Science and management achieving connectivity, coherence and equivalence to ensure the health of estuarine fish communities

The essence of an appropriate and expected structure and function of healthy and sustainable estuarine fish communities lies in achieving and maintaining ecological connectivity between and within coastal systems. This connectivity includes a functionality between the associated components of, and links with, the marine and catchment areas. Ensuring such a connectivity involves removing, preventing or overcoming pressures, barriers and impediments to the ecological functional connectivity along the continuum between riverine, estuarine and marine systems. Those barriers may be permanent physical structures or related to temporary seasonal or spatial adverse water quality. The analysis of connectivity between estuaries and adjacent marine and freshwater aquatic ecosystems also requires an understanding of how it may be impacted by climate change. In addition to connectivity, coherence in environmental management has recently been defined as the ability to have the same management and governance measures in different areas that will achieve the same outputs and outcomes of management. In contrast, equivalence has been defined as having different management and governance measures in different areas but, again, that will produce the same outcomes. Using estuary-associated marine, diadromous and estuarine resident fish species as examples, this review presents these concepts and shows the natural and social sciences aspects required to achieve healthy and sustainable estuarine fish populations and communities. • Connectivity is fundamental to sustainable estuarine functioning. • Connectivity links across the catchment-estuarine-marine continuum. • Removing temporary and permanent barriers is required for connectivity. • Coherence and equivalence are essential for estuarine management. • Examples are given from estuaries globally.