Conserving Wildlife, Delaware Bay, Delaware Bay 2018

The Horseshoe Crab Spawn Continues, Shorebirds Reach Flight Weights – Restoration Is Possible


Horseshoe crabs expanded breeding into neap tides

Read the previous post

The horseshoe crabs extended their breeding period into the neap tide phase after the cold weather of mid-May decreased water temperature during the spring tides.  This is good news because most experts expect breeding during the full or new moon tides ( called spring tides) The crabs roughly require a water temperature of about 59 degrees F before breeding begins in earnest.  Crabs still breed at a lower temperature, but many more will breed above the temperature threshold.

At the same time, crabs also look for spring tides, the higher high tides that come with full and new moons,  because they can breed in sandy places unavailable at lower tides. This year the water cooled during the new moon spring tide and warmed in the neap.  Good spawning during the neap tides was welcome good news.  This May good spawning conditions will raise average egg densities about 50% higher than last year.

We found eggs lying on many beaches including Reeds Beach at the Jetty.  This is better news then it first appears.  Last year shorebirds desperately fed on the eggs at the jetty corner at North Reeds to the delight of many visitors.  Little did they know the birds couldn’t find eggs elsewhere at similar densities and would have avoided the place if they could.  The good news this year is they have.

Higher egg densities on the NJ Bayshore gave shorebirds a welcome boost.  Most gained weight rapidly.  The weights of red knots and ruddy turnstones showed the difference. Most Knots rapidly reached the 180-gram threshold considered necessary for birds to reach the Arctic breeding areas in good conditions and Ruddy Turnstones are in similarly good condition.


horseshoe crab eggs on the beach

A view from the Reeds Jetty looking south. Horseshoe crab eggs piled up after a few days of southerly winds but unlike last year shorebirds did not pile into eat them. It a good sign. The jetty exposes the birds to intense disturbance and they would rather feed in more secure places – and they did because they could


Horseshoe Crab breed on the sod bank of Egg Island and shorebird feed on the eggs as they are being laid. The breeding attempts must fail because eggs cannot incubate in the anoxic environment of marsh mud but its a good sign the crabs are breeding in odd places.


Good Horseshoe Crab Egg Densities Draw 34,500 Red Knots to the Bay

The best news is a direct consequence of these good conditions, the number of knots and turnstones increased this year.  Our season-high estimates show that there are 34,500 knots and 21,000 ruddy turnstones in the bay.  These may be the highest counts on the bay in at least 15 years.

Why?  At first one would conclude the increased numbers on the bay represent a real increase in the size of the population, but it is not.  Shorebirds need time to respond to improving conditions because they are relatively slow breeders, as are most Arctic nesting shorebirds.  Knot numbers on Delaware Bay basically depend on the availability of crab eggs.  In good years numbers go up because birds stay to feed, in  bad years, numbers go down because birds come to the bay and leave quickly.

This was the case last year,  egg densities during May plummeted to less than a few thousand eggs/meter2.  Knots banded in Delaware Bay were resighted days after release in other stopovers like Cape Cod.  Consequently, our  Red Knot count on the bay fell from 24,500 in 2016 to 17,500 in 2018.  We assumed this was not a real decrease in numbers but the result of birds leaving right after finding eggs too scarce or competition too intense on the bay.

Now we have good egg densities and birds are staying longer to be counted.   The longer birds stay, the greater the proportion of the total are seen on one day. So this year we had good egg densities, good weights, and good numbers.  Its one of the best of seasons in recent memory.


red knots on delaware bay NJ

A red knot flock near Straight Creek on Egg Island in NJ. This flock was one of several on Egg island that totaled over 13,000, a third of the entire bay flock. The birds use this remote marsh as a staging site before flying off to the Arctic.


shorebirds at cooks creek NJ

Shorebirds on Cooks Creek Inlet seen from Cooks Beach. The birds practically reside in this inlet and the four others that flow from the marsh behind the beaches from Reeds Beach to Pierce’s Point


Birds in Better Condition than Last Year  but Still Face An Ecological Roulette

With stopover period winding down, we can say the red knot and other shorebird species will leave the bay in better condition than the disastrous condition of last year.  So what does it mean?

First, the last four years have been a sort of ecological roulette for the birds.  Horseshoe crab numbers remain at only 1/3 the potential population possible on Delaware Bay leaving birds at the mercy of good conditions to get enough eggs. Last year water temperatures stayed low during the mid-May depressing the spawn and the density of eggs.  Wind storms halted spawning for days.  Although the average was 8000 eggs/square2, there were less than 2000 eggs/ meters2 in the month of May.  Far less than the average in 1990 of over 100,000 eggs/meter2

This year the weather and water temperature added to a good spawn in May and the birds appeared to have left in good condition.  Unfortunately, it’s only chance, if bad weather or cool temperatures return, they will face another bad year.  We need more crabs to smooth out the rough years.  The bay can support three times the current number.

paper on horseshoe crabs

Read the paper that describes the work of a team of scientists measuring egg densities in 1991 before the overharvest of crabs. 

