He flew into the conference yesterday, passing over the harbour at Majuro Atoll where dozens of fishing boats - mostly foreign - were docked.
Some of the Pacific region's micro-states have small amounts of land area but gigantic exclusive economic zones - Kiribati has fishing rights to 3.55 million sq km of ocean.
New Zealand has already introduced a number of initiatives to help Pacific countries manage their fisheries. It has created training colleges and encouraged rules that require foreign fishing companies to use local labour.
It also provides navy offshore patrol vessels and an air force Orion to watch over fishing grounds and trained monitors to detect unreported catch on tuna vessels.
Mr McCully said one of the most valuable steps Pacific countries could take was to get higher-quality fish to the market faster.
"One of the areas we're trying to focus on is how we help Pacific countries to get up the value chain by moving to fresh sashimi products, rather than canned tuna."
In the Western Province of the Solomon Islands, New Zealand is helping to seal key transport routes as part of a larger plan to speed up the movement of tuna catch from a deep-water port. It also funded the Solomons' international runway, which is expected to help export fresh fish to Cairns and Tokyo.
Rights to fishing grounds were one of the final frontiers for global economic development, Mr McCully said. New Zealand expected to step up its commitment to managing and monitoring the fishery over the next decade as countries on the Pacific Rim increasingly sought access to the Pacific's fishing grounds.
Colours out to welcome Key
Prime Minister John Key has been given a colourful welcome at the very edge of the Pacific.
Mr Key took centre stage in the absence of high-ranking Australian and American officials as the Pacific Islands Forum opened last night in the remote Marshall Islands.
About 1000 children waving flags of the 15 Pacific nations greeted Mr Key, wearing the customary silly shirt.
A group from the Uji Atoll wearing inn, or traditional dress, performed a jobya - a "stick dance", and local women wearing the national colours of blue, orange and white sang the national anthem.
The New Zealand delegation had arrived in the afternoon at Majuro, a coral atoll of 28,000 residents which is so narrow it can barely fit a runway - one of the aircraft's wings hung over the sea as it landed.
Sandbags patched up the runway seawall where a king tide had broken through last month - one of several visible reminders of the threat of climate change in the region.
The forum was expected to be more low-key than last year, when then-Secretary of State Hillary Clinton attended.
The US was this year sending its Interior Secretary and Australia's Prime Minister Kevin Rudd could not attend because of the country's general election.
As talks begin today, the focus will be firmly on the threat of rising waters around the atolls.
