Scientists at the Great Lakes Science Center conduct research on the population dynamics of Great Lakes fishes. Much of this research is used to determine the consequences of natural and human-induced perturbations on Great Lakes fish communities and to aid development of responsive management strategies to ensure continued use and protection of Great Lakes fishery resources.

Research at the Great Lakes Science Center focuses on identifying longterm trends in fish communities and on determining efficient ways to measure these changes. Scientists use information from ongoing surveys and from existing fishery databases to understand changes in the abundance of fish species, the composition of fish communities, and the dynamics of fish communities in the Great Lakes. Two methods are used to study fish populations in the Great lakes:

• Bottom trawl surveys: Because of the unique features of the Great Lakes (size, depth, habitat diversity, productivity, faunal composition), unique fishery surveys have been developed, but all rely on bottom trawls for capturing fish. Trawl survey designs vary according to lake, as do sampling methods, and methods for data analysis. Researchers are evaluating the effectiveness of the sampling design and robustness of estimators of abundance. Using data on relative abundance, researchers provide information to state agencies on the current status of fishery resources in the Great Lakes. Such knowledge is critical to solving complicated and important resource management problems in the Great Lakes basin, particularly with respect to sport fisheries.

• Hydroacoustic surveys: Researchers are also conducting studies to compare information obtained from the two types of survey methods. Preliminary results indicate that the vertical distribution of fish affects the ability of both sampling methods to provide reliable assessments of fish communities in Lake Michigan.