Research Document 1998/45

Recruitment of the North American stock of Atlantic salmon (Salmo salar) relative to annual indices of smolt production and winter habitat in the northwest Atlantic

By P.G Amiro

Abstract

This document explores the utility of an index of annual production of the North American (NA) Atlantic salmon stock to test hypotheses of macro-level affects in the recruitment to fisheries and spawning escapement. Annual indices of smolt production are derived from Miramichi River pre-smolt densities relative to a measured maximum smolt production. The smolt production index is annually calibrated to the total NA stock using the relative performance of the Gulf of St. Lawrence one-sea-winter returns and the proportion that Miramichi returns were of the total NA one-sea-winter (1SW) return. Recruitment models using smolt indices and winter habitat area explained high proportions (0.82 for one-sea-winter and 0.70 for multi-sea-winter salmon) of the variation in recruitment to distant fisheries, local fisheries and to spawning escapement. The addition of YEAR as a variable, suggested by trends in residuals, improved models to explain 0.86 and 0.93 of the variation in recruitment. Forecasts for recruits in 1997 to 1999 were derived using these regressions and simulation of values for proportions represented by the index and forecasts of habitat areas not available at forecast time. Most probable estimates of one sea-winter recruits were low for 1997 at 454x10³ small salmon and increased to 522x10³ in 1998. Modal estimates of multi-sea-winter salmon were very low in 1997 at 75x10³, were similar for 1998, 76x10³ and were improved but low for 1999 at 105x10³. Potential refinements to the model, ecological mechanisms implied from the analysis and implications for management of Atlantic salmon are discussed.

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