Time to rethink trophic levels in aquaculture policy
Cottrell, Richard S.; Metian, Marc; Froehlich, Halley E.; Blanchard, Julia L.; Sand Jacobsen, Nis; McIntyre, Peter B.; Nash, Kirsty L.; Williams, David R.; Bouwman, Lex; Gephart, Jessica A.; Kuempel, Caitlin D.; Moran, Daniel D.; Troell, Max; Halpern, Benjamin S.
(2021) Reviews in Aquaculture, volume 13, issue 3, pp. 1583 - 1593
(Comment)
Abstract
Aquaculture policy often promotes production of low-trophic level species for sustainable industry growth. Yet, the application of the trophic level concept to aquaculture is complex, and its value for assessing sustainability is further complicated by continual reformulation of feeds. The majority of fed farmed fish and invertebrate species are produced
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using human-made compound feeds that can differ markedly from the diet of the same species in the wild and continue to change in composition. Using data on aquaculture feeds, we show that technical advances have substantially decreased the mean effective trophic level of farmed species, such as salmon (mean TL = 3.48 to 2.42) and tilapia (2.32 to 2.06), from 1995 to 2015. As farmed species diverge in effective trophic level from their wild counterparts, they are coalescing at a similar effective trophic level due to standardisation of feeds. This pattern blurs the interpretation of trophic level in aquaculture because it can no longer be viewed as a trait of the farmed species, but rather is a dynamic feature of the production system. Guidance based on wild trophic position or historical resource use is therefore misleading. Effective aquaculture policy needs to avoid overly simplistic sustainability indicators such as trophic level. Instead, employing empirically derived metrics based on the specific farmed properties of species groups, management techniques and advances in feed formulation will be crucial for achieving truly sustainable options for farmed seafood.
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Keywords: aquaculture, feed, policy, seafood, trophic level, Taverne, Aquatic Science, Ecology, Management, Monitoring, Policy and Law
ISSN: 1753-5123
Publisher: Blackwell Publishing Asia
Note: Funding Information: This work is a product of the Food System Impacts and Sustainability Working Group at the National Center for Ecological Analysis and Synthesis (NCEAS), University of California Santa Barbara and was in part supported by a grant from the Zegar Family Foundation. RSC acknowledges funding from NCEAS, University of California, Santa Barbara. On behalf of M.M., the IAEA is grateful to the Government of the Principality of Monaco for the support provided to its Environment Laboratories. HEF recognises support from the University of California, Santa Barbara. MT acknowledges support from Formas Project Seawin (2016-00227). PBM recognises support from the Cornell Atkinson Center for Sustainability and the Packard Fellowship. DM recognises support from the Norwegian Research Council. Funding Information: This work is a product of the Food System Impacts and Sustainability Working Group at the National Center for Ecological Analysis and Synthesis (NCEAS), University of California Santa Barbara and was in part supported by a grant from the Zegar Family Foundation. RSC acknowledges funding from NCEAS, University of California, Santa Barbara. On behalf of M.M., the IAEA is grateful to the Government of the Principality of Monaco for the support provided to its Environment Laboratories. HEF recognises support from the University of California, Santa Barbara. MT acknowledges support from Formas Project Seawin (2016‐00227). PBM recognises support from the Cornell Atkinson Center for Sustainability and the Packard Fellowship. DM recognises support from the Norwegian Research Council. Publisher Copyright: © 2021 John Wiley & Sons Australia, Ltd
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