QJScience: Preserving the horseshoe crab

A recent trip to Ripley’s Aquarium in Toronto gave me the opportunity to learn about some amazing marine and freshwater animals. I was able to touch creatures, bringing on some nostalgia from my trips to Marineland in the 90s. After touching a horseshoe crab, my inner biology student came to life and I read the information the aquarium had on these crabs.

I was surprised to learn they play a pivotal role in the survival of many migratory birds. Incidentally, I’m doing my honours thesis in a bird conservation lab, so I went home and did some research on these crabs. Horseshoe crabs are found along the eastern coast of Canada, down to the Yucatan Peninsula in Mexico. They are especially prominent around the Atlantic coast of New York, New Jersey and Delaware.

Humans exploit them in two ways. First, their blood is used to test biomedical products, as it heavily clots when it comes into contact with bacteria. Companies mix horseshoe crab blood with their products, and if it clots, they know their product is contaminated and must be discarded. About one-third of a crab’s blood is drained before it’s released back into the wild. Studies have shown that a significant number of crabs die during this process. Secondly, horseshoe crabs are the primary bait used to catch American eels and conch. Due to this exploitation, many horseshoe crab populations have drastically declined since the 1990s, including the Atlantic population along the coast of Canada.

This has lead to a decline in the number of red knot birds as well. Red knots make one of the longest migrations of any bird; 10,000 miles! Their main stopover site is Delaware Bay, where they nearly double their weight by feasting on horseshoe crab eggs in order to have enough energy for the rest of their trip. But with fewer eggs available, red knot populations are suffering. Organizations such as the National Fish and Wildlife Foundation have taken steps towards conserving horseshoe crabs and red knots. After Hurricane Sandy last year, the already small extant population of horseshoe crabs were unable to lay eggs due to muddy conditions. These organizations undertook emergency sand restoration projects on key beaches to ensure that crabs could lay their eggs.

Scientists and environmentalists in Canada and the USA have petitioned governments to have strict regulations on horseshoe crab fishing and to list red knots as endangered. New Jersey has temporarily forbidden fishing for horseshoe crabs, and Delaware has restricted fishing to male crabs, since, historically, females have been preferentially harvested.

Current steps toward horseshoe crab conservation are certainly valuable, but more needs to be done to ensure that these crabs and the migrating birds that depend on them don’t reach critically low levels. There should be more effort put towards finding alternatives to horseshoe crab blood use in the biomedical industry, as well as finding alternative bait for catching American eels and conch. More genetic studies on horseshoe crab populations are also needed, because understanding genetics is important when it comes to conserving species.

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