11
Horseshoe Crabs and Shorebirds
Mark Maguire and Matthias Ruth
It seems that species are only commas in a sentence, that each species
is at once the point and the base of a pyramid, that all life is related ...
And then not only the meaning but the feeling about species grows
misty. One merges into another, groups melt into ecological groups
until the time when what we know as life meets and enters what we
think of as non-life: barnacle and rock, rock and earth, earth and tree,
tree and rain and air. And the units nestle into the whole and are inseparable from it . . .
John Steinbeck, from Log from the Sea of Cortez
In this chapter, you will learn about horseshoe crab population dynamics and how these dynamics influence, and are influenced by:
• Shorebird population dynamics, and
• Different types of anthropogenic harvesting activities.
You will also see how a dynamic computer model can be used, in lieu
of sufficient empirical data , to generate consistent initial conditions for
scenario analysis.
11.1. Introduction
Horseshoe crabs are among the oldest creatures on the planet-their fossil
evidence dates from 250 million years ago . Within this span, thousands of
species of animals have become extinct, while horseshoe crab populations
have survived . However, currently horseshoe crab populations are threatened by anthropogenic activities. Adult crabs are caught to serve two main
international markets , the American eel and the conch fisheries. The eel
fishery exploits primarily female adult horseshoe crabs with eggs, while the
conch fishery harvests both male and female crabs (ASMFC 1998). Other
important uses for human needs include the extraction of horseshoe crab
blood for cancer research. While use as bait in fisheries means death for the
individuals that have been caught, only about 10 to 15 percent of them die
if they are caught for their blood and returned to the sea .
Since horseshoe crab eggs provide nutrition for sea- and shorebirds, a
decline in the crab population may influence bird population dynamics .
Declining bird populations, in turn, can affect local ecosystems through the
214
M. Ruth et al. (Eds.), Dynamic Modeling for Marine Conservation
© Springer-Verlag New York, Inc. 2002
Horseshoe Crabs and Shorebirds
Mark Maguire and Matthias Ruth
It seems that species are only commas in a sentence, that each species
is at once the point and the base of a pyramid, that all life is related ...
And then not only the meaning but the feeling about species grows
misty. One merges into another, groups melt into ecological groups
until the time when what we know as life meets and enters what we
think of as non-life: barnacle and rock, rock and earth, earth and tree,
tree and rain and air. And the units nestle into the whole and are inseparable from it . . .
John Steinbeck, from Log from the Sea of Cortez
In this chapter, you will learn about horseshoe crab population dynamics and how these dynamics influence, and are influenced by:
• Shorebird population dynamics, and
• Different types of anthropogenic harvesting activities.
You will also see how a dynamic computer model can be used, in lieu
of sufficient empirical data , to generate consistent initial conditions for
scenario analysis.
11.1. Introduction
Horseshoe crabs are among the oldest creatures on the planet-their fossil
evidence dates from 250 million years ago . Within this span, thousands of
species of animals have become extinct, while horseshoe crab populations
have survived . However, currently horseshoe crab populations are threatened by anthropogenic activities. Adult crabs are caught to serve two main
international markets , the American eel and the conch fisheries. The eel
fishery exploits primarily female adult horseshoe crabs with eggs, while the
conch fishery harvests both male and female crabs (ASMFC 1998). Other
important uses for human needs include the extraction of horseshoe crab
blood for cancer research. While use as bait in fisheries means death for the
individuals that have been caught, only about 10 to 15 percent of them die
if they are caught for their blood and returned to the sea .
Since horseshoe crab eggs provide nutrition for sea- and shorebirds, a
decline in the crab population may influence bird population dynamics .
Declining bird populations, in turn, can affect local ecosystems through the
214
M. Ruth et al. (Eds.), Dynamic Modeling for Marine Conservation
© Springer-Verlag New York, Inc. 2002