Nature Notes: Seapoosing

Spring is springing. Sunday night’s/Monday morning’s rain refreshed the freshwater wetlands, the spring peeper tree frogs are having a blast, almost all of the summer ospreys are back working on their nests, even laying eggs, while bald-faced eagles check out the scene, having decided to nest locally. Watch out, Mr. and Mrs. Osprey! Bald eagles may be our national bird, but when they are hungry, they will stoop to feeding on carrion and maybe a tiny dog or two.

Vicki Bustamante has her eyes on a pair of ravens that have been hanging out atop the old radar building where the military was active in Montauk up until the end of the 1960s. Turkey vultures have bred at least once in Montauk, but never since. As I drive around the East End for this or that reason, I can’t help but notice a spate of roadkills: raccoons, opossums, gray squirrels, an occasional cottontail, and even a turkey. Looks like the roadkills came just in time to feed the common crows, fish crows, and at least one pair of ravens, not to mention the two species of vultures that come to feed on the roadsides here. The first-named have been paired up for a month or more now and are starting to nest.

According to Howard Reisman, alewives are back in force in North Sea Harbor, already traveling up the stream to Big Fresh Pond; it looks like a good year. Of course, the black-crowned night herons are hanging out where Noyac Road runs into North Sea Road. A freshly dead alewife tastes as good as a live one, if herons and other birds have taste buds as we humans have. I hope they do.

I was Googling alewives on Monday evening and I came upon a curious organism, no doubt related in some way to alewives, as it was called an “alewife floater.” I queried Howard, one of Long Island’s few bona-fide ichthyologists, but even he didn’t know what it was. After more internet research I discovered that an alewife floater doesn’t float at all, neither does it swim. It’s a darkish freshwater mussel in the genus Modiolus, sometimes called a freshwater clam, about half the size of a chowder clam, and flattish. In fact, once I put the name with the species, I realized that it is that bivalve that lives on the bottom of Fort Pond in Montauk, a freshwater pond that almost never sees saltwater and the second largest pond on Long Island after Lake Ronkonkoma.

But why the name “alewife floater”? Even the State Department of Environmental Conservation uses that term for this creature. After more digging, I came upon a plausible explanation. The freshwater mussel, like almost all bivalve shellfish, reproduces by the simultaneous expulsion of sperm and eggs into the water column, and the chance combination of the two to form a zygote, which is the very first stage resulting from fertilization. In fact, you and I were zygotes very early on, though we never were told so by our parents.

The zygote then starts dividing into cells, which further divide into more cells, and after a short while the cells become different from one another, the precursors of the organs they will form in the embryo. Shellfish zygotes eventually develop into swimming larvae, which live freely in the water until they reach the shell-producing stage, after which they are ready to go into the bottom and lead a sedentary life filtering out phytoplankton from the overlying water. Apparently these freshwater mussel larvae would rather attach onto the gills of alewives, shad, and other herring species, especially on the gills of those that spend most of their lives in saltwater but enter freshwater to spawn.

Thus, during part of their life cycle, they are parasitic, taking oxygen from the gills and even phytoplankton from the water that the alewives — filter-feeders themselves — pass through their gills and out their opercular openings. But they also get to go back to the freshwater roots when their host alewives become sexually mature, leave the seas, and swim back into the home stream, like salmon, in order to reproduce.

It is not hard to see then, how alewife floaters came to populate Big Fresh Pond in North Sea. The North Sea stream connecting tidal North Sea Harbor with Big Fresh Pond has been in existence for hundreds and hundreds of years. But how did they come to populate Fort Pond in Montauk?

If you look at the old maps showing Fort Pond, some dating to the 1700s but particularly those of the U.S. Coastal Survey and its offspring, the U.S. Coast and Geologic Survey, you will see that at its northern end the pond almost touched Fort Pond Bay. The Montauketts, and the early settlers following in their footsteps, must have seapoosed Fort Pond by opening enough of an outfall stream so that marine fish could swim through it into the pond proper. Note that the freshwater mussels are almost all distributed in the north end of the pond.

Seapoosing was a common practice when Native Americans came to occupy 

the Atlantic Coastal lands from the Carolinas into Maine, all of which areas are lined with coastal ponds that lead to the sea. Seapoosing still goes on today, although the seapoose that used to be created with digging sticks, then shovels, is now done with the use of heavy equipment. The trustees of the various coastal towns on Long Island inherited the practice from the Native American tribes they lived with. Georgica Pond, Sagaponack Pond, and Mecox Bay were regularly seapoosed in the spring and fall of each year.

Alewives still swim into Sagaponack Pond when it is conveniently opened and swim all the way up to Jeremy’s Hole, about 300 yards south of Montauk Highway, to spawn. This year the stream is full, so look for alewives.  The alewives that enter Mecox Bay swim up under Montauk Highway to reach Mill Pond, which is fresh, and used to be ideal for spawning. Now it is so polluted, I wonder if many alewives end up going there. Georgica Pond is sometimes fresh at its northernmost extremity, a few feet from Montauk Highway, but hardly fresh enough for alewife reproduction.

What happened to seapoosing at Fort Pond? At the turn of the 19th century, the railroad track to Montauk station, situated northeast of the pond, was installed on a berm constructed several feet in elevation above the pond’s level. In other words, Fort Pond was cut off from Fort Pond Bay, and has remained so ever since. Lake Montauk, once the largest freshwater lake on Long Island, was regularly seapoosed to Block Island Sound until the mid-1920s, at which point rock jetties were built on each side of what is now the channel. Thereafter, Lake Montauk became permanently tidal, but elvers still make it in large numbers and swim up to Big Reed Pond almost every spring along with a few alewives. The trip is easy for the baby eels, but tough on the alewives because the course to Big Reed is shallow to almost dry and includes many obstacles.

So the next time you are wading in Fort Pond and your bare toe strikes something hard, but not as hard as a rock, bend down and scratch in the sand. You might just find a “floating alewife,” but don’t tell anybody. They’ll never believe you, especially not in Montauk.

Larry Penny can be reached via email at [email protected].