Static penetration test on deep-sea shark skins - reports on needle types and penetration forces for developing an autonomous <i>in situ</i> biopsy equipment

Abstract

Top predators play an important role in maintaining biomass and biodiversity of most ecosystems. However, functional roles of the top predators in deep sea are still poorly understood. Large, predatory sharks are considered as the top predators in the deep sea, some of which are known to have a long-life span and a long-term maturation period. Most studies of the sharks have been conducted using lethal methods such as deep-sea trawls without attention to their vulnerability. It is urgent to develop non-lethal approaches for the shark studies. An autonomous in situ biopsy equipment is one solution, which collect a small amount of soft tissues non-lethally from the target fish. For developing the equipment, we conducted static penetration tests using three types of biopsy needles, i.e., conical, bevel, and trigonal pyramid shapes with the tip angles of 20, 30 and 40 degrees. Three species of deep-sea sharks, the roughskin dogfish Centroscymnus owstonii, the kitefin shark Dalatias licha, and the rough longnose dogfish Deania hystricosa, were applied for the penetration tests. The lowest penetration forces were 22.1 N on the skin of D. hystricosa using the trigonal pyramid needle with the tip angle of 30 degrees, 65.3 N on that of C. owstonii, and 95.3 N on that of D. licha both using the trigonal pyramid needle with the tip angle of 20 degrees. The highest forces were recorded on the D. licha skins among the three sharks using any types of needles, which were 3.6 to 6.0 times larger than that of D. hystricosa and 55.3 times larger than that of the chub mackerel Scomber japonicus. We concluded that the trigonal pyramid with the tip angle of 20 or 30 degrees is the most suitable shape for our biopsy needle and that the shooting force has to be larger than 95.3 N for collecting tissues from hard-skin species such as D. Licha.