By Blaise Jones
Determining the sex of an animal you are unfamiliar with can be a difficult task. More so when it comes to creatures such as fish. Usually you’ll have to have a keen eye for details and be able to identify the subtle differences in color, shape, and size. However, this is not the same for sharks. Unlike their bony fish cousins, there is simple method of telling male and female sharks apart.
Like many other species, sharks use something known as “sexual dimorphism” which is when the male and female members of a species have unique physical characteristics that set them apart. Some other sexually dimorphic animals are cardinals, gorillas, and of, course, human beings.
Sexual dimorphism in bony fishes and sharks tends to be subtler than it is in many land animals. For example, the female bonnethead shark has a slightly rounder head, whereas the male bonnethead head forms a more a shovel-like point.
While species-specific sexual dimorphism does occur across many different species of shark, there are a few traits that are universally dimorphic across the species as a whole that differentiate the males from the females.
As a general rule, female sharks are larger than males. While using size is not the most reliable way of sexing a shark, there is an important reproductive reason behind why female sharks tend to be bigger. By being larger, the females have more body mass in which to store energy that can be used for reproduction.
Their energy is stored in the form of fat. Having larger fat reserves means that the females sharks have more energy to burn when it comes time to gestate their eggs or offspring, depending upon the species. The bigger the female shark is, the more eggs or pups she can produce.
Another external difference between male and females sharks is their skin thickness. Female shark skin is approximately three times thicker a male’s. Females need this thicker skin to protect them during mating. Male sharks often bite down during reproduction, and the thicker skin helps the females avoid permanent damage. This leads to another sign to look for when sexing a shark: mature females are usually covered in scars.
While size and the presence of scars can serve as a starting point when it comes to sexing a shark, the only guaranteed way of telling male and female sharks apart is to look for claspers. Claspers are a pair of rod-like organs that sprout from either side of the cloaca, which is a slit-like opening between the two pelvic fins where sharks expel their wastes. Most reptiles and birds have a cloaca.
Claspers are the external male reproductive organ and thus are only found on male sharks. While they may be difficult to see on juveniles, claspers are prominent on mature male sharks.
Conversely, females only have a cloaca and no claspers on their ventral (bottom) side. While they use this opening to expel waste like males do, females also use it this opening for reproduction. They intake the male’s reproductive material through their cloaca, which fertilizes them. When it comes time to lay eggs or give birth, depending upon the species, their offspring leave through the cloaca.
Some species, like turtles, can also use their cloaca to breathe underwater.
- “The Encyclopedia of Sharks” by Steve Parker