What price are you willing to pay for food? As humans, we face thischallenge each time we shop, but for some seals and dolphins this may be alife or death decision.
Modern medical scanning reveals the steep price some marine mammals arewilling to pay for food, after a stranded fur seal was discovered with morethan a dozen facial wounds inflicted by its seafood prey.
The extreme dangers facing hungry marine mammals are revealed in a new studypublished today (Monday 4 May 2020) in the journal Diseases of AquaticOrganisms, led by marine biologist Dr David Hocking from the Monash UniversitySchool of Biological Sciences.
“Marine mammals like whales, seals and dolphins need to eat seafood tosurvive,” Dr Hocking said. “But, we seldom consider what the fish think ofthis situation. Obviously, they are less than enthusiastic about being eaten,and some of them have evolved elaborate defence systems to help them fight offwould-be predators.”
The study describes a stranded seal found at Cape Conran in south-easternAustralia, which – according to Dr Hocking – “followed its stomach one fishtoo far”. Unusually, a fish spine was seen poking through the seal’s cheek,prompting the researchers to CT scan the seal using the cutting-edgefacilities at Monash Biomedical Imaging.
“We were shocked to discover not one, but six fish spines embedded in theseal’s face,” said Associate Professor Alistair Evans, a co-author on thestudy, also from the Monash School of Biological Sciences. These were lateridentified by comparing them with specimens at Museums Victoria.
“The fish spines turned out to be tail barbs from stingarees [a small type ofstingray] and serrated spines from the back fin of Australian ghostsharks.”
While seals are known to feed on these types of prey, this is the first timethat researchers have understood how dangerous this process can be. Thisraises an interesting question: is the Cape Conran seal just an unusual case,or have similar injuries in other stranded individuals simply been overlooked?
“In New Zealand, fur seals target ghostsharks regularly. With that in mind,similar facial wounds may actually be rather common, even though they haven’tbeen recognised much,” said co-author Dr Felix Marx from Museum of New ZealandTe Papa Tongarewa. “That’s perhaps not surprising, as the injuries couldeasily have been hidden beneath the seals’ thick fur.”
Animals from future stranding events will be examined using X-ray and medicalimaging to look for further evidence of facial injuries – a unique yetgruesome window into the eternal battle between predator and prey.
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