By providing management partners with food web data across all of the Great Lakes the USGS-GLSC is playing a crucial role in Great Lakes ecosystem management. USGS-GLSC researchers are identifying critical trophic interactions for fisheries management, studying energy transfer and bioenergetics of fish, and identifying contaminant pathways in Great Lakes food webs. Researchers are also studying how biotic and abiotic factors, such as human-mediated changes in nutrient input and threats such as invasive species and climate change, drive long-term community and population dynamics. To understand causes of recent declines in multiple fish species, researchers are also focusing on how perturbations at lower trophic levels ripple up through the food web to affect valuable prey and predator fish dynamics.
Food Web Assessment
In the Great Lakes and elsewhere, increases in temperature, freshwater inputs, and eutrophication are predicted to result in a northward expansion of cool and warm water fish populations and a reduction in habitat for cold water species. Lake Erie’s bathymetry provides a natural laboratory where this situation occurs on a seasonal basis through the displacement of fish due to temperature changes, thermal stratification, and hypoxia. LEBS scientists are using standard and biochemical techniques to examine seasonal food web changes and develop analytical metrics that can serve as synoptic measures of the effect of these climate forces on food web structure and fishery resources.
USGS scientists are deciphering how food webs in the Great Lakes are being altered by invasive species and nutrients entering the lakes, and specifically how changes in these two factors influence productivity of the fishery and the overall ecosystem. This study includes all five Great Lakes, with focus on one lake per year following the Cooperative Science and Monitoring Initiative (CSMI). By deploying similar sampling designs across all lakes, USGS scientists can make food web comparisons across the Great Lakes and develop decision-support tools that incorporate these ecosystem dynamics. In 2014, LEBS scientists will assess how environmental stressors unique to Lake Erie, such as harmful algal blooms and hypoxia, as well as nutrient inputs and invasive species, influence trophic interactions that support fisheries production.
Fish bioenergetics modeling, which involves quantification of the fish's energy budget, has played an important role in managing Great Lakes fisheries, as well as other fisheries around the world. Additionally, fish bioenergetics modeling has been used to: (1) better understand fish growth and consumption in lake, rivers, and oceans, (2) predict changes in growth and food consumption by fish under various climate change scenarios, (3) estimate the strength of predator-prey trophic links in aquatic food webs, (4) determine the role of fish in cycling nutrients in aquatic ecosystems, and (5) identifying the major factors regulating contaminant accumulation in fishes. Fish bioenergetics modeling has been widely applied to problems and issues in fishery biology and fish ecology around the world.
Despite frequent application, fish bioenergetics models have several limitations at present. First, more evaluations of model performance are needed to identify conditions under which model performance is poor. During the past 10 to 15 years, efforts have been made to evaluate fish bioenergetics model performance in the laboratory and the field. But, substantially more effort is needed to fully evaluate the suite of available fish bioenergetics models. In addition, fish bioenergetics models are still unavailable for many species of fish. Second, the fish bioenergetics software contains "bugs" and is out of date. Certainly, there is a need to correct the errors in the software and to modernize the software approach, while still allowing the software to be easily applied by users. Third, the current versions of the fish bioenergetics models have no resolution with regard to sex-specific activity or sex-specific resting metabolic rates (standard metabolic rates or SMRs). Yet, results from contaminant survey work, as well as results from the few telemetry studies, have indicated that adult male fish are more active than adult female fish and that resting metabolic rate is higher in adult males than in adult females.
The objectives of this study are to address the above-mentioned limitations of fish bioenergetics modeling. First, for fish bioenergetics models that have not been thoroughly evaluated to date, model performance will be evaluated in the laboratory and in the field. Laboratory evaluations will be conducted by monitoring both food consumption and growth in laboratory tanks. Field evaluations will be done using polychlorinated biphenyls (PCBs) as tracers for food consumption. Additionally, laboratory respirometry will be used to develop new fish bioenergetics models. Second, a new fish bioenergetics model software package, Fish Bioenergetics 4.0, will be developed. This package will most likely be written in R, and will be available on a website. A new user's manual will also be prepared. Third, to address sex-specific activity and sex-specific SMR, the following research initiatives will be pursued: (1) determine the pervasiveness of the characteristic of males being about 20% higher in PCB concentration than females in fish populations from the Great Lakes region as well as fish populations from around the world, (2) determine the pervasiveness of the characteristic of males being about 10% higher in mercury concentration than females in fish populations around the world, (3) when possible, use telemetry to assess the difference in activity between the sexes, and (4) use laboratory respirometry to quantify the difference in SMRs between the sexes. Males have been shown to be about 20% higher in PCB concentration than females in walleye, lake trout, coho salmon, burbot, sea lamprey, lake whitefish, and cisco populations. It has been hypothesized that males are about 20% higher in PCB concentrations than females due to higher activity in males and a higher SMR in males, and that this characteristic is possessed by all or most fish populations across the world. One objective of this study is to assess the pervasiveness of the characteristic in fish populations from around the world. Males are about 10% higher in mercury concentration than females in lake trout, coho salmon, sea lamprey, and lake whitefish populations. Another objective of this study is to determine the pervasiveness of this characteristic in fish populations around the world. Additionally, explanations for the relative difference between the sexes differing between PCBs and mercury will be explored. It has been hypothesized that, as juveniles, SMR does not differ between the sexes of fish. Then, as fish approach maturity, the SMR for males exceeds that of females by 10 to 20%. Laboratory estimates of SMR will be used to test this hypothesis. Ultimately, sex-specific bioenergetics models will be developed. Finally, telemetry will be used, when feasible, to document higher activity by males compared with females. Telemetry will be used both in the laboratory and in the field.
This project is focused on identifying and measuring key ecological parameters of the pelagic fish communities of lakes Michigan and Huron, the third and second largest of the Great Lakes by area. This study has developed from one focused on providing annual measures of abundance of key forage fish like alewife, rainbow smelt, and bloater, that were complementary to bottom trawl data to one focused on understanding the lakewide patterns in abundance, distribution, life history, and interactions of these fish. Sampling is conducted using scientific echosounders and a variety of trawls and limnological samplers. The surveys represent the only annual lakewide fisheries surveys in Great Lakes and are collaborative in nature, with sampling conducted by U.S.G.S., Michigan Department of Natural Resources, and U.S. Fish and Wildlife Service. Data from this project are for both research and management. Data from this study are used to inform decisions made about stocking rates for economically important sport fish like Chinook salmon as well as to inform harvest quotas for species like bloater. Key objectives for this work include:
- Assessment of abundance of the species making up the pelagic fish communities
- Evaluate distribution patterns of key species
- Provide information required to estimate vital rates of important populations (e.g. mortality)
- Provide information on the ecological roles of key species and the communities as a whole