Hard on the bladder

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Kim Westerskov

There has been an outcry over the new Total Allowable Catch (TAC) of bladder kelp (Macrocystis pyrifera), now set at 1238 tonnes for the East Coast of the South Island by the Minister of Fisheries and Aquaculture, Phil Heatley. It’s a conservative figure, according to the Ministry of Fisheries, yet it comes as a surprise to those involved in the consultation process, who reviewed options of 40, 70 or 375.8 tonnes. Moreover, most submissions from groups such as conservationists, fishing industry leaders, tangata whenua and marine scientists either did not support any of these options or preferred the lower limits.

Kelp can be a lucrative product. It is used in food technology and cosmetics for its thickening and texturing properties, and also in fertilisers because it is rich in nitrogen and potassium.

But the wider ecological effects of kelp-harvesting in New Zealand are relatively unknown.

“This species is different from any other managed under the Quota Management System in that it is a habitat for a multitude of other species—seaweeds and animals,” says Otago University marine scientist Rebecca McLeod.

The kelp forests are also habitat for economically important fish and shellfish and food sources for a wide range of invertebrates and fish. Kelp is one of the keystone species of the marine ecosystem. Kelp forests also buffer wave flow, offering protection against coastal erosion and shelter for subtidal communities. But because of the growing interest in kelp-harvesting, including it in the Quota Management System is an important step because it regulates the industry, even if the TAC were to be set at zero.

Although kelp is sustainably harvested in places such as California, the environment for kelp growth in New Zealand is markedly different, as are the scale and size of the beds, and the effects of harvesting on the wider ecosystem have yet to be established.

The guidelines dictate a maximum cutting depth of 1.2 m. According to
the ministry, this will take around 50 per cent of the kelp mass, allowing it to easily regenerate. However, this doesn’t take into account differing amounts of biomass present in the canopies around the country, and tide level at time of harvest.

Victoria University post-doctoral researcher Shane Geange is undertaking a three-year project that will evaluate the effects of commercial harvesting on subtidal communities supported by bladder kelp, concentrating on Wellington, Otago and further south. This will hopefully provide some much-needed answers, even as the harvesting goes ahead.

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