DISTRIBUTION PATTERNS OF REDFIN PERCH PERCA FLUVIATILIS LINNAEUS AND WESTERN PYGMY PERCH EDELIA VITTATA CASTELNAU IN THE MURRAY RIVER SYSTEM WESTERN AUSTRALIA

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Introduction: Various workers including Moyle (1976) and Jackson and Williams (1980) have presented evidence that introduced fish species have a negative impact on native species. Fletcher (1986) summarized what is known about the effects of introduced fish in Australian aquatic environments. One introduced species little known in this regard, is the redfin perch Perca fluviatilis Linnaeus. Cadwallader (1978) speculated that this species may have adversely affected some native fishes in the Murray Darling River system.

During research into the distribution of fishes in the Murray River System Western Australia, it was noted that the western pygmy perch Edelia villata Castelnau was apparently absent from most of the main stream. This absence was surprising as E. villata has been easily collected by dip net in 1979 between the mouth of Nanga Brook and Bob's Crossing (A and B Figure I). Large numbers of pygmy perch were also noted in the Murray River in 1951 (Anonymous 1952). A recent addition to the fish fauna of the Murray River below Driver Road Ford (Figure I) is the redfin perch Perca fuviatilis. A survey of anglers which commenced in 1987 (Hutchison unpublished), revealed that redfin first began to appear in anglers' catches in the early 1980's near Yarragil and the Baden Powell Water Spout. By 1986 anglers were capturing redfin from the vicinity of Coolup and Pinjarra. Previously redfin had only been known from near Driver Road Ford and further upstream (see Figure I for localities). Redfin were introduced to the upper Murray System early this century (Coy 1979), probably before 1912, by which time many perch were established in dams between York and Cranbrook (Braysich 1966). This paper documents the distribution of E. vitlata and P. fluviatilus in the Murray River system and suggests that it represents circumstantial evidence for the possible elimination of E. vitlata by P. fluviatilus.