In recent years, Baltic Sea salmon Salmo salar, have suffered high larval mortality (M74) which can be cured by thiamine treatment. Analyses of lung term mortality records (1928 1998) from two salmon hatcheries suggest that before the 1970s M74 did not occur, or was less frequent. This indicates that varying M74 did not cause the long-term fluctuations of Baltic salmon catches in this period. The frequency of M74 has been correlated positively to the abundance of the salmon's primary prey, sprat Sprattus sprattus. Sprat, herring Clupea harengus and three-spined stickleback Gasterosteus aculeatus dominated the diet in both the periods of study, 1959-1962 and 1994-1997. The mean size of consumed sprat was significantly smaller in 1994 1997 compared with 1959-1962. Herring and, to a lesser extent, three-spined stickleback; increased in the diet of salmon, while sprat appeared to constitute a smaller part of the diet in 1994-1997. The cause of M74 and the thiamine deficiency involved remains unknown, but is thought to be related to changes in thiamine or thiaminase content in forage fish, winter-feeding of salmon or general changes in the pelagic food web. caused by overfishing or eutrophication. (C) 2001 The Fisheries Society of the British Isles.
|Journal||Journal of Fish Biology|
|Publication status||Published - 2001|