Environmental influences on the spatial ecology and spawning behaviour of an estuarine-resident fish, Macquaria colonorum C.T. Walsh a, b, c, * , I.V. Reinfelds d , M.C. Ives b , C.A. Gray b , R.J. West c , D.E. van der Meulen b a NSW Department of Primary Industries, Batemans Bay Fisheries Centre, PO Box 17, Batemans Bay, NSW 2536, Australia b NSW Department of Primary Industries, Cronulla Fisheries Research Centre of Excellence, PO Box 21, Cronulla, NSW 2230, Australia c University of Wollongong, School of Biological Sciences, NSW 2522, Australia d NSW Office of Water, PO Box 53, Wollongong, NSW 2500, Australia article info Article history: Received 27 March 2012 Accepted 28 December 2012 Available online 8 January 2013 Keywords: acoustic array biological rhythms environmental factors estuarine-resident Macquaria colonorum spawning migrations abstract Estuarine-resident fishes are highly susceptible to the effects of environmental and anthropogenic im- pacts on their assemblages and habitats. We investigated the distribution, movement and spawning behaviour of estuary perch, Macquaria colonorum, in response to selected environmental variables using an acoustic telemetry array in a large tidal river in south-eastern (SE) Australia. Adult M. colonorum were monitored for up to two years, covering two consecutive spawning periods between September 2007 and 2009. Salinity, water temperature and river flows all had a significant relationship with their estuarine distribution. In particular, large-scale movements were influenced by large freshwater inflow events and the resultant reduction in salinity levels, together with the seasonal cooling and warming trends in water temperatures associated with spawning behaviour. During the winter months, male and female M. colonorum migrated from their upper estuarine home ranges to the lower estuarine spawning grounds in synchrony, with numbers of individual visits by both sexes consistently higher in the ‘wetter’ winter/spring period of 2008. Location, arrival, departure and occupation time within the spawning grounds were similar between sexes and years. Both resident and migrating M. colonorum exhibited strong diel, and to a lesser extent, tidal behavioural patterns, with fish more likely to be detected at night and during the ebb tides. It is postulated that the effect of environmental fluctuations on the distribution and movement of M. colonorum is influenced by behavioural mechanisms in response to osmoregulatory stress, predatoreprey interactions and reproductive activity. The results also demonstrate the impor- tance of accounting for autocorrelation inherent in telemetry data, and for developing management strategies that are more robust to the effect of future climate trends on estuarine fish populations. Crown Copyright Ó 2013 Published by Elsevier Ltd. All rights reserved. 1. Introduction Estuarine environments are characterised by marked temporal and spatial fluctuations in abiotic conditions (e.g., salinity, water temperature and turbidity) due to competing influences of fresh- water inflows and tidal flow (Bennett and Branch, 1990; Kimmerer, 2002; Heupel and Simpendorfer, 2008). Strong relationships exist between the distributions of estuarine fish and such environmental factors (Blaber and Blaber, 1980; Whitfield, 1994; Marshall and Elliott, 1998). Salinity has long been recognised as a primary factor influencing the use, movement and community composition of fishes in estuaries (Harrison and Whitfield, 2006; Selleslagh and Amara, 2008), while water temperature has been found to control key physiological, biochemical and life-history processes (Beitinger and Fitzpatrick, 1979). Fish in estuaries have evolved strategies to deal with fluctuating environmental conditions. For example, sed- entary estuarine fishes tend to osmoregulate over a broad range of salinities, whereas more mobile fishes may move to areas that are more suitable as environmental conditions change (Whitfield,1994; Heupel and Simpendorfer, 2008). Biotic factors, including the dis- tributions and behaviour of predator and prey species also influence the movement of fish in estuaries (Marshall and Elliott, 1998; Elliott et al., 2007). This is not unusual as the behavioural rhythms of fish and invertebrates have been found to be similarly linked to cyclical events such as diel, tidal and moon phase (Morgan, 2001). Many estuarine-resident, including estuarine-dependent fishes have well defined home ranges for most of their routine activities before migrating to distant discrete spawning areas (Pittman and McAlpine, 2001; Crook et al., 2010; Walsh et al., 2012b). The * Corresponding author. NSW Department of Primary Industries, Batemans Bay Fisheries Centre, PO Box 17, Batemans Bay, NSW 2536, Australia. E-mail address: chris.walsh@dpi.nsw.gov.au (C.T. Walsh). Contents lists available at SciVerse ScienceDirect Estuarine, Coastal and Shelf Science journal homepage: www.elsevier.com/locate/ecss 0272-7714/$ e see front matter Crown Copyright Ó 2013 Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ecss.2012.12.009 Estuarine, Coastal and Shelf Science 118 (2013) 60e71