The media and various stakeholders routinely raise questions about potential impacts that may result from the increasing number of seals in New England waters. The Northwest Atlantic Seal Research Consortium (NASRC) recognizes that healthy populations of all marine resources including fishes, seals, whales, and other species are important components of healthy marine ecosystems.
We are committed to providing answers to questions about seal populations by using comprehensive research data and analysis. Below are some of the most frequently asked questions and answers from the Consortium.
How many seals are there and where did they come from?
- Harbor and gray seals were bounty hunted in Maine and Massachusetts between 1880-1962 until state protection was granted (1965 in MA). 72,284 to 135,498 seals were bounty hunted during that time (Lelli et al. 2009).
- Gray seals were extirpated completely in the U.S., and only a few hundred harbor seals remained in the Gulf of Maine.
- While we do not have pre-exploitation numbers, genetic studies reveal that there was a much more diverse and robust population than currently exists (Cammen et al. 2018).
- The Western North Atlantic gray seal population in Canada is estimated at approximately 500,000+ individuals.
- In the U.S., the current stock assessment estimate (2018) of gray seals is estimated at 27,131 (22-33,000) *minimum is 23,158 based on pup production (Hayes et al. SARS 2017). These numbers mainly reflect the breeding population, and do not reflect seasonal changes in abundance as animals move to/from Canada to forage.
- The 30-50,000 estimated count of gray seals on Cape Cod derived from Google Earth Images reflects seasonal changes in abundance (Moxley et al. 2017).
- Genetic studies show there is an open population structure between the US and Canada with gray seals regularly moving between these habitats. (Gray seal tracked by satellite can make the trip from Nova Scotia to the Cape in as little as five days).
- The trajectory of harbor seal populations is less well known. Population estimates changed from 99,000 in 2001 to appx. 70,000 in 2012. Numbers in Canada are not known.
- The abundance of seal populations in recent decades suggests a marine ecosystem that is healthy enough to sustain those populations, even with increasing human uses of marine resources over the same timeframe.
Do seals compete with fishermen for target fish or depredate on target catch?
- Some seals do depredate on catch and interact with commercial fishing operations.
- Changes to fishing gear or practices may be able to reduce this depredation, though this has been a challenge in other areas and fisheries with seal depredation issues.
- Data from studies conducted along Cape Cod indicate that spiny dogfish cause more of an impact and depredate more than harbor seals (Rafferty et al. 2012, Sirak et al. 2015). Quantity and costs have not been assessed relative to gray seals.
- Long term data studies on seal diet in the U.S. indicate that the primary diet of gray seals are sandlance, hake species and flatfish (Wenzel et al. 2017, Ampela 2009). More research is underway using stable isotopes, fatty acids and prey DNA to fully understand the diet of seals in the U.S.
- Given their diverse diet, it is unlikely that seals are controlling the population of any particular species of fish. However, additional research is needed to review a wide temporal and spatial scale.
- The National Marine Fisheries Service (NMFS) estimates that 1,800-2,300 seals were seriously injured or killed each year between 2009- 2011 for mid-Atlantic gillnet and New England sink gillnet fisheries (Orphanides CD. 2011, 2013).
- Unlike commercial fisheries, recreational fishery interactions are not regulated and documentation is scarce.
- Participants of NASRC are currently working with local fishermen to reduce seal interactions with the long term goal of developing fishery modifications that will reduce bycatch.
- Working together, partners can help to preserve both seals and fisheries for future generations.
Are seals taking over beaches and causing beach closures due to their feces?
- A recent Woods Hole Oceanographic Institution (WHOI) study based on data collected by the Massachusetts Department of Public Health indicated that seals are not driving beach closures. Over time, water quality closures of beaches near seals did not increase and may, in fact, have decreased, while water quality closures of beaches far from seals remained steady or increased. Additional research is needed to confirm that beach closures are caused by effluent from human sources.
- The majority of seal haul-outs are on offshore rock ledges (harbor seals), sand bars (both species), or remote islands.
- Work is being done in collaboration with the MA EPA to source track fecal pathogens of all wildlife.
Why was the Marine Mammal Protection Act (MMPA) created?
- The Marine Mammal Protection Act (MMPA) is a highly effective and successful federal law. It has enabled us to recover a number of marine mammal populations (e.g., seals, whales, dolphins, etc.) that were reduced to low levels in U.S. waters due directly to human activities.
- The MMPA also was enacted because of the understanding that data lacking on the effects of removal of these organisms from an ecosystem has detrimental effects to the entire system.
- The MMPA is still needed, as species information are poorly understood and still still vulnerable to human activities. Additionally, it provides important resources for responding to strandings and entanglements.
- The MMPA also provides guidance on how to legally apply deterrents and manage recovered population.
