North Pacific Krill, Euphausia pacifica
North Pacific Krill, Euphausia pacifica. Krill collected off the surface with a bait net near the Gordo I Bank, Baja California Sur, May 2001.
Phylogeny: The North Pacific Krill, Euphausia pacifica (Hansen, 1911), is a member of the Euphausiidae Family of Krill. The Euphausia genus is one of ten genera in the Euphausiidae Family, and there are thirty-one species in the Euphausia genus. They are also known as Isada Krill and in Mexico as Eufausiáceo and Kril Pacífico. There are two families that make up the Krill Order – Benteuphausiidae and Euphausiidae; these only families differ in that Euphausiidae Krill are bioluminescent. The name krill is Norwegian, meaning whale food. The genus name Euphausia comes from the Greek words meaning “good light” or “true light”.
Morphology: North Pacific Krill are small, shrimp-like animals in the phylum Arthropoda, meaning that they have jointed legs. They are crustaceans, with the carapace fused to the thoracic segments, and their eyes on stalks. Their pleopods (abdominal segments) function as swimmerets. North Pacific Krill have large, round eyes. They lack a rostrum and abdominal spines. There is one pair of lateral denticles on the carapace. They are translucent whitish in color. They reach a maximum of 2.5 cm (1.0 inches) in length.
Habitat and Distribution: North Pacific Krill are a pelagic species. They are abundant in the temperate and polar regions of the Pacific Ocean, often comprising the greatest biomass in these areas. They can form dense (up to 10,000/ cubic meter) shoals that can stretch for miles. North Pacific Krill are strong vertical migrators, spending the day 400-1,000 meters deep and ascending to surface waters during the night. This behavior helps them avoid shallow water predators and still feed in the nutrient rich surface waters. The North Pacific Krill in Mexican waters of the Pacific Ocean are limited to the west coast of the Baja Peninsula, from Magdalena Bay, Baja California Sur, northward along the central and northwest coasts of the Baja Peninsula. Water Temperatures, currents, and El Niño/La Niña patterns strongly impact their north/south range. North Pacific Krill are one of fifteen species of krill found along Mexico’s west coast.
Diet: North Pacific Krill are omnivores that feed on planktonic algae, diatoms, and zooplankton. They feed on phytoplankton by filter-feeding, but can also raptorially feed on larger particles.
Predators: North Pacific Krill are vitally important food for birds, fish, seals, squid, and are mainly finfish and baleen whales. Krill are a large dietary proportion of many local finfish (hake, herring, rockfish, salmon) and if krill stocks should fall, finfish could be affected.
Reproduction: North Pacific Krill are gonochoric (male or female for life). They reproduce sexually, with males producing spermatophores and transferring them to the female’s abdomen. The female stores the male’s sperm and releases it to fertilize her eggs. The fertilized eggs hatch as non-feeding nauplii, living off the yolk. They pass through several larval stages, over about four months time, before reaching their adult phase. Females can produce many sets of eggs (totaling more than 20,000) during the summer spawning season. Males take part in one breeding season and live about two years. Females live longer and take part in two breeding seasons.
Ecosystem Interactions: The Apostome Ciliate, Collinia oregonensis, and other epibionts attach to eggs of the krill. The parasite Thalassomyces fagei, of the Ellobiopsidae family, is known to affect the maturation, molting, and growth of North Pacific Krill. Krill constitute the ocean’s richest source of protein and are rich in vitamins (especially vitamin A). They play a key role in transferring energy from lower to higher trophic levels.
Human Interactions: North Pacific Krill are harvested mainly as a food supplement for both fish farms (giving salmon their ‘pink’ color) and aquariums. In the western Pacific they are also used for human consumption in limited quantities. They are critically important in supporting many other fisheries. From a conservation perspective they have not been formally evaluated however they are common with a wide distribution and should be consider to be of Least Concern.
Synonyms: None