Ecosystems Fisheries-Oceanography Coordinated Investigations
Photos pertaining to FOCI studies in Alaskan waters.

Bering Sea Ice Expedition
Research Activities - Fish and Acoustics

We will study the relationship between the abundance of fish and other animals and the position of the Bering Sea sea ice edge. Although there are major fisheries in the Bering sea, very little is known about the distribution of fish and plankton during winter months when much of the sea is ice covered. 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 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 distinguish echoes from fish and plankton (mostly shrimp-like krill) by looking at the way that they reflect four different frequencies of sound. Other scientists will collect information on birds, mammals, sea temperature and the amount of ice at the surface at the same time. Both ships on the expedition will be using acoustics to map the distribution and abundance of fish and plankton: Healy will work primarily in the ice-covered areas, while 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 along 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.

NOAA - National Oceanic and Atmospheric Administration