Status and trends of pelagic prey fishes in Lake Huron, 2012

Abstract

The USGS Great Lakes Science Center conducted acoustic/midwater trawl surveys of Lake Huron during 2004-2008. The 2008 survey was conducted during September and October, and included transects in Lake Huron’s Main Basin, Georgian Bay, and North Channel. Main Basin estimates of pelagic fish density and biomass were higher in 2008 compared to surveys in 2004-2007 because of increases in both age-0 and adult bloater. Native species now comprise the majority of the Main Basin biomass. We also observed substantial increase in the abundance of threespine and ninespine sticklebacks, although they contributed little to total community biomass increase due to small size. Rainbow smelt densities and biomass appeared similar to other years, and both alewife and emerald shiner were scarce. Also notably absent was cisco which historically were an important pelagic prey fish in Lake Huron. Unlike previous surveys, we did not observe differences in fish density or biomass among Lake Huron’s basins; during 2008 both density and biomass in the North Channel, Georgian Bay, and Main Basin were similar. This appeared to be a result of increases in the Main Basin and not declines in other areas. Main Basin prey availability for salmonids will depend largely on the extent of their predation on bloater which now comprise the majority of the prey biomass there. The Georgian Bay prey biomass had almost equal proportions of bloaters and rainbow smelt, while the North Channel pelagic biomass remained dominated by rainbow smelt. The present situation in Lake Huron where bloater is relatively abundant but alewife and other prey are scarce may result in dependence on bloater as the primary prey for salmonids.