There are two types of sea urchins in Tasmanian state waters, the
short spined sea urchin,
Heliocidaris erythrogramma which is endemic to Tasmania and has well established markets and the long spined sea
urchin Centrostephanus rodgersii. The long spined urchin has only recently become established in Tasmanian waters following changes to the East Australian Current allowing this invasive species to be transported from New South Wales to the east coast of Tasmania. The two species have different spine morphology and length and are usually a different colour.
In the commercial fishery, there is no size nor catch limit for
Centrostephanus but for
Heliocidaris there is a total allowable catch of 166 tonnes and a size limit of 60 mm (circumference of test or shell inside the spines).
Short Spined Sea Urchin Fishery
Short spined sea urchin
The short spined sea urchin
has shorter, solid spines. They have a number of colour variations all made up of purple, green and/or white which often differ between the spines and the teste (shell).
The short spined urchin is the preferred species taken by commercial divers as the roe is highly prized particularly by Asian markets. However, the short spined urchin only produces about 5% to 6% of its body weight as roe which is about half the amount of roe produced by the introduced long spined urchins but markets pay well for the short spined delicacy at around $50-$60/kg.
In recent years, the fishery has taken around 70-80 tonnes live weight annually. The short spined urchin commercial fishing season is generally from late July until February after which time spawning leaves the quality and quantity of roe uneconomically viable.
While the short spined urchin may form barrens, the extent of their development is far less intrusive than those formed by the invasive long spined urchins.
Long Spined Sea Urchin Fishery
Long spined sea urchin
The long spined sea urchin has spines longer than half its shell diameter. This urchin is dark brown to black with a turquoise-like sheen on the spines with red down their centre - however colours can vary.
The long spined sea urchin is considered a threat to Tasmanian ecosystems as it feeds on the marine algae leaving large barren areas on the sea floor and depriving abalone, rock lobster and other species of their feed and habitat. The impact on Tasmanian fisheries is already a serious concern.
Until recently, it was believed that there were no viable markets for the long spined urchin as the roe was believed to be bitter and unpalatable. In 2008, some interest had been shown in the product leading to the development of a processing technique that showed promise for potential markets. Initially, focus was centred on the Pacific Islands but more recently there has been interest from Japan, Hong Kong, China and Singapore.
The long spined sea urchin season runs from around January to July each year. Spawning takes place in July and the urchins don’t gain enough condition to make harvesting viable until the beginning of the following year.
In 2008/09, about 7.5 tonnes (live weight) of product was sold. This has been gradually increasing, reaching 97 tonnes in 2013/14. With the incentive of a subsidy provided by the abalone industry in 2017/2018 there has been increased interest from processors which resulted in a harvest of 186 tonnes in 2017/2018 for the year.
This year the long spined urchin has been averaging around 12% of body weight of roe which is graded into A grade (top quality) and B grade (low quality). The amount of A and B grade roe is quite uniform with about 50% of each produced by the urchins. The A grade beach price is around $20/kg and the B grade only $8.00/kg.
There have been a number of research projects undertaken by the Institute of Marine and Antarctic Studies (IMAS) in the past which have investigated the best means of control including encouraging predators and the development of a commercial fishery. The extent of the barrens formed by long spined urchins also first mapped by IMAS in 2005.
Although it is unlikely that the long spined urchin will be totally eradicated from Tasmanian waters, it is considered that the use of a multi-pronged approach including control mechanisms like culling programs and uses for urchins such as a strong commercial fishery will keep the threat in check.