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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