An assessment of the European eel population on the Azores Archipelago

Cowan, George

Abstract

The European eel (Anguilla anguilla (L.)) is well documented throughout most of its extensive continental range, nonetheless, the existence of individuals at the Azores Archipelago, the extreme west of the species ́ continental range, were acknowledged but not studied. Geographically isolated and with the shortest migration to their putative spawning ground, individuals of the Azores would be expected to have the greatest chances of spawning success and may provide an important contribution of adults to a heavily declined and threatened population. Until now, it was surmised that freshwaters of the Azores did not constitute natural habitats for the species and freshwater individuals did not reach the ́silver ́ migratory phase, therefore, exempting this autonomous region of Portugal from European Eel Management Plans established to conserve the species.
Sampling on four Azorean islands has verified that eels were distributed throughout the majority of the river systems sampled and in one brackish lake. Larger individuals were found higher in catchments and natural barriers forcing a limiting effect on upstream distribution. The lack of estuaries and reduced availability of sheltered habitat in mainstem rivers acted to restrict the highest eel abundance to the most upstream point of sampling and to smaller watercourses. The single brackish lake sampled showed the highest abundance of eels on the archipelago, likely a result of its productive and sheltered habitat and because it presented the only suitable inland habitat for eels on that island. Multiple silver eels were caught in freshwaters from October-December, with males seemingly completing downstream migration earlier than females.
The verification of freshwater residence and silvering on this strategically located archipelago, at least 1300km closer to the putative spawning ground than the rest of mainland Europe, should be followed by an extension of Portugals’ existing Eel Management Plans to specifically incorporate the Azores archipelago.

Citation

Cowan, G. (2019). An assessment of the European eel population on the Azores Archipelago. (Thesis). University of Hull. Retrieved from https://hull-repository.worktribe.com/output/4223140

• Thesis Type: Thesis
• Deposit Date: Apr 21, 2021
• Publicly Available Date: Feb 23, 2023
• Keywords: Fisheries
• Public URL: https://hull-repository.worktribe.com/output/4223140
• Additional Information: Hull International Fisheries Institute, The University of Hull
• Award Date: Aug 1, 2019