Capelin, a small forage fish, are spawning on beaches around Alaska and your observations can contribute to our understanding of beach spawning behavior and the health of marine ecosystems.
Detecting Long-term Changes in Forage Fish Populations in Prince William Sound, Alaska
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By Alaska Science Center
March 21, 2025
Forage fish are small pelagic schooling fish that play a key role in transferring energy between plankton and top marine predators. Many seabirds, marine mammals, and commercial fish species depend on forage fish to grow and survive.
Return to Ecosystems >> Marine Ecosystems >> Seabirds and Forage Fish Ecology
Project Overview
Media
Sources/Usage: Public Domain. View Media Details
As part of the Gulf Watch Alaska long-term ecological monitoring program, we are collecting data on forage fish abundance and condition in order to better understand how the abundance and nutritional quality of key prey species changes over time. This information is helpful for understanding predator-prey interactions, especially in light of recent seabird die-offs in Alaska.
Why are we studying forage fish?
Forage fish are the link between plankton and predators. In this way they are a key to healthy marine bird populations. As the U.S. Department of Interior (DOI) has Trust responsibility for monitoring and conservation of all seabirds, our studies on forage fish and impacts of environmental change on seabird prey populations are vital to our research role in USGS and DOI.
Where are we working?
Northern Gulf of Alaska, including Prince William Sound, Cook Inlet, and the continental shelf region.
How do we monitor forage fish?
Since we define forage fish as a group of species that play a functional role in ecosystems, and because each species has a different seasonality and habitat due to differing life history strategies, we use a variety of methods to count, catch, and measure forage fish populations. For example:
Media
Sources/Usage: Public Domain. View Media Details
- Collect forage fish in seabird diets: Seabird diets provide some of the longest timeseries data on forage fish in the Northern Gulf of Alaska. Middleton Island is located at the continental shelf break in the Gulf of Alaska. Seabirds catch their food in the ocean around their colony and bring it back to their nests, making it easy to collect information on their food.
- Sample fish from a boat during aerial surveys: We sample forage fish that are surveyed by airplanes in coastal areas of Prince William Sound. Skilled observers in the plane have a better view than we do in the boat and they can direct us to the fish schools so we can find them more easily.
- Measure fish density in the water column with hydroacoustics: From our research vessel USGS R/V Alaskan Gyre we conduct acoustic-trawl surveys in summer and fall. This method uses sonar technology that transmits and recieves sound in the water. When we find acoustic fish sign in the water column we send a net down to the correct depth to identify the fish species and size.
- Sample forage fish habitat: We also collect information on the type of habitat forage fish occur in by measuring ocean temperature, salinity, turbidity, light availability, nutrients, phytoplankton, and the abundance of zooplankton (forage fish food) in the water.
Media
Sources/Usage: Public Domain. View Media Details
WhaleFest 2019 Podcast
To learn more, listen to USGS Research Ecologist Mayumi Arimitsu's interview for a podcast about whale prey, forage fish, and seabird die-offs. Arimitsu talked about research on changes in forage fish populations that were first signaled by large die-offs of seabirds during the 2014-2016 North Pacific marine heatwave – aka “The Blob.”
Below are other science projects associated with this project.
Seabirds and Forage Fish Ecology
Alaska's coastal and offshore waters provide foraging habitat for an estimated 100 million birds comprising more than 90 different species; from loons and seaducks that nest inland, to petrels and puffins that breed on islands off shore. All these birds depend on the sea to provide a wide variety of food types— from clams, crabs and urchins nearshore— to krill, forage fish, and squid offshore. The...
Tidewater Glacier Influence on Marine Ecosystems
Where glaciers meet the sea in the Gulf of Alaska (GOA), they create unique and productive marine habitats. Ringed by the continent’s tallest coastal mountains, 20% of the GOA coastal watershed is covered by glacial ice and the annual freshwater discharge into the GOA from glacial melt is comparable to that of the Mississippi river.
Seabird Die-offs in Alaska
Beginning in 2015, large numbers of dead seabirds have been appearing on beaches in most marine areas of Alaska. Although seabird die-offs are known to occur sporadically (e.g. 1970, 1989, 1993, 1997/1998, and 2004) in Alaska, these recent die-offs have been distinguished from past events by their increased frequency, duration, geographic extent, and number of different species involved.
Cook Inlet Seabird and Forage Fish Study
A massive die-off of Common Murres was documented in the Gulf of Alaska (GOA) during the fall and winter of 2015-2016 in association with a record-breaking marine heat wave in the GOA.
