Measuring a mere 2 centimeters in length, North Pacific krill (Euphausia pacifica) are the most abundant krill species in the northern hemisphere. They range from North America to Japan and are found in the waters surrounding the Aleutian Islands. Preferring open water, North Pacific krill congregate near the edge of the continental shelf at depths of less than 1,000 feet. Feeding mostly on plankton, they rise to the surface at night to feed, returning to the depths during the day. Males of the species live for approximately two years and females for nearly three. Despite being aggressively harvested for the commercial trade, North Pacific krill are not endangered or threatened.
One of the largest varieties of krill, Antarctic krill (Euphausia superba) is the basis of the Antarctic ecosystem. Despite being tiny creatures less than 2 inches in length, swarms often include more than 2 million tons of krill spread over 175 square miles. Individuals can live for six years, making them one of the longest living species. Antarctic krill are the most intensively harvested of all species with nearly 100,000 tons netted each year for use in nutritional supplements. Research scientists believe that such intensive harvesting has caused the numbers of Antarctic krill to plummet by 80 percent in the past 30 years.
Found in the north Atlantic, northern krill (Meganyctiphanes norvegica) are physically similar to North Pacific krill with the exception of their guts, which have a reddish cast. Approximately 3 centimeters in length, northern krill weigh less than .003 grams yet comprise a huge portion of the north Atlantic food chain. They live in slightly shallower water than other species of krill, seldom found below depths of 800 feet. Northern krill is the only known species in the genus Meganyctiphanes.
Deep sea krill (Bentheuphausia amblyops) is the only genus and species within the family Bentheuphausiidae. It is an unusual species occurring at depths below 3,300 feet in water that is completely devoid of sunlight. Reaching 2 inches in length, deep sea krill have several morphological differences from other species, including underdeveloped eyes and a lack of bioluminescence.
