White Sharks By the Numbers


White Sharks By the Numbers
White Sharks
By the Numbers
By Greg Skomal
I am most frequently asked, “How many are out there?” In the past,
I’ve typically danced around the subject. That’s because there was no
real answer—until now or, perhaps, a few months from now.
For more than 25 years, I have been studying the biology of sharks for
the Massachusetts Division of Marine Fisheries through the
Massachusetts Shark Research Program. Over that period, most of
my work had focused on the more common species, such as blue,
mako and basking sharks. When the white shark phenomenon hit, I
was clearly in the right place at the right time. Working with a
commercial harpoon vessel, the F/V Ezyduzit, and funding from a
variety of sources, including the Discovery Channel, our efforts from
2009-2013 involved tagging white sharks with sophisticated
electronic tags. These tags showed us that some sharks migrate
south along the coastline when they leave Cape Cod, while others
move well offshore into the mid-Atlantic and dive to depths in excess
of 3,000 feet before returning to Cape Cod the following summer.
These were the very first insights into the movement ecology of
white sharks in the Atlantic.
In response to growing local interest in the number of white sharks
visiting our region, we shifted gears slightly in 2014 and initiated a
study to estimate the white shark population. Such a shift involved a
Greg Skomal and his team identified 68 white sharks last year along the
coastline from Coast Guard Beach to the southern tip of Monomoy.
more sophisticated sampling design, more time on the water, and
more money. While we were content with devising the study from a
methodological point of view, time on the water and funding came
largely from our friends at the Atlantic White Shark Conservancy
(www.atlanticwhiteshark.org), a local nonprofit with the sole purpose
of funding research and educating the public about white sharks. It is
only through the efforts of the conservancy and its contributors that
we were able to launch this study in grand fashion.
Based on a traditional method for estimating fish population sizes,
called mark-recapture, our goal was to get on the water twice per
week from mid-June to the end of October for the purpose of
identifying as many individual white sharks as possible. Using spotter
pilot Wayne Davis, a vessel contributed and operated by Chatham
residents John and Pam King, and pole-mounted video cameras, we
located and documented white sharks along the coastline from Coast
Guard Beach to the southern tip of Monomoy. Each white shark was
identified based on color patterns, fin shapes and scars—a method
we call video fingerprinting. How many did we find? We identified
(drum roll) 68 individuals and tagged 18 during the summer of 2014.
So what does that mean? We know that at least 68 white sharks
visited Cape Cod last summer, but to expand this number to a
population estimate, we need more data. During the next several
months, we are going to repeat our sampling to determine the
proportion of previously identified white sharks returning to the area.
This information will then allow us to generate local and regional
population estimates. Stand by!
Greg Skomal, Ph.D., is senior marine fisheries scientist at the
Massachusetts Shark Research Program.
It’s no secret that white sharks are the talk of the Cape, particularly in
those towns facing the Atlantic. It’s also apparent that the resurgence
of white sharks in our waters is tightly linked to the robust gray seal
population. Once hunted to the brink of extinction, gray seals have
responded to more than four decades of protection and their numbers
are growing throughout the region. These blubber-lined porkers are
like Scooby Snacks for white sharks. Like customers to a new café,
white sharks are stopping by for a meal.
Although it could be argued that the great white shark is the most
charismatic species on earth, we know remarkably little about the
natural history and biology of this species. This is particularly true in
the Atlantic Ocean, where research has been hampered by our
inability to predictably find this species. We first noticed the growing
presence of white sharks about 10 years ago, but it wasn’t the sharks
we were seeing, just ghastly remains of partially eaten seals on the
beach. In 2009, we started to actually see white sharks off the coast
of Chatham, and this is when we got serious about the research.