River-specific target spawning requirements for Atlantic salmon (Salmo salar) based on a generalized smolt production model

Abstract

Atlantic salmon (Salmo salar) management in eastern Canada is based on ensuring that there is sufficient spawning escapement to meet an egg deposition target that maximizes the production of smolts. Using available egg deposition to smolt production data, we show that the present strategy of basing spawning targets on the presence-absence of lacustrine habitat for the rearing of juvenile salmon is a valid approach. We further show that a general smolt production model that accounts for this difference in available habitat when combined with the biological characteristics of the recruiting adults provides river-specific spawning targets. Targets corresponding to maximum yield tend to be less than half the target values currently used. A target representing the egg deposition for 90% of maximum yield serves as an example of a risk-averse strategy. The lower target values relative to those currently used are in large part determined by low sea survivals. The targets that we derived for four example rivers would correspond to the currently used target egg depositions if the long-term sea survivals were 2-3 times those observed in the last 6 years.