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Monday, November 16, 2015

16/11/2015: What do we know about krill?

by Malachi Stone, International Aquafeed Magazine 
 
First published in International Aquafeed, September-October 2015

Less than you might think, and certainly less than we should, considering its vital importance to many marine ecosystems.

Euphausia superba (probably the most important species commercially) is to be found within a wide but asymmetric band of water completely encircling the continent of Antarctica, narrowest in the area south of the Pacific Ocean.

However, the actual distribution of individuals within this area is often rather hard to determine. Although there is evidence to suggest they are relatively strong swimmers, it appears they are still very much at the mercy of ocean currents, which have been known to sweep them into superswarms as large as 450km2.

Estimates of global krill biomass have varied widely over the years, between about a hundred to around a billion metric tonnes. Hence, the great difficulty in assessing how far stocks have fallen in the past decades. Estimates vary from 38 to 75 percent per decade since 1976.
    
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Even the lower of these two figures is worrying. Why? Because krill are pretty much the foundation of the Antarctic Ocean's food web. They eat phytoplankton, and are in turn eaten by a vast number of marine mammals, fish, birds and cephalopods. If they go, as far as we can see, a great deal of the ecosystem goes with them.

Krill prefer to eat phytoplankton, but will accept a wide variety of foodstuffs, including their own shed skins and even their own faeces. Cannibalism is also not unheard of: eggs, larvae and adults alike, should the necessity arise.

Captured krill should be processed within three hours, otherwise the meat becomes tainted by their own internal organs. The protein content is high - 40 to 80 percent dry weight - yet some studies have shown a lower growth-rate in fish fed protein sourced only from krill, compared to those obtaining it from fishmeal.

Source: FAO  
 
Read the magazine HERE

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