Life history characteristics, abundance, and distribution of Mysis diluviana in the South Arm of Rainy Lake, Minnesota and Ontario

Kallemeyn, Larry; Weber, Michael; Maki, Ryan; Lafrancois, Brenda

Information on the abundance, distribution, and life history characteristics of Mysis diluviana in the South Arm of Rainy Lake, Minnesota and Ontario, was obtained through a combination of daylight and night sampling with vertical net tows. From 1998 through 2002, daylight sampling was done bi-weekly at eight fixed stations from May through September. In 1998 and 2000, daylight versus night comparisons of Mysis catches in vertical tows were made from June through September at three of the fixed stations. Additionally, sampling was done along 21 line transects arranged cross-contour, with sample sites stratified by 10-m depth zones. Mysis abundance and biomass varied from year to year and increased with depth. Mean densities of adults and juveniles determined from daylight samples ranged from 13.3 to 41.3/m2 for adults and from 184.6 to 453.5/m2 for juveniles. The mean late summer biomass ranged from 110.62 to 218.40 mg/m2. Comparable daylight and night samples showed that Mysis were concentrated on or near the bottom during the day and migrated vertically at night. The night migrations into the epilimnion, particularly of the smaller juveniles, exposed them to temperatures >20°C. Reproduction, brood size, and growth of Mysis in Rainy Lake generally followed life history patterns reported for the species from other temperate zone lakes. Size frequency distributions showed that Mysis in Rainy Lake have a 1-year life cycle, with the influx of juveniles occurring in early summer. Summer growth rates of juvenile Mysis (1.7–2.5 mm/month) exceeded values reported for both oligotrophic lakes (<1 mm/month) and mesotrophic lakes (1–1.5 mm/month). Correlation analyses suggested that juvenile growth was negatively affected by abundance of juvenile and adult Mysis and by higher summer temperatures in the epilimnion. Negative correlations between Mysis abundance and predatory Rainbow Smelt and Cisco were consistent with other field observations.

Life history characteristics, abundance, and distribution of Mysis diluviana in the South Arm of Rainy Lake, Minnesota and Ontario

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