Abstract

Although Australia is free of introduced crayfish species, some native species have been extensively translocated outside their natural ranges. Cherax destructor was probably first introduced into Tasmania in the 1960s, and at least seven separate areas of infestation are known. Although it is generally found in irrigation dams, one population is known from a natural, permanent stream also inhabited by the endemic crayfish Astacopsis franklinii. Surveys of this stream showed that the two species did not overlap since C. destructor was confined to a single open, slow flowing section, while A. franklinii was only found in shaded, rocky, fast-flowing sections. In the laboratory, A. franklinii dominated interactions with equal-sized C. destructor in bare arenas, and C. destructor did not dominate interactions unless they were at least 12% bigger in carapace size. Equal sized A franklinii were the first to occupy a shelter in 68% of trials, but even when they were large enough to be dominant in bare arenas, C. destructor only entered shelters first in 31% of trials. Similarly, equal sized A. franklinii maintained shelter ownership in 88% of trials while dominant C. destructor only held them in 48% of trials. Both species preferred to shelter amongst cobbles rather than on pebbles or sand in substrate preference trials, but A. franklinii was able to oust a significant proportion of C. destructor from their preferred substrate. This appears to be the first record of a native crayfish which is more aggressive than an introduced species, but further laboratory and field work is required in the field before the danger posed by C. destructor to A. franklinii and other native Tasmanian crayfish can be properly assessed.

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