Mayor Phil Goff's warned on any decision to move the port, which is 100 per cent owned by the council and which he said delivered a dividend of more than $50 million annually.
But Gaskin questioned the source of those annual dividends.
"Ports of Auckland can only pay $50m to the council by increasing debt," he said.
But a port spokesman said the business disagreed with Gaskin.
"Most companies carry debt and pay dividends at the same time. It's normal. At times debt will increase, as it is for us at the moment as we gear up to handle Auckland's rapidly growing freight demand. Debt will reduce again once this investment phase is over. We're not borrowing to pay a dividend. We're borrowing to increase capacity," the port spokesman said.
Gaskin said that last year, the port's net debt increased from around $297m to $384m.
"This is because, even before paying a dividend to the council, there was less money coming in via operating cash flow than was going out in investing cash flow," Gaskin said.
"To give you some context, the metric that is typically used to assess the amount of debt a business has, is net debt divided by earnings before interest, tax, depreciation and amortisation. This ratio for Ports is now 3.9 times, which is high.
"The same ratio is only 2.6 times at the larger and more diversified Port of Tauranga, and only 2.2 times at the Port of Napier which has wisely decided that 2.2 times is a sensible level of debt, and are planning to partially list on the NZX with the council retaining 55 per cent," Gaskin said.