Snow petrel (Pagrodama nivea) fishing at tide crack during winter

That these animals are prepared to undergo so much to find their food is testament to the nutritional value of that food - krill. Here snow petrels (and in the first photograph a crab eater seal too) are taking advantage of a tide crack to fish through in the case of the birds and to breathe at in the case of the seal. A tide crack is a long narrow open lead of water that stretches between two points such as nearby islands or exposed rocks. It arises when the tide rises and falls, when the tide rises the crack opens when it falls, the crack closes. Such tide cracks can easily stretch for several kilometres, but never being more than about 50cm wide.

The snow petrels space themselves out along the tide crack and sit patiently waiting for a krill to swim by at which point they jump out and hover just above the surface to take the tasty morsel.
 

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Paul Ward - Pentax equipment, 100mm lens, 35mm film, K64.
This picture may not be copied or used in any manner without prior written permission.