When it comes to sexual experimentation, horseshoe crabs put humans to shame. Volunteers counting horseshoe crabs on Tashmoo beach beneath the full moon of May 14 had tallying categories such as “lone crab,” “mating couple,” “two males one female,” and “confused males,” including a tally with the side-note: “One romantically involved with Doyle’s boots.”
The volunteers, Jill Macy of Vineyard Haven and Ellen and Doyle Bunch of West Tisbury, were out that night on behalf of Felix Neck Wildlife Sanctuary and the Massachusetts Division of Marine Fisheries (DMF) as part of Martha’s Vineyard’s participation in a statewide effort to measure the health and abundance of the horseshoe crab fishery. This is the sixth year the Vineyard has participated. The surveys began during the full and new moons of May and June in 2009 following anecdotal accounts of fewer horseshoe crabs, which are harvested by fishermen for bait and by the international biomedical industry. Horseshoe crab blood contains an enzyme used to test for dangerous bacteria in injections. Decreasing populations have not yet been confirmed by the DMF and the results of the studies won’t provide conclusive evidence for a few more years. However, since the surveys began, the DMF has regulated horseshoe crab harvest during their spawning period in an effort to increase populations.
“We’re using a protocol from the DMF, which was just updated, to get a sense statewide of the health of the horseshoe crab fishery,” said Felix Neck teacher and naturalist Susan Bowman, who directed volunteers during the first five surveys and now focuses on education. “DMF scientists devised this way of measuring crabs coming in to mate and nest, which was updated last year. The surveys go faster than they used to when we divided the beach into squares, because now we just flip a coin to decide which end of the beach to start at and go one way, counting all the crabs within 5 meters of the shore. This is basically standard scientific protocol to reduce variables and bias in the study.”
Ms. Bowman taught three two-hour training sessions this year, including one with Oak Bluffs middle school students. The training involves a slideshow orientation, an anatomical review of horseshoe crabs, and a quick review of the demand in medical industries and for bait.
Due to the particular physiology of horseshoe crabs, they’ve become a favorite of medical researchers. “Because a test using horseshoe crab blood takes only 15 to 20 minutes in a test tube, and it’s much more sensitive than other measurements,” said Ms. Bowman, “the FDA has mandated it as a replacement for rabbit tests. They used to test injections by administering them to rabbits and seeing if they got sick, which took weeks, but now it’s very quick and horseshoe crab has become in demand in other countries.”
Ms. Bowman appreciates the medical application, but she worries about the vitality of the horseshoe crab fishery. “Fishermen love to use horseshoe crabs to bait conch and eel in their traps as well,” she said “Anecdotally, we’ve heard from people walking on the beach that there are less and less horseshoe crabs every year, and we’ve seen that since we started our studies. Also, because it takes 10 years for a female to reach reproductive maturity, any regulations will take years before they impact the population.”
Nonetheless, the situation has improved. “The first few years we did the survey the fishermen would be out there too,” she said. “We would go down the beach counting crabs, and the fishermen would come right after us and pick them up. Now the DMF doesn’t allow harvesting during mating days, because harvesting them while they were spawning makes no sense.”
As a result, Ms. Macy and Ms. and Mr. Bunch were the only people in Tashmoo waters a few meters from the public beach during the full moon last week.
“It’s like a soap opera,” said Ms. Macy, aiming her flashlight at two males fighting over a female a couple meters from shore. “Who knew they bumped each other off like that?”
Horseshoe crab genders are determined by size and shell. “If there is a couple, you can tell which one is the female because she’s the big one,” said Mr. Brunch. “If it’s alone, you pick it up and look at the shell and the legs. The males have these grips on their legs for the indents on the back of the female’s shell, the love handles.”
“Love handles is the scientific term,” Ms. Brunch joked.
A lone male crawled toward Mr. Brunch’s feet.
“Sorry, Doyle’s boot is not a female,” said Ms. Brunch. “Should I write that in my notes?”
Mr. Brunch laughed. “One particular not so particular male,” he said.
The three humans covered several hundred yards of beach and tallied 10 mating couples, three sets of two males and one female, 10 lone males, three lone females, three couples digging into the sand to nest, one female laying eggs alone, and “two confused males, one romantically involved with Doyle’s boots.”
All three volunteers plan to participate again during the second survey later this month or one of the two in June. “This was a great introduction for doing this again at the end of the month,” said Ms. Bunch. “And I know they’re always looking for more volunteers.”
The second set of surveys will take place around the new moon on May 26 at 7:24 pm, May 28 at 8:50 pm, and May 30 at 10:15 pm.
The third set of surveys will take place around the full moon on June 11 at 7:42 pm, June 13 at 9:10 pm, and June 15 at 10:55 pm.
The fourth set of surveys will take place around the new moon on June 25 at 7:14 pm, June 27 at 9:10 pm, and June 29 at 10:16 pm.
All surveys take place on the public beach on Tashmoo in Vineyard Haven. Times may vary according to the high tide and are subject to change, so volunteers are asked to arrive 30 minutes before the scheduled time at the Tashmoo parking lot at the end of Herring Creek Road. More information on volunteering and directions to the beach can be found by calling Felix Neck Wildlife Sanctuary at 508-627-4850.