Beautiful eagle ray pups swimming in SEA LIFE Kelly Tarlton’s Turtle Bay Display in Auckland New Zealand. Photo by author (Jade-Ceres Violet Munoz)
I visited SEA LIFE Kelly Tarlton’s Aquarium today in Auckland, New Zealand after hearing of the wonderful birth of two new eagle ray pups. I am quite taken by these beautiful creatures since interacting with them and feeding them in the wild last year.
People have generally been scared of stingrays after the death of Australian wildlife specialist Steve Irwin, whose death was caused by a stingray barb to the chest while filming in the Great Barrier Reef in 2006. Irwin's chest was punctured several times by the jagged barb causing massive injuries to his heart.
While it is true that they have a defense mechanism in place to protect themselves, stingrays are generally docile and friendly creatures. They are actually pretty cute and in the last interaction I’ve had with them, they were acting more like puppies of the sea than anything else.
There was a bit of a mystery surrounding the birth of the two new eagle ray pups at the aquarium since the mothers have not been with any male species for over two years. According to the aquarium representatives, the pups were born to two mothers on New Year’s Eve. The mothers reside in the walk-through fish tunnel display, which currently does not house any male eagle rays.
Louise Greenshields, a member of the animal care team at the aquarium, said they first noticed the two females were pregnant because they were looking “quite round”. Eagle rays have oviparous reproduction -- they incubate eggs in their uterus. The gestation period lasts between 6 to 8 months. In the wild, eagle rays usually give birth to between 3 to 7 pups.
Another amazing thing about the birth is that the female eagle rays, named Nibble and Spot, gave birth to the two pups at the same time. “Interestingly, the births were about five minutes of each other,” said Greenshields.
In a statement, Kelly Tarlton’s team explains two possible scenarios for the conception of the pups: “Whilst we were surprised to see Nibble and Spot give birth to pups because they haven’t been with a male in two years, it’s not completely unheard of," says Andrew Christie, Curator at SEA LIFE Kelly Tarlton’s.
"It could have occurred through a process called parthenogenesis, which is a rare reproductive strategy where an embryo develops without fertilization. Alternatively, Nibble and Spot could have stored sperm inside their bodies for the last two years. Sperm storage has been recorded in several shark and ray species, so we think this is the more likely scenario."
Sperm storage is a relatively common strategy in several fish species but has also been recorded in other animals such as insects, bats, and turtles. It is a form of insurance against failing to find a partner in the wild. Studies have seen that sperm can be stored in the body between one to two years and would be ready for use during ovulation.
Another SEA LIFE Aquarium had a similar case in 2018. 11-year-old Freckle, a female spotted eagle ray (a close relative of the Auckland ray species) located in Sydney’s SEA LIFE Aquarium, gave birth to a pup despite not being in contact with a male for nine years. It is said that this birth is from parthenogenesis.
Adele Dutilloy, a fisheries modeler at the National Institute of Water and Atmospheric Research (NIWA) was recently interviewed by the Guardian about the case of the Auckland eagle ray pups. She said that for the case of the surprise births, the most likely explanation was the natural process of asexual reproduction. She adds that if the birth of the two pups are through sperm storage, that it would be the first such time that it has been documented in eagle rays.
“The only way you can really confirm it for sure is through genetic testing… It would be a really cool thing to do because it's never been looked at before,” she said to the Guardian.
“It seems to be particularly common in species that don’t encounter each other that often,” said Dutilloy. Earlier this month Dutilloy discovered the first evidence of sperm storage in species of deep-sea sharks, which needed to “make the most of mating opportunities” – not least because of the associated danger. “Shark mating can be very aggressive,” she said.
Compared to sharks, Dutilloy says sperm storage was relatively uncommon in rays. Maddy Seaman, displays manager at Kelly Tarlton’s, said DNA testing to confirm or deny parthenogenesis would be possible once the pups were older.
The pups are yet to be named. They are not currently on display at the aquarium but are held in a separate tank and are being fed mussels and fish fillet. Because of their small size, they are still vulnerable to larger fish. They will eventually be displayed in the aquarium’s Turtle Bay with the other eagle ray pups in the aquarium.
"We'll keep them out back until they grow a little bit more because at the moment their wingspan is only between 20 and 25 centimeters so we can grow them up a bit and make sure they're all happy and healthy and feeding okay which at the moment they seem to be and then we can pop them out and everyone can come visit." Said Greenshields of their plans for the newborn pups.
Eagle rays are a type of cartilaginous fish -- who have cartilage instead of bones in their body. They have a wide, flat snout like a duckbill. They are found in New Zealand waters and can be identified by their pointed wings, long tails, and the flapping motion they make when they swim (like an eagle in flight).
Eagle rays can grow to huge sizes of up to five meters long and weigh up to 230 kilograms. They have been seen leaping out of the water while swimming close to the surface. They are usually found from the water surface to depths of more than 60 meters.
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