Fatty acids provide a marker of the diet of fish. The fatty acid compositions of pre-winter herring should vary spatially because the prey fields in bays should differ. Consequently, the herring in different bays should have different initial compositions and if the fish are not feeding those compositions will serve as natural tags during winter allowing us to determine if individuals move between bays.
The project uses a laboratory study to examine how the fatty acid composition depends on prey and if those compositions are maintained during fasting. Juvenile herring collected in various locations and over time will then be examined to see if there is evidence of feeding or movement of the herring between locations.
We will learn if there is enough spatial variability in diet for the fatty acids to be used as a marker associated with feeding during the fall. We will then examine if there is evidence that juvenile herring migrate between bays, which would violate our assumption that nursery bays are closed systems when we are estimating overwintering survival.