Tracing European eel in the diet of mesopelagic fishes from the Sargasso Sea using DNA from fish stomachs

Trophic interactions in complex mesopelagic ecosystems are generally poorly understood, but tracing diet remains of predators provides key insights into these. In many cases, however, the prey remains obtained from predator stomachs are unidentifiable by visual inspection and identification depends on new molecular techniques.

Here, we search for predators on larvae of the critically endangered European eel (Anguilla anguilla), a species which has shown a dramatic decline in recruitment to the stock. We sampled for predators among mesopelagic fishes using pelagic trawling in the known area of spawning and larval distribution of A. anguilla in the Sargasso Sea.

We aimed at developing a species-specific quantitative PCR (qPCR) system, targeting the nd4-region of mitochondrial DNA (mtDNA), to search for eel remains in the stomachs of 17 mesopelagic fish taxa (62 specimens). Remains of A. anguilla were confirmed in 9.7% of all fish stomachs investigated, representing six species (Lampanyctus cuprarius, L. photonotus, Myctophum selenops, Notoscopelus caudispinosus, Melamphaes typhlops, and Chauliodus danae).

Thus, our study documents that mesopelagic fishes in the Sargasso Sea to some extent predate the A. anguilla larvae, motivating further studies on upper-level trophic interactions in this oceanic ecosystem.