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Part 2, Sec. 2B2f
Sanctuary Resources - Natural Resources
Marine Mammals

f. Marine Mammals

Thirteen species of marine mammals are known to frequent the waters over and around Stellwagen Bank, and rare sightings of an additional two species have been recorded. Resources of the Bank environment provide important sources of food for a seasonal variety of large and small cetaceans, and serve as nursery grounds for some of these species. Two species of pinnipeds have also been documented in the Stellwagen Bank area.

1. Endangered Cetaceans

Humpback whales (Megaptera novaeangliae; 30 to 60 feet, or 9.1 to 18.3 meters in length) are perhaps the most easily identified of large cetaceans due both to their distinctive markings and long flippers and to their highly-visible feeding and socialization behaviors. The species was first scientifically described based on observations made of an individual taken off the coast of Maine, and hence, the Latin name novaeangliae, which means "New England". In spite of this description, humpback whale populations may be found in all oceans, although overall numbers remain depleted compared to pre-exploitation levels. The species has been protected from commercial hunting since 1962, and classified as "endangered" under the Endangered Species Preservation Act since 1970. (The Endangered Species Preservation Act was the predecessor to the 1973 Endangered Species Act). The Western North Atlantic population of humpbacks is currently estimated at 5,505 animals (NMFS, 1991).

Migrating north from calving and mating grounds in the eastern central Caribbean, a significant number of humpback whales, estimated at around 550, arrive in the Massachusetts Bay area annually, beginning approximately in early March, when they are first observed within Cape Cod Bay waters. By April, humpbacks begin to move farther offshore toward the Bank, where they generally remain until mid-November, intensively engaged in feeding activities. Primary prey of the humpback whales in this area is the American sand lance (Ammodytes americanus), whose populations are seasonally prolific in the Bank environment. Other species of fish occasionally taken by humpbacks include herring, mackerel, cod, and hake. Generally, humpbacks consume 95% fish, 5% zooplankton. North of Stellwagen Bank, capelin (Mallotus villosis) is the preferred prey. The Bank also serves as an important nursery area for mothers with calves. This "residency" period of approximately 7-1/2 to 8 months of the year in the Stellwagen Bank vicinity is one of the longest such periods known anywhere in the world. By mid- to late-November, the humpbacks begin their annual migration south to warmer coastal waters.

Due to their distinctive fluke patterns, photo identification has been possible for at least 500 individual humpbacks by local cetacean research organizations during the past 12 years. The growing photographic and other data bases on humpback whales in the Stellwagen Bank area have added much to understanding the biology and habitat requirements of this species. Combined with the accessibility of the Bank to land points, public observation of humpbacks has in recent years become an increasingly popular recreational activity in the New England area.

Northern right whales (Eubalaena glacialis; 20 to 50 feet, or 6.1 to 15.2 meters in length) are the most seriously depleted species of large cetaceans. Estimates for the two known populations (found in the Atlantic and the Pacific Oceans) indicate the total world population may number fewer than 400, and probably does not exceed 500 individuals (Marine Mammal Commission, 1991). The population for the North Atlantic stock is thought to be between 300 and 350 whales (NMFS, 1990). Although this species has been protected from almost all hunting since 1935, it has not recovered to anywhere near its pre-exploitation numbers which are thought to be around 10,000 animals (NMFS, 1989).

In May 1990 the Right Whale Recovery Team, pursuant to Section 4 of the Endangered Species Act, petitioned the National Marine Fisheries Service to designate three areas off the eastern seaboard as critical habitat for this species, including Cape Cod Bay (Figure 5). Additionally, the Recovery Team also recently published a Recovery Plan for the Northern Right Whale.

Given its endangered status, the photo-identification of at least 100 northern right whales using the Bank seasonally indicates the particular importance of this system to a significant portion of the existing total North Atlantic population for feeding and nursing activities. Right whale courtship behavior may also be observed during spring, summer and fall months, with calving occurring in coastal waters off Georgia and Florida during late winter (NMFS, 1990).