Below are multimedia items associated with this project.
Capelin flyer
Capelin, a small forage fish, are spawning on beaches around Alaska and your observations can contribute to our understanding of beach spawning behavior and the health of marine ecosystems.
young of the year walleye pollock
Photo of young of the year walleye pollock, Prince William Sound, Alaska. Although adults are targeted in one of the largest commercial fisheries in the world, young of the year walleye pollock are important in diets of many marine predators.
Photo of young of the year walleye pollock, Prince William Sound, Alaska. Although adults are targeted in one of the largest commercial fisheries in the world, young of the year walleye pollock are important in diets of many marine predators.
Pacific herring in Prince William Sound, Alaska
Pacific herring in Prince William Sound, Alaska
Pacific herring in Prince William Sound, Alaska
Key forage fish, Cook Inlet, Alaska
Key forage fish in Alaska (from top to bottom): Pacific capelin, Pacific herring, Pacific sand lance, and juvenile walleye pollock. Cook Inlet, Alaska
Key forage fish in Alaska (from top to bottom): Pacific capelin, Pacific herring, Pacific sand lance, and juvenile walleye pollock. Cook Inlet, Alaska
Common Murres in the water
Large amount of Common Murres in the water
Schools of Pacific sand lance in Cabin Bay, Prince William Sound
Schools (shadows along the shore) of Pacific sand lance in Cabin Bay, Prince William Sound
Schools (shadows along the shore) of Pacific sand lance in Cabin Bay, Prince William Sound
Black-legged Kittiwake captured 2 Pacific sand lance
Black-legged Kittiwake captured 2 Pacific sand lance.
Black-legged Kittiwake captured 2 Pacific sand lance.
Black-legged Kittiwake foraging on Pacific sand lance
Black-legged Kittiwakes foraging on Pacific sand lance.
Black-legged Kittiwakes foraging on Pacific sand lance.
Scientist conducting marine bird and mammal survey
Scientists on the bow of the R/V Alaskan Gyre looking through binoculars
Scientists on the bow of the R/V Alaskan Gyre looking through binoculars
Erica Madison bringing in the mid-water trawl on the R/V Alaskan Gyre
Scientist pulling in the beginning of the mid-water trawl on the R/V Alaskan Gyre
Scientist pulling in the beginning of the mid-water trawl on the R/V Alaskan Gyre
Pulling in the mid-water trawl from the R/V Alaskan Gyre
Pulling in the mid-water trawl from the R/V Alaskan Gyre
Pulling in the mid-water trawl from the R/V Alaskan Gyre
Black-legged Kittiwake on a nest
Black-legged Kittiwake on a nest on the side of a rock face in the Aleutian Islands.
Black-legged Kittiwake on a nest on the side of a rock face in the Aleutian Islands.
Pacific sand lance from a purse seine in Prince William Sound
Pacific sand lance in a sieve that were captured in a small purse seine in Prince William Sound, Alaska
Pacific sand lance in a sieve that were captured in a small purse seine in Prince William Sound, Alaska
Scientist with a Pacific Herring caught in Prince William Sound, AK
Sarah Schoen with a Pacific Herring in her hand that was caught in Prince William Sound, Alaska
Sarah Schoen with a Pacific Herring in her hand that was caught in Prince William Sound, Alaska
Scenic Prince William Sound, Alaska
A scenic view of the mountains and the ocean in Prince William Sound
A scenic view of the mountains and the ocean in Prince William Sound
Beautiful Prince William Sound, Alaska
A scenic view of the sea and the mountains in Prince William Sound
A scenic view of the sea and the mountains in Prince William Sound
Catch of forage fish from a trawl in Prince William Sound, Alaska
Catch of forage fish from a trawl in Prince William Sound, Alaska. Trawling was part of detecting long-term changes in forage fish populations.
Catch of forage fish from a trawl in Prince William Sound, Alaska. Trawling was part of detecting long-term changes in forage fish populations.
Mayumi Arimitsu sorting forage fish on the R/V Alaskan Gyre
Mayumi Arimitsu sorting through fish caught in the mid-water trawl on the R/V Alaskan Gyre
Mayumi Arimitsu sorting through fish caught in the mid-water trawl on the R/V Alaskan Gyre
A catch of Pacific sandlance, capelin and other forage fish
A catch of Pacific sandlance, capelin and other forage fish
A catch of Pacific sandlance, capelin and other forage fish
Forage fish are small pelagic schooling fish that play a key role in transferring energy between plankton and top marine predators. Many seabirds, marine mammals, and commercial fish species depend on forage fish to grow and survive.
