Discriminating Rainbow Trout Sources Using Freshwater and Marine Otolith Growth Chemistry

Abstract

Rainbow Trout Oncorhynchus mykiss are nonindigenous to Newfoundland. Subsequent to the development of marine cage rearing of Rainbow Trout in the Atlantic provinces in the early 1970s, Rainbow Trout have been captured in 33 rivers on the west and south coast of Newfoundland. These escapees may have negative impacts on wild populations, particularly Atlantic Salmon Salmo salar and Brook Trout Salvelinus fontinalis. In this study, the chemical fingerprints in the freshwater and marine growth sections of otoliths were used to distinguish three groups of Rainbow Trout of known origins: two hatcheries and one wild population. The results were then used to assign fish of unknown origin to the three known-origin groups and thus estimate the proportion of escapees. The three known sources produced distinct chemical fingerprints in the freshwater growth of the otoliths (cross validation test, average accuracy of over 93%); whereas, the marine growth in the otoliths produced a single chemical fingerprint for the two hatchery-origin groups distinct from the wild population. Results indicated that at least 60% of the unknown-origin fish were aquaculture escapees. Vaterite was encountered in 70–80% of the known hatchery-origin fish, 0% in the wild population, and 50% in the escapees. It appears that escapees with vaterite had a lower survival rate. The presence–absence of vaterite did not appear to be useful in distinguishing escapees from a wild population.

Received February 28, 2012; accepted June 29, 2012

ACKNOWLEDGMENTS

This project was wholly funded by the Government of Canada, Department of Fisheries and Oceans. We extend thanks to George Furry for extraction of otoliths and Milton Shears for preparing and sectioning otoliths. Neila Cochrane provided technical assistance in the preparation of the manuscript. Aquaculture samples were generously provided by Markland Seafoods Limited and True North Salmon.