Connectivity of Large-Bodied Fish with a Recovering Estuarine Tidal Marsh, Revealed Using an Imaging Sonar
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SPECIAL ISSUE: CONCEPTS AND CONTROVERSIES IN TIDAL MARSH ECOLOGY REVISITED
Connectivity of Large-Bodied Fish with a Recovering Estuarine Tidal Marsh, Revealed Using an Imaging Sonar Mark A. Bennett 1
&
Alistair Becker 2 & Troy Gaston 1 & Matthew D. Taylor 1,2
Received: 29 April 2020 / Revised: 5 August 2020 / Accepted: 25 August 2020 # Coastal and Estuarine Research Federation 2020
Abstract Tidal wetlands represent important fish habitats, particularly as nurseries for many exploited species. However, usage of these habitats by large-bodied fish is poorly studied. Imaging sonar represents a relatively novel technology for ecologists and allows for the discrete observation of fish in conditions where a light-based camera is ineffective, such as turbid estuarine habitats. An imaging sonar uses sound waves to create video-like images where swimming direction, fish length and distance from the sonar can be inferred. This technology was applied to examine connectivity of large-bodied fish between a recovering Ramsar-listed wetland and the adjacent estuary, by censusing fish traversing the entrance to the wetland. Fish lengths ranged between ~ 8 and 109 cm. More fish were observed traversing the entrance to the wetland during the day (~ 365 fish h−1) compared with night (~ 198 fish h−1), possibly as a predator avoidance strategy. Under some conditions, biomass flux of large-bodied fish was estimated to exceed 100 kg fish h−1. Fish did not appear to have a consistent preference for moving with or against the flow of the tide. These novel findings highlight the utility of imaging sonar for conducting fish census in wetland habitats and also highlights that wetlands are valuable habitats for large-bodied fish. Keywords Saltmarsh . Wetland . DIDSON . BRUV . Census . Restoration
Introduction Tidal wetlands are common estuarine habitats across temperate and subtropical regions (Ziegler et al. this issue). These wetlands occur throughout estuaries and are productive systems characterised by a large biomass of primary producers, such as mangrove, saltmarsh grasses and saltmarsh succulents (Saintilan 2009). Consequently, tidal wetlands function as important sources of primary productivity (Groenendijk 1984), but also provide physical structure that is exploited by a diversity of aquatic and terrestrial fauna (Boesch and Turner 1984). Further, tidal wetlands can improve estuarine water
Communicated by Henrique Cabral * Mark A. Bennett [email protected] 1
School of Environmental and Life Sciences, University of Newcastle, Newcastle, New South Wales 2308, Australia
2
New South Wales Department of Primary Industries, Port Stephens Fisheries Institute, Locked Bag 1, Nelson Bay, NSW 2315, Australia
quality by cleansing terrestrial runoff before it enters the broader estuary (Creighton et al. 2015). An important ecosystem service provided by tidal wetlands is the support of species that are exploited through commercial or recreational fisheries (Raoult et al. 2018). Many of these species are associated with, or rely o
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