Return to Ecosystems >> Marine Ecosystems >> Seabirds and Forage Fish Ecology
Project Overview
Media
Sources/Usage: Public Domain. View Media Details
As part of the Gulf Watch Alaska long-term ecological monitoring program, we are collecting data on forage fish abundance and condition in order to better understand how the abundance and nutritional quality of key prey species changes over time. This information is helpful for understanding predator-prey interactions, especially in light of recent seabird die-offs in Alaska.
Why are we studying forage fish?
Forage fish are the link between plankton and predators. In this way they are a key to healthy marine bird populations. As the U.S. Department of Interior (DOI) has Trust responsibility for monitoring and conservation of all seabirds, our studies on forage fish and impacts of environmental change on seabird prey populations are vital to our research role in USGS and DOI.
Where are we working?
Northern Gulf of Alaska, including Prince William Sound, Cook Inlet, and the continental shelf region.
How do we monitor forage fish?
Since we define forage fish as a group of species that play a functional role in ecosystems, and because each species has a different seasonality and habitat due to differing life history strategies, we use a variety of methods to count, catch, and measure forage fish populations. For example:
Media
Sources/Usage: Public Domain. View Media Details
- Collect forage fish in seabird diets: Seabird diets provide some of the longest timeseries data on forage fish in the Northern Gulf of Alaska. Middleton Island is located at the continental shelf break in the Gulf of Alaska. Seabirds catch their food in the ocean around their colony and bring it back to their nests, making it easy to collect information on their food.
- Sample fish from a boat during aerial surveys: We sample forage fish that are surveyed by airplanes in coastal areas of Prince William Sound. Skilled observers in the plane have a better view than we do in the boat and they can direct us to the fish schools so we can find them more easily.
- Measure fish density in the water column with hydroacoustics: From our research vessel USGS R/V Alaskan Gyre we conduct acoustic-trawl surveys in summer and fall. This method uses sonar technology that transmits and recieves sound in the water. When we find acoustic fish sign in the water column we send a net down to the correct depth to identify the fish species and size.
- Sample forage fish habitat: We also collect information on the type of habitat forage fish occur in by measuring ocean temperature, salinity, turbidity, light availability, nutrients, phytoplankton, and the abundance of zooplankton (forage fish food) in the water.
Media
Sources/Usage: Public Domain. View Media Details
WhaleFest 2019 Podcast
To learn more, listen to USGS Research Ecologist Mayumi Arimitsu's interview for a podcast about whale prey, forage fish, and seabird die-offs. Arimitsu talked about research on changes in forage fish populations that were first signaled by large die-offs of seabirds during the 2014-2016 North Pacific marine heatwave – aka “The Blob.”
Below are other science projects associated with this project.
Seabirds and Forage Fish Ecology
Alaska's coastal and offshore waters provide foraging habitat for an estimated 100 million birds comprising more than 90 different species; from loons and seaducks that nest inland, to petrels and puffins that breed on islands off shore. All these birds depend on the sea to provide a wide variety of food types— from clams, crabs and urchins nearshore— to krill, forage fish, and squid offshore. The...
Tidewater Glacier Influence on Marine Ecosystems
Where glaciers meet the sea in the Gulf of Alaska (GOA), they create unique and productive marine habitats. Ringed by the continent’s tallest coastal mountains, 20% of the GOA coastal watershed is covered by glacial ice and the annual freshwater discharge into the GOA from glacial melt is comparable to that of the Mississippi river.
Seabird Die-offs in Alaska
Beginning in 2015, large numbers of dead seabirds have been appearing on beaches in most marine areas of Alaska. Although seabird die-offs are known to occur sporadically (e.g. 1970, 1989, 1993, 1997/1998, and 2004) in Alaska, these recent die-offs have been distinguished from past events by their increased frequency, duration, geographic extent, and number of different species involved.
Cook Inlet Seabird and Forage Fish Study
A massive die-off of Common Murres was documented in the Gulf of Alaska (GOA) during the fall and winter of 2015-2016 in association with a record-breaking marine heat wave in the GOA.
Below are multimedia items associated with this project.
