11.2. Horseshoe Crab and Shorebird Ecology
215
disturbance of predator-prey regimes, and affect local economies as a consequence of disrupted ecosystems and reduced abundance of birds for bird
watching. These secondary and tertiary effects of declining horseshoe crab
populations are difficult to quantify . Yet, they may be relevant if we wish to
better understand the extent of anthropogenic effects on horseshoe crab
populations.
Population surveys have shown a general decline in horseshoe crab populations since the late 1980s, most notably on the North American Atlantic
coastline . While the issue is receiving much attention in the media, census
counts and population studies of horseshoe crabs are few in number.
The main goals of this chapter are to investigate the potential effects of
alternative rates of horseshoe crab exploitation-with specific attention to
the differential impacts of harvests for the eel versus conch fishery-and
the development of a model that can begin to address potential ripple effects that crab harvests may have for seabird populations. Since little data is
available on crab population dynamics, and even less on interrelations between horseshoe crab and seabird population dynamics, the model also
serves the purpose of guiding future data collection . Despite these caveats
as to the empirical validity of the model, some valuable conclusions crystallize from the model which have implications for anthropogenic exploitation of horseshoe crabs .
11.2. Horseshoe Crab and Shorebird Ecology
11.2.1. Horseshoe Crabs
The model focuses on horseshoe crab and seabird populations in the
Delaware Bay, a part of the US mid-Atlantic coast, during the peak spawning and migration period, and documents the effects on both populations
due to commercial exploitation. The region consists of approximately 160
kilometers of beaches along both the New Jersey and Delaware shorelines.
With its protected beaches and suitable temperatures, the bay is home to
one of the world's largest spawning areas for horseshoe crabs . In the
Delaware Bay, peak spawning activity usually occurs during May and June
during peak high tides (ASFMC 1998). About 90% of the total population of
the crab species Limulus polyphemus lives along the mid-Atlantic coastline,
with the largest concentration in Delaware Bay (Virtualbirder 2000). The
Delaware Division of Fish and Wildlife reports an increase in horseshoe
crab landings of 1,500,000 pounds, approximately 43,000 crabs, from 1990
to 1997 (ASMFC 1998). Management programs exist to protect horseshoe
crab populations from overexploitation, though recent evidence shows
their success to be questionable.
Limulus polyphemus is the most common species of horseshoe crab in
North America. Each year for a number of weeks, adult crabs emerge from
215
disturbance of predator-prey regimes, and affect local economies as a consequence of disrupted ecosystems and reduced abundance of birds for bird
watching. These secondary and tertiary effects of declining horseshoe crab
populations are difficult to quantify . Yet, they may be relevant if we wish to
better understand the extent of anthropogenic effects on horseshoe crab
populations.
Population surveys have shown a general decline in horseshoe crab populations since the late 1980s, most notably on the North American Atlantic
coastline . While the issue is receiving much attention in the media, census
counts and population studies of horseshoe crabs are few in number.
The main goals of this chapter are to investigate the potential effects of
alternative rates of horseshoe crab exploitation-with specific attention to
the differential impacts of harvests for the eel versus conch fishery-and
the development of a model that can begin to address potential ripple effects that crab harvests may have for seabird populations. Since little data is
available on crab population dynamics, and even less on interrelations between horseshoe crab and seabird population dynamics, the model also
serves the purpose of guiding future data collection . Despite these caveats
as to the empirical validity of the model, some valuable conclusions crystallize from the model which have implications for anthropogenic exploitation of horseshoe crabs .
11.2. Horseshoe Crab and Shorebird Ecology
11.2.1. Horseshoe Crabs
The model focuses on horseshoe crab and seabird populations in the
Delaware Bay, a part of the US mid-Atlantic coast, during the peak spawning and migration period, and documents the effects on both populations
due to commercial exploitation. The region consists of approximately 160
kilometers of beaches along both the New Jersey and Delaware shorelines.
With its protected beaches and suitable temperatures, the bay is home to
one of the world's largest spawning areas for horseshoe crabs . In the
Delaware Bay, peak spawning activity usually occurs during May and June
during peak high tides (ASFMC 1998). About 90% of the total population of
the crab species Limulus polyphemus lives along the mid-Atlantic coastline,
with the largest concentration in Delaware Bay (Virtualbirder 2000). The
Delaware Division of Fish and Wildlife reports an increase in horseshoe
crab landings of 1,500,000 pounds, approximately 43,000 crabs, from 1990
to 1997 (ASMFC 1998). Management programs exist to protect horseshoe
crab populations from overexploitation, though recent evidence shows
their success to be questionable.
Limulus polyphemus is the most common species of horseshoe crab in
North America. Each year for a number of weeks, adult crabs emerge from