A Day in the Life of a Shark
Author Hunter Wortmann
Just like for you and me, every day is different for a shark in the wild. For us, every day starts by waking up in the morning, but is it the same for a shark? Just like us sharks switch between restful and active periods, but what makes them different is that they do not truly sleep. Just like the tiger shark, most sharks must be moving at all times for water to pass over their gills and oxygenate themselves via a process called ram ventilation. Other sharks, like the nurse shark are much less active and manually pump water over their gills via a process called buccal pumping as they rest on the ocean floor. Many species of sharks are solitary creatures and are usually traveling alone throughout their day. In order to survive the harsh, wild oceans sharks have a few things on their daily to-do list they need to check off.
The first thing you may think about when you wake up in the morning is grabbing a bite to eat. However, many sharks are more active at night and hunt for prey in the darkness which is an adaptation that gives them an edge. They may not successfully make a kill every day, and some sharks go months without eating but when they do it is crucial they make the kill. Depending on the shark species there are many different foods a shark can eat and just like when you are at a restaurant, their selection of food depends on their location and the type of shark they are. Sharks have evolved for millions of years before humans even existed and have very specific diets which do not include us. Sharks feed opportunistically, however smaller fish and invertebrates like crustaceans and mollusks are some of their favorite foods. Larger species prey on turtles, seals and other marine mammals. Sharks can go up to 6 weeks without eating and sharks are not always hungry depending on when they ate their last meal.
Great Hammerhead shark with a snack Image Credit: Jillian Morris
Just as eating is necessary for the survival of the individual, mating is necessary for the survival of the species. After sharks reach maturity they keep their eye out for a mate, which is usually later in their life cycle due to the fact that they are k-selected species like humans and have slower growth rates. Female sharks give off chemical pheromones to attract a mate when they are ready to reproduce. The mating dance commences when a male bites onto the female as a mechanisms of holding on and inserts his claspers into her cloaca as they fall toward the ocean floor. As mating can be very similar among sharks, birth is very different depending on the species. Some sharks are oviparous species and lay eggs- you may even find egg casings strewn on kelp forests of over rocks if you are diving! Other sharks are viviparous which means they perform live births just like humans. What makes humans different from sharks is the fact that some sharks like the blue shark can give birth to up to 100 live sharks at once!
Small-spotted catshark eggcase Credit: Lauren Smith
Mating whitetip reef sharks Credit: Ron Watkins
After mating and eating it has been a busy day for our sharks, but you may be wondering: what do they do at night? Good thing our friend the kitefin shark can glow in the dark! This is not the only one of our fellow sharks who can glow in the dark. This guy uses bioluminescence which is a chemical reaction made by small organisms living on the shark’s dermal denticles. Just like many other traits sharks have evolved, bioluminescence confuses predators and helps the shark stay alive which is the most important to-do for any shark!