An appeal against a Federal Court decision to allow Tassal to operate a fish farm in Okehampton Bay has been in part upheld.
Bob Brown and Graeme Wood challenged the federal Environment Department's decision to allow the fish farm to operate but this was struck down by the Federal Court last year.
An appeal against the case was on Monday upheld in part due to the department's decision not to write into the permit a requirement for the company to use K-Grid netting and use bundled feed and servicing lines.
This netting would allow for greater protection for migrating species such as the Southern right whale.
While the company already uses this type of netting on its 28-pen fish farm, which extends over 86 hectares, the court decision has now made it a legal requirement.
Part of the appeal also focused on the visual impact the pens had on the World Heritage-listed Darlington Probation Station on Maria Island but this was dismissed.
Roland Browne, who represented Dr Brown and Mr Wood, said the decision has confirmed the department had not handled the notice correctly.
"Tassal will now have to comply very carefully and scrupulously with this permit because if they don't, it's a criminal offence."
Dr Brown said it was now up to the two parties to write into the environment notice new requirements regarding the netting of fish pens.
Tassal chief executive Mark Ryan said the ruling provided certainty over continuing operations at Okehampton Bay