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Jun 17, 2019 4:06 PMPublication: The East Hampton Press & The Southampton Press

Sebonac Creek Nature Paddle

Note the huge webbed feet, and a slipper shell, on this female diamondback terrapin. MIKE BOTTINI
Jun 17, 2019 4:06 PM

The theme of last week’s nature paddle with the Peconic Land Trust was “marine egg-layers,” and we didn’t have to leave the launch site at the end of Sebonac Inlet Road to witness evidence of one: The sandy intertidal zone was pockmarked with dozens of horseshoe crab nests.Although it was close to high tide, we did not encounter any of the strange-looking and interesting creatures, but we did get a close look at their eggs in three different stages of their two-week-long incubation period: freshly laid eggs that were gray in color and stuck together in masses of 50 or more; slightly larger single eggs, bluish-green in color; and transparent eggs tinged with a light tan color from the shell of the embryo inside. These latter eggs, found just below the highest apparent tide line, probably hatched on Monday’s full moon high tide.

Each female will deposit up to 4,000 eggs in each of 20 nests, for a total of approximately 80,000 eggs per year. Nest sites are chosen by sediment type and grain size, as well as position in the intertidal zone. This is a trade-off between moisture and oxygen requirements: The eggs need to remain moist, and thus need to be in wet sand, but also need oxygen; therefore, they need to be exposed to air at low tide and surrounded by a specific sand grain size to allow some drainage but not enough to completely dry them out.

I was surprised to learn that, as with some turtle hatchlings, some horseshoe crab hatchlings remain in the sandy nest through the summer and overwinter there.

The 2019 Horseshoe Crab Benchmark Stock Assessment issued by the Atlantic States Marine Fisheries Commission rated New York’s stock status as “poor.” New York allows a commercial horseshoe crab harvest for baiting conch and eel traps, with the 2019 harvest quota set at 150,000 crabs. Some conservationists question the long-term sustainability of the state’s harvest quota.

Scientists at the University of Delaware have developed an alternative commercial bait that still uses horseshoe crab but reduces the amount needed by 90 percent, and researchers affiliated with Cornell University are working to make that available to commercial fishermen.

Crossing over toward the creek side of Tern Island, we managed to find another egg-layer in the shallows of the spartina alterniflora, or salt marsh cordgrass. This was a mature female diamondback terrapin, one of our most beautiful native turtles and the only one that inhabits the salt marsh and estuary ecosystem year round.

I was excited to find not just one but eventually three mature females during our morning paddle. The local population of this interesting creature has declined dramatically over the past three decades that I’ve been paddling on the East End. It was not unusual, at one time, to count three dozen diamondbacks on a summer morning paddle.

Diamondbacks look for open sandy areas above the reach of the highest tides, and their June journeys from the estuary in search of suitable nesting habitat can put them on roads, where they run the risk of motor vehicle encounters. But their main problems include excessive predation of nests by raccoons, a species that has become very abundant on Long Island in recent years, and drowning in trap gear set out for blue crabs.

To mitigate the latter, scientists have developed and tested a simple Turtle Excluder Device, or TED, that is secured to the openings of the crab traps. The roughly 1.75-inch-wide-by-5-inch-long wire or plastic device is designed to allow blue crabs access to the traps but is too small for mature females to enter. Some males and young females may be caught and drowned, but studies have shown that this size excluder will reduce turtle mortality by 80 percent without impacting crab catches.

These simple devices will be required on crab traps set by commercial crabbers in designated areas of Long Island estuaries inhabited by diamondbacks. Conservation groups have provided funding to purchase the excluders and provide them to crabbers at no cost. The next step is to promote and require their use among recreational crabbers.

Our third egg-layer actually doesn’t “lay” but carries her eggs throughout the two-week-long incubation period: the fiddler crab. She was out of sight, but I managed to excavate one from her burrow at the upper edge of the intertidal zone.

Mature female fiddler crabs mate and remain in their burrows during their entire incubation period, not even emerging to feed for the duration. When the eggs are ready to hatch, she will emerge and head to the water’s edge to release the larvae into the bay, where they join billions of ribbed mussel, blue crab, lady crab and green crab larvae to form an estuarine zooplankton soup that nourishes juvenile fish and mature filter feeders.

Once released of her larvae, she will spend two weeks feeding before mating again and retiring to a burrow for a second incubation period. The month-long process of feeding, mating and incubating is repeated a third time in August, such that females end up spending half of the summer out of sight in burrows. The result is that the visible population of fiddlers seems to be largely skewed toward males.

One aspect of the fiddler crab’s life history that always surprised me is their seeming lack of predators. They are so conspicuous, in such large numbers, during the daytime low tide, yet, despite the presence of predators such as gulls and crows, which will eat almost anything, I have never seen one go after the easy pickings that fiddler crabs offer.

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