Across the worlds oceans, sea urchins are on the march and thats not a good thing. Reports on how a new system of population management can stem a damaging swell in numbers while meeting a growing demand for their... you-know-whats

From the outside, urchins look anything but tasty. Crack open that spikey exterior, though, and you will find a delicacy highly coveted by sushi lovers and some experimental chefs: uni – the urchin’s gonads. As demand for uni continues to increase, urchin fisheries have declined due to overfishing. It is somewhat ironic, then, that in some places such as Australia, Norway and California, the combination overfishing of urchin predators and warming waters has given rise to armies of these slow-moving omnivores, which are eating their way through kelp forests, reducing them to ‘urchin barrens’.

Loss of kelp forests means loss of essential habitat for myriad other species, including some of commercial importance. Unfortunately, we can’t simply fish the urchins where they are being most problematic and sell them. Urchins on barrens have eaten themselves out of house and home – and hungry urchins do not make good uni. And this, Brian Tsuyoshi Takeda believes, is the perfect opportunity for conservation and aquaculture to work together.

Pioneered by Takeda, Urchinomics is essentially a form of ‘ranching’, with a conservation twist. Urchins are removed from those places where they are being most destructive and popped into trays suspended from existing oyster or mussel lines. There they – or rather their gonads – are ‘fattened up’ until they are perfect for sale.

Ranching urchins may need very little in the way of high-tech equipment, but it does rely on good quality feed.  Developed by Nofima, the feed consists primarily of kelp and around 10% fishmeal.  Including species from higher up the food chain in the feed has caused some to question its sustainability.  Mr Kjell Åge Rognli, Business Development Manager at Nofima explained, fishmeal is a proven source of marine protein for most farmed species; “dietary protein is needed to secure rapid growth and survival in farmed sea urchins”.  Indeed, in feed trials, urchin roe content increased from 5% to 25% in just 2 to 3 months. 

Mr Takeda also emphasised that Norwegian fishmeal is created from of MSC-certified fishery by-products; “after a fillet is cut, the remaining head, tails, bellies and bones get turned into fish meal”.  Both Mr Rognli and Mr Takeda hopes that the fishmeal will eventually be replaced by alternative proteins - such as from insects or plants.  Funding allowing, Mr Rognli commented “we aim to perform research trials to study whether it is possible to reduce or fully replace fishmeal in feed for sea urchin and still achieve zero mortality and high growth rates, as is done with the present feed composition”.

Urchinomics has certainly caught global attention. In British Columbia, Canada Dr Christopher Pearce, Research Scientist with the Department of Fisheries and Oceans (DFO) is leading pilot trials, focusing primarily on the suitability of the feed for two species of urchins found in the region.  “We have four different treatments: green urchins fed kelp, green urchins fed prepared diet, red urchins fed kelp, and red urchins fed prepared diet”, he explained.  Alongside taking various measurements of the urchin size and weight, the trials will also look at the impact of the feeds on the urchin’s gonads – their wet weight, percent yield, colour, texture, and firmness. 

The trials are also examining the potential impacts of feed and urchin faeces on the seafloor; “Build-up of organic material can cause anoxia and have impacts on the benthic community”, Dr Pearce explained.  It will be some time before the trials are completed, but indications suggest that in terms of the seafloor, Urchinomics be one of the lowest impacting aquaculture systems currently available.  Mr Takeda emphasised the amount of feed used in the first place is very low.  “We are not really contributing to somatic growth, but just gonadal growth.  This is the reason why our farming cycle is only 12 weeks or so”.  Dr Pearce also highlighted design features that would reduce the amount of material entering the ocean.  “The trays [used in the farm] are actually designed to collect a lot of the uneaten fed and faeces for removal by the aquaculturalist.  I suspect that the impact, if any, of any commercial-scale operation would be low”. 

With the urchins coming from the wild in the first place, Urchinomics’ sustainability goals also rely on ensuring that, in the long run, the urchins are not overharvested as they have been in a number of fisheries.  “Industry proponents [in British Columbia] are talking about only taking urchins from the current TAC (Total Allowable Catch)” Dr Pearce noted.  Mr Takeda agrees with this approach. “We can work within the existing regulations and quotas.  We would then add to the body of science by continuing to monitor and report our ecological impact/contribution to the relevant authorities and scientific bodies”. 

For those areas where regulations or quotas are lacking or poorly enforced, Mr Takeda envisions working with local scientists, regulators, ecologists and stakeholders.  “We should be able to increase the coastal ecosystems' ability to produce more food and help feed the 9 billion people we expect on this planet by 2050… all while achieving commercial profits and creating jobs in coastal, rural communities”.

This story appeared on The Fish Site.