Red Knot, Horsecrab Populations Continue to Decline

REEDS BEACH – There is no evidence that either the Horseshoe Crab or Red Knot population is increasing along Delaware Bay.
The amazing story of the Red Knot arriving each year on Delaware Bay shores from southernmost Argentina at the same time Horseshoe Crabs are coming out of the water to lay their eggs has been repeated for ions.
The long and short of it is the Red Knots feed on the eggs here, rests a week or two, gain a considerable amount of weight and then fly to the Canadian Arctic Circle to raise a family. In the last decade, the number of Horseshoe Crabs has been decreasing meaning fewer eggs for the birds to consume on the shoreline, lessening their chances of having the energy to fly to the Arctic Circle.
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.
He said in England, shore birds are called waders. Sitters said he has been coming to Reed’s Beach to study the birds for 14 years.
In 2008, there was a mismatch. Horseshoe Crab spawning was too late and the birds did not get enough food, said Sitters.
“The evidence seems to be there has been no real change in the size of the crab population,” said Sitters.
“In the distant past, before the overharvesting of the crabs, there were so many crabs and they spawned for such a long period of time, there were always plenty of eggs but we’ve now got the situation where the timing is critical,” he said.
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.
In some years, all of the Red Knots arrive with no departures to the Canadian Arctic which reflects the total number of birds that come to Delaware Bay. In other years, some birds depart before others arrive affecting the peak count.
Some Red Knots stop off at other sites on the east coast such as the Virginia barrier islands. He said where they stop may be based on the food supply at both locations.
For the last several years, the Red Knot and Horseshoe Crab population “have been sort of bumping along the bottom,” said Sitter, with no major change in either population in the past four to five years.
He said counts of the Red Knot are conducted in its wintering area in Tierra del Fuego at the southernmost tip of South America where the number of birds has been “bumping up and down.”
Sitters said the winter population has averaged in the 16,000 to 17,000 range.
“There is no evidence of a recovery of the Red Knot population at all,” he said.
A full moon occurred on May 26 bringing a lot of crabs from the bay to spawn both at Reed’s Beach and on beaches in Villas. On May 27, this reporter saw one Red Knot among a huge gathering of sea gulls on Reed’s Beach eating tiny, green Horseshoe Crab eggs. Those who had been watching bird activity for several hours from the observation platform reported seeing an occasional Red Knot.
Both New Jersey and Delaware placed moratoriums on Horseshoe Crab harvesting in 2006 and 2007.