Massive mortalities of the black bream Acanthopagrus butcheri (Sparidae) in two normally-closed estuaries, following extreme increases in salinity

Salinities in some normally-closed estuaries in the central south coast of Western Australia are now frequently becoming highly elevated. This is due to: (1) high evaporation rates in water volumes that, by summer, are already low as a result of atypically dry winters; and (2) increased salt run-off following vegetation clearing in the catchments. A few black bream (Acanthopagrus butcheri) died in the basin and lower reaches of the main tributary of Culham inlet when salinities reached ∼ 77 and 67, respectively, and an estimated 1.3 million black bream died in the tributary during the next two months when salinities continued to increase. All black bream in the basin and the lower reaches of the tributary of another estuary were apparently killed when salinities reached ∼ 83–85. It is proposed that A. butcheri becomes stressed at salinities of 60 and typically die before they reach ∼ 85. In both estuaries, a rock bar in the tributary prevented black bream from moving to refugia in upstream areas where salinities were lower.