Ecological Energetics of Rainbow Smelt in the Laurentian Great Lakes: An Interlake Comparison

Abstract

its role as a producer and a predator in Great Lakes ecosystems. We measured the weight (W, g) and temperature (T. °C) dependences of routine metabolism: R (cal-g ' -h !) = 0.3646- W~o.2i6. ^0.036 T yjc evaluated seasonal and ontogenetic patterns of rainbow smelt energy density. Seasonal and size-dependent diet composition was estimated based on an extensive analysis of smelt diets in Lakes Michigan and Ontario and a synthesis of published diet data for all of the Great Lakes. For each lake, we employed lake-specific temperature regimes, growth rates, mortality rates, and abundance estimates. Model simulations for the average individual rainbow smelt in the various lakes revealed gross food conversion efficiencies (GCE) of 13.8-15.8% averaged over all age-classes. For the youngest age-class, GCE was usually close to 20% and two or three times greater than for age-classes 4 and 5. An empirical estimate of daily ration in Lake Michigan in late August was between 0.017 and 0.037 g food/g smelt, depending on the value assumed for stomach evacuation rate. Our model predicted a ration of about 0.022 g-g ' for that same period. Total annual rainbow smelt production and predation were about 100 times greater in Lake Erie than in Lake Superior. Biomass-specific consumption (C:B) ratios per age-class in Lake Michigan were highest for rainbow smelt of ages 0 and 1 (14.64 and 9.00) and lowest for ages 4 and 5 (4.60 and 4.54). Production was concentrated in the first three age-classes in all the lakes and ages 0 and 1 accounted for about 87% of the total production in Lake Erie. Population GCE was highest in Lake Erie (20.4%) and lowest in Lake Ontario (15.6%). Production: biomass (P:B) ratios varied from 1.54 in Lake Erie to 1.10 in Lake Ontario. The highest P:B ratio for any age-class was 2.97 for age-0 rainbow smelt in Lake Erie and the lowest was 0.29 for age-4 fish in Lake Huron. Simulations indicated that rainbow smelt biomass is concentrated in age-classes that may be thermally segregated from salmonine predators and that increased mortality of older smelt age-classes can reduce predation by smelt on other fishes. Abstract.—We developed an energetics model for rainbow smelt Osmerus mordax to quantify