Waltham, Nathan J., McCann, Jack, Power, Trent, Moore, Matt, and Buelow, Christina (2020) Patterns of fish use in urban estuaries: engineering maintenance schedules to protect broader seascape habitat. Estuarine, Coastal and Shelf Science, 238. 106729.

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Abstract

Estuaries are experiencing high rates of modification because of urban development and on-going associated maintenance works which impacts their ecosystem functions and services. This research appraises the fish and crustacean community occupying urbanised estuaries, and whether necessary maintenance works (dredging, mangrove pruning) could be timed to better protect the ecosystem values. Using a range of sampling equipment we collected fish and crustacean assemblages from urban, semi-urban, and non-urban estuaries, in addition to water quality, tidal inundation, and marine plant densities to determine relationships among sites. Seasonal differences in body size distributions of socio-economically important species were also examined to infer timing of juvenile recruitment. Despite common assumptions that urbanised estuaries are degraded and provide little habitat value for coastal species, we found that the species composition of aquatic assemblages was similar between urban and non-urban sites, but differed according to tidal position (i.e. supralittoral vs. lower tidal). Seasonality in body size distributions differed among socio-economically important fisheries species, with some species showing juvenile recruitment during the wet season, dry season, or throughout the year. This study demonstrates that, regardless of urban vs. non-urban context, estuaries provide habitat for many aquatic animals, including socio-economically important fish species. Complexity associated with the dynamism of estuarine ecosystems and variability in constituent species’ life-history patterns makes management decisions regarding timing and delivery of urban waterway maintenance difficult. However, maintenance works that occur during Austral dry season (May to October) would provide the best protection for marine plants (non-flowering season for mangroves), while also reduces downstream movement of sediments and contaminants during wet season rainfall flow. Undertaking necessary maintenance works in the dry season provides grounds for wide scale seascape ecosystem optimism.

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