Mobulid rays feed on euphausiids in the Bohol Sea

Area of Science:

• Marine biology
• Fisheries science
• Ecology

Background:

• Mobulid rays exhibit conservative life histories, making them vulnerable to overexploitation from direct fisheries and by-catch.
• Effective fisheries management requires understanding the habitat, prey preferences, and trophic interactions of target species.

Purpose of the Study:

• To assess the feeding ecology of four mobulid ray species (Manta birostris, Mobula tarapacana, M. japanica, M. thurstoni) in the Bohol Sea, Philippines.
• To identify key prey items and potential trophic overlap among these species.

Main Methods:

• Stomach contents analysis of mobulid ray specimens.
• Fisheries-dependent sampling conducted between November and May from 2013-2015 in the Bohol Sea.

Main Results:

• Mobulid rays predominantly consumed euphausiid krill (Euphausia diomedeae), accounting for 91% of analyzed stomachs.
• Minimal trophic separation was observed among the four species, with E. diomedeae being the primary food source for all.
• M. japanica and M. thurstoni exclusively consumed E. diomedeae, while M. tarapacana and M. birostris had varied diets including fish and copepods.

Conclusions:

• Vertically migrating mesopelagic species like euphausiid krill are vital food resources for large filter feeders in tropical, oligotrophic waters.
• The overlap in foraging grounds and prey highlights the need for integrated management strategies to mitigate fishing impacts on mobulid rays.