It is a new year with a great wide ocean full of opportunities for interesting creature features! For the year of 2015 we are going to focus on sharks. There are over 400 known species of sharks, which means that there is a shark to learn about for every day of the year and more! Each month, we will highlight habitats in a different region of the world and just a few of the sharks that inhabit those areas. Sharks are members of the class Chondrichthyes (remember all that we learned about taxonomy?), which means that their skeleton is made up of cartilage instead of bones. Sharks, rays, and skates all fall under this category.
We are going to kick off the year in the Northwest Coast of North America. The most commonly found shark in the San Francisco Bay area (and MSI’s official mascot) is the Leopard Shark (Triakis semifasciata). These docile sharks can usually reach a length of 5ft for males and 6ft for females, though the largest have been measured to as long as 7ft! Why do the females reach a larger size? To answer that question, consider human females. Though women are generally smaller in stature than men, they have comparatively larger hips and higher fat count because that is most advantageous for bearing children. For leopard sharks, females are larger because the increased size is the best adaptation for bearing shark pups.
“Wait!” you may exclaim. “A leopard shark is a fish and fish lay eggs!” To which we would say “Very observant, but in this case NAY!!” Not all sharks lay eggs. Leopard sharks are what scientists call ovoviviparous (pronounced “oh-vo-vye-vip-are-us”). Instead of the young shark growing in an egg case outside of the mother’s body (which is known as being oviparous), it grows inside the mother shark. It may sound like a viviparous (babies grown inside and born live like humans) gestation process, but there are some important differences. For instance, your belly button is what is left of the umbilical cord that connected you to your mom while you grew in her tummy. It is what gave you your nutrients as you developed. Ovoviviparous sharks, like leopard sharks, lack that connection and instead the pups are connected to a nutrient rich yolk sack as they grow inside their own egg casing. They will hatch inside the mother and be birthed live. Once the pups are born they will continue to feed on the yolk sack until it disappears. The leopard shark gestation period will last for 10-12 months and litters can contain up to 30 pups.
Leopard sharks prefer to feed on crabs, worms, clams and other marine invertebrates until they reach a larger size. Once they reach adult size, they can then feed on a variety of larger fish. Leopard shark mouths are located on the bottom of their heads, near to the ground which makes it easy to feed on benthic (bottom) dwellers. One of the most captivating characteristics of sharks are their many teeth. All species of sharks have multiple rows of teeth so when they lose one or more, the ones behind will rotate forward. The arrangements of teeth in different sharks are a good indicator of where and on what they are feeding. Leopard sharks teeth are short and overlapping allowing for easier mashing and grinding on creatures such as clams and crabs.
Leopard sharks are often caught by Californian fishermen and are considered to be very tasty. Any leopard sharks fished recreationally must be a regulation catch size of 36 inches and no more than three can be caught. Leopard sharks that live in the San Francisco Bay Esturary have been known to have higher mercury content due to feeding on the benthos. Though levels have since been contained, the estuary was inundated with mercury through the runoff resulting mostly from hydraulic mining during the gold rush. If you do occasionally dine on fish from the San Francisco Bay, limit it to two servings per month for adults.
Check back next week to learn about another shark found in the Northwest Coast of North America.
Edited by KC O’Shea
Photography by Elizabeth Sheets and MSI photo library