At the NEFSC, our seal research mainly focuses on harbor seals and gray seals, and sometime harp seals, principally in New England waters (Maine to New York).
There are two species of seals that breed in New England: harbor seals and gray seals. There are three other species that breed in the Arctic that occasionally can be found in the area: the harp seals (the most numerous seal in the NW Atlantic), the hooded seal (the largest seal in the NW Atlantic), and rarely, the ring seal (the smallest seal in the NW Atlantic).
Fossil records indicate that the ancestors of modern seals first entered the ocean on the west coast, about 28 – 30 million years ago.
Like all marine mammals, seals get all the water they need from their food. Their bodies are very efficient at removing and recycling water from their food, but they avoid drinking sea water and if a seal drinks too much sea water it can become seriously sick. Arctic seals, which spend time on ice, may sometimes eat fresh water ice and snow.
Seal have many well developed whiskers (vibrissae), much like a cat. Like cats they have a very acute sense of touch. Scientists think seals can use their whiskers to feel vibrations from swimming prey. Blind seals in the wild seem to be able to hunt and feed without sight.
Seals can hear very well both above and below water. They can hear high pitched sounds well above the range of human hearing.
Seals see very well under water – better than they do in bright light above water. Their eyes are adapted with round lenses (like fish) and a large iris that fully opens underwater. On land the iris closes the pupil to a small pin point that lets the seal see clearly through the round lens on land. A seal’s eye is also adapted for low light vision with a lining (similar to a cat’s eye) that reflects and amplifies the weak light at depth in the ocean.
Seals make many sounds both out of the water – like elephant seals, and under water – like harbor seals. Scientists have recently started to use the sounds harbor seals make during mating season to identify and track them.
Seal mothers and pups (as opposed to other pinnipeds) generally stay close together on shore and are not separated while nursing. Harbor seals are an exception, and mothers will leave pups on shore to feed offshore. Seal mothers and pups can stay in contact by sound. Harbor seal pups make distinctive calls that can be heard for up to a kilometer. When in close contact mothers and pups can identify each other by scent, recognizing scent from glands in the skin of their flippers and around their muzzles. If you see a harbor seal pup on shore, observe it from a distance and do not approach –its mother may be offshore – and seal pups are naturally attracted to moving objects that are bigger than they are. This can help a pup stay near its mother, but can also make a pup follow things that it shouldn’t (like you).
We don’t really know how seals navigate, but we do know that they are very good at finding their way while traveling at sea, in all types of weather conditions, day and night, while spending much of their time underwater. Recent improvements in tracking technology (satellite tracking, GPS tracking) has shown that seals can travel great distances and return to the same spots on shore with great precision . Grey seals can swim from Cape Cod to Nova Scotia in a matter of days.
Seals, sea lions and walruses are currently placed in a sub-order, the Pinnipedia, of the Order Carnivora (which includes bears, dogs, racoons, weasels (including otters), hyenas cats, and mongooses). There have many recent studies on the genetic and fossil history of these groups and their place in the scheme of mammalian classifcation may well change in the near future.
Three families of living pinnipeds are recognized, the Phocidae (hair seals or true seals), the Otaridae (fur seals and sea lions) and the Odobenidae (walrus). The term pinnipedia translates from Latin as "fin foot". All of these animals must come ashore to breed, give birth and nurse their young, though some species are at sea for several months at a time while others return to the shore every day.
A seal’s body stores enough fat in the blubber layer to allow the animal to go for extended periods of time without eating. In addition, most seals are opportunistic feeders and will consume a variety of fish, shellfish, and crustaceans. Seals do not eat on land.
It is absolutely normal for seals to be on land. Seals are semi-aquatic, which means they often spend a portion of each day on land. Seals need to haul out for a variety of reasons: to rest, pup, and molt (annual shedding of old hair). Young seals may haul out on land for up to a week.
Seals do not need to be wet constantly. They come out of the water to get dry; wetting them is actually a form of harassment.
It is against the law to touch, feed, or otherwise harass seals. Harassment occurs when YOUR behavior changes THEIR behavior. If your presence causes any of the following reactions on land or in the water, then you are too close:
- Increased vocalizations by seals
- Movement back into the water (single animal or the herd).
- All eyes are on you (single animal or several in the herd).
- Disturbance from normal resting position (lifting their head to watch you, stretching, waving foreflippers, yawning).
The average size for a male or female adult harbor seal is approximately 4 -5 feet in length and 220-250 pounds. Their coloration ranges from dark gray to tan and is overlaid with many leopard-like spots. They have small heads, very large eyes, and a face that resembles a cocker spaniel.
Adult harbor seals will usually retreat to the water when approached, but juveniles will often remain on the beach. They are commonly seen resting on their side in a “banana” shape, on rocks along the coast.
In New England, harbor seal pupping occurs between mid-May to mid-June. Mothers nurse their pups for 4-6 weeks and will temporarily leave them during foraging trips.
The latest harbor seal stock assessment reports indicate that the minimum population estimate is around 66,884 animals. This includes animals distributed from the eastern Canadian Arctic and Greenland south to southern New England and New York (occasionally down to the Carolinas). Trends in the harbor seal population are uncertain; there is evidence to suggest that the population may be declining, or perhaps shifting its distribution.
Male gray seals are characteristically larger than females. The average size of a male gray seal is approximately 7-8 feet in length and between 660-770 pounds in weight. Females will average approximately 6.5 feet and between 330-450 pounds in weight. Males’ coloration is typically darker than females’. Males are dark brown, gray, or black with smaller, lighter spots and females have a tan or light gray background with darker spots. Their most distinctive feature is the shape of their head. They have been nicknamed “Horse-heads” because of the long, straight, slope of their profile.
Single animals will usually stand their ground when approached, while herds/groups of gray seals will generally retreat to the water. They can be very vocal and aggressive.
Gray seals are born from mid-December to early February. In the United States, pupping takes place on islands in Penobscot Bay and Frenchman Bay, Maine, and on Muskeget, Tuckernuck, and Monomoy Islands in Nantucket Sound, Massachusetts. Mothers nurse their pups for approximately 16 days. After pups are weaned, mothers may leave the colony but pups remain for several more days or weeks living off blubber reserves.
We do not have a good estimate of how many gray seals are currently in US waters. Canadian population models estimate that there are likely around 505,000 in Canadian waters. Gray seal abundance appears to be increasing.
Warming ocean waters are bringing the sharks further north for longer periods of time. Seals are a prey source of marine mammal eating sharks, so this and the growing gray seal population may be the reasons we are seeing more great whites closer to shore in Massachusetts when seals are present during the summer. For safety, never swim near seals or haul out sites.
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Unless otherwise noted all color artwork is © Ray Troll 2002, © Terry Pyles, colorization 2002. These images may not be utilized in whole or in part by any entity other than NMFS without the express permission of NMFS' Office of Constituent Services and the copyright artist, Ray Troll.