Research Document 1998/62

Estimates of wild Atlantic salmon smolt production in Gold and Medway Rivers derived from concurrent abundance and survival of wild and hatchery smolts in LaHave River, 1996

By P.G. Amiro

Abstract

Wild Atlantic salmon (Salmo salar ) smolt production was estimated from known hatchery smolt stocking, the concurrent wild smolt migration estimate and the subsequent one-sea-winter return rate from smolts stocked above Morgan Falls on the LaHave river. A range of possible return rates was applied to known stocking numbers of hatchery smolts in the Gold and Medway rivers in 1996, and estimates of proportions of wild and hatchery fish in the harvest fishery for fish less than 63.0 cm in 1997, to derive estimates of the wild smolt emigration from these rivers in 1996. The 1997 return rate of hatchery smolts from above Morgan Falls was 0.00469 and the modal ratio of wild to hatchery return rate was 4.6565 (4.82 - 4.53; 5^th and 95^th percentiles). The modal estimate of the wild smolt run in the Gold River in 1996 was 6,894 (6,692 - 7,096; 5^th and 95^th percentiles) or 0.389 smolts m^-2* 100. The modal estimate of the wild smolt run in the Medway River in 1996 was 6,788 (6,589 - 6,987; 5^th and 95^th percentiles) or 0.1005 smolts m^-2* 100. The numbers of smolts spawner^-1 was 15 above Morgan Falls suggesting that low areal smolt production was not the result of low survival from egg to smolt. Applying this technique may assist in rationalizing estimates of required conservation escapements to these lowland and acid-impacted rivers.

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