Research Document 1997/03
Ratio of adults to experimental ponds area juveniles in a stock assessment of Atlantic salmon (Salmo salar L.) in the Gander River, Newfoundland with a projection of adult returns in 1997
By P.M. Ryan, R. Knoechel, M.F. O'Connell, and E.G.M. Ash
Abstract
Spring population sizes of juvenile Atlantic salmon were determined by Schnabel multiple, mark-recapture methods in two Experimental Ponds Area (EPA) lakes at the headwaters of the Gander River from 1979-96. Juvenile abundance in 1995 and 1996 was considerably higher than expected as indicated by a previously derived stock-recruit relationship between juvenile abundance and adults returning to the Salmon Brook fishway on a lower river tributary four years earlier.
Total river adult (small salmon <63 cm) returns were obtained over the period 1989-96 at the counting fence near the mouth of the river and the fish angled downstream of the fence. Changes in the ratios of returning small salmon to the juvenile abundance one year earlier were indicative of a more than four-fold (4.5 X) increase in the average marine survival of Gander River salmon following closure of the commercial fishery in 1992. However, our results suggest that marine survival of the 1995 migrants was decreased relative to the other years during the closure of the commercial fishery. Total river adult returns in 1997 were projected from 1996 juvenile abundance and the post-commercial fishery ratio of returning small salmon to the juvenile abundance one year earlier. Projections indicate that 50,103 small salmon should return to the Gander River to spawn in 1997 and exceed the current conservation spawning requirement.
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