Seabirds
Introduction
Descriptions of the Species
Loons
Albatrosses
Fulmars
Shearwaters
Storm Petrels
Gannets and Cormorants
Phalaropes
Alcids
Gulls, Jaegers and Skuas
Terns
Introduction
Seabirds
spend between 50 to 90 percent of their lives at sea, usually only returning
to land to breed. Their migrations follow the seasonal abundance of
their prey. Prey are most abundant in upwelling areas and at coastal
fronts due to an influx of nutrients and zooplankton to the surface
(Bachus and Bourne, 1987; Powers 1982). Therefore, the distribution
and abundance of seabirds at Stellwagen Bank are associated with the
availability of prey. There are over 40 species of seabirds that can
be found at Stellwagen Bank throughout the year, but they are frequently
specialized in their feeding behavior. There is consequently a small
amount of overlap in preferred prey species (e. g. fish, fish larvae,
cephalopods, crustaceans, and offal) (U.S. DOC 1993d). The high biological
productivity along with the presence of fishing vessels leads to a predictable
and large variety of coastal and pelagic seabird species.
Throughout
the year, 10 groups of seabirds account for over 95% of Stellwagen Bank's
seabirds (Table 10). By monitoring the variation in the numbers of birds
at Stellwagen Bank, useful information about the biological changes
in the ecosystem could be gathered. In addition to these species groups,
several species of scoters occur in the Stellwagen Bank area, as well
as eiders, mergansers, and oldsquaws (Payne and Seltzer, 1986). These
species include:
Melanitta
deelandi. White-winged scoter (sea duck)
M. negri, Black scoter (or sea duck)
M. perspicillata Surf scoter (or sea duck)
Somateria mollisima, Red-Breasted merganser
Clangula hyemalis, Oldsquaw
Additional
occasionally-seen migratory species include the Sharp shinned hawk (Accipiter
striatus), Osprey (Pandion haliaetus), Peregrine falcon (Falco
peregrinus), and Atlantic brant (Branta bernicla hrota).
With
a single exception, Leach's storm petrel, (Oceanodroma leucorhoa),
all seabirds occurring around the Stellwagen Bank area are either migrants
or non-breeding residents. In general, spring months are the time of
greatest seabird abundance on the Bank. (Powers and Brown, 1987).
It is
possible that some limited hunting for sea duck species (such a oldsquaws,
mergansers, scoters, and eiders) may occur within the area of the Sanctuary,
pursuant to licenses issued under the Migratory Bird Treaty Act (MBTA).
However, as most sea duck hunting occurs in sheltered bays or inlets
adjacent to land, hunting near the open ocean Stellwagen Bank is likely
to occur only on an infrequent basis, if at all.
U.S.
Fish and Wildlife Service analysis of National Marine Fisheries Service
sea sampling data (1989 - 1990) also indicates that incidental take
of sea bird species generally resulting from commercial or recreational
fishing activities does not happen frequently, or pose an exploitation
threat to any species.
Table
10: Species/Species Groups of Marine Birds Occurring in the Southwestern
Gulf of Maine.
Descriptions
of the Species
The following
is a listing and brief description of the primary seabird
species found in the vicinity of Stellwagen Bank:
Loons
The Common
loon (Gavis immer), and the Red-throated loon (Gavis stellata)
breed in northeastern North America and migrate along the Atlantic seaboard.
While Red-throated loons are primarily found in nearshore waters and
the western margin of the Gulf of Maine, Common loons additionally cross
over Georges Bank during May and November. Loons are pursuit divers,
feeding as tertiary carnivores, primarily on fishes, and as secondary
carnivores on crustaceans, mollusks, and aquatic insects (Palmer, 1962).
Loons have been recorded frequently offshore during spring and fall
migrations.
Albatrosses
Two species
of albatrosses, the Yellow-nosed (Diomedea chlororhynchos) and
the Black-browed (D. melanophris), are considered rare visitors
to western North Atlantic waters; at least one yellow-nosed albatross
was reported on Georges Bank in 1976 (Powers and Brown, 1987).
Fulmars
The Northern
fulmar (Fulmarus glacialis). The pelagic distribution of northern
fulmars encompasses the North Atlantic; in the Western North Atlantic,
fulmars extend as far south as the Mid-Atlantic Bight. As "opportunistic"
secondary and tertiary carnivores, fulmars consume a large variety of
zooplankton, fish, squid, crustaceans, and offal from fishing vessels.
They are found off the New England coast throughout the year, with the
exception of August, when they move northward. Peak abundance over the
Stellwagen Bank/Georges Bank area is usually from approximately January
to April, when flocks of several thousands have been recorded (Powers,
1983).
