The relative efficacy of stocking fry or yearling rainbow trout (Oncorhynchus mykiss) into a large impoundment dominated by redfin perch (Perca fluviatilis) in south-western Australia

To compare the efficacy of stocking fry and yearling rainbow trout. Oncorhynchus mykiss. into reservoirs of south-western Australia, 20 000 fry and 1400 yearlings were stocked into Lake Navarino and sampled over a five-month period. Oncorhynchus mykiss fry were collected via seine-nets within 24 h of stocking: however. within 60 h of stocking, no O. mykiss fry could be located, suggesting the total mortality of fry Within 24 h of stockin2. O. mykiss fry were present in the guts of Perca fluviatilis and Salmo trutta. A simple risk analysis of stocking O. mykiss fry, based on gut contents and relative abundances of predatory fishes.. indicated that P.fluviatalis has a relative predatory impact on O. mykiss fry more than 100 times greater than other fishes. Perca flurviatilis also has a greater relative predatory impact on freshwater crayfishes than either species of trout. The results demonstrate the advantages of stocking yearling O. mykiss in impounded waters dominated by P. fluviatilis. Existing data of relative abundances of predatory fishes and relative predatory impacts can be used by managers as a powerful and simple toot to assess strategies for stocking fish and the application of other management options.