Lake Michigan Hydrodynamics: Mysis and Larval Fish Interactions

Abstract

I studied the interactions between Lake Michigan hydrodynamics (the spring thermal bar) and Mysis, deepwater sculpin, and burbot larvae. The thermal bar is a zone of sinking 4º С water that separates warmer inshore water from colder offshore water. Mysis was a major bycatch of sampling for larval fishes. The density of Mysis did not differ statistically between inshore (about 6º С) and offshore of the thermal bar, but the percentage of Mysis that were newborns was significantly higher inshore (P = 0.007). These "early start" coastal Mysis may have an advantage in growth and survival, but with the risk that, unless they drift offshore, they will be at bottom depths that are ultimately inhospitable. The thermal bar period, and shortly thereafter, may be the only time that Mysis and the invasive Hemimysis anomala significantly overlap spatially. The most important impact of these newborn Mysis may be for newly free-swimming and free-feeding Age-0 lake trout (Salvelinus namaycush) which, for coastal reefs, emerge from spawning reefs during the period of thermal bar dynamics. The density of larval deepwater sculpin was higher inside of the thermal bar. For four out of nine sampling dates, inshore deepwater sculpin were significantly (p