Background
Historically, oyster reefs were once widespread in NSW estuaries but have been lost due to disease, poor water quality, and unsustainable harvesting. Recently DPIRD has led the way to restore these lost habitats and have created over 7.5 ha of intertidal Sydney rock oyster reefs in Port Stephens. Our seasonal monitoring shows we have created habitat for more than 35 species of fishes, including recreationally important Yellowfin Bream (Acanthopagrus australis), and Dusky Flathead (Platycephalus fuscus) that were also observed to be more abundant associated with the oyster reefs than bare sediment.
Methods
Using acoustic telemetry we tracked the fine scale movement of dusky flathead and yellowfin bream, as well as monitoring broader movements. In Port Stephens, we deployed an array of 18 receivers along the restored oyster, complemented by a broader array of 10 receivers across the estuary (including at a second restored oyster reef). Fish were tagged during two periods (December 2023 and April 2024), and overall provided 4 months of data.
Results
All tagged fish were detected within the fine-scale array, for an average of 31 days. Both species primarily spent most of their time subtidally, with movements into the oyster reef during tidal inundation. Flathead exhibited stronger association with the restored reef (61% of total area use), compared to bream (25%), although core habitat use was lower for both species. At the broader scale, only bream were detected. Notably, one individual travelled to another restored oyster reef.
Conclusions
This project demonstrated connectivity by fish moving among multiple restored oyster reefs within an estuarine system. Furthermore, we were able to demonstrate that fish, particularly flathead utilise restored oyster reefs during high tides. Importantly, we were able to successfully demonstrate the ability to acoustically track fish in a complex and structured intertidal habitat.