The Migratory Behaviour of Juvenile Greenshell ^TM Mussels ( <i>Perna canaliculus</i> )

ABSTRACT Migratory behaviour is a major cause of juvenile mussel (spat) losses, with estimates of 50%–100% in many parts of the world, significantly impacting production efficiency. Reducing spat losses due to their migratory behaviour is essential for improving yields and sustainability, as it can help decrease substantial economic losses, such as the over $15 million annually experienced by the Greenshell industry. One approach is identifying manageable environmental and nutritional conditions that trigger migratory behaviour in mussel spat for mitigation. Another is growing spat to a size where they may no longer express migratory behaviour. Therefore, this study observed the migratory behaviour of Greenshell mussel ( Perna canaliculus ) spat ranging from 0.6 to 24.4 mm in shell length that were either well‐fed or starved and placed in static or turbulent seawater for 60 min. Migratory behaviour was expressed by spat of all sizes of up to 24.4 mm. Most spat initiated migratory behaviour only by crawling (well‐fed: 76%, n = 390; starved: 54%, n = 143) in static seawater, whereas in turbulent seawater spat initiated migratory behaviour both by crawling (well‐fed: 43%, n = 337; starved: 25%, n = 148) and/or mucous drifting (well‐fed: 76%, n = 337; starved: 41%, n = 148). Overall, a larger proportion of spat exhibited migratory behaviour in turbulent seawater (well‐fed: 95%, n = 337; starved: 61%, n = 148) versus static seawater (well‐fed: 76%, n = 390; starved: 54%, n = 143). Additionally, the crawling behaviour was initiated more quickly in turbulent seawater (well‐fed: 2.3 min interquartile range [IQR: 1.1–4.9], starved: 8.2 min [IQR: 3.2–13]) versus static seawater (well‐fed: 5.2 min [IQR: 2.3–11.4], starved: 7.4 min [IQR: 3.2–16.3]). These results indicate that starvation and static seawater reduce migratory behaviour in Greenshell mussel spat, highlighting the importance of selecting coastal farm sites with minimal turbulence to minimise spat losses. Overall, these findings have significant implications for improving nursery management to prevent losses from migratory behaviour.