Please select your home edition
SWC newsletters (top)

Together again: White sharks and gray seals off Cape Cod

by NOAA Fisheries 4 Aug 2019 13:26 UTC
A white shark swims close to a pack of gray seals in the shallow water off Lighthouse Beach in Chatham. © Massachusetts OEEA

In 1975, the movie Jaws made "Cape Cod" and "shark" synonymous, even though white sharks were rare in these waters. Today gray seals are becoming equally associated with Cape Cod, although the once-resident populations were eliminated by the early 1970s.

Now, sharks and gray seals share coastal waters off the Cape in numbers not seen in most of our lifetimes.

You might think that these two animals have nothing in common other than a "bitey" relationship, but think again. Adversity, resilience, and an important role in the ocean ecosystem bind them closer than predator and prey.

Hunted to low numbers

People have sought white sharks for their fins, teeth, jaws, meat, and as a trophy fish. From the 1880s until the mid-20th century, gray and harbor seals were numerous off New England. Both Maine and Massachusetts paid bounties for each one killed, as did places in Atlantic Canada. Although it's hard to figure out the exact contributions of fishing, culls, and bounties to population numbers, it's generally agreed that it wasn't increasing them.

Protected by law

Domestic and some international laws protect white sharks and marine mammals like seals. Fishermen may hook a white shark, but must release it. The Marine Mammal Protection Act protects seals, as well as all other marine mammals in U.S. waters, from harassment, hunting, capture, or killing.

Recovering populations

It's hard to estimate how many white sharks are in our oceans, as they are relatively rare. Research shows that protections for sharks have likely improved their numbers, particularly in the Northwest Atlantic. For gray seals, the rebound is clear to the naked eye: once there were none, now there are several thousand living on Cape Cod shores. Gray seals now living on Cape Cod originated from larger Canadian herds, and have only recently started to again live on the Cape year-round.

Usual prey off the menu? No problem

Both of these predators have an array of dining options. They just aren't that picky. Off Cape Cod gray seals eat mostly sand lance, hakes, and flatfish. White sharks eat fish and (::ahem::) seals, as well as other marine mammals. Both will sometimes snatch fish off an angler's line or a commercial fisherman's gear.

Top level predators

We'd give the top spot to white sharks here. They much prefer a seal over fish by the time they are adults and you probably won't read a "gray seal bites white shark" story anytime soon. That said, they are both top level-predators. Very few other animals are large enough and interested enough to rely on them for prey.

Top-level predators help keep an ecosystem in balance. When, where, and what they eat regulates the animals below them on the food chain. This directly affects the diversity of life and indirectly helps ocean plants and corals thrive.

Related Articles

Determining how old fish are
Scientists use technology and ingenuity to get their work done from home Sometimes it's a good thing to "take your work home with you." A team of scientists at NOAA's Alaska Fisheries Science Center is demonstrating that it is possible to accomplish a lot while teleworking. Posted on 13 Jul
North Atlantic right whales classification updated
There are about 400 individuals remaining, and likely fewer than 100 breeding females The International Union for Conservation of Nature recently changed its Red List Category for North Atlantic right whales from Endangered to Critically Endangered. Posted on 12 Jul
What is nearshore habitat?
Restoration focuses on valuable shoreline habitat where juvenile fish grow There is an especially valuable environment in Puget Sound made up of the beaches, bluffs, inlets, and river deltas: the nearshore. Posted on 28 Jun
Returning rescued sea turtles to the wild
Learn about the operations that go into rescuing, rehabilitating and releasing protected sea turtles We work with organizations along the Atlantic coast to help rescue and rehabilitate protected animals such as sea turtles. A successful rescue takes months of work and coordination between many partners. Posted on 27 Jun
Twentymile river whale update
It lingered in the river for more than a week The gray whale that was first reported in Twentymile River near Girdwood, Alaska on Memorial Day has likely died. It had lingered in the river for more than a week before swimming back into Turnagain Arm. Posted on 27 Jun
Celebrating sea turtle conservation
Conserving and protecting sea turtles is a part of our core mission at NOAA Fisheries NOAA Fisheries is committed to the protection, conservation, and recovery of sea turtles. We conduct research to inform conservation management actions and we work closely with our partners to advance conservation and recovery of these amazing animals. Posted on 22 Jun
Large whale entanglements report confirmed in US
More than 100 large whale entanglements were confirmed nationally in 2018 Many large whale populations are increasing in the United States, but entanglements in fishing gear or marine debris are a growing threat to the continued welfare and recovery of these species. Posted on 20 Jun
Autonomous vehicles help scientists estimate fish
An innovative scientific approach to survey Alaska pollock this year Scientists are capitalizing on existing technological capabilities and partnerships to collect fisheries data. This will help fill the information gap resulting from the cancellation of FY20 ship-based surveys due to the COVID-19 pandemic. Posted on 5 Jun
Newly weaned seal pup needs community help
NOAA and partners are requesting beach goers and ocean users keep their distance A recently weaned female Hawaiian monk seal pup has been resting along the shoreline and swimming in the waters along O'ahu's Kaiwi Coastline. She has appeared near some busy beach areas and hauled out in areas with a lot of vehicle activity on the beach. Posted on 30 May
Researchers probe orca poop for microplastics
What are microplastics and why are researchers looking for them in whale feces? You might worry about your toddler chewing on a plastic toy with toxic chemicals. Some orca researchers are beginning to worry about whales ingesting a gut full of microplastics, and what that might mean for their health. Posted on 29 May
MBW newsletters (top)