating cultured mussels. Four fish species were identified as frequent inhabitants of the mussel farms, with Australasian snapper (Chrysophrys auratus) and parore (Girella tricuspidata) the most abundant at three out of four mussel farm sites. Australasian snapper was the most common predator, taking as many as 2880 bites of the dropper lines holding mussels in a single 11 min 47 s video recording. Snapper formed feeding aggregations around dropper lines holding juvenile mussels (> 20 mm SL), indicating their potential to remove mussels from nursery farms in a short amount of time. Observations of the feeding behaviour of parore indicated their potential to contribute to the losses of mussels on recently seeded spat farms with these fish recorded tearing apart seeded lines, possibly targeting the macroalgae that is seeded out with the mussel spat. Besides confirming the identity and the predatory behaviour of fish species that are contributing to crop losses from mussel farms in New Zealand, this study also confirms the effectiveness of RUV methods for this purpose. This knowledge can be used to begin to develop mitigation strategies aimed at reducing crop losses in mussel aquaculture.