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Do sharks still bite undersea fiber optic cables?

November 13, 2009  »  Broadband10 Comments


A recent article in Business Daily Africa examines how telecoms, specifically in Kenya, have taken measures to prevent downtime across their fiber optic networks. Interestingly, however is the potential for shark bites to interrupt fiber optic service to parts of Africa. I’m not sure if the author is basing this information on current fact, or past fear from what happened in the early days of undersea fiber optics. He writes:

The undersea cables are prone to shark attacks which may lead to losses if there are no other alternative routes to connect them to other parts of the world.

If true, such news is worrisome considering shark attacks on fiber optic lines were first noted over 20 years ago. Time Magazine even wrote a story on the subject. At that time, AT&T was testing a fiber optic line in the Canary Islands at a relatively shallow depth. Shark teeth were discovered embedded in parts of the cable and researchers scrambled to solve the mystery.

Unlike short-haul terrestrial fiber cables or old copper cables where the fiber did not emit noticeable fields, undersea cables must carry high voltage power to the undersea repeaters, which result in both electric and magnetic fields around and along the cable. A significant 50 Hz field is caused by AC current induced into the power feed system for the cable. In addition, a weak low-frequency field is generated by the DC current on the cable. Some sharks mistaken the electric fields for distressed fish and attempt to feed on the cable. Sharks also bite the cables as they are deployed, recovered, or lifted for repair.

What happens when a shark bite tears into a fiber optic cable? explains in detail:

When the deepwater sharks bit into the light wave cable, the teeth penetrated the medium density polyethylene (MDPE) jacket on the cable. This exposed the copper tube, surrounding the core of the cable, to seawater. The electric current, which flows through the copper tube to power the amplifiers, arced into the sea and short-circuited the power system, causing the cable to lay lifeless at 9,000 feet (2,744 m).

Since the costs of unearthing and repairing a cable are not cheap, measures have been taken to prevent damage by curious sharks. The results of the testing showed that the layers of 0.15 millimeter steel and a high density 0.05 millimeter polyethylene jacket protect that insulation from shark attack. Generally, sharks do not feed below 1,500m, so only cables shallower than this depth need extra reinforcement from sharks. However, boat anchors are still a risk.

African undersea cables will not last for long if they are easily damaged and require costly maintenance. However, it seems unlikely that the cables would be susceptible to shark attacks after hundreds of millions of dollars of planning and investment. Either way, no one can criticize the telecoms for taking the time to ensure network stability.