Why aren't there more Atlantic salmon (Salmo salar)?

Numbers of wild anadromous Atlantic salmon (Salmo salar) have declined demo nstrably throughout their native range. The current status of runs on river s historically supporting salmon indicate widespread declines and extirpati ons in Europe and North America primarily in southern portions of the range . Many of these declines or extirpations can be attributed to the construct ion of mainstem darns, pollution (including acid rain), and total dewaterin g of streams. Purported effects on declines during the 1960s through the 19 90s include overfishing, and more recently, changing ocean conditions, and intensive aquaculture. Most factors affecting salmon numbers do not act sin gly, but rather in concert, which masks the relative contribution of each f actor. Salmon researchers and managers should not look for a single culprit in declining numbers of salmon, but rather, seek solutions through rigorou s data gathering and testing of multiple effects integrated across space an d time.