It's a behavior that's been documented since the 1960s, but the recent discovery of a 4.5-meter (almost 15-foot) bigeye thresher shark with a swordfish's spike embedded in its back is the first illustrated example of the lethality of these bizarre long-nosed fish. Discovered on the shores of Libya, the unfortunate shark had washed ashore where it was discovered and reported to the citizen science initiative Marine Biology in Libya. Bigeyes have long swishy tails that they use to stun fish while hunting, but it seems this weapon was futile against the blade, or rostrum, of a swordfish. The finding was published in the journal Ichthyological Research.
As the below video shows, the bigeye’s injury was not immediately obvious but on closer inspection the citizen scientist discovered a single penetrating trauma that was about 8 centimeters (3 inches) in width. Upon removal, the “sword” was identified as Xiphias gladius owing to the flattened appearance and the absence of denticles on the surface. At 30 centimeters (11.8 inches) long, it’s no surprise the skewering proved fatal, and researchers used mathematical modeling to estimate that the offending swordfish would’ve been an adult with a body length of around 2 meters (6.6 feet).
It's big. It's dead, and it's been stabbed in the head. Video and images by Faraj Habrisha and Abdalhakim Ahmed Al sebaihe
No necropsy was performed to examine the damage caused by the swordfish rostrum, but given its length and the position of the stab it's possible it pierced the shark’s heart. An unusual way to go for an apex predator, but a fate met by this bald eagle at the hands (or beak, as it were) of a loon.
Swordfish skewerings are not uncommon, and the rostrums of these animals have found their way into wildlife, ships, and even humans. The motivation behind these “attacks” isn’t clear, but it’s thought that skewerings in objects are most likely failed predation attempts on smaller fish that zip out of the way at the penultimate moment having been sheltering by a boat.
There does, however, appear to be mounting evidence that swordfish are utilizing their rostrums as weapons, as they’ve been observed using them aggressively when under threat from harpoons, fishermen, and perhaps, in the case of our unlucky bigeye, predatory sharks. In 2017 and 2019, there were reports in the Mediterranean of several adult blue shark strandings who were found with swordfish rostra embedded in their heads. All the rostra were revealed to belong to juvenile swordfish who are especially vulnerable to large sharks like the blue shark, indicating the stabbings may have been in self-defense. Impaling is, however, a costly strategy as swordfish use their rostrums to feed, so whoever is the owner of the bigeye’s murder weapon may still be paying the price of this encounter.