MYSIS-RELICTA - ASSESSMENT OF METALIMNETIC FEEDING AND IMPLICATIONS FOR COMPETITION WITH FISH IN LAKES ONTARIO AND MICHIGAN

Mysis relicta and planktivorous fish in Lakes Ontario and Michigan bot h feed on crustacean zooplankton in the metalimnion. Are these zooplan kton sufficient to meet the energy requirements of mysids? Could mysid s remove a significant proportion of zooplankton production? Are the e nergy requirements in the two lakes similar? Comparisons in Lake Ontar io of zooplankton consumption based on clearance rates, with energy re quirements based on bioenergetic modelling, revealed that individual m ysids, particularly larger ones, required additional energy sources. T he denser mysid populations beyond 100 m depth in Lake Ontario could e xert high mortality rates on metalimnetic zooplankton, remove a signif icant proportion of daily zooplankton production, and consequently, po tentially compete with planktivorous fish. At depths <100 m, the mysid population was smaller and could remove only 6-19% of zooplankton pro duction per day in summer when competition with planktivorous fish wou ld be maximal. Generation time is shorter in Lake Michigan because win ter growth rates remain high. Consequently, less energy is required to complete a generation in Lake Michigan than in Lake Ontario.