An Assessment of Growout Strategies for the Green Sea Urchin (Strongylocentrotus droebachiensis) in the Gulf of Maine

The green sea urchin Strongylocentrotus droebachiensis fishery in Maine collapsed in the 1990’s due to high demand for its edible gonads (“uni”). This thesis explores various echiniculture methods, including sea ranching and land-based farming. The rise, decline, and management of the fishery are described in Chapter 1. Chapter 2 describes sea-based urchin ranching. Experiments were conducted to examine growth and survival of tagged hatchery-reared urchins released onto two lease sites in Penobscot Bay, at Job Island and Sloop Island. In February, 2010, a group of 10,500 juvenile urchins was released onto each site, at initial densities of 26.25 urchins/m2, and with initial mean diameters (mm ± SE) of 10.5 ± 0.18, and 11.3 ± 0.23, respectively. Urchins were sampled at six dates between April, 2010 and May, 2012, and reached final densities of 1.4 and 18.1 tagged urchins/m2, and mean diameters of 8.5 ± 0.74 and 18.8 ± 0.71, respectively. Results indicated loss of larger urchins, most likely due to predation. Chapter 3 describes the use of a recirculating tank system (RAS) to grow a third group of hatchery-reared urchins to harvestable size. Urchins grown in the RAS had an initial mean density of 0.5 – 2.9 kg/m2 (different by tank), and a mean diameter (mm ± SE) of 9.2 ± 0.2. Feed trials were also conducted to examine the effect of feed type and feed frequency on growth in our RAS. Groups fed Nofima, an experimental feed, and catfish feed from Cargill, USA, had specific growth rates (SGR in %/day) of 0.51 (319% increase in weight) and 0.45 (257% increase in weight), respectively. It was determined that both feed type and urchin size had significant direct and interactive effects on growth, which was higher for the group fed Nofima, and increased with decreasing size. A second trial examined the effect of feed frequency and size on urchin growth. Groups fed every 3, 7, and 14 days had SGRs of 0.19 (46.9% increase in weight), 0.12 (27.4% increase in weight), and 0.10 (22.5% increase in weight), respectively. Feed frequency and size had a significant direct and interactive effect on growth, which increased with feed frequency and decreasing size. Overall, the group of urchins grown in the RAS had a final density of 5.1 – 14.8 kg/m2, by tank, and a final mean diameter of 38.3 ± 0.69, with less than 5% mortality during the two-year study period. In Chapter 4, an economic assessment was completed for each method, considering a commercial-scale model. While a 2-acre sea ranching lease has lower operating and harvesting costs ($10,636 + extra dive days), substantial losses meant that profits from harvest would not be sufficient to cover expenses, ending with a net loss of $12,216. High costs for a 15.2-m3 RAS ($21,723) offset higher survival and growth, and resulted in a loss of $6,793. Our results indicated that neither method would be economically feasible under our research conditions. With cost-saving measures, however, both methods may have some potential for the culture of S. droebachiensis in the future