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The world's fastest shark, with an aggressive streak and an appetite for almost anything, is being blamed for an attack on sonar equipment which has stalled the search for containers from the stricken Rena.
Maritime New Zealand said the Braemar Howells recovery team was not able to do any work as a result of the damage, thought to have been caused by mako sharks.
The sharks may have been attracted to the warmer water near Astrolabe Reef, shark expert Clinton Duffy said.
"It would not be out of the ordinary for them to be attacking a `sonar fish', because that's what the equipment would have looked like to these sharks," Mr Duffy, a Department of Conservation marine scientist, said.
Because of the sonar gear's elongated shape and propeller, the sharks could have mistaken it for a large fish.
"Mako sharks are known to feed on fish that are larger than themselves, including swordfish and even other sharks." Mr Duffy described mako sharks as "aggressive" and said they had been known to attack humans.
The growing numbers of kahawai and small fish in the area were also attracting mako and other shark species.
The recovery team willsurvey Whale Island and a helicopter will today fly to Motiti Island to inspect beaches for container debris, Maritime New Zealand said.
Over the weekend, 17 containers were taken off Rena, taking the total removed by salvors to 227.
When Rena struck the reef off the coast of Tauranga on October 5, 1368 containers were on board. A container with meat products inside fell off on Sunday and was recovered, taking the total number washed overboard to 89.
Braemar Howells was processing more than 200 containers that have been brought ashore.
"Dive inspections have been conducted on a regular basis and buckling damage adjacent to the No 6 hold on the starboard side continues to develop," MNZ said. A narrow sheen of oil was also visible off the bow of Rena to the northwest.
• Fastest of all shark species in the world, can swim at speeds of 90kmh when hunting.
• Can sometimes leap out of water.
• Feeds on primarily tuna and swordfish, but will eat nearly anything.
• Aggressive by nature, they have been known to attack humans although do not eat people.