The waters and sandy shores of Cape Cod, Massachusetts, serve as a gathering point for marine mammals, particularly seals. Following conservation efforts, seal populations have increased substantially. The Cape’s geography, with its dynamic sandbars and remote islands, creates ideal haul-out locations where seals can rest, molt, and socialize in large numbers.
The Primary Cape Cod Seal Species
Two species of “true” seals, which lack external ear flaps, are the primary residents of the Cape Cod area: the Gray Seal (Halichoerus grypus) and the Harbor Seal. The Gray Seal is the larger of the two, with adult males often reaching up to 8 feet in length and weighing over 800 pounds. These seals are year-round residents along the Atlantic coast.
The Harbor Seal (Phoca vitulina) is smaller, typically measuring around 5 feet long and weighing between 100 and 300 pounds. While Gray Seals are present throughout the year, the Harbor Seal is a seasonal resident, with their numbers peaking in the Cape’s waters from late autumn through early spring. Rare visitors, known as vagrants, like the Harp and Hooded seals, occasionally migrate down from Arctic waters during the winter months.
How to Distinguish Between the Main Types
Distinguishing between the two species focuses on head shape and overall size. The Gray Seal is often nicknamed “horsehead” due to its elongated snout and straight profile, sometimes described as a “Roman nose.” A view of the Gray Seal head-on reveals wide-set nostrils that form a distinct ‘W’ shape.
The Harbor Seal possesses a rounded, concave head and a short muzzle that gives it a characteristic “dog-like” appearance. Their nostrils are close-set, forming a small ‘V’ shape. The Gray Seal is clearly the larger animal, with adult males being nearly twice the size of an average Harbor Seal. Coat patterns also differ: Harbor Seals have distinct, small spots, while Gray Seals display a more mottled or blotchy pattern.
Seasonal Presence and Best Viewing Locations
Gray Seals are present all year, with their breeding season occurring locally from late December through February, notably on islands like Monomoy in Nantucket Sound. Harbor Seals are most numerous from September to May, using the Cape’s protected areas as a winter foraging and resting ground before moving north to Maine to pup in the late spring.
The best opportunities for viewing are near large haul-out sites, which are often exposed sandbars at low tide. Popular locations include the Monomoy National Wildlife Refuge, visible from the mainland at Chatham, and the beaches of Provincetown, such as Long Point and the west end of the harbor. Observing seals within two hours of low tide is most productive, as this is when the animals congregate on the exposed land to rest. Bringing binoculars is recommended to view the animals from a respectful distance without causing disturbance.
Safety and Legal Observation Guidelines
All marine mammals, including seals, are protected by the federal Marine Mammal Protection Act (MMPA), which strictly prohibits harassment, feeding, or any actions that alter the animal’s natural behavior. This legal protection makes it mandatory for observers to maintain a safe distance from the animals.
It is recommended to stay at least 150 feet, or about 50 yards, away from seals on the shore and in the water, which is roughly the length of half a football field. Never attempt to feed the seals, as this can habituate them to humans and lead to aggressive behavior. If a seal appears injured, stranded, or alone, the public should not intervene but should instead contact the local authorized marine mammal stranding network for professional assistance.