The diet of salmon (Salmo salar) in the Baltic sea and connections with the M74 syndrome

Most Baltic salmon populations are affected by the M74 syndrome, which has been linked to the feeding ecology of sea-run fish. A 2-year study in 1995- 1997 showed that sprat (Sprattus sprattus) dominated the salmon diet in the Baltic proper (45-90% of the stomach content by weight), followed by herri ng (Clupea harengus, 9-39%) and three-spined stickleback (Gasterosteus acul eatus, 0-14%). These figures are similar to those recorded in the early 196 0s. There was a consistent tendency for sprat to make up a higher proportio n of the diet in the winter from January to April, and later in the year th e proportion of herring and sticklebacks increased. When comparing the east ern and southern parts of the Baltic proper, there was also a tendency in t he eastern part in January-September for the diet to have a lower proportio n of sprat and a higher proportion of herring, This difference was, however , not significant according to the more conservative of 2 different statist ical tests. There were also indications that wintertime feeding by salmon h ad increased compared with the early 1960s. In a regression study, the inci dence of M74 was found to be strongly correlated to several parameters that describe the status of the Baltic sprat stock, two of which were weights o f sprat. This suggests that the analysis of factors influencing the develop ment of M74 needs to be expanded to include lower trophic levels as well.