PARENT SESSION
Contributed Oral Session 10: Aquatic Trophic Systems I
Monday, August 8, 8:00 AM - 11:30 AM, Meeting Room 519 B, Level 5, Palais des congrès de Montréal

Interactive effects of elevated nutrient and suspended sediment inputs on larval gizzard shad performance in reservoirs.

gonzalez, maria^*,, knoll, lesley,

ABSTRACT- Biomass of gizzard shad, a common fish species in USA reservoirs, increases with lake productivity. We evaluated effects of elevated dissolved nutrients and allochthonus sediments on larval shad performance. We hypothesized that larval performance will be maximal under elevated dissolved nutrients (because of increased zooplankton production) and no allochthonus sediment inputs (because of low turbidity) and that larval performance will be minimal under elevated allochthonus sediments and no dissolved nutrients. We conducted a mesocosm experiment with four treatments: 1) Control, 2) Nutrient addition (N), 3) Sediment addition (S) and 4) Nutrient and sediment additions (NS), with four replicates/treatment. After eight weeks, larval fish survivorship was significantly lower in the control than in other treatments. However, we detected a significant NxS interaction on growth rate and final biomass. Growth was significantly lowest in the S treatment and highest in the N treatment. Final biomass was significantly lowest in the control and highest in the NS treatment. These results indicate that in highly productive systems elevated nutrient inputs can compensate for detrimental effects of high turbidity.

Key words: Reservoir, larval fish, allocththonous inputs