Development of scientifically base management towards a sustainable fishery of the common sea urchin, Paracentrotus Lividus, in Sardinia

Abstract

In recent years sea urchins have become a premium commodity in the world where both males and females of the species are harvested for their gonads, generally referred to as “roe” in the fishery and catering market. Fishing for sea urchins can be a very profitable business during the first 5 to 10 years operations on a new fishing ground. However, after that short period of time, wild populations decline due to the high efficiency and selectivity of the employed fishing techniques. In several countries fisheries declined considerably since their peaks and stocks are now likely to be over-exploited. Paracentrotus lividus is the main echinoid consumed in Mediterranean and Atlantic Europe. France is the world’s second largest consumer of sea urchin. In Italy, sea urchin fisheries occur in the South and the Islands. Recent studies suggest that the risk of collapse of the sea urchins stocks in Sardinia could be imminent, unless the fishery agencies take on immediate strategies for the species conservation. Considering such preconditions, the general aim of my PhD project have been to develop possible alternative strategies to improve the sustainability of current management practices for sea urchin fishery in Sardinia. In detail, the goal is to encourage a science-based management in order to avoid the collapse of this resource. This overarching objective has been achieved through: a) investigation the pre- and post-effects caused by fishing harvesting on spatial patterns, abundance fluctuations and total mortality rate; b) improvement of the knowledge of the effect of habitat on the ecology behaviour of the species; c) introduction of aquaculture as operational tool to improve wild stocks numbers via restocking and to provide viable alternatives to commercial fishery. The development and application of a geostatistical approach for determining the spatial distribution and resilience of P. lividus population were studied in a fishing ground of western Sardinia (Western Mediterranean). The framework proposed, combining field data collection, experimental modelling and mapping, was adequate for biomass estimation and assessment of sea urchin resource. The effect of different habitats was investigated on spine and gonad colouring and the gonad index in the purple sea urchin, Paracentrotus lividus. Colorimetric analyses of spines and gonads were conducted by a digital colorimeter using CIELAB colour spaces, which defines the colour in terms of 3 coordinate values: lightness (L*), redness (a*) and yellowness (b*). The results suggested that that habitat does affect spine colour but not gonad colour. Spine colour seems to be site dependent while the gonad index depends solely on the habitat. A land-based rearing system for sea urchins was set up in Sardinia to produce juveniles of P. lividus for restocking purposes and develop and test protocols on echiniculture. The results coming from the hatchery are promising, we obtained over 8,000 post-larvae for each of the 150 l tanks , that means at least 250,000 post-larvae will be cultured per year. In conclusion, my suggestion to guaranty the sustainability of the fishery in the future should be: 1) start a collaboratively consultative process between fishermen, researchers and policymakers to review and provide advice regarding the current management issues in order to propose a new management plan for the fishery; 2)develop a fishery-independent stock assessment in Sardinian seas; 3) develop a plan for the fishery-dependent monitoring in order to reduce/avoid the poaching and to provide appropriate data for assessment strategy; 4) testing the effectiveness of restocking by cultured juveniles in overfished areas; 5) increasing the profitability of sea urchin roe production by echiniculture, aimed to reducing harvesting pressure on wild stocks