Do Horn Sharks Lay Eggs? Their Unique Reproduction Method
Horn sharks, Heterodontus francisci, are a distinctive species found in the coastal waters of the eastern Pacific Ocean, primarily off California and Baja California. They are unique among many shark species because they reproduce by laying eggs. This oviparous method sets them apart from sharks that give live birth or retain eggs internally.
The Distinctive Horn Shark Egg
The horn shark’s egg case is remarkably unique, characterized by its iconic spiral shape, often referred to as a “mermaid’s purse.” This corkscrew design serves a crucial function in the egg’s survival. Initially soft and light brown, the egg case quickly hardens and darkens to a tough, leathery texture over a few days, often becoming dark brown or black.
This distinctive spiral form, made from collagen protein strands, allows the egg to be securely wedged into rocky crevices or other underwater structures. The ridges of the spiral act like a screw, anchoring the egg firmly against strong currents and waves. This also makes it significantly more challenging for predators to dislodge or consume the developing embryo. The egg case typically measures 10 to 12 centimeters (4-5 inches) in length and 3 to 4 centimeters (1.2-1.6 inches) in width.
Where and How Eggs Are Laid
Female horn sharks exhibit a rare form of parental care when depositing their eggs. They prefer to lay them in secure locations such as rocky reefs, within crevices, or among kelp forests, typically in waters ranging from 2 to 13 meters deep. The female will often pick up the newly laid egg case in her mouth and carefully wedge it into a safe, tight spot. This deliberate placement helps protect the egg from dislodgement and potential predators.
Horn sharks generally lay their eggs during a season that spans from February to April. During this period, a female can produce up to 24 eggs, typically laying them two at a time, approximately every 11 to 14 days. The deposition of a single egg case can take several hours.
Development Within the Egg
Once laid and secured, the horn shark embryo undergoes a lengthy developmental period inside its protective casing. The incubation period for these eggs can range from six to ten months, though some observations suggest it can extend up to a year, influenced by environmental factors like water temperature. Each egg case contains a single embryo, which is nourished by a yolk sac. This yolk sac provides all the necessary nutrients for the embryo’s growth and development.
The tough, leathery casing allows the embryo to develop fully before hatching. The young horn shark emerges as a miniature, fully formed version of an adult, typically measuring 15 to 17 centimeters (6-7 inches) long. The newly hatched shark still carries an internal yolk sac, providing initial sustenance, allowing it to survive for about a month before needing to actively forage for food.