Right whales begin to enter the Massachusetts and Cape Cod Bay systems by late winter or early spring from coastal Georgia and northeast Florida waters; and from other offshore over-wintering areas. The Massachusetts/Cape Cod Bays area is one of five identified "high-use" areas for Western North Atlantic northern right whales. (The other four areas are: coastal Florida and Georgia; the Great South Channel east of Cape Cod; the Bay of Fundy; and Browns and Baccaro Banks south of Nova Scotia.) The whales generally remain in this system until approximately July, when most begin moving further north toward the lower Bay of Fundy, or areas on the southeastern shelf off Nova Scotia. By October, the whales have generally begun migrating to wintering areas.

Northern right whales feed primarily below the surface, and exclusively on zooplankton; the primary prey at Stellwagen Bank are copepods (in particular Calanus finmarchicus), and juvenile euphausiids. Because of the whales' slow movement, and a tendency to rest at the surface, the species is vulnerable to collisions with ships.

Fin (or Finback) whales (Balaenoptera physalus; 30 to 70 feet, or 9.1 to 21.3 meters in length) are the most common species of large baleen whale in the Gulf of Maine. While the preferred feeding habitat for the North Atlantic population of fin whales is over deeper waters of the continental shelf (300 to 600 feet), they are regularly observed anywhere from coastal to very deep water areas. Some fin whales overwinter near Cape Cod; however, their abundance near Stellwagen Bank peaks between April and October. Fins' behavior around boats is usually more restless than humpbacks; however, they will sometimes approach still and quiet vessels (Katona, et al. 1983).

An asymmetric coloration of the head -- the right side (including lip and baleen areas) always white or pale gray; and the left always dark -- is unique to fin whales, and may play an important role in feeding behavior. Fin whales are often observed circling in a clockwise direction (thus with their light colored side down), herding prey fish for easier consumption. Various species, especially sand lance, capelin, and herring, form the primary diet of fin whales (90%); the species is often seen feeding with humpbacks. Smaller individuals may also consume copepods and squid.

The pre-exploitation Western North Atlantic population is not known. The current Western North Atlantic population is thought to number between 3,590 and 6,300 individuals (NMFS, 1991); and the worldwide population is roughly estimated at about 120,000.

Sei whales (Balaenoptera borealis; 25 to 50 feet, or 7.6 to 15.2 meters in length) are smaller and darker than fin whales, but difficult to identify. Sei whales were first positively observed feeding in the Stellwagen Bank area in 1986; and the numbers recorded since then have been relatively low. They feed exclusively on zooplankton, primarily copepods and euphausiids (and krill in other feeding habitats). There are no recent population estimates for sei whales in the North Atlantic. NMFS has estimated approximately 4,000 individuals may be present in this overall area. (NMFS, 1991). In 1988, approximately 40 individual sei whales were photographically identified at Stellwagen Bank; however, a greater number were present.

Blue whales (Balaenoptera musculus; 25 to 100 feet, or 7.6 to 30.5 meters in length) are the largest mammals on Earth. The first documented sighting of a blue whale on the east coast of the United States was recorded in October 1986 on the western edge of Stellwagen Bank. Two additional sightings of blue whales were recorded at the Bank in 1987. In all instances, the whales were observed feeding, probably on euphausiids. Blue whales may also occasionally feed on copepods, fish, and squid.

Although blue whales have been seen regularly during summer months in the Gulf of St. Lawrence, and around southern and northern Newfoundland, there are few data available on Western North Atlantic populations. The worldwide, pre-exploitation population level is estimated at 300,000 animals. Current population estimates for the North Atlantic range between 100 and 555 individuals. (NMFS, 1991).

2. Non-Endangered Cetaceans

Minke whales (Balaenoptera acutorostrata; 15 to 30 feet, or 4.6 to 9.1 meters in length) are the smallest of the balaenopterid species of cetaceans. Although reliable population figures for the Western North Atlantic stock are not known, minke whales are commonly seen in the northern Stellwagen Bank and southern Jeffreys Ledge area from March until November. The species may also overwinter in these areas; although further winter surveys would be necessary to make this determination.

Minke whale abundance in the study area is highest in the spring and the late summer/early fall. Larger concentrations of minkes appear during the latter period, frequently observed in the immediate vicinity of fin whales. It is likely that the seasonal movements of this species are similar to those of fin whales.

Minkes feed primarily on schooling fish and euphausiids, in particular herring, sand eel, capelin, cod, pollack, mackerel, squid and copepods. Although surface feeding patterns have been documented, minkes more normally feed below the surface. Calves are not generally seen in these feeding areas. Due to their inconspicuous appearance and behavior, population counts have been difficult to obtain.

