Interaction between Halobatrachus didactylus and Anguilla anguilla: What happens when these species occur in sympatry?
The Lusitanian toadfish, Halobatrachus didactylus, and the European eel, Anguilla anguilla, are benthic fish species, which occur in sympatry in the southern Iberian Peninsula and north-west Africa. The consequences of this sympatry were evaluated through the analysis of distribution, abundance and feeding ecology of both species in the Mira estuary, a small system located on southern Portugal. A total of 1734 toadfish and 196 eels were caught with a beam-trawl in six sampling areas covering the entire estuary. Both species showed burrowing habits and a high diet overlap. The dominance and voracity of the toadfish, which includes glass and yellow eels in its diet, may contribute to explain the spatial segregation between the species, with eels occupying peripheral areas upstream (freshwater and upper estuary) and downstream (Zostera spp. beds near the sea). This spatial segregation reduces habitat availability for eels, which may have serious consequences on a population already subjected to an important loss of habitat due to anthropogenic causes. If this situation results from the interaction between the two species, it may become even more unfavourable to eels because subtropical species like the Lusitanian toadfish may spread northward as a result of raising temperatures caused by climate change.