From Ions to Ecosystems (IONECO): A Novel Framework for the Biomonitoring and Management of Vulnerable and Commercial Fishes

Climate change, pollution and habitat degradation are causing rapid and often unpredictable changes in animal behaviour and physiology. These changes are leading to population declines, species redistribution, and alterations to the delivery of key ecosystem services. Migratory fishes are particularly vulnerable to global change given their reliance on multiple and often geographically dispersed habitats. Yet identifying the critical habitats supporting their growth and survival is notoriously difficult in aquatic environments, particularly for early life stages too small and fragile to tag. Here, we are developing an integrated ‘toolbox’ to address these knowledge gaps, providing novel solutions for the sustainable management of aquatic ecosystems in the 21st Century. Our state-of-the-art ‘tools’ span the fields of geochemistry, sclerochronology, biochemistry, telemetry, genetics, machine learning and numerical modelling. We are using them to estimate fish movements and environmental experiences, and to understand the drivers of growth variation and physiological state. We have shown the power of combining chemical records and growth rings in archival structures such as fish otoliths (earstones) and eye lenses to improve our ability to estimate provenance, life history traits and movement histories. We also developed new techniques to estimate past exposure to pollutants and hypoxia (low oxygen zones), opening new avenues to understand how sublethal stressors affect growth and reproduction. Here, we consolidate our research portfolio into a methodological toolbox that we will apply to a series of commercially and culturally valuable fish species: European sea bass, Atlantic and Chinook salmon, and Baltic cod. First, we will estimate the contribution of juvenile sea bass from various estuaries to the adult stock, integrating these data with fish health proxies (condition indices, growth and metabolic rates) and pollution markers to provide estuary-specific management advice. We will then combine otolith daily rings and electronic tagging data to estimate spawn timing to help optimise fisheries closure periods. Second, we will combine chemical and genetic markers to monitor the provenance and migration routes of Chinook and Atlantic salmon across freshwater and marine realms, and to understand population-specific interactions with spatially explicit features (e.g. offshore wind farms). We will then use otolith daily rings and bioenergetic modelling to predict salmon growth and survival under alternative climate scenarios. Third, we will quantify the impacts of hypoxia on cod growth, reproduction and blood physiology, incorporating biochemical assays into our toolbox to understand individual acclimation responses and assess the potential for tissue tracers to reconstruct reproductive histories. By feeding these data into species distribution and integral projection models we will predict how Baltic cod biomass will change under future climate scenarios. This project represents a step-change in how we integrate chemical tracers and biochronologies into a multidisciplinary framework to inform fisheries and habitat management and ecological forecasting. We will share the outcomes through our international collaborators and beneficiaries, a multidisciplinary conference, and via the EXploration, TRanslation and Application of Chemical records in animal Tissues (EXTRACT) network. The EXTRACT website also includes learning resources (e.g. instructional videos) and an online forum to build the community and support capacity building. In the future, the EXTRACT community will form the basis for a Centre of Applied Sclerochronology that provides training opportunities and workshops to advance the application of these multidisciplinary toolboxes to support monitoring and management, and ultimately, to improve the health and sustainability of our wild fish populations.