The occurrence and spawning of cultured Atlantic salmon (Salmo salar) in a Canadian river

Abstract

The New Brunswick Bay of Fundy salmon aquaculture industry expanded from 6 t in 1980 to 16 380 t in 1995. With the growth of the industry came an increase in the frequency of escaped cultured salmon entering and spawning in fresh water. Since 1992, the Magaguadavic River, located in the centre of the New Brunswick salmon aquaculture industry, has been monitored to show changes in the proportions of wild and escaped cultured salmon entering the river. Wild salmon numbers steadily declined over 5 years, whereas cultured salmon numbers generally increased. Cultured salmon entered the river later than wild salmon and the majority of cultured salmon were sexually immature. Present ratios of multi-sea-winter to one-sea-winter for wild salmon are 0.4: 1, compared with 2: 1 a decade earlier. Eggs were sampled from 20 redds in the Magaguadavic River in 1993. Analysis of carotenoid pigments revealed that 45% of the redds were made by females of definite wild origin, at least 20% by females of definite cultured origin, and the remaining 35% contained eggs with pigments indicating a possibility of cultured origin. Thus, redds of cultured escapees could be as high as 55% of the total examined. The location of the Magaguadavic River, and the availability of data on wild and cultured salmon in the river dating back to 1992, make this an ideal site for a Canadian reference river to monitor interactions between wild and cultured salmon. 0 1997 International Council for the Exploration of the Sea