Shearwaters
Four species
of shearwaters occur with regularity over the Stellwagen Bank/Georges
Bank area: Cory's shearwater (Calonectris diomedea); Greater
shearwater (Puffinus gravis); Sooty shearwater (P. griseus);
and Manx shearwater (P. puffinus). A fifth species, Audubon's
shearwater (Puffinus Iherminieri), normally is found on southern
edges of Georges Bank during the summer.
Cory's
shearwaters are abundant in New England waters generally from July until
October; and in some years significant numbers of this species have
moved into the Gulf of Maine and stayed until the autumn (Powers and
Brown, 1983). The largest local concentrations have occasionally been
recorded at 30-100 birds/km2 (Powers, 1983). The species feeds at or
near the surface as secondary and tertiary carnivores on fish, fish
larvae, cephalopods, and crustaceans.
The Greater
shearwater is highly abundant over Georges Bank, beginning in May and
peaking in June and July, when densities may reach 25 birds/km2. The
species is most numerous over Stellwagen Bank during summer and autumn
months. Like the Cory's, the Greater shearwater feeds as a tertiary
carnivore on fish and cephalopods; as a secondary carnivore on crustaceans;
and as a scavenger on offal from fishing vessels.
Between
May and September, Sooty shearwaters migrate in a clockwise manner around
the North Atlantic basin; they are abundant on Georges Bank from late
May to mid-July, and are found over Stellwagen Bank during the summer
months. Typically, the species feeds at or near the surface as a secondary
or tertiary carnivore on fish, cephalopods, and crustaceans; however,
this species does not appear as frequently in association with fishing
vessels as other shearwaters (Wahl and Heinemann, 1979).
Manx
shearwaters occur over Georges Bank from June to October (Powers and
Brown,1983); and are occasionally seen over Stellwagen Bank during summer
months. Like other shearwaters, the Manx is a secondary and a tertiary
carnivore, feeding on small fish, cephalopods, crustaceans, and probably
offal.
Storm
Petrels
Of the
two species of storm petrels occurring in and around the Stellwagen
Bank area, Wilson's (Oceanites oceanicus) and Leach's (Oceanodroma
leucorhoa), the Wilson's is by far the more commonly seen.
Wilson's
storm petrels arrive in the Gulf of Maine by late May, and reside through
the summer months; this residency largely coincides with the seasonal
peak in zooplankton. The species is primarily a surface-feeder on zooplankton,
euphausiids, and amphipods, and (to a lesser degree) as a tertiary carnivore
on small fish and cephalopods. Also known as Mother Carey's chick (Powers
and Brown, 1983), the Wilson's storm petrel is the second most abundant
seabird species during the summer over the Georges Bank/Stellwagen Bank
area.
Leach's
storm petrel are also found in this region between April and November,
although they are more abundant on the Southern Scotian Shelf, to the
north. This is the only seabird species which utilizes northern areas
as breeding habitat, in particular, the Bay of Fundy region (Powers
and Brown, 1983).
Gannets
and Cormorants
The Northern
gannet (Sula bassanus) are tertiary carnivores feeding almost
exclusively on fish and squid, although the species is known to scavenge
offal from fishing vessels and may who take fish directly from fishing
nets near the surface (Powers, 1983). Gannets are most numerous in the
Gulf of Maine, and in particular over Stellwagen Bank and through the
Great South Channel. During winter-spring, large concentrations of gannets
have been observed feeding in association with cetaceans (Payne and
Seltzer, 1986).
Two species
of cormorants occur very occasionally over Stellwagen Bank; they are
more typically coastal inhabitants. The Great cormorant (Phalacrocorax
carbo) and the Double-crested cormorant (Phalacrocorax auritus)
exhibit migratory movements in the spring and autumn in the western
Gulf of Maine, and feed primarily on fish.
Phalaropes
Of the
two species known to occur occasionally in the vicinity of Georges Bank/Stellwagen
Bank, the Red phalarope (Phalaropus fulicaria) is more frequently
observed than the Red-necked, or Northern, phalarope (Phalaropus
lobatus). Both species are most common during April to June and
again during August to October, during migratory passages. The spring
migration northward occurs largely along the outer edge of the shelf
(60 to 200 meters, or 196.8 to 656 feet); although some of both species
have been known to follow the coast into the western Gulf of Maine on
their northward migration (Powers, 1983). Both species feed at the surface
as secondary carnivores on planktonic crustaceans, fish and squid eggs,
and larvae.
Alcids
At least
five, and possibly six species of alcids occur in the Gulf of Maine/Stellwagen
Bank vicinity. Razorbills (Alca torda) are pursuit-diving birds,
feeding as secondary and tertiary carnivores on crustaceans and fish.
The species is present in the area from late November to May, most commonly
in shoal areas around Cape Cod, over the Great South Channel, and along
northern parts of Georges Bank. The Georges Bank area appears to be
an important wintering area for this species (Powers and Brown 1983).
