Identification by Scale Analysis of Farmed Atlantic Salmon Juveniles in Southwestern New Brunswick Rivers

Abstract

A procedure was developed to identify whether the natal origin of juvenile Atlantic salmon Salmo salar in the Magaguadavic River, New Brunswick, was farmed or wild. Farmed juveniles enter this river as escapees from commercial hatcheries. The discriminant function was developed using measured scale characteristics for the first year of growth, as determined from samples of farmed and wild juvenile Atlantic salmon of known origin. Eight scale characteristics proved to be significant predictors of origin. In a jackknife cross-validation, the discriminant function was 90% accurate in predicting the origin of juvenile Atlantic salmon in the Magaguadavic River. The procedure was then applied to juvenile Atlantic salmon of unknown natal origin sampled from the Magaguadavic and neighboring Waweig and Digdequash rivers, which also support salmon hatcheries. Of the juvenile Atlantic salmon sampled in the Magaguadavic River in 1996, 1997, and 1998, 36, 59, and 43%, respectively, were estimated to be of farmed origin. During 1998, an estimated 9% and 42% of juvenile Atlantic salmon sampled from the Digdequash and Waweig rivers, respectively, were of farmed origin. The study indicated that farmed juvenile Atlantic salmon escaped from hatcheries and occupied suitable habitat in all three rivers.