Enhancement of an underexploited fishery - Improving the yield and colour of roe in the sea urchin Centrostephanus rodgersii by reducing density or transplanting individuals

A large proportion of the sea urchin Centrostephanus rodgersii resource in New South Wales is unfished because of the unmarketable condition (i.e. yield and colour) of its roe. This unfished proportion of the population occurs in Barrens habitat, where urchin densities and grazing pressure limits development of the algal assemblage, their primary source of food. Using field experiments at different spatial and temporal scales, we investigated how the yield and colour of roe can be improved by increasing the urchins' access to food, either by reducing densities in Barrens or by transplanting individuals to other habitats. Significant improvements in both colour and yield occurred after reductions in density over short periods of time (i.e. 3 months), and greater improvement was observed after two years. Significant increases in yield occurred where density was reduced by as little as 33%, but the greatest significant increase to yield (i.e. >2 times) occurred where density was reduced by 66%. Urchins transplanted to habitat with an abundance of macro-algae showed significant improvements in colour and yield of roe after six weeks, although the magnitude of change depended on density and season. Although improvements to the condition of sea urchin roe over one year did not reach the levels observed in the normal commercial harvest from productive habitats, the enhanced roe from transplanted urchins was marketable and the operation was considered profitable. Given the results of the experiments were reasonably consistent at different spatial scales it is considered that C. rodgersii could be commercially harvested in generally unfished Barrens areas with the aid of density reductions or transplanting.