Dead Seabirds Are Found on Beaches, Studied for Disease

By ROBERT A. CULBERT
Special to the Vineyard Gazette

A variety of seabirds have died and washed up on Vineyard beaches in
the past few months. Many different people have noticed the
above-average mortality rates, especially of common eiders. Scientists
from the Seabird Ecological Assessment Network (SEANET), which is part
of Tufts University's Cummings School of Veterinary Medicine, have
discovered that the mortality is most likely due to starvation because
of major parasite infestations, rather than avian flu or oil pollution.

In late February, people started noticing the dead birds washing up
at Squibnocket Point in Chilmark. On March 2 I found 12 dead sea ducks
on a four tenths of a mile stretch of beach at Squibnocket, which is
more than I can remember finding in more than 25 years of watching sea
ducks in the winter on Martha's Vineyard.

In the last two weeks of March, 17 volunteers surveyed a total of
24.1 miles of shoreline on 20 different beaches. We found 142 carcasses
of 10 species. Most of them (118) were common eiders - including
adult males, first winter males and females. Many other carcasses are
either on beaches that were not surveyed or did not wash ashore at all.
While this mortality is higher than normal, it may not be significant to
the eider population since hundreds of thousands of them spend the
winter near the Vineyard. Other species that we found dead included four
red-breasted mergansers, three great black-backed gulls, two each of
northern gannets and herring gulls, and one each of red-necked grebe,
great cormorant, surf scoter, American black duck and razorbill. Six
unidentifiable gulls and two unidentifiable scoters were also found.
Because only a few of each species were found, their winter mortality is
probably not unusual.

The highest densities of carcasses included 30 per mile at
Squibnocket Beach, 20 per mile at Stonewall Beach, 10 to 15 per mile
along the north shore and less than five carcasses per mile in Vineyard
Haven harbor and Chappaquiddick beaches. Beaches with no carcasses
included Joseph Sylvia State Beach, South Beach from the left fork to
the opening of Edgartown Great Pond, Long Point Wildlife Refuge and Lucy
Vincent Beach.

Mortality has also been reported from Cape Cod and Nantucket. We
observed a combined rate of 5.9 carcasses per mile on Martha's
Vineyard for the month of March. To put this rate of mortality into
perspective, SEANET documented 716 carcasses of 62 species on 2,731
miles of beaches from New Jersey to Maine between 2002 and 2005, for an
overall density of .3 carcasses per mile. Cape Cod beaches had 402 of
the 716 carcasses found, with the most abundant species being great
black-backed gulls (57), herring gulls (51), black ducks (31), and
common eiders (30). The highest density of carcasses reported on Cape
Cod was 33 carcasses per mile.

Rebecca Harris, the SEANET Coordinator at Tufts University, reports
that five common eider carcasses have been necropsied. All five were
emaciated and had major acanthocephalan (thorny-headed worm) parasite
infestations. The acanthocephala is a phylum of parasitic worms
characterized by spines on their heads, with the spines used to attach
themselves to the host's gut lining. There are more than 1,100
species of acanthocephalan parasites, but one genus (Polymorphus) is
known to parasitize seabirds, especially common eiders. Small crabs
(including Asian crabs and mole crabs) and periwinkles are the most
frequent hosts for the larvae cysts of these parasites. Eiders become
parasitized when they eat these alternate foods, which they will do when
their preferred blue mussels are not available. These parasites kill
their hosts when ingested in large quantities.

There are hundreds of thousands of common eiders wintering in the
coastal waters of the Cape and Islands. Most of these eiders are present
in large rafts (flocks) near large beds of blue mussels. An eider can
swallow a medium sized blue mussel whole, crush the shell in its
digestive tract, consume the meat, and excrete the ground up shell.
Major rafts of eiders near the Vineyard can be found off Squibnocket
Point, Aquinnah, the north shore and off Chappaquiddick's East
Beach, which corresponds to the observed distribution of eider
carcasses.

But this year Vineyard birders, including Matt Pelikan, Gus Ben
David, Susan Whiting, John Nelson, Allan Keith and myself, have also
observed common eiders in our coastal salt ponds, which is unusual for
these seaducks. These eiders are undoubtedly eating crabs rather than
mussels, and thus may be more likely to come into contact with the
acanthocephalan parasites. If these pond-feeding eiders were the only
ones dying from these parasites, the distribution of carcasses would be
different from what we observed.

Beachcombers are advised to leave the carcasses alone to allow the
natural processes of sunlight, scavengers and decomposition do their
work. Another alternative is to bury the carcasses either on the upper
beach or to the landward side of the dunes, without disturbing the beach
grass that stabilizes the beach. The burial hole should be at least two
feet deep to reduce the chance that dogs, skunks or raccoons dig up the
carcasses. Wear gloves, avoid touching the carcasses and use a shovel to
carry them from the beach to the burial hole

Although we know the approximate cause of death for these eiders, we
will not fully understand what ecological shifts have ultimately caused
this winter die-off until we have a better understanding of the ecology
of the common eiders, blue mussels and the distribution of the
acanthocephalan parasites. Are the large old beds of blue mussels
declining or shifting to new locations? Do blue mussels now host the
parasites? Are the crabs that host the parasites now colonizing the
large beds of blue mussels? Do the small crabs living in our coastal
ponds host the parasites? Or, perhaps the unusually high level of eider
mortality observed in March and April is an isolated event that will not
be repeated in future winters. We do not yet know.

Robert A. Culbert is an environmental consultant who lives in Oak
Bluffs.