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Population-specific bycatch risks in two vulnerable anadromous clupeids: Insights from otolith microchemistry
David J Nachón1, Alejandro Pico-Calvo1, Françoise Daverat2
1Departamento de Zooloxía e Antropoloxía Física, Facultade de Bioloxía, Universidade de Santiago de Compostela, Santiago de Compostela, Spain.
Journal of Fish Biology
|July 12, 2026
Summary
Bycatch in Iberian fisheries impacts European shads (Alosa alosa, Alosa fallax) from diverse origins, with major rivers facing the greatest losses. Management must consider natal origins and dispersal to protect these vulnerable populations.
Area of Science:
- Marine Ecology
- Fisheries Science
- Conservation Biology
Background:
- European shads (Alosa alosa, Alosa fallax) are ecologically important but face threats from fisheries bycatch.
- Understanding their natal origins and dispersal patterns is crucial for effective conservation management.
Purpose of the Study:
- To analyze the natal origins and dispersal of European shads caught as bycatch in western Iberian fisheries.
- To assess how species-specific dispersal capacities influence bycatch vulnerability and metapopulation dynamics.
Main Methods:
- Otolith microchemistry analysis to determine natal origins of bycaught European shads.
- Spatial analysis of bycatch risk and natal origin diversity across marine areas.
- Comparison of dispersal strategies between Alosa alosa and Alosa fallax.
Main Results:
- Bycatch included individuals from a wide range of natal origins, with abundant source rivers experiencing disproportionately high losses.
- Alosa alosa exhibited extensive long-distance movements and higher natal origin diversity than Alosa fallax, which had more restricted dispersal.
- Bycatches were dominated by individuals from the most abundant continental populations, indicating export from source to sink populations.
Conclusions:
- Species-specific dispersal capacities and metapopulation structures critically influence bycatch vulnerability.
- Effective management requires incorporating natal origin and dispersal data into ecosystem-based approaches, including targeted fishing restrictions.
- Conservation efforts must safeguard metapopulation dynamics and ecological connectivity for European shad populations.
