Additional moratoriums on horseshoe crab harvesting may not immediately be part of broader conservation efforts if the U.S. Fish and Wildlife Service designates the red knot as a federally threatened species.
As long as the crabs are harvested under a model that considers the number of birds, then the number of eggs is enough to sustain the current red knot population as the birds use the Delaware Bay as a rest stop on their flight north, said Wendy Walsh, a biologist with the U.S. Fish and Wildlife Service.
But if the bird population increases, rules may need to change to ensure further protection for the crabs, Walsh said.
The red knot, a robin-sized migratory shorebird that flies between the far southern reaches of South America and the Arctic ever year, was proposed earlier this year for listing as a federally threatened species. The knots, along with multiple other species of shorebirds, rely on billions of tiny horseshoe crab eggs for food every spring as they use the Delaware Bay as a pit stop on their journey north.
However, as commercial harvesting has drastically reduced the number of horseshoe crabs that lay eggs every spring, the number of birds also has dramatically declined. That linkage is one of the reasons the federal government has proposed listing the bird as a threatened species.
New Jersey has had a legislatively mandated moratorium on crab harvesting in place since 2007 and surveys have shown a modest increase in the number of juveniles that were counted in state waters. However, harvesting still occurs in Delaware, Maryland and other nearby states.
Earlier this year the Atlantic States Marine Fisheries Commission enacted a complex model to determine how many horseshoe crabs could be harvested annually and still maintain the population as well as sustain the birds, Walsh said. The model ties the harvest numbers with the number of red knots, she said. “If we feel the model is not complete and not functioning correctly, we would reconsider that,” Walsh said.
Walsh said the agency has until September to decide whether to list the bird as threatened, or even as endangered, or not to list the bird at all. While the public comment period has closed, she said, the agency will hold at least one public hearing in the coming months.
“We are now trying to figure out the best way to schedule one or more hearings,” Walsh said. “The challenge is the (red knot’s) range within the U.S. is very large.”
The federal designation for the red knot also will benefit other species, said David Mizrahi, vice president for research with New Jersey Audubon. “It will improve conditions for a whole host of species that use the same habitat and follow similar migration routes. It creates an umbrella (of protection) for a host of other migratory shorebirds.”
Since the 1980s the red knot population has declined by about 80 percent, Mizrahi said. And compared to other migratory shorebirds that follow similar paths, he said, the red knot’s population was much smaller to begin with.
Red knots are known as “supermigrants,” because they travel from the far reaches of South America, where they spend the winter feeding on tiny clams, mussels and crabs, to the Canadian Arctic where they breed. On their journey north every year, tens of thousands used to stop off at the Delaware Bay in May to refuel for the rest of the flight. The billions of horseshoe crab eggs that coat some of the beaches with carpets of green dots, are the perfect fuel because they are full of protein and fat and are also easy to digest.
In the past few years the red knot population has effectively stabilized, but at a number that is about 20 percent of the peak years. The crab numbers also have stabilized, but juveniles take at least nine years to mature, so the gains in the number of eggs may not be seen for a few more years, Walsh said.
If the red knot were listed as federally threatened, New Jersey’s management would not change much, said Dave Jenkins, head of New Jersey’s Division of Non-Game and Endangered Species. The big change, he said, would be that researchers would need to get additional permits in order to do the annual surveys, which involve trapping birds and putting identification bands on them.
New Jersey temporarily closes multiple Delaware Bay beaches during the peak of the horseshoe crab spawn so the birds are not disturbed, Jenkins said. “I don’t think there will be any significant change in how we manage the beaches.”
However, Mizrahi said a big effect may be on how other states manage their horseshoe crab harvest. Currently the amount of crabs that can be harvested is decided by the Atlantic States Marine Fisheries Commission’s model. Right now only about 100,000 males can be harvested, which are then used for bait in the conch fishery.
Horseshoe crabs also are harvested for their blood, which is used to create a substance called Lysate that is used to test the purity of multiple types of drugs. Mizrahi said the biomedical industry says the overall mortality is between 4 percent and 5 percent, but other studies think as much as 30 percent of the crabs die from the bleeding process and other factors.
“Nobody in the conservation community would advocate we stop using horseshoe crabs in the biomedical industry,” Mizrahi said. “We hope (the federal listing) will allow an evaluation of the mortality involved and other things in the guidelines for how the crabs should be handled.”
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