Alien salmonids in Australia: impediments to effective impact management, and future directions

Salmonids, mainly brown and rainbow trout (Salmo trutta and Oncorhynchus mykiss) were introduced into Australia in the mid 1860s and early 1890s respectively, and now support economically valuable recreational fisheries. These alien species have established self-sustaining populations in many aquatic environments in south-eastern and southwestern Australia, and stocking of hatchery-produced or wild-caught fish in larger systems is undertaken when fisheries targets are not met (e.g., fish numbers or appropriate size). Salmonids have established self-maintaining populations in many waters not targeted or managed as fisheries, colonising the entire catchment in cooler upland areas of Australia. These populations usually comprise a high abundance of small fish in small first-to-third-order tributaries. These waters are infrequently targeted by anglers, and populations may not contribute individuals to downstream fisheries. Negative impacts of alien salmonids on native aquatic fauna (including fish, frogs, spiny crayfish), mainly through direct predation and to a lesser degree competition for resources, have been noted for over 140 years. Impacts on some faunal groups have been severe enough to eliminate entire populations and severely fragment species across their range. Despite these impacts, salmonid management is focused largely on providing improved recreational angling opportunities, whereas management of their impacts is almost non-existent. Management of the symptom of salmonid impacts, i.e., declining native species, begins only after native species have become imperilled. This paper focuses on impediments to effective management of salmonid impacts, existing and potential management or control options, and future directions and research needs.