Fifty years of marine tag recoveries from Atlantic salmon

The number of wild Atlantic salmon (Salmo salar L.) has periodically declined throughout their native range (Chaput, 2012; ICES, 2015). This has been offset to some degree by historical management initiatives such as habitat protection and restoration, harvest restrictions, and fish health actions which have mitigated some declines. For at least two decades, however, declines in abundance have continued (ICES, 2015) and mitigation options are limited (Parrish et al., 1998), which has led to the call for more focused marine research to assess the reasons for this persistent decline. The status of the wild salmon populations in both North America and Europe has shown a clear geographical pattern over the past 30 years, with most populations in the southern extent of their range in decline, with more northerly populations being generally stable, while populations at intermediate latitudes have been more variable (e.g. Parrish et al., 1998; ICES, 2002). While some of the problems can be attributed to the construction of dams, pollution (including acid rain), water abstraction, overfishing, changing ocean conditions, and intensive aquaculture, many declines cannot be fully explained.