How to Identify Seal in Massachusetts

Grey Seals are significantly larger, with bulls reaching 7 to 8 feet and weighing up to 900 pounds. Their heads are proportionally long and narrow, and their nostrils meet in a straight line down the center of the muzzle, creating a distinctive roman-nose profile. Their coloring ranges from silver-grey to brown, often with dark patches. Harbor Seals are smaller, more compact animals with rounded heads and V-shaped nostrils splayed to the sides. Harbor Seals typically weigh 150 to 300 pounds and appear smoother and rounder in the water. Both have spotted or mottled coats, but Grey Seals tend toward bolder patterning. When hauled out on rocks, the size difference is obvious; in the water, watch for head shape and the nose profile as your primary field marks.

All seals have prominent whiskers, or vibrissae, that radiate from their muzzles and help them detect fish in murky water. Both Grey and Harbor Seals use these to hunt effectively. The eyes sit on the sides of the head and are relatively large and dark. Seals have no external ears, just ear holes. On closer inspection or in photos, Grey Seal eyes are positioned lower and more forward on the head than Harbor Seal eyes, which sit higher and farther back. This contributes to the rounded appearance of Harbor Seals versus the more elongated face of Greys. In live encounters, especially at seal haul-outs on Cape Cod or the North Shore, the eye and head placement becomes clearer as animals rest and turn toward observers.

Three species are documented in Massachusetts sightings: Grey Seal (2,068 iNaturalist observations), Harbor Seal (943 observations), and Harp Seal (57 observations). Hooded Seals are extremely rare, with only 1 observation on record. Grey Seals have recolonized the Atlantic coast over the past few decades and now form stable breeding colonies at Seal Island and other locations off Massachusetts. Harbor Seals were historically common and remain steady residents. Harp Seals arrive irregularly from the north during winter months, typically between December and February, when young seals wander southward from Canadian breeding grounds. They are not residents and should be treated as a winter visitor rather than a permanent species.

No. Harp Seals are rare in Massachusetts, appearing sporadically in winter. Only 57 documented observations exist in iNaturalist records, compared to over 2,000 for Grey Seals. When Harp Seals do arrive, they are typically juveniles drifting south from breeding areas in the Canadian Arctic. They can be identified by a saddle-shaped dark marking on their backs (resembling a harp) and a generally lighter body compared to the patterned Grey and Harbor Seals. Adult Harp Seals are mostly white with black heads and markings. If you encounter an unusually pale or marked seal on a Massachusetts beach during winter, consult a field guide or photo documentation before confirming the identification.

Seal haul-outs are rocky islands and coastal rock outcrops where seals rest, breed, and molt. Major haul-outs in Massachusetts include Seal Island and nearby skerries off the Isles of Shoals, the rocks off Cape Cod (particularly near Chatham and Orleans), and harbors along the North Shore, especially near Marblehead, Manchester, and Gloucester. Seals also haul out on sandy beaches, jetties, and man-made structures like docks and navigation markers. The best viewing locations are boat tours originating from these regions, which maintain a safe distance and do not disturb hauled-out animals. From shore, binoculars and spotting scopes are necessary to identify individuals without causing disturbance.

Peak seal watching occurs during summer months, with June, July, and August receiving the most sightings on iNaturalist. July and August are especially productive, coinciding with higher water temperatures, increased fish activity, and optimal conditions for boat tours. Sightings remain consistent through fall and winter, with November recording 273 observations and December 221. Winter months also bring occasional Harp Seals from the north. Spring and early summer see moderate sightings. If you plan a dedicated seal-watching trip, aim for July or August when conditions are pleasant and seal activity is highest.

Seals are often confused with sea lions or other marine mammals. Seals have no external ears and move with a caterpillar-like undulation; sea lions have prominent ear flaps and rotate their hind flippers forward, allowing them to gallop on land. In water, seals propel themselves vertically with rear-flipper strokes and ride lower in the water, with only the head and shoulders exposed. Sea lions and fur seals hold their heads high and move more horizontally. Dolphins and porpoises are smaller, sleeker, and break the surface with a rolling motion. Manatees, where they rarely overlap with seal range, are much larger and slower. When you spot a head in the water near the Massachusetts coast, the low, vertical rise and the broad, whiskered face usually indicate a seal.

Seal pups are significantly smaller than adults but share the same species characteristics in miniature. Newborn Grey Seal pups weigh around 30 pounds and are covered in a fluffy white or cream coat called a lanugo. This juvenile fur is replaced by the spotted adult coat after several weeks of nursing. Harbor Seal pups are born more developed and can swim within hours; they lack a fluffy coat and resemble miniature adults. Harp Seal pups have a distinctive creamy white coat with brown or black saddle markings. Young seals observed hauled out with adults are likely staying close to mothers or nursing sites. If you see a pup separated from a seal haul-out on a beach, consult local wildlife authorities rather than approaching; many seemingly orphaned seals are actually monitoring parents and do not require intervention.

Yes. Individual seals often carry distinctive scars, notches in flippers, or coloration patterns that can distinguish one animal from another. Researchers and long-term observers use these features to track seal populations and movement. Serious observers can contribute sightings of marked seals to projects like the Grey Seal photo ID database maintained by marine research organizations. However, for casual field identification of species, focus on the primary field marks: head shape, nose profile, size, and overall coloring. Individual scars and marks are supplementary cues useful for confirming a sighting or recognizing a previously photographed animal, not primary ID tools.