Fishermen have an uneasy relationship with seals, which are increasingly eating more of their catch.
Photo by Jeni Smith
This story from May 2018 was at the top of the list for science stories.
By George Maynard
As anyone who spends time near the water knows, seals have made a dramatic comeback. Check out Google’s aerial images of Monomoy National Wildlife Refuge; see all those little ant-like blobs on the beach? Each one is several hundred pounds of ocean-going carnivore. We’re a long way from the early 1900s, when both Maine and Massachusetts paid bounties for seals, and we nearly exterminated them from the region.
Following passage of the Marine Mammal Protection Act, both gray and harbor seals have become massive success stories, as evidenced by presentations at the Northwest Atlantic Seal Research Consortium conference in New Bedford a few weeks back. One presenter joked she no longer needs to plot the outline of Sable Island, Nova Scotia in her maps of pup sightings because almost every available inch of the coast is covered in young seals. Another scientist estimated that more than 100,000 pups will be born this year at breeding sites in the Northwest Atlantic Ocean, including Monomoy Island.
Such rapid population growth certainly has consequences. Each seal needs around 4,000 calories per day just to maintain their body condition, and that number increases if they are pregnant or growing. Population estimates for Cape Cod show between 30,000 and 50,000 seals living in our backyard, meaning their caloric intake is upwards of 120 million calories (the equivalent of 400,000 Boston cream donuts) every day. That’s a lot of fish, which is concerning for fishermen who don’t appreciate the competition, for scientists and managers trying to decide what fishing quotas should be, and for people who care about balance in the marine ecosystem. But, gray seals eat a lot more than just fish, including baby harbor seals, harbor porpoises, and even baby gray seals.
Perhaps this goes without saying, but all of that food has to go somewhere. Canadian researchers estimate that seals have a digestive efficiency of about 85%. The remaining 15% or so is waste, and (barring some major seal potty-training initiative), most of it ends up on the beaches or in the water. Nature has ways of dealing with some of the waste; one seal’s poop is another seagull’s dinner. But even seagulls aren’t insatiable, leaving plenty of leftovers. While a 2012 analysis of beach closures here on the Cape did not find that seals impact water quality at current population levels, research from Puget Sound has shown that in high concentrations, seals produce enough waste to contaminate shellfish and close beaches. Seal scat can also harbor parasites that infect cod, halibut, and flounder.
But some good also comes from having so many seals around. Tourists flock to businesses that offer seal viewing tours, and people line up along the beaches to watch seals hauled out. Additionally, recent research from California suggests that seals may function as a “prey buffer” against shark attacks, drawing sharks away from swimming beaches and towards seal haul-outs.
The law that helped bring all this about, the Marine Mammal Protection Act, was written at a time when seals were few and far between, and has not been revised since. As a consequence, both harbor and gray seals are “protected” even though the International Union for the Conservation of Nature lists them as “species of least concern” and their populations are growing here in New England. There is no accepted estimate of the ecosystem’s carrying capacity for seals, even though the Act’s goal is an “optimum sustainable population, keeping in mind the carrying capacity of the habitat.”
Dr. Sean Hayes, head of NOAA’s Protected Species Branch, noted during his address to the seal symposium that the idea of “protected species” is a societal construct. Our neighbors to the north annually cull more than 3,000 seals from their herd. Some 1,000 additional seals are killed every year as part of Canada’s tightly regulated commercial harvest. Here in the United States we manage deer, coyotes, bears, elk, wolves, and many other mammals through regulated culls, harvests, and sterilization. These activities allow us to put the brakes on animal populations that can become problematic for people (think bears rooting through trash cans or deer running into cars).
Our conversation about seals is different though, largely because we’ve been socialized to think about these creatures as distinct individuals. Many animal welfare organizations name individual seals they rehabilitate. A picture of “Winnie” gazing into the camera is a powerful tool for fundraising, but it changes the conversation. It’s also much harder to discuss management measures like sterilization when some people worry that “Silver” or “Kwang” might not be able to have pups of their own. Another difference is that more people interact with seals as wildlife viewers than as commercial fish harvesters; consider that in places where farmers outnumber deer-watchers, hunting is much less controversial.
So what is the true goal of the Marine Mammal Protection Act? Is it protection for the population as a whole, or population for each individual animal? Should we be incorporating human health into our determination of how many seals our ecosystem can support? How do other stocks we’re trying to restore, such as cod and flounder, fit into the picture? Remember, seals fish without a management plan. If we aren’t willing to impose limits on seal populations, are we willing to let the ecosystem self-correct through disease, starvation, and all the other unpleasant symptoms of overpopulation?
We might not be at that point now, but there’s only so much longer we can kick this can down the road. As fishery managers explore Ecosystem-Based Fisheries Management, it is imperative that we make an honest effort to understand as much of our environment as possible. Seals are a part of it, and getting a handle on what role they play will help facilitate an honest discussion about the impacts of management action — or inaction.
(George Maynard is Policy and Research Coordinator for the Alliance)