Assessing overfishing based on the distance-to-target approach
Authors: Vanessa Bach, Arnaud Hélias, Marco Muhl, Aurélie Wojciechowski, Henk Bosch, Michael Binder, Matthias Finkbeiner
Published in The International Journal of Life Cycle Assessment
Overfishing has been a global challenge for several decades with severe impacts on biodiversity and ecosystem services. Several approaches for assessing overfishing in life cycle impact assessment exist, but do not consider scarcity in line with current policy and science-based targets. Furthermore, comparisons of results with other impact categories, e.g., climate change, are not possible with existing methods. Therefore, five approaches to assess overfishing based on the distance-to-target approach are introduced.
Three global species-specific approaches (stock in the sea, target pressure, and fish manager) and two regional midpoint approaches were developed. For the stock in the sea, the weighting factor was derived as the relation of available biomass of the considered species to biomass at sustainable limits. Within the target pressure, the current pressure on fish stocks is set to the maximal sustainable pressure. For the fish manager, the catch is set in relation to the maximum sustainable yield. The catch is used for normalization in all three approaches. The two regional midpoint approaches consider production and consumption based catch of fish stocks in relation to the fully fished share. The overfishing indicator based on pressure on fish stocks serves as the characterization factor. Normalization occurs with the characterized catch.
Results and discussion
To demonstrate the applicability of the approaches, a three-level case study was derived: (i) determining ecofactors for ten specific fish species in specific oceans; (ii) deriving ecopoints for production of fish meal and oil in Europe; (iii) comparison of fish oil with rapeseed oil for the categories overfishing, climate change, land use, and marine eutrophication. The highest ecofactors for the global approaches are characterized by high normalization and weighting factors. For the regional approaches, high overfishing characterization factors determine the result. The species contribution increases with rising amounts. Main challenges are data collection and interpretation which limit the overall applicability. The sensitivity analysis shows that the overall results vary significantly depending on the composition of the fish oil and meal.
It was shown that four of the five approaches are able to account for overfishing. However, only the production-based regional midpoint approach allows for comparison with other impact categories and is therefore most suitable for integration into life cycle assessment. The developed approaches can be used for a more comprehensive assessment of environmental impacts of different diets as well as aquaculture feed solutions.
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