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The Pacific WildLife Foundation is a non-profit coastal and marine research and education society  that inspires an appreciation for objective scientific research and conservation of the ocean. We conduct original research, develop novel education programs, and inspire an appreciation for conservation of the ocean. 

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Krill Euphausiids

Euphasiids is the scientific name for many species of tiny crustaceans known colloquially as krill. These tiny planktonic animals form the base of the ocean’s food chain throughout the world. The food chain begins with tiny floating plants known as phytoplankton that store the sun’s energy during photosynthesis. Euphasiids convert the plant sugars in the phytoplankton into animal tissue and they then are eaten by fish, birds and marine mammals. Major predators of krill in the north Pacific are salmon, herring and hake and the baleen whales. The hake is so closely allied to the krill as a food species that the two are almost inseparable. The Cassin’s auklet and ancient murrelet eat krill directly and many other seabirds eat herring, sandlance and other small fish that eat krill. The red colouration of krill is derived from carotenoid pigments. In high density, the red krill can turn surface waters a reddish hue. There are about 85 species of euphasiids in the world’s oceans of which 15 species are found in all oceans. About twenty species of euphausiids have been recorded off British Columbia with five species being most numerous: Euphausia pacifica, Thysanoessa spinifera, Thysanoessa inspinata, Thysanoessa longipes and Thysanoessa rashii. About 25 species are abundant off California. Unlike most zooplankton, euphausiids can live at depth in the ocean. They move between the ocean depths at night and surface waters during the day. The average krill is about 16 mm long and can live one or two years. Spawning occurs in spring and summer to coincide with periods of high phytoplankton abundance. Euphausiids are harvested as a feed supplement for fish farms to give salmon flesh its pink colour and as fish food for aquarists, and as a fishery for human consumption. 


Krill Behaviour

Krill Breeding Biology

The predominant euphausiids in the Gulf of Alaska are Thysanoessa inermis and Euphausia pacifica. Gravid females of T. inermis release eggs in April and May continually over a three day period. Gravid female E. pacifica are numerous in July to October and release eggs only for one day. Large females release the most eggs. Eggs hatch simultaneously over a few hours depending on incubation temperature creating ‘blooms’ of plankton in the ocean.



Krill Migration and Distribution

We don’t usually think of plankton as being capable of migration but each evening, these tiny crustaceans make an extraordinary journey of 500 or more meters between the depths of the ocean and  the surface waters. During a 24 hour period, these animals may pass through a range of temperatures of 16°C.




Abraham, C.L., G. S. Wolfe, J. M. Hipfner and W.J. Sydeman. The seasonal cycle of euphausiid zooplankton in the California Current system: A predator’s perspective. PISCES On line

McFarlane, G.A., and R.J. Beamish. 1985. Biology and fishery of Pacific Whiting, Merluccius productus, in the Strait of Georgia. Marine Fisheries Review 47:23-34

Yin, K. P. J. Harrison, R. H. Goldblatt and R. J. Beamish. 1996. Spring bloom in the central Strait of Georgia: interactions of river discharge, winds and grazing. Marine Ecology Progress Series 138: 255-263.


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