Mysis zooplanktivory in Lake Champlain: A bioenergetics analysis

Mysid shrimp are important both as predators on zooplankton and as prey for a variety of fish species across most of the Laurentian Great Lakes. In Lake Champlain, where little is known about mysids, this may also be true. We evaluated the role of Mysis diluviana as a planktivore in Lake Champlain using hydroacoustics, gut content analysis, stable isotopes, cohort analysis, and bioenergetics models to estimate Mysis density, diets, growth rates, and prey consumption rates. Density of Mysis in the water column of the deeper Main Lake was lower in July-August of 2008-2011 (38, 38, 21, and 74 Mysis/m2, respectively) than historical values from the 1970s. Mysis selectively foraged for cladocerans, but also consumed cyclopoid and calanoid copepods in 2011. Stable isotope data suggest a mostly carnivorous diet, although agreement between isotope mixing models and observed diets varied. Cohort analyses revealed growth rates ranging from 2.7 mm/month in late spring to 1.3 mm/month in late summer. In contrast to the offshore areas of Lake Ontario and Lake Huron, zooplankton consumption by the Mysis population was low relative to zooplankton density and production indicating that Mysis are not currently a major zooplanktivore in Lake Champlain.