For the longest time, many hard working enthusiasts and conservationists have bridged the gap to keep the runs alive. Always hoping that some day the magic bullet would be found that could open the door to dramatically larger sustainable returns. To think that a natural resource as the Atlantic Salmon was being harmed by certain singular events was too simple an approach. Today we know that conservation and seeding of rivers was but a small finger in the dike that has greater influence.
A set environment, in this case a certain river, has and exacting number of young that can be supported. This number changes from year to year based on weather patterns over the course of the young fishes in river life. But in most years these numbers are constant. For example a river with a usual return of 5000 fish creates an exacting number of eggs that then hatch and over the next two years creates smolt in numbers that the river supports. That same river in a poor year might only have 3000 fish return and the number of smolt ready for ocean travel will be exactly in the same relative numbers as the good year. Biologists call this the escapement level as it pertains to returns.