However, while its new managing director in New Zealand, Julian Brevis, said larger, more financial ports would benefit the port companies and also shipping lines, he believed a monopoly on 70%-80% of South Island imports and exports could be created by a merger.
"If this goes ahead, it might cause competitive concerns with the Commerce Commission. The prospect may arise of one entity being dominant," he said when contacted yesterday.
Port Otago and Lyttelton Port of Christchurch announced the merger proposal yesterday, with a loose timeline to advise shareholders of options by March next year.
The most likely scenario at present is of one company and one board, perhaps listed on the stock exchange, controlling both ports' business interests.
Port Otago chairman John Gilks said a "key consideration" within the merger proposal would be whether government legislation or Commerce Commission approval had to be sought for the merger.
"Now that the memorandum of understanding is signed, regulatory approval is an issue high on the agenda for the boards to consider," Mr Gilks said.
Mr Brevis rejected industry claims that shipping lines held a stranglehold on New Zealand ports - claims they were able to play one port off another to secure lower berthing fees in return for patronage.
He said the claims were "too adversarial" and that shipping lines, Maersk and others, made port-of-call choices based on ports' infrastructure and services and respective economics of the call.
"Cargo has a substantial voice in this and shipping lines will follow," where there was cargo availability , he said.
He noted a merger could see a large, more financial port entity arise, which was better able to undertake big infrastructure programmes, such as multimillion-dollar channel deepening proposed by both companies during the past year, but he needed more detail on the proposal before commenting further.
Unrestricted access to ports by shipping lines proved the concept of why competitiveness in sea-freight was a good thing, Mr Brevis said.
• In late August, Maersk cut more than 100 ship calls from Port Chalmers, equating to 22% of the port's container volumes, in a decision which took Port Otago by surprise at the time.
Port Otago received no advance warning from Maersk before it advised it was withdrawing 104 ship calls from its Southern Star Service, from September 1.
Container numbers were expected to drop from 225,000 to between 170,000 and 180,000 in the present financial year.
The decision affected mainly "trans-ship" container handling movements - where exports from other cities are routed through Port Chalmers.
