Fish, including sharks, have a long history of biting cables as identified from teeth embedded in cable sheathings. Barracuda, shallow- and deep-water sharks and others have been identified as causes of cable failure. Bites tend to penetrate the cable insulation, allowing the power conductor to ground with seawater. Attacks on telegraph cables took place mainly on the continental shelf and continued into the coaxial era until 1964. Thereafter, attacks occurred at greater depths, presumably in response to the burial of coaxial and fibre- optic cables on the shelf and slope. Coaxial and fibre-optic cables have attracted the attention of sharks and other fish. The best-documented case comes from the Canary Islands, where the first deep-ocean fibre-optic cable failed on four occasions as a result of shark attacks in water depths of 1,060–1,900 m [3,478 to 6,234 feet].