Fish in urban environments

Abstract

In the urban environment the impact of human activity often results in the construction of tidal barriers to estuarine fish passage and/or highly modified fish habitats. The modified, shallow estuarine habitat of the urban Rockdale wetland corridor, Botany Bay, is used by estuarine fish and its functional equivalency compared with similar non urban habitats is demonstrated. The argument is presented that estuarine fish are part of the urban wildlife fauna and they should be included in education and advisory programs developed and coordinated by various groups to protect, enhance and maintain wildlife populations in the urban environment. 83Urban wildlife: more than meets the eye Estuarine fishThere are many studies related to fish in NSW estuaries and the importance of shallow water habitats and wetlands (SPCC 1981 a,b,c; Burchmore et al. 1985;Middleton et al. 1984; Bell and Pollard 1989; Ferrell and Bell 1991;McNeill et al. 1992;Worthington et al. 1992; Ferrell et al. 1993;Pollard 1984Pollard , 1994 Gray et al. 1996;West and King 1996; Hannan and Williams 1998;Pease 1999; Gray et al. 2000;West and Jones 2001). The focus of these studies is normally the recreationally or commercially important harvested species and/or the recruitment of juveniles.The above studies demonstrate the density of fish in estuaries is greater in the seagrass habitats than bare sand or mud habitats. Fish community structure within and between estuaries is similar with differences observed related to estuary morphology rather than latitudinal differences. This latter finding is however, partially confounded due to differences associated with water quality and habitat quality. One of the prime drivers of juvenile fish distribution is the availability of shelter, calm water, food, and also predator interactions. Most of the studies show that the fish fauna is diverse within both the urbanised and non-urbanised estuaries. There are large commercial and recreational catches of fish in both groups of estuaries.There is considerable movement of fish between habitats in estuarine systems. This occurs at different life stages or on a seasonal basis. For example the general life cycle pattern for sea mullet Mugil cephalus, a common species in NSW estuaries, is for the adults to spawn in the open ocean, during autumn to early winter. The planktonic larvae then recruit to shallow mangrove/seagrass areas when they are about 30 millimetres long in late autumn and winter. The fish then move as subadults to river channel, mud and sand flat areas in late spring, and by that stage, they are about 125 millimetres long.In comparison yellowfin bream Acanthopagrus australis adults spawn in the surf zones near the entrances to estuaries in winter, and the larvae recruit at about 15-20 millimetres in spring/summer to the seagrass meadows. This is when the mullet are leaving the shallow seagrass habitats. Then the juvenile bream move to deeper waters at about 120 millimetres long, this occurs in autumn/ winter, which is when the mullet are recruiting.There ...