Abstract:Life cycle assessment is used in this study to evaluate the potential environmental impacts of producing gilthead seabream in an offshore sea farm exposed to storms in the Spanish Mediterranean Sea. The farming methods used can be considered as "basic" since no centralized or automatic food distribution system exists and there is no control system. This study aims to identify the main hotspots under these conditions and to propose and compare viable alternatives to them. Contribution analysis found that the component of the system with the greatest potential environmental impact (48% of the overall impact) was fish feed, especially the raw material used. Other contributory factors were the fuel consumed by the vessels operating in the farm (35%), the dumping of N and P in the environment due to the metabolism of the fish (12%), the cages and their anchorage system (5%). A sensitivity analysis showed that a significant reduction in potential environmental impact can be achieved by increasing feeding efficiency. Feed formulation in raw materials is also an important factor and could serve to diminish overall adverse effects. A balance needs to be found between productive performance (growth, survival and feed conversion rate), feed price and its influence on production costs and the overall environmental consequences.
Four ongrowing cycles of common octopus (Octopus vulgaris), each with two stocking densities, were carried out in an offshore area in order to evaluate the effect of the following variables on growth (G, % body weight day−1) and mortality (M, % day−1): weight (W, 0.5–3.0 kg), temperature (T, 14–26 °C), stocking density (SD, 6–46 kg m−3), size dispersion, expressed as coefficient of variation (CV, 13–42%) and significant wave height (SWH: 0.4–1.2 m). The assays were performed in an 8 m3 stainless‐steel floating cage divided into two compartments of 4 m3 each. For the range of temperatures considered (14–26 °C), G depended significantly on T and SWH, with maximum G values being obtained at 18.5 °C and with an important negative effect of SWH. M depended significantly on T, W and CV, mortality being minimal at 18 °C. The two other variables had an antagonistic effect, mortality increasing with greater size dispersion – suggesting that animals should be graded throughout the process – although the effect diminished as the sizes increased. The results point towards two alternatives for the commercial ongrowing of octopus under the particular conditions of the present study: (A) two ongrowing cycles of 3.5 months to reach a final weight of 2.5 kg or (B) one 5‐month cycle to reach a final weight of 3.5 kg.
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