Temporal and spatial variation of early mortality syndrome in salmonids from Lakes Michigan and Huron

To assess the extent that early mortality syndrome (EMS) impacts different Pacific salmonid stocks and the association of EMS with thiamine, we collected eggs of coho salmon Oncorhynchus kisutch from three Lake Michigan tributaries (Platte River, Thompson Creek, and Root River) in 1996-2001. We also obtained eggs of Chinook salmon O. tshawytscha from Lake Michigan (Little Manistee River) and Lake Huron (Swan River) in 1998-2001. Unfertilized eggs from individual females were frozen for thiamine analysis, and the remainder were fertilized and reared until first feeding. We observed a high incidence of EMS in offspring when total egg thiamine levels were less than 1.7 nmol/g in both coho and Chinook salmon. In Lake Michigan strain coho salmon from the Platte River, EMS occurred in more than 70% of monitored families in 1996, 1999, 2000, and 2001, while 1997 and 1998 were years when EMS was low (70%) in 1999, 2000, and 2001. Chinook salmon from Lake Huron exhibited high (>70%) EMS in 2001, moderate (40-60%) EMS in 1999, and low (