Get in My Belly! What Do Lake Huron Bloater like to Eat?

The Lake Huron food-web has undergone fundamental changes since 2002 from declines primary production to the collapse of fisheries.  One fish species, bloater Coregonus hoyi appears to have at least partially benefited from the changing ecosystem.  Bloater is an important native forage fish that consumes both benthic invertebrates and zooplankton and has increased in abundance since the mid-2000s, although its growth and condition appears stunted.  One possible explanation for these changes is a shift in zooplankton community composition and domination of the benthic invertebrate community by invasive dreissenid mussels (which bloater cannot consume).  To evaluate which prey species were important to bloater consumption, we calculated Vanderploeg’s W´ index of selectivity in April, July, and September 2012 at two depths (46 m and 82 m) near Hammond Bay and Thunder Bay in northern Lake Huron.  We hypothesize that bloater selected for larger calanoid prey such as Epischura lacustrus as well as Mysis. Preliminary results from gut analysis indicate that bloater consumed Mysis, Bythotrephes longimanus, several copepod species, and some other cladoceran zooplankton.  Should bloater be selecting for prey that are declining in abundance, it could help explain their truncated size distribution and lower than expected physiological condition.