LIFE-HISTORY AND PRODUCTION OF NEOMYSIS-MERCEDIS IN 2 BRITISH-COLUMBIA COASTAL LAKES

The life history and production characteristics of Neomysis mercedis from two British Columbia lakes were examined for their potential influence on zooplankton and limnetic fish communities. During the day, mysids in shallow Muriel Lake (less-than-or-equal-to 45 m) were on or near the bottom; in Kennedy Lake (> 100 m), mysids remained deeper than 50 m. In both lakes, mysids spent summer nights at 0-15 m depths despite > 20-degrees-C temperatures. Mysid density was not strongly correlated with lake depth. Mysids generally displayed spring to early summer minima and late summer to fall maxima in numbers and biomass. Single peaks in gravid females and juvenile mysid abundance, and the absence of pronounced seasonal size changes of gravid females suggest that N. mercedis produced a single generation each year. Fecundities of study lake mysids are the lowest on record, and although size-dependent, exhibited unusually high variability. Annual productivity of mysids averaged 485 mg m-2 y-1 (range 205-690). Calculations indicate mysids consume several times more zooplankton per annum than limnetic fish do. N. mercedis is likely an important competitor of juvenile sockeye salmon (Oncorhynchus nerka) since: (i) sockeye exhibit food limited growth and survival patterns in coastal lakes, (ii) mysids and sockeye consume similar zooplankton plankton prey and (iii) mysids do not contribute greatly to sockeye diet (i.e. < 26% of summer and fall diets by numbers or weight).