Red Knots and Horseshoe Crabs in Delaware Bay by Common Good Productions.

A Shore Bird Biologist's Perspective

MARINE DEFENDER: JOANNA BURGER
RUTGERS UNIVERSITY, Department of Ecology, Evolution, and natural Resources

DEFENDING THE RED KNOTS
​CAPE MAY, NEW JERSEY

Dr. Joanna Burger, a specialist in shore birds, visited Cape May, New Jersey, in the Spring of 2012 with a group of bird biologist to witness a remarkable annual event.  Each year, Red Knots stop along this rocky shore for a brief period to feast on eggs laid by spawning horseshoe crabs.  

Red knots, although they are small in size, are one of the most intrepid navigators on the planet, traveling the span of the planet and logging over 15,000 each way from the tip of South America to the Canadian Arctic, and back, each year.

The birds typically stay about 12 days and can double their body weight if horse shoe crab eggs are plentiful.  Birds that don’t gain enough weight have far lower survival and breeding rates.  

Each year between 50% and 80% of the entire species visit Delaware Bay, which spans the Atlantic coast from Delaware to New Jersey, which makes them highly vulnerable to pollution and loss of key resources. 

In January 2018, a survey by the Western Hemisphere Shorebird Reserve Network found that the numbers of Red Knots wintering in Tierra del Fuego, South America had fallen dramatically – to just 9,840 birds. This was a 25% decrease on the number recorded the previous year in January 2017 (13,127).

Bird Life International reports that this decline was likely caused by low ocean temperatures which delayed the Horseshoe Crabs’ journey ashore to breed in May 2017. 

When the Red Knots showed up to feed in Delaware Bay, there was little to eat, and the hungry birds didn't survive the journey to the arctic to breed.

The Red Knot was listed as a federally threatened species under the United States Endangered Species Act in the fall of 2014.

The Atlantic Flyway

Major flyways in the US. The Atlantic flyway is marked in purple. ​ Credit: US Fish & Wildlife Service

In the Western Hemisphere, birds typically migrate in a north-south direction.

There are several places where the paths of migratory animals cross and concentrate like smaller tributaries feeding into a river. These migratory paths for birds are called flyways.

Massachusetts and New Jersey are both central stops along the Atlantic Flyway, which is bordered by the Appalachian Mountains to the west and the Atlantic Ocean to the east.  

Delaware Bay. Source: Smallbones

The Flyway funnel: Delaware Bay

In New Jersey Prevailing westerly winds carry migrating birds down the coastline where they get funneled into an ever-tighter cone that starts in Camden and peaks at the Cape May County peninsula, and then carries them over Delaware Bay.

Every year, an estimated 425,000 to 1,000,000 migratory shorebirds converge on Delaware Bay to feed and rebuild energy reserves before continuing further north to their breeding grounds.   The marshes and tributaries of the Delaware River also provide a stopover and wintering habitation for more than 200 species of migrating birds, including Canada Geese.

But air currents aren't the only reason for migrating birds to stop here.  The bay is also home to the largest annual horseshoe crab spawing event in the world.

Eco-Profile: Delaware Bay​

The Delaware Bay is New Jersey’s largest estuary, mixing fresh water from the Delaware River with the saltwater of the Atlantic Ocean.  The Bay makes up New Jersey’s southern border, beginning with Cape May in New Jersey and Cape Henlopen in Delaware, and stretching northwest to the Delaware River, touching on Wilmington, Delaware; Philadelphia, Pennsylvania; and Trenton, New Jersey.

Like all of New Jersey’s coastline, the Delaware Bay is important both economically and ecologically.
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One of the world’s largest freshwater port systems, approximately 85% of all oil shipped to the East Coast of the United States passes through the Delaware Bay.  Every year, more than 70 million tons of cargo is also moved through these waters.

Horseshoe Crabs mating in Delaware Bay. Credit: CGP

Horseshoe Crabs ​

Tens of thousands of horseshoe crabs climb onto the bay's beaches to lay their eggs in the spring. 

