Krill – Behavior, Diet, and Life Cycle

Krill are zooplankton, small invertebrates that live in gigantic ocean swarms near the ocean’s surface. They resemble tiny shrimp and are a critical component of the marine life ecosystem as a food source for other species, including whales, seals, squids, penguins, and numerous other birds and fish.

There are more than 85 known species of krill, each measuring on average two and a half inches or the average length of a human pinky finger.

Krill are generally transparent in appearance with a red tint and large black eyes. With a hard exoskeleton, they have multiple legs and a segmented body. Krill are sometimes call “light shrimp” as they can put out light, produced by bioluminescent organs.


Krill travel in swarms, mainly as a defense against predators and spend daytime among the lower depths, rising to the surface at night to feed. Krill swarms can be massive, reaching densities of 30,000 individuals in a 10-square foot area. They have been known to forms schools that can stretch for miles wide and miles deep. Swarms are so dense that at times can be seen from space.

Krill makes for an easy target for large prey such as baleen whales, which takes in an enormous amount of water and filter the krill through its baleen plates. Krill try to avoid predation by swimming backward, rapidly flipping their back end in a method known as lobstering. They can reach speeds of two feet/second, which is pretty fast for a critter less than three inches long.


Krill feed on phytoplankton, microscopic, single-celled plants near the ocean’s surface. Like terrestrial plants, phytoplankton produces their own food through photosynthesis, a process that requires carbon dioxide and sunlight.

Life Cycle

Female krill can lay as many as 10,000 eggs at a time. They have been known to give birth several times during the spawning season (January to March). Females spawn their eggs near the surface, which subsequently sink in the ocean over a 10-day period before hatching. Krill can live a maximum of about 10 years if they can avoid being someone’s meal.

Commercial Fishing & Protections

Commercial fisheries, most prominent in South Korea, Japan, Poland, and Norway, harvest krill and ground them up as meal or oil to feed livestock and fish, or to use as bait. Krill is also used to make omega-3 fish oil for human consumption.

Despite their abundant status, overfishing in key areas puts other species at risk. To mitigate that risk, the National Oceanic and Atmospheric Administration (NOAA) Fisheries Service put in place rules prohibiting krill harvesting by fishing vessels within 200 nautical miles of the U.S. in Washington, Oregon, and California.

Marine Sanctuaries Where Krill Can Be Found

On the international level, there are also regulations restricting over-fishing in the Southern Ocean where Antarctic Krill are the most abundant. The rules set by the Commission for the Conservation of Antarctic Marine Living Resources restrict fishing in geographic areas and sets limits on the amount of krill that can be harvested.

Future Concerns

Scientists also worry about the impact of climate change. Krill depend on stable ocean conditions, particularly in the Antarctic where sea ice is used for shelter in winter months, providing protection for juvenile krill.

Krill Facts:

  • If insufficient nutrition is available, krill can reduce their body size to conserve energy
  • There are an estimated 500 million tons of Antarctic krill
  • An individual krill can weigh up to 2 grams
  • Krill is used for heart-healthy omega-3 fish oils as a nutritional supplement for human consumption

You can do your part of helping to protect krill populations and help species that feed on krill by choosing sustainable and responsibly-sourced krill products.

The National Marine Sanctuary System

Spanning more than 620,000 square miles, from Michigan to Florida and Cape Cod to American Samoa, the National Marine Sanctuary System includes 13 national marine and Great Lakes sanctuaries and two marine national monuments. These unique waters sustain critical, breathtaking marine habitats that provide homes to endangered and threatened species. They preserve America’s rich maritime heritage. They are literal living laboratories for science, research, education, and conservation. Sanctuaries also offer world-class outdoor recreation experiences for all ages and support local communities by bringing billions of dollars to their economies.

The National Marine Sanctuary Foundation

The National Marine Sanctuary Foundation is the national non-profit partner for the National Marine Sanctuary System. Founded in 2000 by America’s most influential ocean conservation leaders, the Foundation raises awareness of and support for national marine and Great Lakes sanctuaries and their vital role to ensure a healthy ocean.

The Foundation directly supports America’s national marine sanctuaries through our mission to protect species, conserve ecosystems, and preserve America’s maritime heritage. We accomplish our mission through community stewardship and engagement programs, on-the-water conservation projects, public education and outreach programs, and scientific research and exploration. The Foundation fosters innovative projects that are solution-oriented, scalable, and transferable, and develop strategic partnerships that promote the conservation and recovery of species and their habitats.

Click here to help us protect marine species, from krill to whales and everything in between.