A pre-1960 2.5m narwhal tusk is to auction in Charles Miller's October 29 Maritime and Scientific Sale with a £4,000-6,000 ($6,393-9,589) estimate.

Narwhal tusks were collected in large numbers before the mid 20th century

Narwhal are found in the waters of the Arctic. Males display a prominent tusk formed from a canine tooth which is thought to be used in mating rituals.

The tusks are rare (they are illegal to harvest) and as are result are highly collectible, although as with elephant ivory its sale is controversial. Last year an exceptional specimen realised £30,000 ($47,829) at Charles Miller.

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