Pilot whales (Globicephala spp.; 10 to 20 feet, or 3.0 to 6.1 meters in length) are distinguished by the species' large bulbous head. The most common species occurring in the Gulf of Maine is Globicephala melaena, though in the Western North Atlantic, this species is found in the same areas as short-finned pilot whales (Globicephala macrorhyncha). These small jet black whales are generally observed along the shelf edge in the company of bottlenose dolphins (100 to 1,000 meter contour), but may also be seen in central and northern Georges Bank/Great South Channel/ Gulf of Maine areas between May and October.

Pilot whales feed almost exclusively on squid (Illex spp.), with fish and invertebrates as alternative prey. Average pod size is approximately 20 animals.

Orca (or killer) whales (Orcinus orcus; 22 to 30 feet, or 6.7 to 9.1 meters in length) are most commonly seen in the southwestern Gulf of Maine from mid-July to September, although these whales are also known to overwinter in the Gulf of Maine. Orcas have been frequently recorded on Jeffreys Ledge, between the Isles of Shoals and on Stellwagen Bank, where they are thought to follow schools of bluefin tuna. As opportunistic feeders, orcas consume a variety of fishes including tuna, herring and mackerel, and have also been known to attack pinnipeds, seabirds, and other cetaceans.

White-sided dolphins (Lagenorhynchus acutus; 7 to 9 feet, or 2.2 to 2.7 meters in length) are widespread throughout the Gulf of Maine/Georges Bank environment all year, and are particularly abundant in the southwestern portion of the Gulf (incorporating Stellwagen Bank). These highly social cetaceans are found only in the North Atlantic, and are generally present on northern portions of the Bank and on Jeffreys Ledge at all times of the year. They are frequently seen feeding with fin whales, and may also be seen bow-riding fins or humpbacks, as well as vessels. Pods of white-sided dolphins may range in size from 10 to over 1,000 animals, although most groups number between 25 and 150. Calves are also observed in this area throughout the year. Prey species include a variety of fishes, such as herring, hake, smelt, capelin, cod, and squid.

White-beaked dolphins (Lagenorhynchus albirostris; 8 to 10 feet, or 2.4 to 3.0 meters in length), like the white-sided dolphins, are found only in the North Atlantic; although they generally follow a more northerly range, from Cape Cod to Greenland. White-beaked dolphins are considered casual visitors to the northern end of Stellwagen Bank, where sightings usually occur between April and November. While in the Gulf of Maine, white-beaked dolphins likely feed on sand eels; squid may also be consumed. In the 1950's, white-beaked dolphins were more abundant in the overall Gulf of Maine; they have been displaced by increased numbers of white-sided dolphins.

Harbor porpoises (Phocoena; 4 to 6 feet, or 1.2 to 1.8 meters in length) are locally abundant in temperate waters of the Bay of Fundy and the northern Gulf of Maine during summer months. The species exhibits seasonal patterns in spatial distribution within this general region, and is particularly concentrated in the southwestern Gulf of Maine, the Great South Channel, Jeffreys Ledge, and coastal Maine during mid-spring months. Sightings are generally recorded from south of Cape Cod north to the Bay of Fundy during spring months. Following April, harbor porpoises are only rarely seen in Cape Cod waters, and the decrease in sighting frequency suggests a general northeast movement toward the northern Gulf of Maine and Bay of Fundy. (Cited in T. Bigford, NMFS/NER, April 1991).

The summer population estimate of approximately 16,000 harbor porpoises in the Gulf of Maine is considered somewhat unreliable, due to seasonal changes in species distribution, which make survey consolidation difficult. The Northeast Fisheries Center of NMFS planned a summer 1991 survey of harbor porpoise, which should produce more reliable population estimates. (T. Bigford, NMFS/NER, April 1991). Harbor porpoise diet consists primarily of small schooling fishes, polychaetes, and cephalopods. In the Gulf of Maine, likely prey species include mackerel, herring, squid, and sand eel.

A number of harbor porpoises annually are entangled and killed incidentally in both U.S. and Canadian gillnet fisheries in the Gulf of Maine. Although reliable estimates of affected harbor porpoises in the U.S. fishery do not exist at this time, the possibility exists that the species may be declining due in part to entanglement losses. (T. Bigford, NMFS/NER, April 1991). Through the Marine Mammal Exemption Program, (§ 114 of MMPA) and the gillnet industry, NMFS is currently seeking to assess and rectify this problem.

