March of the Alewife

One of the many Long Island firsts that we can be very proud of is the annual alewife march from the marine waters of the Peconic Bay into North Sea Harbor, thence to Big Fresh Pond, also in the hamlet of North Sea, every spring.

Once in the freshwaters of the pond, the males fertilize the eggs of the females, which are “broadcast” into the lake waters. Following fertilization, the eggs develop into larvae in a matter of weeks, then grow and swim in swarms until ready to leave in summer to retrace the trails of their parents, but in the opposite direction, as they head upstream and then into the marine waters from which their parents came.

Apparently, such reproductive behavior has been going on since historical times, perhaps even as far back as when the Native Americans first settled these parts, many centuries before the European invasion.

In modern times, the alewives have to contend with crossing under two busy roads, Noyac Road and North Sea Road, via engineered underpasses, which they seem to manage each new year without too many losses. Those adults that don’t make it each spring are rarely wasted, as they become food for herons, egrets, ospreys and, now, bald eagles, as well as foxes, weasels and, perchance, mink.

It is one of those annual Long Island events that puts the South Fork on the map! Alewives try to enter other streams in Southampton and East Hampton, and the villages of Sagaponack, Sag Harbor and Southampton, and the hamlet of Montauk, but seldom make it all the way up to the pond feeding the streams leading to either the Peconics or the Atlantic Ocean.

Riverhead, where the Peconic River enters Peconic Bay, is another large alewife rallying point, but the many dams encountered by upstreaming fish make it difficult for alewives to get to the ponds feeding the river.

And so there is much still to be done to have that system rival the one in North Sea, as far as alewife breeding is concerned.

Since alewives don’t spawn in streams, only in the ponds feeding them, many pondless streams on Long Island aren’t a bit suitable as breeding systems. Not so, perhaps, for an alewife lookalike and close relative in the same family, Alosa aestivalis, the bluebacked herring, which has not been well studied here. These fish cannot easily be told apart from the alewife, only separable from the alewife by the trained eye of an ichthyologist.

Those fishes such as the brook trout, rainbow trout and Atlantic salmon, which spend most of their time in saltwater but come to freshwater for spawning, are known as anadromous. The American eel, which grows up in freshwater but enters the saltwater of the ocean and travels up to a thousand miles south to spawn in the Sargasso Sea, is called a catadromous fish. The elvers, still almost transparent by the time they reach our latitude, have little trouble making it to their ancestral freshwaters, e.g., Big Reed Pond or Lake Agawam, in which to grow up.

There are some 29,000 separate fish species described, half in marine waters, half in freshwaters. Each year, many new species of fish are described as we continue to explore the depths of the oceans.

The old theory concerning the evolution of jawed fishes from jawless ones like the lamprey, 400 million years ago, has marine fishes giving rise to freshwater ones. The latest studies, however, strongly suggest that freshwater fish gave rise to marine ones.

There have been very few studies of alewives entering and breeding in Big Fresh Pond. Matthew Draud of Long Island University’s C.W. Post had two students study the North Sea alewife population in 2008. They counted thousands moving through the stream into the pond to breed. We don’t know if any bluebacked herring were discovered among the common alewives.

But whether more scientists join the fray or not, one thing we can be sure of: As long as there is the Peconic Bay system, and as long as there is a Big Fresh Pond and a stream connecting the two systems, there will be an alewife run each spring to the pond, and another leaving the pond each late summer.

What I find the most fascinating about the Big Fresh Pond alewives, however, is not the alewives themselves but the freshwater mussels that occupy the pond’s bottom.

In a feat that needs to be studied in detail but probably never will be in this pond, as Southampton College is no longer, we only know that mature alewives that leave the pond after spawning carry in their gills the tiny young of those mussels, which go to sea to find the food that will be necessary for them to pass through several intermediate stages on their way to adulthood.

But adulthood only comes after the alewives hosting them return to Big Fresh Pond and shed them, after which they drop to the bottom and develop the bivalve shell covering protecting them, so they can filter feed and develop and reproduce, creating more of those seafaring larvae to continue the cycle.

Adults can live into their 40s, during which period they can remain reproductively active and carry on like normal bivalve shellfish.