Discrimination of wild and cultured Japanese eels based on otolith stable isotope ratios

Abstract

We successfully discriminated wild and cultured anguillid eels without artificial tagging. For the purpose of population restoration of anguillid eels, stocking has been widely conducted in the European Union (EU) and Japan, although the net benefits of stocking remain unclear. To evaluate the effectiveness of eel stocking for population restoration, the survival, growth, escapement, and reproduction of stocked eels should be tracked. In this study, we explored the potential of using otolith oxygen and carbon stable isotope ratios as a natural tag to discriminate between wild and cultured eels, because cultured eels are often stocked into natural rivers and lakes. A discrimination model was developed based on wild (n = 95) and cultured (n = 314) Japanese eels as a training dataset. The results of accuracy estimation based on leave-one-out cross-validation were 96.8%. We then tested the applicability of the model to stocked–recaptured eels (n = 20); 100.0% were successfully identified as cultured eels, indicating that these eels spend their early continental phase in aquaculture ponds before stocking. This method could be widely applied to assess the effectiveness of eel stocking by determining the proportion of stocked eels among those captured from rivers, coastal areas, or spawning grounds.

European spiny lobster recovery from overfishing enhanced through active restocking in Fully Protected Areas

“…Therefore, the efficacy assessment and enforcement of conservation/management measures that, at the same time, ensure short-time fishery benefits while preserving ecosystems’ ability to produce goods and services, are crucial issues to be addressed jointly by scientists, stakeholders and policy makers. In this regard, FPAs are recognized as fundamental parts of the multifaceted toolkit available for the conservation of heavily exploited species 12,14,17,22,23,30 . The effects of overfishing on single species may be reversible, but the actual time required for recovery is generally long 31 .…”

“…Conservation measures do need places where nature is left wild. In the most protective end of the conservation tools spectrum, there are Fully Protected Areas (FPAs), which are equivalent to No-Take marine Reserves (NTRs), where any consumptive activity on marine stocks is prohibited 14 . FPAs are expected to protect many quantitative and compositional components of biodiversity and, at the same time, to potentially help overexploited stocks to recover 15–17 .…”

Distribution of wild and stocked Japanese eels in the lower reaches of the Tone River catchment revealed by otolith stable‐isotope ratios

“…, Rivers or lakes of where wild eels (W7–11) were collected for baseline samples of the discrimination model; , rivers where wild eels (W1–6) were collected; , prefectures where cultured eels (C1–14) were collected by Kaifu et al . (); , study area in the Tone River catchment for collecting samples of unknown origin…”

A pan-Arctic assessment of the status of marine social-ecological systems

“…Our AOHI assessment provides a starting point for consideration of pan-Arctic social-ecological dynamics, which like other composite indicators can be iteratively improved over time as more and better data become available and dynamics are better understood (Burgass et al 2017). Understanding current limitations and how social-ecological systems are changing is necessary for effective management (Harris et al 2017). Many of the goals within the AOHI are transboundary in nature and require co-management (biodiversity, marine mammal harvest, coastal protection, tourism and recreation, clean waters, and fisheries).…”

“…Pan-Arctic plans for environmental protection and sustainable development would limit ad hoc developments, which could otherwise pose severe risks to unique ecological communities or areas of biodiversity. Similarly, given the heterogeneity of the region and in order to protect and restore the full range of biodiversity across the Arctic, coordinating efforts across large scales is required to ensure an ecologically coherent network of protected areas (Harris et al 2017).…”