Trull: Don't Blame The Seals

By: Elizabeth Van Wye

Topics: seals

Seals are being blamed for everything from depleting stocks of cod to attracting sharks to the region, but scientist Peter Trull said the issues are more complex, and federal protections ensures that seals are here to stay. FILE PHOTO

Why are there virtually no codfish to be found in the waters off Cape Cod? Depending on who you ask, it's because of the eating habits of the thousands of gray seals now living in local waters, or it's because of decades of chronic overfishing plus ecological changes, like warming oceans.

Peter Trull, Pleasant Bay Community Boating Curriculum Developer and Naturalist, comes down squarely on the latter cause. He calls blaming the seals "the biggest misconception" that exists on this topic today.

At last week's Pleasant Bay Community Boating Friday Speaker Series event, Trull addressed the interaction of seals, sharks and commercial fishing, the subject of his 2015 book "The Gray Curtain." Trull, a teacher who has been involved in field research and education on Cape Cod for 40 years, has also served as education director at The Cape Cod Museum of Natural History and at the Provincetown Center for Coastal Studies.

From the 1950s until the '70s, gray seals were slaughtered and nearly wiped out by bounty hunters. The Marine Mammal Protection Act of 1972 halted the practice, Trull noted, and with that protection the gray seal has been recovering.

"Until Jan. 18, 1991, other than on an island off Nantucket, there were virtually no gray seals on Cape Cod," he said. While hundreds of harbor seals were seen in the '80s, a documented sighting of a gray seal mother and her pup on that date on Monomoy Island was the first for the species in recent times. In subsequent years new pups have been born by the thousands each winter on Monomoy Island.

"I don't care if you love them or hate them," Trull said. "They're protected and that won't change anytime soon."

Studies of seal feces have shown that, like whales, stripers and many other local fish, the gray seal's diet consists mostly of sand eels, which are plentiful in local waters. Seals eat as much as 20 to 40 pounds a day of the four- to six-inch eels. Trull acknowledged there have been regular sightings of dead striped bass along the shoreline, with one massive seal bite taken out of their stomachs. Seals are lazy, Trull explained, and those stripers probably had a stomach full of sand eels. Chowing down on those stomachs is an easier way for gray seals to get a mound of sand eels than chasing around after the individual eels.

With the rising number of seals, the arrival of the apex predator great white shark is not a surprise. For the first time, Cape Cod beaches are now dotted with shark warning signs and sightings and encounters by swimmers and boaters are now a frequent occurrence. "Who'd have thought 10 years ago we'd see all these signs?" Trull said.

In response to questions, Trull was skeptical about the ability to control seals or sharks. "There are an estimated 18,000 to 24,000 gray seals in Chatham," he said, and they are an oceanic species. Just a few hundred miles north, on Sable Island off Nova Scotia, there are more than a quarter of a million gray seals. "A swim for a seal from there to here is a hop, skip and a jump," Trull said. "If you kill all the seals here there are 250,000 more right up there."

One species of seal on Cape Cod, the harp seal, is now encountering another predator. Harp seals are here in the winter and they will often leave the water to bask in the sun on sand dunes. Local coyotes, with their blend of eastern wolf and Texas coyote, have now taken to preying on these harp seals. "It's a new ecological niche," Trull said. "This activity never existed before."

So if the seals aren't the culprits, why are there no cod? Trull pointed to a number of reasons over the years for the decimation of the species in the waters off Cape Cod. Chief among them are overly high catch levels, underreporting of catches, destructive fishing practices (like dumping of immature or non-target fish), foreign overfishing and ecological changes. With waters warming, "what cod there are is now being caught off Iceland," he said. "They need the deep, cold water."

Trull was asked about water quality and possible negative effects of excrement in the water from thousands of seals. After reminding listeners that "Google is not research," he pointed to multiple research papers done on the subject by the Center for Coastal Studies and NOAA scientists in Woods Hole. These studies, available on Google Scholar ( have shown that E. coli bacteria in the water from humans through runoff is many times higher than from seals, which flushes out at every tide. "There are a lot of people flushing in July and August," he quipped.

The Pleasant Bay Community Boating Speaker Series is held on Fridays in the summer and fall. More information is available at