To address the complex interactions between round gobies and smallmouth bass, we formulate two general hypotheses:
Hypothesis 1 - Given their increasing numbers in both the environment (i.e., Lake Erie) and in predator stomachs, round gobies will influence smallmouth bass growth dynamics.
Hypothesis 2 - Round gobies will alter contaminant (i.e., polychlorinated biphenyl; PCB) dynamics and eventually increase contaminant concentrations in higher trophic levels (i.e., smallmouth bass).
To address our two hypotheses, we develop specific objectives including the following:
1. To experimentally test the hypothesis that round gobies are preferred prey by smallmouth bass (as compared to emerald shiners Notropis atherinoides, and crayfish Orconectes rusticus).
2. To experimentally test the hypothesis that round gobies are energetically desirable prey for smallmouth bass (by measuring caloric content, lipid content, etc.).
3. To experimentally assess PCB assimilation efficiency and elimination rates for smallmouth bass that ingest PCB-spiked round gobies.
4. To test the hypothesis that consumption of round gobies by smallmouth bass can increase predator growth rates (via bioenergetics modeling).
5. To test the hypothesis that consumption of round gobies will affect PCB bioavailability to smallmouth bass (via our bioenergetics-bioaccumulation model).
6. To forecast and evaluate (based on smallmouth bass diets) a variety of potential dietary exposure pathways for smallmouth bass.

Exotic species continue to invade and spread. Recently, round gobies have spread rapidly throughout all of the Great Lakes. The invasion by round gobies into areas occupied by zebra mussels Dreissena polymorpha creates problems. Singularly, each of these species can have negative effects on native species via consumption and competition for limited food resources. Taken together, however, these two exotic species can greatly alter energy and contaminant dynamics. They can return contaminants destined for sediment deposition back into the sport-fish food web. Ingestion of zebra mussels by round gobies can complete a food chain from contaminated algae and sediment - zebra mussels - round gobies - smallmouth bass. The recent population explosion and inclusion of round gobies into diets of many sport fishes has raised concern among fishery managers. This concern arises from uncertainty about how the inclusion of round gobies will affect predator growth rates and contaminant concentrations in this growing smallmouth bass fishery.

We will conduct an experiment to quantify the feeding rate of smallmouth bass on three prey types (round gobies, crayfish, and emerald shiners), as prey densities increase. We then will conduct predator selection experiments, in which each predator will be allowed to chose among the three prey types. In this experiment, behaviors and predators and prey will be recorded. Measurements of prey responses, predator search time, predator handling of prey, and prey consumption for each prey type will be recorded. We will compare these measurements to energetic gains for round gobies and assess whether round gobies are energetically efficient prey. We then will conduct an assimilation efficiency/elimination rate experiment of smallmouth bass ingesting PCB-spiked round gobies. Finally, we will use these data and species-specific physiological information to parameterize a bioenergetics model for Lake Erie smallmouth bass. From this, we can predict changes in growth rate and PCB bioaccumulation in smallmouth bass, due to their recent dietary inclusion of round gobies.

To date, our progress on specific objectives is as follows:

• Predator preference experiment. Experiment is completed, and preliminary data analyses are done. These results have been presented at scientific meetings (see below).
• Are round gobies are energetically desirable prey for smallmouth bass (by measuring caloric content, lipid content, etc.). We have completed bomb calorimetry for about 150 round gobies from Lake Erie. We will combined these data with our experimental data.
• In 2001, we completed field sampling of our sites for smallmouth bass, round gobies, and zebra mussels. We currently are analyzing these samples for PCB concentrations.
• Dietary PCB uptake in smallmouth bass fed PCB-spiked round gobies. This experiment is ongoing. We currently house 30 smallmouth bass that are being used in this experiment. They have been fed PCB-spiked round gobies. This experiment will end in Feb 2003. Bioenergetic modeling. Winter 2003 .
• Bioenergetics-bioaccumulation model. Winter 2003 To forecast potential dietary exposure pathways for smallmouth bass. Ongoing.