Posts tagged ‘Horseshoe Crabs’

Horseshoe Crab Monitoring 2016 Recap and Results

NYC Audubon Conservation Biologist Debra Kriensky breaks down the horseshoe crab numbers from this year’s monitoring efforts in Jamaica Bay

 

Horseshoe Crabs Photo by NYC Audubon

Photo: NYC Audubuon

We are happy to report that 2016 was a great year for horseshoe crabs in Jamaica Bay!

 

New York City Audubon once again ventured out during the new and full moons in May and June to count and tag spawning horseshoe crabs. This was our eighth year collecting data on horseshoe crabs in Jamaica Bay, part of a larger project run by the New York State Department of Environmental Conservation and Cornell University Cooperative Extension.

 

In 2015, a colder than usual spring resulted in unusually low counts at some of our beaches, such as Plumb Beach East. This year, however, the shores were full of mating horseshoe crabs and our counts indicate that numbers continue to stay relatively stable in Jamaica Bay. This is great news, given how important horseshoe crab eggs are to the migratory shorebirds that come through New York City each spring on their way north.

 

With the help of 163 volunteers (a record!), we were able to count spawning horseshoe crabs at four locations: Plumb Beach East, Plumb Beach West, Big Egg Marsh, and Dead Horse Bay. Spawning activity peaked during the full moon around Memorial Day this year. The high counts were 205 crabs at Plumb Beach East, 21 crabs at Plumb Beach West, and 451 crabs at Big Egg (and that was only what we counted in our quadrat samples!). At Dead Horse Bay, where we take a total count of the horseshoe crabs, the high count was 493.

Volunteers Counting Horseshoe Crabs, Photo by Tracy Pennoyer

Volunteers Counting Horseshoe Crabs, Photo by Tracy Pennoyer

We were able to tag 797 crabs this year, making a total of 4,380 horseshoe crabs tagged since we started in 2009. We had 78 re-sightings of tagged crabs this year – 55 of which were tagged earlier in the spawning season, indicating that many of the horseshoe crabs we see stick around at the same beach for several nights and even weeks.

 

We also saw nine crabs we had tagged in 2015, two we had tagged in 2014, and one had tagged in 2013! In addition to all of these horseshoe crabs that are returning to the same beach night after night and year after year, we also saw 10 tagged crabs that were put out by other organizations. So far, we know that one was tagged last year in Cliffwood Beach, NJ and another was tagged in 2012 at Breezy Beach in the Rockaways. It will be interesting to eventually find out where and when the others were tagged.

 

If you ever spot a tagged horseshoe crab, write down the number and report where and when you found it to the U.S. Fish & Wildlife Service here.

Tagged Horseshoe Crab Photo by NYC Audubon

Horseshoe Crab Tagged "341401"

Thank you to all the amazing volunteers who came out to count with us this year, especially our dedicated volunteer site coordinators, who make it all possible! We’re also very thankful to Patagonia, the Williams Companies, and Investors Bank Foundation for their generous support of this year’s horseshoe crab and shorebird work.

 

We’re already excited for next year’s spawning season! We hope to have another record number of volunteers for next year’s counts. Please email volunteer@nycaudubon.org if you are interested in getting involved in this important (and fun!) citizen science study.

 

Field Notes: Horseshoe Crab Monitoring at Plumb Beach

Summer intern Debra Kriensky reports on a recent field expedition

 

Molted shells from young horseshoe crabs (approximately two-to-three years old). Photo © Susan Elbin

Molted shells from young horseshoe crabs (approximately two-to-three years old). Photo © Susan Elbin

On July 23, NYC Audubon staff and interns went out to Plumb Beach in Brooklyn to help horseshoe crab researcher Mark Botton search for baby crabs. Though we couldn’t help but stop to look at the birds—we saw several oystercatchers, plenty of gulls and terns, and a flock of juvenile barn swallows—the tiny, newly hatched horseshoe crabs stole the show.

 

Though the horseshoe crab hatchlings we were looking for were in the same shape as the adult crabs we count and tag during the spawning season, they were considerably more difficult to find. Smaller than a ladybug and the same color as the sand, the crab larvae were practically invisible in the shallow waters of the low tide. Fortunately, we were able to find a few of the baby crabs, which were promptly measured and released. During our search, we also stumbled upon the molted shells of several older horseshoe crabs that likely hatched two or three years ago.

 

In addition to searching for hatchlings, Botton’s team was also there to measure

A newly hatched horseshoe crab © Debra Kriensky

A newly hatched horseshoe crab found in the shallows being held in a shell until it could be measured. Photo © Debra Kriensky

the density of eggs at different depths of sand at several points along the shoreline. Using five-cm and 20-cm cores, the group collected a total of 120 samples of sand to analyze back at the lab. This data can be used to determine where crabs are laying their eggs on the beach, among other things. For example, since birds can only reach eggs close to the surface of the sand, looking at the egg densities in the five-cm core sample can help clarify just how much of this important food resource is available for shorebirds on Plumb Beach.

 

-Debra Kriensky