Consequences of Juvenile Fish Movement and Seascape Connectivity: Does the Concept of Nursery Habitat Need a Rethink?

Abstract

Estuarine and adjacent inshore habitats have long been recognised as important nursery areas for fishes before they disperse to coastal habitats. Assessing nursery function supports spatial and fisheries management, yet work commonly focusses on singular habitat types. Re-considering how juvenile fish connect habitats may improve our understanding of nursery function and the scales that recruits are supplied to coastal fisheries. This study quantified the juvenile movements of two harvested fishes in south-eastern Australia, luderick (Girella tricuspidata) and yellowfin bream (Acanthopagrus australis). Acoustic tags were used to track 33 luderick and 20 yellowfin bream from seagrass meadows for up to ~400 days in Jervis Bay Marine Park. Both species had relatively small home ranges (< 7 km²) and exhibited site attachment to seagrass meadows where they were released. Most luderick and yellowfin bream were detected moving 100’s metres to kilometres to reefs adjacent to seagrass, although these movements were not habitat shifts. Rather, reef-ward movements represented repeated visits that lasted days to months before fish returned to seagrass, suggesting that these movements may be explorations in search of suitable adult habitat. Strong retention within an existing marine reserve was observed, with only five of 33 fish tagged within reserves crossing the boundary into fished waters. Overall, our results demonstrate that juvenile fish use and connect multiple habitat types during their movements. These findings support the broadening of the nursery concept from single habitats to a mosaic of functionally connected habitat patches (dubbed ‘seascape nurseries’).