Stomach contents of a megamouth shark Megachasma pelagios from the Kuroshio Extension: evidence for feeding on a euphausiid swarm

Abstract

More than 50 specimens of the megamouth shark Megachasma pelagios have been reported so far, but biological obser- vations on the species are still limited. We examined a female megamouth specimen that was captured by the bonito purse seine fishery in the Kuroshio Extension in July 2007 and donated to the Okinawa Churaumi Aquarium. The specimen was an immature female, 3,667 mm in total length and 361 kg in weight. The stomach contents measured 2,200 mL excluding the portion that was lost from the specimen before measurement. Detailed examination of a small part (14.6 mL) of the stomach contents revealed un- damaged worm-like organisms, 10 partially damaged euphausiids and abundant fragmented pieces of euphausiids. The worm-like organisms were probably parasites such as tapeworms. The partially damaged euphausiids were identified as Euphausia pacifica except for one individual of Nematoscelis difficilis. Based on the number of fragmented right mandibles, which were less damaged than the other fragmented appendages, the total number of euphausiids in the stomach contents is estimated to be at least 18,000 in- dividuals. The high abundance of euphausiids in the stomach contents suggests that the present specimen has fed on a swarm of E. pacifica in an oceanic area.