ARTICLE BY DAVID S. MIZRAHI, PH.D.
VICE-PRESIDENT FOR RESEARCH AND MONITORING
NEW JERSEY AUDUBON SOCIETY
Conserving wildlife is difficult work,
especially when securing federal protection. It's even harder
when the species have commercial value or interrupt commercial
enterprise. The suspension of horseshoe crab harvesting in
Delaware Bay to protect the Red Knot is an example from our own
backyard.
Although attaining legal protection for
species requires the efforts of many dedicated people, the
burden to demonstrate need for regulatory protection falls on
biologists. It means years of painstaking research and
documentation and even then, protection is not guaranteed. Such
is the case in the Delaware Bay.
The first hints that Delaware Bay was a
critical stopover area for migrating shorebirds came in the late
1970s. Pete Myers, then with the Philadelphia Academy of
Science, and Brian Harrington and Linda Leddy of Manomet
Observatory were among the first to study shorebird migration
ecology in the Bay. Their work led to our early understanding of
relationships between shorebirds and horseshoe crabs.
Harrington, now a world authority on the
Red Knot, helped introduce the idea that a handful of stopover
sites, like Delaware Bay, were linchpins along migration routes.
Geography and food resources make them critical stops between
wintering areas in South America and breeding grounds in the
Arctic.
In 1981- 1982, Pete Dunne and colleagues
flew aerial surveys to quantify the number and species of
shorebirds in Delaware Bay during spring migration. They
revealed that as many as 425,000 individuals were staging in the
Bay and that Red Knot (95,000), Semipalmated Sandpiper
(175,000), Ruddy Turnstone (80,000) and Sanderling (30,000) were
the predominant species. These data suggested that Delaware Bay
hosted approximately 70 to 80 percent of the Western
Hemisphere's Red Knot and Ruddy urnstone populations and half of
the world's Semipalmated Sandpipers. By 1986, New Jersey's
Division of Fish and Wildlife (NJDFW), led by Principal
Zoologist Kathy Clark, instituted annual spring aerial surveys.
Guy Morrison and Ken Ross, biologists
with the Canadian Wildlife Service, flew surveys in South
America to catalog the number and distribution of shorebirds
during the non-breeding season. Their data suggested that
between 80,000 and 100,000 Red Knots wintered in South America,
most found in the southernmost parts of the Atlantic Coast. They
also documented more than 2 million Semipalmated Sandpipers
wintering along the northern coast.
During these years, horseshoe crab
harvesting was nearly nonexistent except by a handful of eel
fishermen. Shorebird populations appeared healthy and numbers
were stable. Fast forward to the mid 1990s. I conducted research
for my Ph.D. on the migration ecology and physiology of
Semipalmated and Least Sandpipers in Delaware Bay. Larry Niles,
then Bureau Chief of NJDFW Endangered and Nongame Species
Program (ENSP), instituted a monitoring program for Red Knot,
Ruddy Turnstone and Sanderling with the help of international
shorebird biologists. A similar effort was mounted in Delaware.
These work documented seasonal patterns of weight gain in
shorebirds during their stopover in Delaware Bay Here,
shorebirds appeared to accumulate sufficient energy reserves to
successfully complete their migration to the Arctic. In years to
come these baseline data would prove critical in demonstrating
that horseshoe crab harvesting, and a reduction in horseshoe
crab eggs for consumption, reduced shorebird weight gain
potential.
The two-state monitoring programs marked
birds with unique combinations of colored leg bands then
resighted them during subsequent days and years. These data,
coupled with the Delaware Bay aerial shorebird survey data
helped determine how long birds were in the Bay during migration
stopover periods and their annual survival rates.
Horseshoe crab harvesting increased
meteorically. By 1998 nearly 3 million animals per year were
harvested, more than half from the Delaware Bay population. Most
harvesting was done to supply bait to a rapidly growing whelk
(conch) fishery. In 1996, then New Jersey Governor Christie
Whitman imposed a one season moratorium on horseshoe crab
harvesting. Data collected during the next few years verified
major changes in the viability of Delaware Bay as a
hemispherically important shorebird stopover site.
By 2000, I was working for New Jersey
Audubon Society. My first project was to reconstitute the
shorebird work I started five years before and it became
immediately apparent that things were amiss. In five years
weight gain rates in Semipalmated Sandpipers were down 50
percent.
My state and international colleagues
continued documenting the annual peregrinations of Delaware
Bay's shorebirds where a similar pattern emerged. Shorebirds
stopping in Delaware Bay were not gaining as much weight or
gaining weight as fast as they had. With no major stopover site
north of Delaware Bay, birds were at risk of lacking the fuel to
complete their migration. If they did reach the breeding
grounds, they might not survive until snow and ice melt
uncovered foraging habitats.
Harvest quotas imposed by the Atlantic
State Marine Fisheries Council reduced annual landings of
Delaware Bay horseshoe crabs by 25 percent. Harvest quotas were
a direct result of evidence provided by shorebird biologists.
However, the preferential taking of female crabs and the effects
of high harvest levels translated into drastically reduced crab
egg availability.
Shorebird weight gain remained well
below mid-1990s levels for the next six years, but evidence of
an adverse effect on shorebird population health was not
immediate. Aerial survey data for Delaware Bay suggested a
relatively stable population through the late 1990s and early
2000s. Aerial surveys of the South American regions were
conducted for three seasons starting in 2000 and suggested
stable Red Knot numbers as well.
The proverbial bottom dropped out in
2003. The maximum count for Red Knot in Delaware Bay based on
the aerial survey plummeted to just over 16,000, or 60 percent
fewer birds than the 17-year average. Declines in Ruddy
Turnstone (50%), Semipalmated Sandpiper (60%) and Sanderling
(35%) counts dropped as well. The South American survey
similarly found Red Knot numbers down from 67,000 in 1986 to
30,000 in 2003.
Horseshoe crab egg surveys indicated
that egg availability was crashing. Using a sophisticated
chemical approach, stable isotope analysis, Michael Harramis, a
biologist with the U.S. Geological Service, demonstrated that
horseshoe crab eggs caused the majority of weight gain. Without
crab eggs, shorebirds were unlikely to attain the fuel reserves
necessary for successful completion of migration to the Arctic.
A paper published in the Proceedings of
the Royal Society of London in 2003 authored by Allan Baker of
the University of Toronto and a team of contributors indicated
that a persistent lack of crab eggs over several years would
have a catastrophic effect on the Red Knot possibly resulting in
extinction.
With these alarming data,
conservationists pressed for listing Red Knot as a federally
threatened species and a full moratorium on crab harvesting in
Delaware Bay. Opposition, was strong, but we can claim some
significant victories. After a two-year horseshoe crab harvest
moratorium in NJ lapsed, Governor Corzine has signed legislation
extending the moratorium until shorebird recovery targets are
met. Significant harvest quota reduction efforts have occurred
in Virginia, and we remain hopeful that Delaware and Maryland
will follow the leadership of the other two states.
Unfortunately, little change in the
plight of Delaware Bay shorebirds has occurred. Through 2008,
weight gain rates remained low. Shorebird numbers in Delaware
Bay are well below average for all four primary species as are
Red Knot numbers in Argentina and Chile. New evidence suggests
that numbers of Red Knot wintering in Florida and the northern
coast of Brazil, are also declining. Time will tell if new
regulations will have a positive effect on Delaware Bay
shorebirds.