Capelin flyer
Capelin, a small forage fish, are spawning on beaches around Alaska and your observations can contribute to our understanding of beach spawning behavior and the health of marine ecosystems.
Capelin, a small forage fish, are spawning on beaches around Alaska and your observations can contribute to our understanding of beach spawning behavior and the health of marine ecosystems.
young of the year walleye pollock
Photo of young of the year walleye pollock, Prince William Sound, Alaska. Although adults are targeted in one of the largest commercial fisheries in the world, young of the year walleye pollock are important in diets of many marine predators.
Photo of young of the year walleye pollock, Prince William Sound, Alaska. Although adults are targeted in one of the largest commercial fisheries in the world, young of the year walleye pollock are important in diets of many marine predators.
Pacific herring in Prince William Sound, Alaska
Pacific herring in Prince William Sound, Alaska
Pacific herring in Prince William Sound, Alaska
Key forage fish, Cook Inlet, Alaska
Key forage fish in Alaska (from top to bottom): Pacific capelin, Pacific herring, Pacific sand lance, and juvenile walleye pollock. Cook Inlet, Alaska
Key forage fish in Alaska (from top to bottom): Pacific capelin, Pacific herring, Pacific sand lance, and juvenile walleye pollock. Cook Inlet, Alaska
Common Murres in the water
Large amount of Common Murres in the water
Schools of Pacific sand lance in Cabin Bay, Prince William Sound
Schools (shadows along the shore) of Pacific sand lance in Cabin Bay, Prince William Sound
Schools (shadows along the shore) of Pacific sand lance in Cabin Bay, Prince William Sound
Black-legged Kittiwake captured 2 Pacific sand lance
Black-legged Kittiwake captured 2 Pacific sand lance.
Black-legged Kittiwake captured 2 Pacific sand lance.
Black-legged Kittiwake foraging on Pacific sand lance
Black-legged Kittiwakes foraging on Pacific sand lance.
Black-legged Kittiwakes foraging on Pacific sand lance.
Scientist conducting marine bird and mammal survey
Scientists on the bow of the R/V Alaskan Gyre looking through binoculars
Scientists on the bow of the R/V Alaskan Gyre looking through binoculars
Erica Madison bringing in the mid-water trawl on the R/V Alaskan Gyre
Scientist pulling in the beginning of the mid-water trawl on the R/V Alaskan Gyre
Scientist pulling in the beginning of the mid-water trawl on the R/V Alaskan Gyre
Pulling in the mid-water trawl from the R/V Alaskan Gyre
Pulling in the mid-water trawl from the R/V Alaskan Gyre
Pulling in the mid-water trawl from the R/V Alaskan Gyre
Black-legged Kittiwake on a nest
Black-legged Kittiwake on a nest on the side of a rock face in the Aleutian Islands.
Black-legged Kittiwake on a nest on the side of a rock face in the Aleutian Islands.
Pacific sand lance from a purse seine in Prince William Sound
Pacific sand lance in a sieve that were captured in a small purse seine in Prince William Sound, Alaska
Pacific sand lance in a sieve that were captured in a small purse seine in Prince William Sound, Alaska
Scientist with a Pacific Herring caught in Prince William Sound, AK
Sarah Schoen with a Pacific Herring in her hand that was caught in Prince William Sound, Alaska
Sarah Schoen with a Pacific Herring in her hand that was caught in Prince William Sound, Alaska
Scenic Prince William Sound, Alaska
A scenic view of the mountains and the ocean in Prince William Sound
A scenic view of the mountains and the ocean in Prince William Sound
Beautiful Prince William Sound, Alaska
A scenic view of the sea and the mountains in Prince William Sound
A scenic view of the sea and the mountains in Prince William Sound
Catch of forage fish from a trawl in Prince William Sound, Alaska
Catch of forage fish from a trawl in Prince William Sound, Alaska. Trawling was part of detecting long-term changes in forage fish populations.
Catch of forage fish from a trawl in Prince William Sound, Alaska. Trawling was part of detecting long-term changes in forage fish populations.
Mayumi Arimitsu sorting forage fish on the R/V Alaskan Gyre
Mayumi Arimitsu sorting through fish caught in the mid-water trawl on the R/V Alaskan Gyre
Mayumi Arimitsu sorting through fish caught in the mid-water trawl on the R/V Alaskan Gyre
A catch of Pacific sandlance, capelin and other forage fish
A catch of Pacific sandlance, capelin and other forage fish
A catch of Pacific sandlance, capelin and other forage fish