Are seals are attracting white sharks that, in turn, can cause beach closures and threaten tourism and human safety?
- Although some large white sharks eat seals, older and younger white sharks also eat other marine life including fish and whale carcasses. We do not fully understand what influence, seal populations have on the abundance, distribution, or behavior of white sharks across the NW Atlantic.
- Sharks have been known to predate on seals on Cape Cod and the NW Atlantic for decades. White sharks and seals are historically documented in the region for centuries (Bigelow and Schroeder 1953).
- Sharks and human interactions have occurred in Florida, California and Hawaii yet those states have thriving coastal tourism. Learning from areas where seals, sharks and humans interact is key in the NW Atlantic where these animals are returning.
- Healthy and abundant shark and seal populations sustain ecotourism in the region.
- A study in California showed that the risk of a white shark attacks on humans has actually decreased over the past 60 years, due to in part to the recovery of pinniped populations in the area (Ferretti et al. 2015).
Can seals spread diseases to humans and pets?
- Data from stranding networks show that disease transmission is unlikely. If it were to occur, it would be limited to people directly handling seals.
- Seals can also get pathogens from humans and their pets, and care should be taken to keep pets leashed and away from seals.
- Like all wildlife, the public should not approach seals or allow pets to interact with seals.
- Most, if not all, can be prevented by proper personal protective equipment (PPE) and human behavior.
Were seals always here?
- Yes. prior to the bounties, seals were present. We have archaeological records for this that go back at least 4,000 years (Allen 1880, Ritchie 1969, Spiess & Lewis 2001).
- Genetic studies (K. Cammen et al. 2018) also indicate that there were many more gray seals as determined by the genetic diversity that is missing from modern seals.
What is the Ecological Role of Seals?
- Seals are mesopredators- They consume the predators of commercially important fish, and can enable a recovery of these commercial stocks.
- Seals eat pelagic fish like hake and herring that are predators of the eggs and larval stages of other fishes like cod and pollock (Frank et al. 2005, Heithaus et al. 2008, Baum and Worm 2009, Li et al. 2010). Cascade effects occur with the removal of predators (sharks, large fish) and mesopredators (seals).
- Seals have diverse diets that vary seasonally and by physiological needs including reproductive stage, molt stage, age and sex.
- How much do they eat? This varies. This is cited by NOAA as 4-6% of their body weight daily, but this percentage changes daily, monthly, seasonally and differs by sex and age class
- Species consumed by gray seals include but not limited to: red/white hake, silver hake, sandlance, flatfish, redfish, cod, pollock, squid, dogfish and skate. Given their diverse diet, it is unlikely that seals are controlling the population of any particular species of fish. However, additional research is needed to review a wide temporal and spatial scale.
- Ecological interactions between seals and fisheries are far more complex than just a predator-prey relationships (e.g. seals eating cod).
- For example, consider the ecological Role of Australian Fur seals: their gut microbiome contributes to greater nutrient availability for primary production/plankton (Lavery et al. 2012).
- Other marine mammals also give us an idea of the ecological role of these mesopredators. Experimental studies have demonstrated clearly that sea otters strongly affect kelp forest communities through predation on sea urchins, they also suggest that gray whale and walrus feeding can affect the structure of benthic invertebrate communities, and that dugongs may cultivate the seagrass community upon which they feed. Changes in the abundance of many species following large-scale harvesting of whales in the Southern Ocean further suggest top-down effects of marine mammals (Bowen et al. 2012).
- Marine mammals contribute and circulate nutrients important to both terrestrial and open ocean systems (Roman et al.2010). This has been described as the “whale (poop) pump” and applies to pinnipeds as well.
- Terrestrial ecosystems have been shown to benefit from the presence of nutrients provided from seals, including on Cape Cod, MA (Woods 2016) and Sable Island, CA (Lysak 2013).
What is the Human Impact on Seals?
- The National Marine Fisheries Service (NMFS) estimates that 1,088 seals were seriously injured or killed each year between 2010- 2015 in the mid-Atlantic gillnet and New England sink gillnet fisheries (Orphanides CD. 2011, 2013, Hayes et al. 2017).
- The Potential Biological Removal (PBR) for gray seals is 1,389 (Hayes et al. 2017).
- Unlike commercial fisheries, recreational fishery interactions are not regulated and documentation is scarce their impact is not documented.
- Contaminants, plastics, harmful algal toxins and reduction of habitat are increasing threats to all marine mammals including seals. Many of these threats have been shown to impact health and survival in seals.
- Seals habituate to being fed (provisioned). It is important NOT to feed seals. Not only is it illegal, but it reduces wariness of people and makes seals associate fishing vessels or other human activity with food. Seals can become more aggressive and increase these unwanted interactions.
Last updated: February 7, 2019