Predicting and managing the effects of hypersalinity on the fish community in solar salt fields in north-western Australia

Five concentrator ponds (CPs) of a solar salt field in Port Hedland, Western Australia were sampled by seine and gill nets over a 12-month period in order to describe the fish community and examine relationships between diversity, abundance and catch per unit effort (CPUE) with salinity. Salinity varied between 40.2 and 113.7‰ during the sampling period. Forty-one species of fishes were recorded from the CPs, with fewer species recorded from CPs of higher salinity. A significant inverse relationship was identified between salinity and the number of species (diversity) captured in gill nets, indicating that one species is lost with every 16‰ increase in salinity. A significant relationship between salinity and CPUE was also identified with gill-net samples, indicating a reduction of 1 kg h−1 with every increase in salinity of 5.5‰. As CPs are connected by one-way flaps, fish movements are only possible into CPs of higher salinity. Thus, reductions in diversity, abundance and CPUE suggested fish mortalities, likely as a result of maximum or rapidly changing salinities exceeding the tolerance ability of individual species. As fish kills are not infrequent events in solar salt fields and result in economic losses due to loss of production and clean-up costs, the results may allow managers to identify high risk species and times of year of fish kills by using salinity measurements. Commercial, indigenous and/or recreational fishing opportunities are viable options for reducing fish biomasses within the CPs and are discussed. Although absolute salinity values were higher than those recorded from tropical Australian estuaries, salinity deviations within each CP are similar to other estuaries and the effect on the ichthyo-community is likely to be similar.