HARVESTING a marine pest is paying dividends for a Tasmanian entrepreneur, writes SARAH HUDSON

Taking a mid-winter dip in Tasmania's 12C ocean is not most people's idea of fun.

James Ashmore, though, begs to differ, saying it's one of the delights of life and a perk of his job.

"It's great fun and so beautiful. You'd only want to go diving in winter in Tasmania because it's so clear and healthy," James says.

"Anywhere north of the latitude of Mildura the algae dies off and the coral starts and so south of that there's no coral, but you'll find bull kelp as thick as your dad's arm."

Beautiful it may be, but it's the profitability of algae that sees the 46-year-old brave the glacial waters.

James - who is the owner of Ashmore Foods Tasmania, which specialises in trading oysters and salmon - has taken to diving in order to harvest an unusual crop of seaweed: undaria pinnatifida, or undaria as it is commonly known.

Lovers of sushi and Japanese cuisine will be more familiar with the seaweed's fronds, called wakame, a subtly sweet flavoured green sea vegetable used in salads and soups.

Chefs are more familiar with the seaweed's gelatinous root section, called mekabu, used to thicken stocks and stews, as well as products from ice cream to beer.

Native to the shores of Japan, Korea and China, the highly nutritious undaria is nonetheless an invasive species to Australia.

It was first identified in Tasmania in 1988 and is believed to have been introduced via ship's ballast.

"Scientists have since found it's most prevalent where it finds new territory. Where it's established for a few years it starts to find a niche and blends in," James says.

"So in the short-term it causes critical damage, but it's not as invasive long term, when other plants start to resurrect."

In 2011, James saw a silver lining to undaria's spread and decided to apply for a permit with Tasmania's Department of Primary Industries to harvest the plant.

Being an invasive species that easily spreads, he says only licensed holders can harvest undaria under strict conditions.

He now harvests alongside Hobart's Marinova, which manufactures seaweed for health products.

James, who opened Ashmores in 2004, has started his seaweed business tentatively, processing both the mekabu for chefs - including celebrity chef Simon Bryant and Melbourne's MoVida chef Frank Camorra - as well as the wakame for the local Japanese food market.

This year he plans to expand the business, value-adding to the wakame with ready-to-eat salads and dried product, and making a consumer-friendly mekabu, rather than the commercial quantities he sells to chefs.

Once harvested from the sea, it is brought to Ashmore's Hobart factory where it is separated, graded and blanched.

James, who grew up on the waters around Tasmania, spent periods working in an oyster, salmon and abalone farm before taking a job as a sales manager for Simon Johnson in Sydney, "learning more about food in three or four years than I could learn outside in a lifetime".

James has a quintessential Tasmanian life, combining food and outdoor activities that most mainlanders would kill for.

And in his spare time he takes to the kitchen.

"I chop up the wakame and toss it in sesame oil and sesame seeds and chilli," he says. "And I made a Scottish nage sauce using mekabu the other day, serving it with fresh crayfish."