Ocean to plate: Tracing the geographic origin of fish products using biochemical forensic techniques

Wilson, Juliet (2023) Ocean to plate: Tracing the geographic origin of fish products using biochemical forensic techniques. University of Southampton, Doctoral Thesis, 281pp.

Record type: Thesis (Doctoral)

Abstract

Global consumption of marine food products is steadily increasing, with fisheries and aquaculture production now at a record high. Consequently, traceability of fish and seafood throughout supply chains is becoming ever more important for consumers, producers and regulators, as trade networks increase in complexity and fish stocks face increased exploitation pressure. Marine food products are known to be at particularly high risk of incorrect claims of geographic origin due to the spatially based management of fisheries combined with the highly globalised seafood market. Verifying the claimed catch location of fish and seafood products is challenging, so currently there are no widely accepted forensic tests for spatial origin, despite the vital importance of traceability for maintaining sustainable fisheries as well as protecting fishers, retailers and consumers.
This thesis investigates the potential for identifying the geographic origin of four commercially important fish species using three contrasting biochemical techniques. The number of samples analysed allowed a comprehensive investigation into the accuracy with which individuals could be traced to their catch region, on the spatial scale of ICES subareas. Firstly, I applied stable isotope analysis of carbon, nitrogen and sulfur to discriminate among Atlantic cod (Gadus morhua) from different regions across the Northeast Atlantic, and then extended this technique to two further whitefish species – haddock (Melanogrammus aeglefinus) and European hake (Merluccius merluccius). Atlantic cod is extremely important commercially as well as having social and cultural significance. In the UK, cod had the highest value of all demersal species landed in 2020. Haddock and hake are also very important commercial species in the north Atlantic, since hake is one of the top three most landed demersal species in the EU and haddock is a key species fished by the UK fleet. Both are among the most highly consumed species in the EU and UK. All three species demonstrated varying stable isotope ratios within their white muscle tissue depending on the spatial origin. Cod could be traced to their true origin with an overall mean assignment accuracy of 79%, with accuracies of 90% or greater for cod from certain discrete regions. Haddock and hake were assigned to their correct known origin with slightly lower overall mean accuracies of 70% and 72% respectively, although Mediterranean hake as well as haddock from the Norwegian Sea and Rockall were very distinct and had assignment success rates of 92-100%.
Subsequently, I investigated the use of stable isotope analysis for tracing the origin of the critically endangered European glass eel (Anguilla anguilla) and complemented this with another technique, fatty acid analysis, to assess the potential of these techniques to be used as a forensic tool for detecting illegal glass eel fishing and trade. Neither technique was able to reliably distinguish among glass eels from different European rivers at this stage of their migration, although there were indications that eels from the River Oria (Spain) and River Severn (UK) may be sufficiently distinct to be discriminated under certain circumstances.
Finally, trace elemental profiling by x-ray fluorescence (XRF) was explored as a possible technique for tracing the geographic origin of Atlantic cod, opportunistically using the same cod samples as were analysed for stable isotope composition earlier in the thesis. Two different XRF instruments were used – the Itrax core scanner and the Vanta analyser. The findings demonstrated that the multi-elemental composition of cod muscle tissue, estimated by both XRF instruments, varied with spatial origin. Cod from all sampled regions could be assigned to known origin with at least 74% accuracy, with success rates of >95% for certain regions. Classification to origin using stable isotope and trace element data combined gave an overall mean assignment accuracy of 91%, which is higher than the accuracy obtained using either of the two methods independently.
My research addresses the lack of established techniques available to trace the spatial origin of fish and seafood products, by demonstrating that biochemical techniques have the potential to determine provenance on a scale suitable for fisheries management. However, the findings indicate that any technique used independently is unlikely to provide a stand-alone test to confirm origin for all fishery areas with accuracy suitable for legislative action, but combining approaches may allow the required level of accuracy to be reached.