In an open letter to all staff at the government-owned agency, as well as Primary Industries Minister Jeremy Rockliff, the principal advisor said organisational change had been the most atrociously implemented he had ever encountered.

Biosecurity Tasmania was formed in May last year following a merger of the former Invasive Species Branch and Biosecurity and Product Integrity division.

In a statement released after the letter was made public, Mr Rockliff said he recognised change could be difficult for long-time staff but argued the biosecurity agency was stronger than ever.

Peter Cremasco, who will leave Biosecurity Tasmania today, said he felt like ''the lucky one'' for taking a redundancy package.

''The last 12 months bear testimony to a litany of misinformation, inconsistencies, incompetence, mismanagement, secrecy and deceit, and some of the most appalling regard for human resources I have ever witnessed,'' Mr Cremasco said.

He queried whether advice from department heads had been ignored in restructuring the DPIPWE branch, or not offered in the first place.

Mr Cremasco said the workforce had become increasingly marginalised, with morale at rock bottom.

''It is a sad indictment that the decision to take a redundancy, all the while with no other employment in the pipeline, has still left me feeling like the lucky one,'' he said.

''I’m not angry but I am disappointed that the opportunity, to build a biosecurity agency that Tasmania would have been proud of, has been squandered.''

Mr Rockliff said he was confident the structural changes were positive.

''I have complete faith in Biosecurity Tasmania, its managers and the wider department, and have confidence that the changes we are making will better protect our state,'' he said.