Red Knot Population Holding Steady But Not Growing Yet

In the last two decades, the Red Knot population has steadily decreased. The primary cause seems to be overharvesting of horseshoe crabs, used in medical research and as bait for catching other shellfish. Red Knots and other shorebirds migrating along the Atlantic coast rely on horseshoe crab eggs for food, to the extent that these shorebirds time their arrival to coincide with the peak of horseshoe crab spawning. Recent regulations have tried to stabilize the situation, from a complete moratorium on horseshoe crab harvests in New Jersey to harvest limits in other states.

According to this year's shorebird census, the numbers of horseshoe crabs and Red Knots have not improved yet.

Each year, scientists from as far away as Australia and England take over two rental houses on Reed’s Beach and study Red Knot/Horseshoe crab numbers at the peak of the phenomenon, a full moon in late May or early June. The crabs come out of the bay in the highest numbers under the full moon.

“The crab spawning is happening at the right time in relation to the bird stopover,” said Humphrey Sitters, a scientist from the University of Exeter in England with the International Wader Study Group....

In 2009 and this year, the birds and crabs have arrived at the same time. He said there is some evidence this year at least part of the Red Knot population was delayed in early May in Patagonia, the southernmost portion of South America in Argentina.

Horseshoe Crab numbers reached a peak in 2006-2007 and have since declined, according to Virginia Tech data. Overharvesting by commercial fishermen who cut up the crabs for bait to catch conch and eels has reduced the crab population greatly since 1990.

“If anything, the adult crabs have declined over the last three years (2006-2009) but on the other hand, there seems to be an increase in immature crabs,” said Sitter.

The scientists conduct counts of the number of Red Knots along the bay. Last year, the count increased to about 25,000 birds. He said this year he believed the peak count would be around 17,000 Red Knots.

The population has dropped from a count of 50,000 birds in 1998.

I would not expect the harvest limits to produce a rebound right away since horseshoe crabs take several years to reach maturity and the horseshoe crab population needs to stabilize before the Red Knot population can grow significantly. With that in mind, the increase in immature crabs is encouraging. It is also encouraging that the Red Knots arrived at the same time as the horseshoe crab spawn this year, as that should allow them to gain the weight they need to make it to the Arctic and breed.

According to another article, some of the banders are using geolocators to track where the shorebirds go.

Burger helped to band shorebirds this week with geo-locaters that measure the sun's rays. Red knots nest in pairs far from others of their kind, making them notoriously difficult to find in their arctic breeding grounds. But scientists who capture tagged knots can use the tag's information about sunrise and sunset to pinpoint exactly where they went. So far the scientists have recaptured four red knots they banded with geo-locaters in past seasons.

There are photos from one banding session at the CMBO's blog.

In a related story, a truck full of lobsters and horseshoe crabs overturned on the Parkway at mile 0.7. I assume that the horseshoe crabs were harvested in another state.