Maine Volunteer Monitoring Horseshoe Crab
Spawning Surveys
Horseshoe crabs (Limulus polyphemus) are among the
world's oldest organisms, estimated to be at least 300 million years
old. Horseshoe crabs have been used by people for centuries for
food, fertilizer, and feed for domestic animals. Today, horseshoe
crabs are harvested commercially for use in biomedical research and as
bait. These organisms are also ecologically signnificant to
shorebirds and fish which prey on their eggs.
Horseshoe crab spawning surveys were
initiated in Maine in 2001 in response to anecdotal reports that
populations were declining. This project involves collaboration
among the Maine Department of Marine Resources, Bar Mills Ecological,
Maine Coastal Program, and many other organizations to establish
quantitative baseline population data to determine whether horseshoe
crab populations are stable or declining. Approxinately 50-70
volunteers collect data annually at sites ranging from Casco Bay to
Frenchman's Bay. Volunteers measure water temperature and survey
the number, clustering and location of horseshoe crabs along a transect
during predicted dates of peak spawning activity typically associated
with the new moon and full moon lunar phases of late May and June.
Data reveal that horseshoe crabs in Maine
appear to exist in isolated populations. Although spawning sites
in Casco Bay are scarce given the available habitat suitable for
spawning, two of the most important horseshoe crab spawning sites
statewide are located at Middle Bay and Thomas Point Beach in the
bay. CBEP provided project funding to expand monitoring in Casco
Bay and to develop a volunteer handbook.
