Considerable research has focussed on the fish species utilising estuaries, aswell as their seasonal and spatial variation. Although estuaries support resident species, many other species utilise estuaries during juvenile development, or for migration routes and refuge areas (Elliott et al. 2007). Guilds or groups of speciescanbecategorisedonthebasisof,forexample,estuarine use, feeding and/or reproductive mode. Here, we use the functional groups of estuarine use proposed by Elliott et al. (2007). The range of functional groups encompasses the different groups of fish found in estuaries and their links with either freshormarinewaters(Elliottetal.2007).Briefly,thefollowing 10 categories of fish that use estuaries are recognised: freshwater stragglers and migrants, marine stragglers and migrants (the latter of which are divided into marine estuarine-opportunist and marine estuarine-dependent species), estuarine species (further divided into estuarine residents and migrants) and five categories of diadromous fish (anadromous, semi-anadromous, catadromous, semi-catadromous and amphidromous) (see Elliott et al. 2007 for definitions). Given the differences among these functional groups in their environmental uses and tolerances, climate change is likely to have differential impacts on these different groups of fish.