What Are Shark Claspers and How Do They Function?

Shark reproduction involves a distinct approach compared to many other fish, utilizing internal fertilization. This process is made possible by the unique reproductive organs of male sharks, known as claspers. These structures are central to the mating process, allowing for the direct transfer of sperm to the female.

Anatomy of Shark Claspers

Claspers are the external, paired reproductive organs of a male shark. They are not separate appendages but are modified extensions of the inner edges of the pelvic fins. These rod-like structures are composed of cartilage, the same flexible material that makes up the entirety of a shark’s skeleton. The presence of claspers is the most reliable and straightforward visual method for identifying the sex of a shark.

Each clasper has a groove that functions as a channel for seminal fluid. This groove runs along the dorsal side of the structure, with an opening at both ends. The forward opening, or apopyle, receives sperm from the male’s cloaca, while the rear opening, the hypopyle, serves as the exit point into the female’s reproductive tract.

Function in Shark Reproduction

During mating, which often involves the male biting the female’s back or fins to maintain position, only one clasper is inserted into the female’s cloaca at a time. The male bends the selected clasper forward and inserts it into the female’s reproductive opening. The process is an active and forceful injection of sperm to increase the chances of fertilization.

A siphon sac, a muscular, bladder-like structure associated with the clasper, aids this process. Before copulation, the siphon sacs are filled with seawater. When the clasper is anchored inside the female, the siphon contracts, expelling the seawater with force. This jet of water flushes the sperm down the clasper’s groove and deep into the female’s oviduct. To ensure the clasper remains in place, some species have developed cartilaginous spurs or hooks on the clasper tips that securely anchor it within the walls of the female’s oviduct.

Clasper Development and Variation

Male sharks are born with claspers, but in juvenile individuals, they are small, soft, and flexible. As the shark grows and approaches sexual maturity, the claspers undergo significant changes. They lengthen and harden through a process of calcification, becoming rigid and robust enough for copulation. The rate of this development varies, with smaller shark species maturing in a few years, while larger species may take 15 years or more to reach reproductive age.

The morphology of claspers is not uniform across all sharks. For instance, the presence and arrangement of spurs and hooks can differ significantly. This diversity in clasper anatomy can be a useful tool for scientists in identifying different shark species, as the unique characteristics of these organs are often species-specific.