A recent study published in the latest issue of the journal Ichthyological Research by Japanese scientists have confirmed that the Blue marlin (Makaira nigricans) uses its bill to attack prey.
Tamaki Shimose, Kotaro Yokawa, Hirokazu Saito, and Katsunori Tachihara examined the stomach contents of blue marlin by the surface troll bait fishery and landed at Yonaguni Island over a period of three years.
The authors examined the condition of intact prey items in the stomachs in order to assess the possibility that the blue marlins use their bills to spear or slash their prey.
They found that a total of 130 prey items (38% of 339 undigested prey items obtained from 227 blue marlin) with injuries attributed to spearing/slashing by the bill.
Of these 130 prey items, 14 (11%) had spearing injuries to the body were observed, 105 (81%) had slashing injuries to the dorsal, ventral, and caudal portions, and the remaining 11 (8%) were severed into two or more parts.
According to the authors, ...the deep impalement of the bill followed by head shaking is responsible for the slashing injuries of its prey, which sometimes can completely sever prey items.
For more information, see the paper: Shimose, T, K Yokawa, H Saito and K Tachihara (2007) Evidence for use of the bill by blue marlin, Makaira nigricans, during feeding. Ichthyological Research 54, pp. 420"422.