This is a frame capture from a video I shot earlier this year in Anilao, Philippines. I have found empty egg cases washed up on the beach (beachcombers call them mermaid’s purses), but never one with its little living treasure: a yolk and developing shark embryo. I have no idea what species this is – maybe a bamboo shark, one of several small species of oviparous (egg-laying), bottom dwelling sharks found throughout the Indo-Pacific. I’m familiar with the Brownbanded Bamboo Shark (Chiloscyllium punctatum) and the Whitespotted Bamboo Shark (Chiloscyllium plagiosum); both species are found in the Philippines.
At the beginning of our dive, I was distracted by spawning coral (unusual for the middle of the day) and got separated from Ned and our group. I surfaced and told the boat crew I would stay under the anchored boat, at 15 feet depth, and re-board when I heard them start the engine to pick the others up. The boat was anchored away from the reef, in a spot that was mainly rubble; what we call “alternate habitat”. There are advantages to slowly examining one small area, so I was content to spend my hour in the shallows directly under the boat.
The egg case was firmly attached to the top of a small rubbly coral mound but didn’t look like the shiny, clean cases I’ve found on the beach and seen in aquarium exhibit photographs. It was covered in a thin coat of algae but I could clearly see something bright orange undulating inside. When I gently rubbed a little of the algae off, the embryo stopped moving and I realized I was looking at a developing shark! To my relief, it wasn’t long before it started the undulating motion again.
Back on shore, a quick Internet search turned up quite a few images of shark egg cases and an interesting paper, “Survival of the Stillest: Predator Avoidance in Shark Embryos”. The embryo’s undulating motion aids in moving fresh seawater in and out of the egg case, which aids in respiration. Using Bamboo Shark eggs, the researchers found that the embryonic sharks react to possible predators with a freeze response, possibly to avoid alerting the predator by scent or water movement. If the little embryo froze because it perceived I was a predator, I’m glad it resumed its normal behavior so quickly.
It was difficult to shoot video because there was no place to set my camera down to steady it – but here’s a short bit: