1. Antarctic Krill Are Small Shrimp-Like Animals That Gather in Giant Swarms
Krill are small crustaceans, relatives of shrimp and crabs. They live in oceans all over the world, but one species, the Antarctic krill (Euphausia superba), is the one that matters most around Antarctica. In the wild it probably lives for 3 to 4 years. [1] A full-grown adult is about 5 centimeters (2 inches) long. [3]
Krill eat phytoplankton, the microscopic floating plants that use sunlight to grow, and a little zooplankton as well. In this way they turn the energy of the sun, captured by tiny plants, into food that bigger animals can eat. They also move up and down in the water every day. At night they provide food for predators near the surface, and by day for predators in deeper water. [1]
They gather in super-swarms that can stretch tens of kilometers across and reach more than a hundred meters deep. [2]
2. Together, Antarctic Krill May Weigh as Much as All the People on Earth
Nobody can count krill one by one, so scientists estimate how much there is. The commission that manages krill fishing, CCAMLR, uses an estimate of about 379 million tonnes of Antarctic krill in the Southern Ocean, which it compares with the weight of the whole human population. An Australian Antarctic Division feature gives a figure of more than 400 million tonnes. [1] [2] The numbers differ a little, and both are estimates, not exact counts.
The number of krill also changes a lot from year to year. CCAMLR says this seems to depend mostly on how many young krill join the population each year, which may be linked to the amount of sea ice. [1]
3. Penguins, Seals, Whales, Squid and Fish All Eat Krill, So It Holds Up the Whole Food Web
According to CCAMLR, more than half of all the Antarctic krill is eaten each year by whales, seals, penguins, squid and fish. CCAMLR says that amount is replaced through the krill's reproduction and the growth of young krill, though the population changes from year to year. [1] The Australian Antarctic Division adds that most large predators in the Southern Ocean rely on krill at some point, including penguins, seals and the blue whale, the largest animal that has ever lived. [2]
That is why scientists call krill a keystone species. Like the keystone at the top of an arch, it is one small piece that many other pieces lean on. For many animals in the Southern Ocean, krill make up the largest part of what they eat. [1]
It is tempting to ask which group eats the most. Published estimates exist for seals, whales and others, but they come from different decades and different methods, and even the experts describe them as uncertain, so this article does not pick a winner.
4. People Catch Krill Too, Mostly for Animal Feed and Supplements
Krill support the largest fishery in the Southern Ocean. It supplies a market for nutritional supplements and other products. [4] Reports from Japan's fishing press say recent catches have been roughly 350,000 to 400,000 tonnes a year, mostly taken by Norway, China, South Korea, Ukraine and Chile, and that most of it is made into fishmeal, with some used as food and supplements. [3]
In Japan, krill is also well known as a fishing bait, which is why a Japanese angler may first meet it on a tackle-shop shelf. That krill travels a long way: a Japanese newspaper reports that it takes about 40 days to ship it from the Southern Ocean to Japan. [5] Japan was also an early player. A Japanese fishing company was the first private company in the world to run a krill fishery, in 1974, but it sold its ship in 2012, and Japan does not fish for krill today. [3]
5. An International Commission Sets Limits So That Fishing Does Not Starve the Predators
CCAMLR was set up in 1980 because people worried that a growing krill fishery could hurt the rest of the Antarctic ecosystem. [1] It is an agreement among 25 nations plus the European Union, including the United States. [4] In 2020, NOAA wrote that the current catch limits for the regional fishing areas add up to less than 1 percent of the overall krill stock, a level that had been considered "precautionary." [4]
A small share of the whole stock may sound safe. But ships do not spread out evenly, and that matters.
6. Even Small Catches Can Hurt Penguins Where the Ships Gather
In 2020, NOAA Fisheries described new research published in Scientific Reports. The study found that fishing can remove only a tiny share of Antarctic krill overall and still reduce the food available to predators in certain smaller areas, because the fishing is concentrated there. It found effects on the reproduction and growth of penguins, and the size of those effects could be similar to the effects of poor environmental conditions. [4]
One of the scientists, George Watters of NOAA Fisheries, put it this way: the regional catch limits "are not as precautionary as decision makers presumed" because the impacts show up in the smaller areas where fishing actually concentrates. [4]
So "how much can people catch?" has two answers. Compared with the whole ocean, the amount is small. Compared with what the penguins living in one place can reach, it can matter.
7. Where Can You See the Krill Story Yourself?
Look at the ingredients on a food or supplement label, or at a fishing-supply shop, for the words "krill" or "krill oil." Then look up where the product's krill comes from. You may find that a small animal from the far end of the world is connected to something in your own kitchen or tackle box. To go further, read the CCAMLR page and the NOAA story listed below, and ask yourself what a fair fishing limit might be, while leaving enough krill for penguins and the other animals.