​One female crab can lay as many as 90,000 eggs each season, creating an important food source for hungry migrating birds like the Red Knot. 

Horseshoe crabs also play an important role in protecting human health. Horseshoe crab blood is used by the medical industry in a test to determine whether IV drugs, vaccines, and medical devices contain harmful bacterium that can withstand regular methods of sterilization. The test can also detect contagions like spinal meningitis and urinary tract infections.

THE RED KNOT

Red Knot is a tiny red bellied bird that is one of the planet's greatest long distance travelers.  These birds winter in the Antarctic,  summer in the Arctic, and stop in Delaware Bay, roughly in the middle of their planet spanning flight, to fuel up on crab eggs, often doubling their body weight, so they can continue to make one of the longest migrations on earth.

There are three subspecies of Red Knots in North America, and they all are in decline. The populations wintering in South America dropped over 50% from the mid-1980s to 2003, and are listed as a federally threatened species. 

In January 2018, scientists recorded only 9,840 birds making the journey from Tierra Del Fuego to Delaware Bay. This was a 25% decrease on the number recorded in January 2017. The problem, according to Bird Life International, is that low water temperatures in May 2017 delayed the Crabs breeding schedule, so the Red Knots’ food just wasn’t there in time.  ​

Red Knot in Delaware Bay. Credit: CGP

A Female Blue Crab. Photo Credit: South Carolina Dept of Natural Resources

Blue Crabs

Crabs are abundant all along the New Jersey coast, from the Hackensack River to the Delaware Bay. 

​Blue Crabs, however, seem to be the most beloved species in New Jersey. A study by Rutgers University reports that nearly three-quarters of the state's saltwater fishermen go crabbing, which comprises roughly 30 percent of all marine fishing activity.

The Blue Crab's scientific name is Callinectes sapidus.  Translated from Latin, this means 'beautiful savory swimmer.' Males have blue claws and females have red-tipped claws.

Other crabs found in the Delaware Bay include hermit crabs, horseshoe crabs, rock crabs, spider crabs, ghost crabs, and mole crabs.

Delaware Bay and Oil Spills

One of the world’s largest freshwater port systems, approximately 85% of all oil shipped to the East Coast of the United States passes through the Delaware Bay.
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Every year, more than 70 million tons of cargo is also moved through these waters.

Given its rich biodiversity and importance as a commercial hub, the Delaware Bay is uniquely vulnerable to oil spills.

This vulnerability was exposed in 2004, when an oil tanker named the Athos I stuck a submerged anchor, spilling 265,000 gallons of Venezuelan crude oil into the Delaware River near Philadelphia, PA. Some 115 miles of shoreline were affected.
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Waterfowl were covered with oil and killed by the spill, which occurred near Little Tinicum Island and the John Heinz National Wildlife Refuge. These areas are used year-round by some waterfowl and are occupied even more extensively during the fall and spring migrations along the Atlantic Flyway. Delaware's Pea Patch Island, which contains the largest heronry north of Florida on the East Coast, was also threatened by the spill.

Photo Credit: Delaware Estuary Watershed Database and Mapping Project

Diver covered in oil from the Athos I oil spill. Photo Credit: Delaware Estuary Watershed Database and Mapping Project

Because the Delaware Bay is a migratory hub, the impact of an oil spill or pollution event varies depending on the time of year. The bay is most at risk during the fall and spring, when the most wildlife migrates through.

In the wake of this disaster, citizens and lawmakers called for tougher fines and penalties for oil spills in New Jersey waters.  In 2005, the State of New Jersey raised the cap on oil spill liability to $1,200 dollars per gross ton for vessels, with a maximum of $50 million dollars.

Other major oil spills into Delaware Bay include:
• Mystra spilled 10,000 gallons of crude oil in 1997
• Anitra spilled 42,000 gallons of crude oil in 1996
• Kentucky spilled 13,000 gallons of crude oil in 1994