In the never-ending struggle for survival in this competitive and unforgiving world, it is all about surviving long enough to reproduce and pass on your “fit” genes to the next generation. But the story does not end with reproduction, the offspring must learn to sink or swim if it wants to survive to reproduce in this harsh world. In honor of shark week 2019, I will be discussing briefly a very unique shark adaptation to aid in the survival of its babies. But how could these egg cases with their odd corkscrew shape aid in the survival of its offspring?
Horn sharks, like about 43% of all sharks and rays, lay eggs instead of perform live births. But the horn shark mother does not have time to watch over its eggs all day long once it has been lain. Some animals will diligently guard their eggs for months until they hatch. Instead, the horn shark relies on the unique shape of the egg case. Each egg case houses one embryo along with enough nutrients for that embryo to feed on for about 10 months until it hatches. The mother inserts the corkscrew egg case into tight, rocky nooks and crannies. The shape of the egg case is perfect for lodging into these locations securely (similar to a metal screw being drilled into split wood). This helps to ensure the survival of the young since predators will have a difficult time getting to the wedged egg and the ocean currents cannot carry the egg off to treacherous places. Studies have also found that algae will grow onto the egg case over time, further protecting the egg by introducing camouflage to the scenario.
It is very probable that the baby will emerge from the egg case and survive. The mother helps to ensure recently hatched babies’ survival by placing them in a location with lots of tiny fish and crustaceans for the young to feed off of. Interestingly, scientists have found one predatory that has proven fatal to baby horn sharks within the egg casing. A certain sea snail can sniff out the eggs, use their proboscis to bore a hole into the egg casing, and slurp out the egg yolk.
So this shark week, along with admiring the fierce adult sharks that rip their prey to shreds, also consider the mom and her babies and their unique strategies for survival. Happy Shark Week 2019!
*For more information on horn shark egg cases, and to just see an AWESOME science website and podcast, visit: https://www.sciencefriday.com/articles/picture-of-the-week-horn-shark-egg-case/