Trace Metals in Twaite Shad (Alosa fallax): Patterns Across Two Northern European Populations

Heavy metal contamination poses concerns for managing Twaite shad (Alosa fallax) populations, yet data remain sparse. Intermittent capture as bycatch, with negligible prospects for post-release survival and IUCN Red listing, provides a compelling case for investigation. Concentrations of six trace metals (As, Cd, Cr, Cu, Pb and Zn) in the dorsal muscle tissue of A. fallax from the Curonian Lagoon (Lithuania) and the Elbe Estuary (Germany) were analyzed to evaluate size-related patterns and compliance with international safety standards. Overall, metal levels were uniformly low, with Cd and Pb below EU limits. Cu exhibited a weak negative correlation with fish weight (ρ = −0.35; p < 0.05), while Zn tended to increase in larger individuals, reflecting its essential physiological role. Comparing both adult populations, Cr and Zn, which provide nutritional benefits, were higher in the Curonian Lagoon, whereas toxic As and Pb were higher in the Elbe Estuary. All concentrations complied with EU and FAO thresholds, indicating acceptable risk for human consumption. The findings provide baseline information for A. fallax as a potential bioindicator. Constraints on the number of A. fallax sampled, given its IUCN status, exclusion of Hg and lack of environmental parameters, limit conclusions, but would be mostly remediable by future research.