Keeping an eye on the kids. New Jersey researchers hatch a plan to raise baby horseshoe crabs and then track them in the wild.
Rutgers University marine biologist Thomas Grothues, who goes by Motz, is an academic scientist who spends his working hours studying the migratory patterns of fish. He also studies horseshoe crabs, which aren’t fish but do inhabit the coastal waters along the Jersey Shore where he is based.
For years, New Jersey fishermen harvested horseshoe crabs and used them for whelk bait. Alarmed by the diminishing numbers of crabs, in 2008 the state declared a moratorium on harvesting horseshoe crabs or their eggs for any reason. Motz and his team at the Rutgers New Jersey Aquaculture Innovation Center in Cape May are now studying a way to rebuild the population.
During spawning, a typical female horseshoe crab will lay about 20 discrete egg clusters of about 4,000 eggs each. As part of their horseshoe crab conservation project, Motz’s team has been hatching and growing larvae in aquaculture with the hope of ushering juveniles past this stage to a “size where they are more able to fend for themselves.” They are using eggs collected from the same beaches, with genes from local populations whose individuals successfully lived and spawned in the Jersey Shore environment for many years.
Since 2012, they have raised more than 250,000 horseshoe crabs to early juvenile stages per year — 1 million to date — at the Aquaculture Center. The center calls the program the “Horseshoe Crab Head Start Enhancement Program.” Charles River, which depends upon the distinctive blue blood of horseshoe crabs for manufacturing LAL for mandatory bacterial endotoxin tests, is an active partner in this effort as well. In 2017, Charles River partnered with Rutgers University and the New Jersey Aquaculture Innovation Center to support their efforts to increase the survival rates of young horseshoe crabs by retaining approximately 200 of the baby horseshoe crabs at the Aquaculture Center. In this way, Charles River is able to provide baby horseshoe crabs a jump-start on life.
The reasons for this commitment to horseshoe crab conservation are clear, says Norman Wainwright, Senior Director of Research & Development with Charles River Microbial Solutions. A protein in the blood of horseshoe crabs that Charles River and other biomedical research laboratories rely on is used to detect dangerous Gram-negative endotoxins in medical products requiring sterility, such as vaccines or syringes. Yet despite this out-sized role that horseshoe crabs play in keeping contaminated products off the market, these ancient mariners are not invincible. Horseshoe crabs are diminishing in New England, with man-made forces like overfishing for bait and destruction of coastal habitats due to over development being leading causes. (Thanks to stricter conservation laws, horseshoe crabs appear to be stable and growing in Delaware Bay and South Carolina.)
Partnerships like this one and others with the Mystic Aquarium in Connecticut and the South Carolina Aquarium are a way for Charles River to support the protection of these aquatic animals.
Keeping tabs on the crabs
Last year, Rutgers took its research of juvenile crabs to the next level. Students from Lower Cape May Regional High School were invited to release about 10,000 tiny baby crabs into Delaware Bay. Just three months old and the size of a pea, the crabs ventured into the watery wilderness for the first time, hoping to survive until adulthood when they will lay eggs of their own.
Motz said his team did this because they wanted to discern at which point the chances of survival for juvenile crabs greatly improve and further care is unnecessary.
“What is that point? Is it months, a year or two years? Very little is known about survivorship in the wild because juveniles can move around and bury [themselves] in the sand,” says Motz. “The juvenile stage is a black box to us.”
Mark and detect
Unfortunately, the traditional way scientists track adult crabs—by drilling a small hole in the shell and anchoring a tag in it—isn’t practical for crabs this young since they shed exoskeletons and the external tags along with them. His laboratory instead uses injectable tags called radio frequency identification Passive Integrated Transponders (PIT) tags, which are similar to what a dog owner uses when they have their animals chipped. The injectable tags are useful to mark and detect larger juveniles, and Motz says that tiny injectable wire tags are used to mark even smaller individuals.
“These aim to find the best time and place to release juvenile crabs for a true head start,” he said.
“There is no doubt that horseshoe crab populations in the Northeast have declined, but we think it is primarily because of over-fishing by the bait industry and destruction of habitats of shoreline, especially New England,” says Wainwright.
Charles River is committed to the conservation of this extraordinary animal that plays a role in the everyday health and safety of people all over the world. Our commitment revolves around educating and building awareness of the vital role the horseshoe crab plays in human health and its ecosystem.
Watch our documentary video to see the Horseshoe Crab Head Start Enhancement Program in action. To learn more about how we are helping to ensure the continued population growth of the horseshoe crab, please visit our dedicated web page.