Bottlenose dolphins (Tursiops truncatus; 8 to 12 feet, or 2.4 to 3.7 meters in length) are occasionally seen in the Gulf of Maine during the late summer and fall. This species, generally occurring offshore along shelf areas from Cape Hatteras (North Carolina) to Georges Bank is the larger of two recognized forms of Tursiops truncatus. (The smaller form occurs more frequently in inshore areas of the mid-Atlantic south of Delaware Bay.) While in the Gulf of Maine, bottlenose dolphins feed opportunistically on a wide variety of fish, squid, and invertebrates.

Common (or Saddleback) dolphins (Delphinus delphis; 6 to 8 feet, or 1.8 to 2.4 meters in length) are occasional visitors to the Gulf, particularly in the fall and winter. Saddlebacks are generally seen over northeastern portions of Georges Bank, feeding on fish and squid.

Striped dolphins (Stenella coeruleoalba; 6 to 8 feet, or 1.8 to 2.4 meters in length) are seen occasionally in the Gulf of Maine. This species generally prefers more pelagic waters, along the edge of the continental shelf. Diet consists primarily of fish and squid.

Grampus (or Risso's dolphin) (Grampus griseus; 9 to 13 feet, or 1.27 to 3.96 meters in length) are generally considered absent from the Gulf of Maine, although there have been several individuals recorded. More normally, this species stays outside the 100-meter contour, south of Cape Cod. Grampus feed almost exclusively on squid.

3. Pinnipeds

Two pinniped species occur commonly in the Sanctuary area: the harbor seal (Phoca vitulina); and the gray seal (Halichoerus grypus).

Harbor seals are common from Labrador to Long Island, New York (and occasionally found as far south as South Carolina and Florida). It is the most abundant pinniped species in eastern United States waters. Harbor seals are widely distributed in nearshore waters along the coast, preferring sheltered and undisturbed rocky ledge haulout areas in bays and estuaries from Maine south to Plymouth, Massachusetts.

During the first half of the 20th century, harbor seals bred as far south as Cape Cod Bay, but currently are only seasonal residents in southern New England (from late September until late May). State bounties in southern New England states existed until 1962, and probably caused not only an overall reduction in seal populations, but also a northerly shift in distribution of breeding populations. Breeding occurs from late April until late June, and exclusively north of Massachusetts.

Since the passage of the Marine Mammal Protection Act in 1972, harbor seal populations have increased steadily. In 1983, estimates of Maine's harbor seal population were 12,000 to 15,000 animals, and increasing. Approximately 4,000 of these (or 25% of the New England population) overwinter south of Maine, and 60% of these (or 2,400 animals) occur on and around Cape Cod (Payne, et al., 1983).

Harbor seals are opportunistic feeders, preferring small schooling fishes such as herring, squid, alewife, flounder, and hake. In the relatively deep waters of southern New England, redfish, cod, herring, and yellowtail flounder are also consumed. In the shallower waters adjacent to Cape Cod, and within the Sanctuary proposal area, harbor seals feed almost exclusively on sand eel (or sand lance).

Gray seals (Halichoerus grypus) are the most abundant pinniped species occurring in southern areas of eastern Canada, from Labrador south through the Bay of Fundy. Population estimates for the Canadian Maritimes were 40,000 to 50,000 animals and increasing in 1983. Gray seal colonies in the Gulf of Maine, however are much smaller (approximately 600 animals in 1983).

In the 1940's, the Massachusetts population of gray seals numbered about 70 animals; and by 1963, this population was reduced to 20 or fewer seals as the result of bounty kills. The remaining resident Massachusetts population is located southwest of Nantucket Island, and is the only active breeding population in the eastern United States. Pupping occurs in mid-winter; however, pupping rates have been low. The total gray seal population overwintering in Massachusetts numbered more than 100 animals in 1986, likely due to the immigration of seals from the expanding Canadian population.

Gray seals feed both on fish and invertebrates, as they are available. The Nantucket Island population most commonly feeds on skates, alewife, and sand eel, which are abundant from mid-winter to late spring.

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