Fishes of the King Edward River in the Kimberley region, Western Australia

Abstract

The King Edward River, in the far north of the Kimberley region of Western Australia drains approximately 10,000 km2 and discharges into the Timor Sea near the town of Kalumburu. This study represents an ichthyological survey of the river’s freshwaters and revealed that the number of freshwater fishes of the King Edward River is higher than has previously been recorded for a Western Australian river. Twenty-six strictly freshwater fish species were recorded, which is three species higher than the much larger Fitzroy River in the southern Kimberley. The study also identified a number of range extensions, including Butler’s Grunter and Shovel-nosed Catfish to the west, and the Slender Gudgeon to the north and east. A possibly undescribed species of glassfish, that differs morphologically from described species in arrangement of head spines, fin rays, as well as relative body measurements, is reported. A considerable proportion of Jenkins’ Grunter, which is widespread throughout the system but essentially restricted to main channel sites, had ‘blubber-lips’. There were significant differences in the prevailing fish fauna of the different reaches of the King Edward River system. Thus fish associations in the upper King Edward River main channel were significantly different to those in the tributaries and the main channel of the Carson River. Similarly, the fauna of the Carson River, which was much more diverse than the King Edward River main channel and tributary sites, was characterised by many species that were not found in other parts of the river. The presence of natural barriers, such as waterfalls or rock bars do not permit upstream migrations of fishes and are considered to be the main factor in limiting the distribution of some species. For example, many species are restricted to the lower sections of the Carson River, and include Bony Bream, Lesser Salmon Catfish, Shovel-nosed Catfish, Black Catfish, False-spined Catfish, Freshwater Longtom, Prince Regent Hardyhead, Mouth Almighty, Barred Grunter and Butler’s Grunter. It is hypothesised that these natural barriers were in place long before many of these latter species colonised the King Edward River. Some species tend to only be found within tributary sites, e.g. Kimberley Mogurnda, while others are most abundant in tributaries rather than main channel sites, e.g. Western Rainbowfish and Spangled Perch. Waterfalls are also seen as limiting the number of migratory marine/estuarine species that enter freshwaters. For example, only three species that require the marine/estuarine environment to complete their life-cycle were captured in the freshwaters of the King Edward River system. This compares to 14 species that utilise the freshwaters of the Fitzroy River.