Averting danger under the bridge: Video confirms that adult small-toothed morays tolerate salinity before and during tidal influx

Safety considerations for researchers shape ecological research approaches in dangerous aquatic environments. A series of recent studies has demonstrated that the moray Gymnothorax polyuranodon (Family Muraenidae) occupies freshwater in the adult phase. However, its potential use of tidal habitat remains largely unexplored, due partly to the challenges of performing underwater research within estuarine crocodile territories. In September 2017, opportunistic snorkel-based observations revealed individuals of this species occupying lairs at an upper tidal creek site during low tide (under freshwater conditions). This provided an opportunity to tailor field-based measurements of the salinity tolerance of this species a fortnight later during a more substantial high tide. Specifically, remote underwater video, snorkel and above-water observations of morays, combined with salinity measurements, reveal that G. polyuranodon is capable of tolerating salinity of at least 14.4 for several hours and can inhabit salinity of 19 for a period of several minutes. This finding, when viewed in synergy with other relevant studies of G. polyuranodon, indicates that the species is either catadromous or amphidromous or capable of either strategy.