Appendix A Study Methods: Field Equipment, Sampling and Methods

This appendix aims to provide an overview of the sampling methods that are used to assess and monitor fish assemblages in estuaries based on best practice and standardised approaches. It focuses specifically on sampling for scientific purposes, by using methods developed ad hoc to target specific components of the fish assemblage, or shared with commercial sampling. Given that estuarine fish communities comprise a diversity of species, body morphologies, life stages, functional groups and life strategies (e.g. Whitfield et al. 2022), there is not one-size- fits- all method that is able to provide a representative sample of the whole community, and the use of several different complementary methods is required to capture all components of a fish assemblage. In general, most of the extensive spatial and temporal information gathered on fish populations in estuaries and nearshore areas is required either for deriving assessments of environmental or ecological quality, or for fisheries management. The assessments may be for particular stressors or impacts caused by human activities such as effluent disposal, land-claim schemes or dredging, thus focusing on a localised geographic scale, targeting individual populations, a specific site of interest or a specific area where the activity occurs. Wider scale, coordinated monitoring is also carried out to obtain data on species distributions and trends to assess the structural and functional characteristics and dynamics of natural populations, their response to anthropogenic pressures, or relate to management measures that are implemented (Elliott & Hemingway 2000). Such monitoring, especially long term, provides the evidence support for regional assessments required for estuarine and marine ecosystem protection and the management of fisheries resources (Ducklow et al. 2009, Sukotin & Berger 2013) as, for example, has been conducted on the east coast of the USA (Morson et al. 2019). The latter may relate to commercial stocks within the area studied, or those outside the estuarine area but which are dependent, to some extent, on the success of the estuary in supporting young stages.