The NOAA Ship Miller Freeman will join the Research Vessel Thomas G. Thompson at the Bering Sea ice edge for several days in the middle of the cruise in order to study the relationship between the abundance of fish and other animals and the position of the sea ice edge. Previous work has shown that many fishes avoid very cold temperatures, and one of the things we hope to determine is whether the area of melting sea ice acts as a barrier for fish due to the very cold water and less salty water in this area. Because ice cover makes it very difficult to use fishing nets, we will use specialized equipment aboard the Miller Freeman to measure the amount of animals in the water with sound. These acoustic instruments (called echosounders or fish finders) work by sending pulses of sound into the water, and then measuring the strength of the echo that is reflected back from the animals in the water. Each species reflects sound differently (see figure 1), and we will try to identify species by looking at the way that they reflect four different frequencies of sound. We will use nets (figure 2) in ice-free areas make sure we can tell species groups apart using the echosounders alone. Other scientists will collect information on birds, mammals, sea temperature and the amount of ice at the surface at the same time. The Miller Freeman will work in open water with no ice cover, at the ice edge, and will also enter the ice-covered waters where possible. The information from the echosounders will be used with the information collected by other scientists to examine the relationships between the environment and the location of fish schools, as well as to examine the relationships between large predators such as birds and mammals and their food.