Today, during an early morning walk along Morse Beach, near Sandy Point Bird Sanctuary in West Haven, I noticed many dead horseshoe crab on the sand. One of them had a tag, referring to #2859 and a phone number to report the find.Photograph taken with an iPhone. © KIKE CALVO
Back to the office, I learnt that the Maryland Fishery Resources Office has been coordinating a coast-wide tagging program for horseshoe crabs since 1999. Crabs have been tagged by researchers and biomedical companies conducting numerous studies on horseshoe crabs along the Atlantic Coast. “We really appreciate the support from the public in reporting tag returns,¨ explains Sheila Eyler from the U.S. Fish & Wildlife Service, Maryland Fishery Resources Office. ¨Of the 35,000 tag reports we have received since the program started in 1999, the public is responsible for 20,000 of those reports compared to 15,000 that come from researchers working specifically with horseshoe crabs”. That data has been very critical in understanding horseshoe crab movement, longevity, and other biological information on crab populations.
Horseshoe crabs ( Limulus Polyphemus ), are more closely related to spiders and scorpions, even though they are called crabs. They are believed to have evolved during the Paleozoic Era (540-248 million years ago). Their eggs provide an essential food source for migrating shorebirds. During the high tides of the full moon in spring, females emerge to begin a journey to take part in an amazing spawning ritual.
I have just filled my form at http://www.fws.gov/crabtag/, and will learn more about the individual I found dead, when my certificates arrives on the mail. The program provides data on distribution, movement, longevity, and mortality of the species. “It is important to report dead animals to know about longevity¨, describes Eyler. ¨It can also provide information on movements and migration because dead crabs are typically not transported very far.”
Since live crabs are only on the beach for a relatively short period of time while they are spawning, the amount of time available for the public to see their tags is pretty small. Dead crabs stay on the beach for long periods of time, so even though we get a fair number of reports of dead crabs – those crabs are much more likely to be encountered by the public than live crabs so we adjust for that in our analysis of the tagging data.
Then an emailed arrived with information on my reported dead animal, tagged with #2859. It was originally released on 5/11/12 on Short Beach in Branford, CT by Sacred Heart University.
One last thing, Eyler asks me to remind people that horseshoe crabs are completely harmless. Their claws are not strong enough to pinch very hard, they do not have jaws or teeth, so they can not bite (their mouth is in the center of their legs and they move their legs together to “chew” their food. Their tail is not poisonous and is not used as a weapon, they use it to help flip themselves back over when they get turned upside down on the beach and also use it as a “rudder” when walking in the water.
This random find on the beach has made me learn an amazing fact about horseshoe crabs: They are collected for their blood and then released alive by biomedical companies. Their blood is processed to get a substance called Limulus Amebocyte Lysate (LAL). This LAL is used to test medical equipment and injectable drugs (i.e. vaccines) for bacterial contamination. There is not a synthetic substitute for this test. So much of current human health can be related to our dependence on horseshoe crabs.