A huge female thresher shark, measuring 4.5 metres in length, was discovered washed up on a Libyan beach earlier in the year and researchers are trying to unravel the mystery as to why she was killed.
The shark was impaled by the blade from a swordfish which had penetrated it behind the head and damaged major nerves and bllod vessels they said.
The shocking discovery was made by local scientists in April and the shark still had a 1 metre long part of the blade, called a rostrum, imbedded in it’s neck.
They believe that the swordfish that attacked the shark would have been approximately 3 metres in length.
They wrote in their finding that, although impalement by swordfish was not uncommon it is not fully understood either. Whilst they spear unmoving objects, which is mainly accidental, the scientists say that using their rostrums as weapons has become more frequent in recent years.
According to a report published in the New York Times a similar shark killing took place In Valencia, Spain in 2016 along with six more that have been reported since.
They added that “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 and the potential impairment of high-speed locomotion.”
They went on to say in their findings that “We hypothesise based on the results presented here (similar size and ecology of both species, direction of trauma infliction) that competition could be a driving force for swordfish attacks on sharks or other possible competitors. However, due to the fact that the protagonists are pelagic species and lethal interactions may usually remain undetected, more data is needed to unambiguously support this interpretation and we therefore encourage future studies on stranded sharks to conduct necroscopies and thoroughly search for evidence of swordfish interactions.”
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