Big sharks caught on drum lines off WA's coast have been powerful enough to straighten the hooks and even wrest themselves free from the chains designed to catch them.
Four baited hooks have been pulled out of shape by big sharks caught since the State Government began its cull program a month ago. One hook, off the Perth coast, was found straightened with its bait gone.
The reason for the hook's damage has officially been deemed unknown but it is understood Department of Fisheries experts believe a shark freed itself by thrashing against the chain and straightening the hook in the process.
A Government spokesman said the hooks were designed to catch big sharks and reduce the chance of snaring other marine life with smaller mouths such as dolphins.
"Three drum-line hooks have been damaged and subsequently replaced since the program started in the metropolitan area," he said.
"Two of these hooks were damaged because of line pressure, one during retrieval of a hooked shark on to the vessel, and the reason the third hook was bent is unknown.
"A hook has also been damaged in the South West while a shark was being towed for disposal."
It is not known whether the three hooks were damaged by the weight of the sharks - which were more than 3m long - as the drum lines were pulled up or if the animals straightened them by thrashing about when caught.
Despite the damage, the Government plans to use similar gear if it gets Federal Government permission to target sharks again after its exemption runs out in April.
The first hook was damaged by a 3.3m tiger shark, which was the first shark to be caught in the South West on January 26.
There are 25 drum lines set along the Perth coast, from Mullaloo to Port beaches, and five more devices will be set in the area at the weekend. There are 22 drum lines set along six popular surf breaks in the South West. The State Government plans to have 36 drum lines in each area by the end of April.
In the first three weeks of the cull, 66 sharks have been caught.
Twenty-six of them were destroyed because they were 3m or bigger or were dead when pulled up.
The West Australian understands there are fears among Fisheries officers that sharks impaled on hooks are attracting bigger sharks to coastal areas where the drum lines are deployed.