Great white shark sightings rise in New England. Why this might be happening.

In the news this past week were two major sightings of great white sharks in New England, one off Cape Cod and another in Maine off Harpswell, where a great white was spotted attacking a seal that barely escaped onto the rocks.  

This is early for great whites, and some scientists are citing climate change, others increased seal populations. Since this is new territory for biologists in modern times, I thought that it might be useful to look at another shark species to try and answer some of these questions. At the Oceanarium I am asked at least once a day, “What caused the megalodon sharks to become extinct?”  

To answer that question, let’s look at what we know the great white (Carcharodon carcharias) and megalodon (Carcharocles megalodon) have in common, what scientists think they have in common, and their differences.  

First, their teeth are very similar, large triangles with serrated edges. The megalodons are much larger and fatter, up to 6.9 inches, while the great whites are about 2 inches and flat. Both had several rows of teeth which drop out throughout their life. They are cartilaginous fish, no bones, which is why there are only a few fossilized vertebrae from the megalodon; there is no full skeleton so the size and shape of a megalodon is conjecture using the size of the teeth and comparing it to the body mass of a modern great white. These are both apex predators; they eat anything smaller than they are, and sometimes things that are larger.  

What scientists think they know is that the megalodon was the largest fish ever to exist on earth and most likely the largest predator. Ranging from 33 to 58 feet in length. Some scientists theorize that they may have been as large as 82 feet and between 66,000 pounds and 143,000 pounds compared to the 15- to 20-foot average modern great white. They believe that, like the great white, they gave birth to live young. 

From fossil tooth finds, they believe that megalodons had nursery areas in warm waters off Panama. Again, from the size of their teeth, scientists believe that the newborns were about 6 ½ feet long!

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Scientists also believe that like great whites, the megalodon had blood vessels that ran through the center of their muscles. 

This allows the sharks to heat their blood above the ambient water temperature. So, while sharks are considered cold-blooded animals, these sharks have developed a way to increase their body temperature. This allows them to swim and hunt in colder waters.

This brings us around to extinction and the ability to adapt. While some scientists originally believed that climate change caused the extinction of the megalodon this theory has been mostly disproved by the distribution of fossilized teeth. It does not appear that the numbers of megalodons increased in warm water regimes or decreased in cold water.  

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According to a recent study by Kast, et. al, 2022, a group of scientists have developed a way to determine the nitrogen content of an animal’s diet by examining their teeth. They extrapolate those findings to determine how high up on the food chain an animal is or was. According to this study, it looks like both the great white and megalodons were eating about the same foods at the same time. Some have theorized that megalodons were cannibals. From this, the theory is that the megalodon and great white were competing for the same food in the same niche in the food chain and it looks like the great white out competed the megalodon contributing to their extinction. The great white was smaller and quicker and could survive on less food. The megalodons simply could not adapt and compete with their smaller rivals for food, as reported by the BBC from a study led by Professor Tutken of Johannes Gutenberg University.

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Here is another interesting question, did the megalodons hunt their prey the same way that great whites hunt? The fishermen report sightings of great white often feeding on seal pups in mid-August when the pups have been weened. The first indication of a great white’s presence is a circular blast of white water around a seal. Suddenly the seal disappears beneath the surface occasionally to be replaced by a circle of red blood bubbling up. The sight strikes a sense of fear and awe into those who have witnessed it. They never see the great white, only its fin.  

Now, back to the main question which is what is going on with the great whites? Are they moving just because of the change in climate? Or are they following their food source? Or a little of both? Only time will tell but the one last question would be, “What will cause the extinction of the great white?” Will it be climate change, lack of food, once they eat down the seals or another predator? That is for the scientists who come after us to discover.

Ellen Goethel is a marine biologist and the owner of Explore the Ocean World at 367 Ocean Blvd. at Hampton Beach.