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
Brett W. Molony A B , Chris Bird A and Vinh P. Nguyen AA Department of Fisheries, Western Australia, West Australian Marine Research Laboratories, PO Box 20, North Beach, WA 6920, Australia.
B Corresponding author. Email: brettm@spc.int
Marine and Freshwater Research 55(8) 781-785 https://doi.org/10.1071/MF04119
Submitted: 17 June 2004 Accepted: 21 October 2004 Published: 16 November 2004
Abstract
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 stocking, 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. fluviatilis has a relative predatory impact on O. mykiss fry more than 100 times greater than other fishes. Perca fluviatilis 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 tool to assess strategies for stocking fish and the application of other management options.
Extra keywords: Cherax cainii, diet shift, marron, stock enhancement.
Acknowledgments
We would like to thank Tony Church and Terry Cabassi (PFRC) for producing and stocking O. mykiss used in this trial and the Water Corporation of Western Australia for access to Lake Navarino. We also thank Gary Jackson, Steve Beatty, Rick Fletcher and Greg Maguire for providing comments on drafts and two anonymous referees for providing many useful suggestions for strengthening this manuscript. We extend our thanks to the members of WATFAA for making their data available.
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1 The widespread, common marron was formerly Cherax tenuimanus (Austin and Ryan 2002).