Myliobatis aquila (Linnaeus, 1758)

Ponte, Dário, Barcelos, Luís M. D., Santos, Cristina, Medeiros, João & Barreiros, João P., 2016, Diet of Dasyatis pastinaca and Myliobatis aquila (Myliobatiformes) from the Azores, NE Atlantic, Cybium 40 (3), pp. 209-214 : 212-213

Myliobatis aquila

In their study, Jardas et al. (2004) found that the most frequent prey group of M. aquila was molluscs followed by sipunculids. Among molluscs, bivalves made an important contribution to the diet, followed by gastropods. They also found similarities between their study and previous ones (see Jardas et al., 2004 for details).

We have similar results: molluscs play a major role in the feeding of the species, but we found gastropods in the stomach contents while bivalves were completely absent. In the secondary group of prey, instead of sipunculids as found by Jardas et al. (2004), we found crustaceans, mostly from the hermit-crab family Diogenidae . This led us to think that the eagle ray, a mollusc feeder, searches for the shells, something that could help explain the occurrence of hermit crabs in the stomachs. This particular aspect surely deserves additional studies, including visual monitoring of M. aquila while feeding.

Jardas et al. (2004) refer to other prey groups (Polychaetae, Nemertinae and teleost fish) with a small importance in the diet. We did not find any of these groups in our sample. The extensive work by Jacobsen and Bennett (2013) also reports decapod crustaceans and teleost fish as major prey items of stingrays. However, it would be speculative to compare our small sample from two species with the vast guild studied by these authors.

Low weights of Pachygrapsus marmoratus are most certainly due to the fact that only small specimens, or even just parts of these crabs, were found in the stomachs. A fact that explains the apparent contrast with the comparative high weight of large amphipods.

This study is a first evaluation of the feeding ecology for these two species for the NE Atlantic and in fact outside the Mediterranean basin. Although the number of sampled stomachs was not high enough for a more conclusive evaluation of the diet of Dasyatis pastinaca together with a high VI value, our results are in agreement with the other few studies made for this species. Concerning Myliobatis aquila , despite the most important group of prey being the same (with the exception given by the absence of polychaetes and the above discussed presence of hermit-crabs), there are differences in the feeding ecology of this species between Mediterranean and Atlantic populations. The different niches occupied by our target species reflect their different diets clearly, show- ing D. pastinaca as a crustacean predator and M. aquila with an apparent preference for molluscs and worms.

Acknowledgments. – We which to thank François Chauvin for collecting all specimens and for his work in the laboratory while on a post-graduation program in the Azores University.