Contrasting Seascape Use by a Coastal Fish Assemblage: a Multi-methods Approach

Understanding the range of habitats needed to complete life-cycles is essential for the effective conservation and management of species. We combined otolith microchemistry, acoustic tracking, and underwater video to determine patterns of seascape use by an assemblage of tropical snappers, including two little-known species of high economic importance, the Papuan black bass (Lutjanus goldiei) and spot-tail snapper (Lutjanus fuscescens). All species appeared to have marine larval phases, and post-settlement distributions broadly overlapped across the coastal seascape. However, species and life stages were distributed along a gradient from freshwater to coastal waters. Lutjanus fuscescens is primarily a freshwater species post-settlement, but larger individuals move into brackish estuaries and even coastal waters at times. Lutjanus goldiei appear to recruit to low salinity or freshwater areas. Larger individuals tend to have home-ranges centred on brackish estuaries, while making regular movements into both coastal waters and freshwater. Lutjanus argentimaculatus also ranged widely from fresh to coastal waters, but juveniles were most common in the saline parts of estuaries. Ontogenetic shifts by L. argentimaculatus were similar to those reported from other regions, despite vast differences in the spatial proximity of seascape components. The wide-ranging seascape movements of our target species highlight the importance of maintaining effective connectivity between marine, estuarine, and freshwaters in the region to maintain ecosystem function and support sustainable sport fisheries. The combined approaches resolved some of the ambiguities of individual methods and provide a powerful approach to understanding seascape use by coastal fishes