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Pelagic animals live in the open seas, away from the coast or seafloor. The Pelagic Ecosystem team has the task of studying these predator and prey species in Prince William Sound. Despite the challenge, scientists have already managed to collect decades of data that focus on the interactions between whales, seabirds and their prey.

This information is useful in answering questions such as:

• What are the population trends of key open-ocean predators, such as orcas, tufted puffins, and humpback whales?

• Are the numbers of forage fish, like herring, sand lance, and capelin, going up or down?

• Is it possible to monitor forage fish population trends?

• If it is possible to monitor them, what is the best way to do so?

Forage fish have a big impact on marine ecosystems. They convert a huge amount of energy from lower trophic levels and this energy is transferred into food for larger fish, marine mammals, and seabirds. Forage fish have great numbers of offspring and short lifespans. These traits can cause major changes in their abundance from year to year. If the abundance of forage fish increases or decreases significantly, the predators that eat them will also experience shifts in their population numbers.

Humpback whales are predators of herring. Many humpback whales migrate from Prince William Sound to Hawaii for the winter. Some humpback whales, however, stay in or near the Sound. During the winter, there is not much plankton for humpbacks to feed on, and fish like herring become a good alternative source of food for these whales.

Watch the video below to see how the predators of the pelagic hunt their herring prey.

VIDEO: Bait Ball Feast - BBC One

In late summer, the plankton bloom is at its height and vast shoals of herring gather to feed on it. Diving birds round the fish up into a bait ball and then a humpback whale roars in to scoop up the entire ball of herring in one huge mouthful. From "Nature's Great Events: The Great Feast" by BBC. (1:14)

Video Transcript

Scientists want to know the best way to estimate the numbers of specific fish species, such as herring. They get the data they need using a combination of aerial surveys, hydroacoustics, and various fish-capture techniques.

Check out the video below to hear Mayumi Arimitsu explain some of these techniques.

VIDEO: Forage Fish Studies

Mayumi Arimitsu describes the methods scientists use to monitor forage fish populations. (0:55)

Video Transcript

Scientists working on the humpback whale monitoring project are trying to understand if the whales are having an impact on the recovery of herring populations in Prince William Sound. An important part of this project is maintaining an up-to-date humpback “fluke identification catalog,” a kind of “Who’s Who?” in the Gulf of Alaska whale world.

Watch the video below to learn about how scientists observe and photograph whales included in the fluke identification catalog.

VIDEO: Tracking Humpback Whales

John Moran describes how scientists are studying the importance of humpback whales in the Gulf of Alaska ecosystem. (2:08)

Video Transcript




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Study area map

  Biomass (n): the amount of living matter in a given habitat (i.e. the weight of organisms per unit area, or the volume of organisms per unit of habitat)
  Forage fish (n): small schooling fishes that feed on plankton and are eaten by larger predators
  Hydroacoustics (n): the study of sound in water
  Pelagic (adj): the open sea, away from the coast or seafloor
  Trophic level (n): the position of an organism or species in a food web or food chain