SHARK FOUND DEAD DUE TO UNUSUAL ATTACK IN THE OCEAN
An unusual discovery was made near the town of Brega on the Libya’s shore, where a dead female thresher shark was found washed up on the beach with an irregular object.
A 11.8 inch rostrum which belonged to a six-feet-long swordfish was found piercing the shark’s heart which led to its death.
Researchers further conducted a study on the unusual incident. The finding of the study was published in the journal, Ichthyological Research.
The research confirmed that the rostrum found belong to the swordfish species named Xiphias gladius, which is known to be "a highly mobile, predatory fish known to attack sharks, whales, humans and even boats." Records of such attacks made by the Xiphias gladius dates as far back as the 1960s.
The study further detailed the finding of the incident and explains that, "The animal did not display any external injuries, except for a single penetrating trauma (7.9cm in width and 5.0cm in height) on the dorsal surface at the level of the pectoral girdle with the tip of a rostrum stuck in it. The rostrum was identified as belonging to a swordfish X. gladius, based on the flattened appearance in cross section (i.e. depth less than half the width) and the absence of denticles on the surface. The fragment was 30.1cm long and had a distal and proximal width of 1.4 and 5cm, respectively. To reconstruct the total length of the rostrum, the ratio of maximum width to length of the fragment was calculated and compared with the dimensions of a previously published intact rostrum to determine the breaking point."
Researchers confirmed that the lethal wound found is the cause of the shark’s death. The study further read; "The injury was inflicted recently when the shark was found dead on the beach on April 1st, because the epaxial musculature showed no signs of wound healing or other alterations but still was supplied with blood and exhibited a pink-reddish colouration. This colouration was faded by the date of the second inspection three days later.The location of the injury, timing of wound infliction and lack of other apparent injuries lead us to the conclusion that the impalement was fatal and the ultimate cause of death for the thresher shark."
The incident is thought to have been the result of an accidental collision, however, researchers haven’t ruled out the possibility of an attack. A reason considered for the attack could be an attempt to scare the shark away from food sources.
"Although impalements by swordfish are not uncommon and were reported to occur against a number of species and objects, the nature underlying these attacks, whether they are instances of accidents or were carried out by purpose, still is not fully understood. Intentional impalement as a defensive strategy was also proposed to be the reason for collisions between billfishes and sharks. Although swordfish’ bills are thought to have important hydrodynamic and feeding related functions and their breaking could be seriously disadvantageous for swordfish, it was reported that individual billfishes with damaged, malformed, or even missing rostra were apparently still in good physical shape, leaving room for speculation if swordfish experience a trade-off between averting a threat (e.g. sharks) and the potential impairment of high-speed locomotion. The shark species involved in these incidents are usually either the blue shark Prionace glauca or the mako shark Isurus oxyrinchus, both of which are known to opportunistically prey on fish, including swordfish."