Two species
of murres, the Thin-billed, or Common (Uria aalge) and the Thick-billed,
or Brunnich's (Uria lomvia), are occasionally seen during the
winter in the southern Gulf of Maine, including areas around Stellwagen
Bank. By March, these species are more common on northeast Georges Bank
and over the Northeast Channel to the north. Murres and razorbills are
all large auks, with similar feeding habits. Murres are pursuit divers,
feeding as secondary and tertiary carnivores on crustaceans, fish and
cephalopods.
Dovekies
(Alle) are generally observed from December to May in the Gulf
of Maine, and also south across the Nantucket Shoals. The species feeds
as a secondary carnivore on crustaceans, and may also eat zoop1ankton.
Black
guillemot (Depphus grylle) are also a pursuit-diving birds, feeding
as secondary and tertiary carnivores on benthic crustaceans and mollusks,
and fish. The Black guillemot is primarily a coastal inhabitant, but
is occasionally seen over Stellwagen Bank.
The Atlantic,
or Common, puffin (Fratercula arctica) is found between November
and early June over Georges Bank; little is known about its distribution.
Like other alcids, puffins are pursuit divers, feeding almost exclusively
on fish as tertiary carnivores.
Gulls,
Jaegers, and Skuas
Eight
species of gulls occur with regularity in the southwestern Gulf of Maine,
and over Stellwagen Bank. Among these, the Herring gull (Larus argentatus)
and the Great black-backed gull (Larus marinus) occur in greatest
numbers over Stellwagen Bank. Both species are omnivorous, feeding as
secondary, tertiary, and upper level carnivores on crustaceans, insects,
fish, squids, birds and eggs, and as scavengers on offal and carrion.
Large numbers of both species are closely associated with fishing vessel
activities throughout the year.
Glaucous
gulls (Larus hyperboreus) and Iceland gulls (Larus glauacoides
glaucoids) also feed as secondary, tertiary, and upper level carnivores
on macrozooplankton, fish, and offal, as well as on the eggs and young
of other seabirds. Both species are seen in the Gulf of Maine region
from the autumn through the spring, commonly in association with Herring
and Great black-backed gulls following fishing vessels.
Laughing
gulls (Larus atricilla) are usually seen during summer months
in the Gulf of Maine, surface feeding on small fish and scavenging on
offal. This species is also known to take the eggs of terns on land.
Ring-billed
gulls (Larus delawarensis), Bonaparte's gulls (Larus philadelphis),
and Sabine's gulls (Xema sabini) all appear in offshore areas
throughout the Gulf of Maine during migratory periods only.
Like
the gulls, the Black-legged kittiwakes (Rissa tridactyla) feed
as secondary and tertiary carnivores on crustaceans, fish and squid,
in addition to offal. The species is extremely abundant during November
to March, particularly in the area from Jeffreys Ledge south and east
across the northern portion of Georges Bank. In winter months, the density
of kittiwakes over Stellwagen Bank and Jeffreys Ledge is probably higher
than for any other species of seabird.
Three
species of jaegers occur in the western North Atlantic, although only
two are regularly observed in the southwestern Gulf of Maine, over Stellwagen
Bank: the Parasitic jaeger (Stercorarius parasiticus) and the
Pomarine jaeger (Stercorarius pomarinus). The Long-tailed jaeger
(Stercorarius longicaudus) is only seen very occasionally in
the Gulf. Jaegers are migrants across Georges Bank, principally in spring
and fall months. Jaegers feed at the surface, seizing prey or snatching
from other birds, such as gulls and terns. The species are secondary
and tertiary carnivores feeding on crustaceans, fish and cephalopods,
as well as offal.
Two species
of skuas appear over Georges Bank and the surrounding areas, the Great
skua (Catharacta skua) and the South polar skua (Catharacta maccormickii).
The great skua is most
common from October to March, although individual sightings have been
made every month (Powers and Brown, 1983). The south polar skua, only
recently recognized in the overall western North Atlantic, has been
generally observed from May to October over Georges Bank. Like the jaegers,
skuas feed primarily on fish, cephalopods, and offal.
Terns
All nine
species of terns identified as occurring around the Stellwagen Bank
region feed exclusively on small fish. Of the group, it is known that
Common terns (Sterna hirundo), Arctic terns (Sterna paradisaea),
Roseate terns (Sterna dougallii), and Least terns (Sterna
albifrons) breed along Atlantic coastlines at various points, depending
on the individual species, between Nova Scotia and Florida (and, in
the case of the Least tern, also along the Gulf coast). Terns are typically
seen around the Bank during summer and autumn months. The roseate tern
is Federally-listed as an endangered species.
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