Does The Feeding Area Choice Of Atlantic Salmon (Salmo Salar L.) Affect M74 Mortality?

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The M74 mortality has existed at different levels in the offspring of feral Baltic salmon spawners; between populations, and even within the same population the share of females producing M7 4 offspring varies \lidely. According to the tag recovery data the main feeding areas in the Baltic Proper are located in the surroundings of the Bomholm Deep and Gotland Deep, but salmon also feed in the Bothnian Sea and Gulf of Finland. The distribution of the salmon feeding in these areas varies between populations but also between individuals belonging to the same population. The size of salmon smolt entering the sea varies between 12 and 20 cm within a population when dealing with wild populations and between 14 and 25 cm within hatchery-reared smolt. The length of wild smolt has been, on average 16cm during the 1990s while hatchery-reared smolt have been about 20 cm in the Gulf of Bothnia area. Availability of a suitable size of feed and /or post-smolt size at least partly determine the number of migrating salmon post-smolt stopping to feed in the Bothnian Sea instead of migrating to the Baltic Proper. Herring-based feed available in the Bothnian Sea compared to sprat-based feed in the Baltic Proper leads to the hypothesis that the Bothnian Sea as a feeding ground induces M74. In those years, when an increased abundance of feeding salmon were detected in that area by tag recovery and catch statistic data, increased M74 offspring mortality was observed in the following spawning. Climate-related changes in the hydrography and food webs of salmon have also been considered. The hypothesis is that the quality of feed (abundance of thiamine) available varies in the different feeding grounds in the Baltic Sea and thus affects salmon reproduction .