This increase in the number of horseshoe crabs would transform the bay.  In 199o and 1991, we had 3 times the number of crabs we have now, but we had 10 times the density of eggs because of multiple breedings by one female and more eggs reaching the surface as one crab digs up another’s eggs.  Additionally, it lasted for two months, unlike this year’s eggs which will last only a few weeks. Imagin the boost in baywide productivity if egg densities increased tenfold!


Agencies Should Stop Managing for Stability and Pursue Full Restoration

We could get to full numbers sooner than you think.  The agencies could lead the way.  Ten years ago the Atlantic States Marine Fish Commission and the USGS gathered the conservation groups of Delaware Bay to take part in a “ Structured Decision Making”  process ostensibly to agree on the restoration of the crab population they damaged by allowing an overharvest.  People agreed on a process called the Adaptive Resource Managment (ARM) model as a path to restoration by restricting all harvests to the ARM-based quota.

Unfortunately, they broke that promise this year by allowing the horseshoe crab bleeding industry a pass on killing crabs.  They have already made similar deals by allowing Maryland, Virginia and New York take thousands of crabs even though they cannot prove they have a horseshoe crab population of their own that can support these harvests.  All are very likely taking from the Delaware bay population.

With no increases in numbers after allowing an ARM model quota for over a decade, the goal of the ASMFC is unclear but it is certainly not restoration to full carrying capacity of Delaware Bay.  After ten years of no evidence of change,  its time to take another approach.  Now full restoration must be the goal.


There is no trend in the number of females horseshoe crabs on Delaware Bay according to the ASMFC own survey method, the Atlantic Coast Trawl run by Eric Hallermen and David Hata of Virginia Tech. One must wonder why when in theory none are harvested – except the bleeding industry which is practically unregulated and self-reports mortality


Increase the Number of Adult Crabs by Not Killing Them

We can increase the number of crabs right away.  First, the ARM quota must be sacrosanct or we must start a new environmental action to close the harvest.  The bait and bleeding industries have developed a number of ways to avoid the quota and the lack of any real surveillance encourages abuse.  All horseshoe crabs kill should be restricted to the ARM Quota.

But this is more difficult than it seems.   Crabs can be caught on the Atlantic Ocean outside the 3-mile limit and loaded into boats and taken to other ports.  Crabs are being lost as by-catch to other fishery operations like clam dredging or bottom fish trawling.  These losses must be calculated and assessed against the quota.

We can also develop crab friendly infrastructure. There is virtually no effort to do this now.  In Fortescue, for example, the operators of a state-owned boat ramp dumped concrete rubble on the side exposed to the open sea to protect boaters from waves as they load boats on trailers.  The state failed to improve the ramp so the local Captains Association took matters into their own hands, and hundreds of crabs died trapped in the rock. Sadly these destructive solutions are commonplace on the Bayshore.  Crab friendly infrastructure must be the new standard.

Finally, we can save crabs in the most straightforward way possible – rescue them from certain death.  This is the goal of Return the Favor, a group of volunteers who comb beaches saving crabs overturned by the sea or pulling them from the death grip of wrecked bulkheads and concrete rubble used to defend eroding shorelines. The group has saved the lives of over 250,000 crabs in the last three years.

Delaware Bay Horseshoe crabs trawled off the coast of Md as they winter on the ocean floor


rubble on boat ramp in Fortescue NJ

Rubble on the boat ramp at Fortescue was placed to protect boaters from the direct waves from the bay not seen on the left of the picture. The rubble has already killed hundreds of crabs. The drastic action was taken after the state ( who owns the ramp) would not fix the problem. In many ways, this unfortunate incident tells the wider story of infrastructure on Delaware Bay, a place the state of NJ fails to fund adequate infrastructure while lavishing it on the much richer Atlantic Coast.

Start Now and the Bay Will be Transformed

Even with all these changes, the crab population can only grow slowly.  Recovery demands patience. But the payoff of a fully restored horseshoe crab population can transform Delaware Bay by underpinning the restoration of other fish like weakfish.  Long ago, before the industrial fish machine destroyed the abundance of horseshoe crabs, scientists knew the small fish – the prey of big fish – gorged on horseshoe crab eggs and the young that hatch in mid-summer.  We lost much of that when we lost the bay’s great crab population.  But if we were to increase the current amount of horseshoe crab eggs from 10,000 eggs/meter2  to 100,000 eggs/meter2  the bay fishery would once again blossom. This can, in turn, provide a renaissance of the bay’s fish dependent economy and more.

It all starts with stopping the needless killing of horseshoe crabs.



taken movie of horseshoe crabs

Mandy Dey uses her iphone to take the video shown above on Reeds Beach. Photo by Ren Mott