Effects of stocking density on behaviour and roe yield in kelp-fed green sea urchins (Strongylocentrotus droebachiensis) farmed in a custom-made raceway

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With densities of up to 500 individuals m-2, the green sea urchin, Strongylocentrotus droebachiensis, is adominant grazer in shallow rocky subtidal habitats in the northern Gulf of St. Lawrence (NGSL). A green seaurchin fishery entirely dependent on harvesting individual urchins manually is currently in operation at severalsites in the NGSL. However, success is limited mainly because of the small period, i.e. a few weeks in fall andwinter, during which urchin gonad or "roe" (the urchin's organ marketed for human consumption) must becollected to minimize variability in quantity and quality. This fishery mainly targets urchin grazing fronts,leaving in the barrens high densities of undernourished urchins that could form the basis of a viablecommercial exploitation if these urchins were farmed with the right equipment in land-based facilities.Pêcheries Shipek S.E.C. (PSSEC), a leader in commercial harvesting of key marine fish and shellfish species inQuébec, needs knowledge on the suitability of a custom-made raceway (system of troughs with continuouslyrunning seawater) for quick production of high volumes of green sea urchin roe. In this project, we willexamine how urchin stocking density affects urchin aggregation, feeding, and roe yield in the raceway as a firststep to determining if the raceway can support steady commercial roe production in green sea urchins fed kelp.Weekly trials will be carried out over 12 weeks during which urchins and kelp in multiple sections of theraceway will be filmed at regular intervals and mortality, amount of kelp consumed, and degree of aggregationquantified from the videos. Roe content (somatogonadic index) will be quantified from urchins at the onset andend of the experiment to determine relationship to stocking density and degree of aggregation. Informationgenerated from this new industry collaboration will be used by the company to examine the possibility ofdiversifying the range of species it provides to fishmongers, while exporting a part of its own productiondirectly to regional and global urchin roe markets.