It’s easy to tell a male from a female shark. Flip it over. If it has a pair of claspers — finger-like extensions jutting from the end of the pelvic fins — it is male; no claspers means female. Like a penis, claspers deliver sperm inside the female.
That was marine biologist Alissa Barnes’ understanding until she dissected seven bigeye houndsharks (Iago omanesis) with claspers and found a complete female reproductive system in each. None of the seven sharks had any internal male sex organs. Six were pregnant. Barnes, of the Dakshin Foundation, shared her findings June 25 at the 5th International Marine Conservation Congress in Kuching, Sarawak, Malaysia.
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Barnes stumbled upon these hermaphrodite sharks at a port in Odhisa in eastern India in 2017. She was surveying local fishers to see if changes in their practices might explain a decline in hauls of sharks and rays. When she checked what the fishing vessels brought in, Barnes noticed two oddities. Male bigeye houndsharks greatly outnumbered females. And though males of this deepwater species are smaller than females, she saw immature males as large as female adults. Sensing something amiss, she took some sharks back to her lab for dissection.“I was amazed,” says Barnes, who admits she squealed during the dissections. Even before opening the fish, she had pressed on the bellies of the “male” sharks and felt the pups inside.
“Hermaphroditism is very uncommon in sharks,” says shark biologist Colin Simpdendorfer of James Cook University in Townsville, Australia. He calls Barnes’ seven hermaphrodite sharks “one of the most unusual cases we have heard of” and says it’s an obvious developmental anomaly. Scientists can still use claspers to identify male sharks, Simpdendorfer assures.
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Barnes’ finding isn’t the first among sharks. A 2005 study in the Journal of Fish Biology reported 68 hermaphrodites among 80 longhead catsharks (Apristurus longicephalus) from the Pacific and Indian Oceans. And surveys in the 1990s of bigeye houndsharks found more than 20 hermaphrodites among more than 60 sharks down the coast from where Barnes found hers.
With these other finds, Barnes is convinced “there is something going on” with the sharks. She suspects it might be pollutants in the water or hormonal changes — human-caused or otherwise — and is keen find out.