The Barnett Government has had to cut the length of its shark-kill by a third after concerns about migrating whales getting tangled in drum lines.
Under the Government's plans revealed in December, baited drum lines were to be set off Perth and South West beaches annually between September and April.
Announced after a series of fatal shark attacks in WA waters, the policy was aimed at catching great white, tiger and bull sharks bigger than 3m.
However, plans submitted by the Government to State and Federal environment watchdogs reveal the policy will be enforced only from November 15 to April 30 over the next three swimming seasons.
It is understood the decision to cut the drum-line season was made amid fears migrating whales, including humpback and southern right whales, could get caught in them.
The mammals usually migrate from their Antarctic feeding grounds north along WA starting in May before returning south in spring - a period which would have overlapped the start of the drum-line season as originally proposed.
In July, then fisheries minister Troy Buswell said the Federal Government had threatened to take away lucrative rock lobster export licences after a rise in whale entanglements in lobster pot lines. The revelation prompted the creation of a task force - comprising government and industry representatives - to find ways to avoid entanglements.
Details of the change in shark policy came a day after the Environmental Protection Authority confirmed it would subject the drum-line program to a full public environmental review.
That process usually takes between six months and two years.
It is believed the Government moved to shorten the drum-line season to placate concerns about its effect on whales. The EPA assessment, along with Federal scrutiny, threatens to delay the Government's hoped-for setting of drum lines by November 15.