Saving Small Fish on Long Island Will Help Big Predators, Too

Posted: 09-May-2005; Updated: 22-Feb-2006

An Alewives Tale

It is winter, and somewhere along the Atlantic coast swims a school of small, silvery fish. These fish are at most a foot or so in length, with a single triangular dorsal fin along their back and a deeply forked tail.  The fish are alewives (Alosa pseudoharengus), a member of the herring family (and sometimes called river herring). They are bound for the South Shore of New York's Long Island.

The alewives are about to embark on a remarkable migration that will take these humble fish from the depths of the ocean, along the coast, through estuarine bays, into rivers and streams and past Long Islanders' backyards. Their goal is to reach freshwater habitats far upstream along the Atlantic coast, including those in the South Shore tributaries, to spawn.  But in many Long Island rivers and elsewhere, the journey will end abruptly at a wall of concrete. 

Dams block nearly every major nursery area upstream of Great South Bay and its neighboring bays, from Hempstead to the Hamptons. These dams have been built from Colonial through modern times with little regard for their impact on fish.     
 
The Incredible Journey

The fish will make an incredible and often treacherous journey before confronting these barriers.  As spring approaches, the alewives somehow know it is time to migrate.  We do not know what exactly signals this change.  In any case, as winter nears its end, alewives know it is time to move.

	A school of alewives make their way upriver to spawn. (Photo: NOAA)

We also do not know where exactly our school is located when it begins its migration.  We know the fish do not travel far out into the open ocean but can still cover the continental shelf.  Many will not hug the coastline, as they can be caught in large numbers in depths of around 200 feet.  They are spread from the mid-Atlantic states up through the Canadian maritime provinces.  

But where they begin their migration does not necessarily relate to their final destination: alewives tagged in Nova Scotia's Bay of Fundy have been recaptured still within Nova Scotian waters, but have also been found in Massachusetts, Maryland and North Carolina.  Much of the offshore, over-winter phase of an alewife's life remains a mystery.     

Dinner for a Host of Sea Life

Over the winter, some of the alewives will fall prey to hungry tunas, billfishes, whales, dolphins and cod.  Leaving the deeper offshore waters hunted by these predators, the surviving members of the school make their way to the South Shore from late March to early June. Once there, they cross between the thin, sandy barrier islands that make up the Fire Island National Seashore and separate Long Island's southern bays from the Atlantic Ocean. Now within the South Shore Estuary Reserve, more alewives will die from the fierce thrashing attacks of bluefish or be swallowed in the broad gape of a striped bass. Seals will also move into coastal bays when the alewives begin their spawning run to feed on the migrating fish.

	An osprey catches an alewife to help refuel after its long migration. (Photo: courtesy Tom Arter)

The blues and stripers have also recently returned to Long Island from distant over-winter haunts. Bluefish have migrated the length of the Atlantic coast from the warm waters off Florida.  Striped bass have not traveled quite as far south to over-winter, but have still made a considerable trip from the waters off North Carolina and Virginia. Great South Bay and its smaller neighboring bays are now a convergence point of these Atlantic coast migrations of predators and their prey. 

The members of our alewife school that survive the gauntlet of blues, stripers and seals as they cross the bays and reach the river mouths now begin the final leg of their journey out of the brackish waters of the estuary and into freshwater.  As the spawning run progresses upriver, yet another migration meets that of the alewives. 

Ospreys have flown thousands of miles from the lush tropical rainforests of Central and South America to nest, breed and feed along the Long Island coast.  Their arrival is a time when they desperately need to replenish energy supplies in preparation for breeding. These agile and sharp-sighted "fishing hawks" scan the surface waters of rivers and bays for fish, ideally those up to 10 or 12 inches in length and one pound in weight. Those dimensions perfectly describe an adult alewife, and so the ospreys actively hunt the energy-rich fish. 

Hoping to dodge the ospreys' sharp talons as they dodged the hungry jaws of bluefish, striped bass and a myriad of other  predators, the remaining alewives push on upstream toward their spawning grounds.  Here is where the alewives often run up against dams and their long journey is abruptly ended. 

Removing Barriers for Alewives Has Cascading Benefits for Wildlife

Not only does the blockage of their migratory routes compromise the alewives' reproduction, but it also prevents them from acting as an living link between the sea, bays, rivers and lakes. For alewives play an important ecological role by delivering nutrients upstream. As diadromous fish  (species that use both marine and freshwater habitats during their lifetimes), they swim against the river's flow and help cycle nutrients back upstream that rivers have washed downstream.

	The narrow spillway at the Swan River dam in Brookhaven (left) prevents fish from reaching the large area of spawning habitat in Swan Lake (top right). Installation of a fish ladder like this one (bottom right) from the Parker River in Massachusetts can allow fish to swim past this obstacle (ladder photo from NOAA).

Many of these dams have outlived their purpose and could be torn down.  All could be redesigned with simple fish ladders to accommodate the migrations of alewives and other fish.  It is time to let the fish back in.

Despite the blockages, some fish will still spawn; alewives are quite resilient and can use a range of bottom types, flow conditions and salinity levels. But they often miss out on the most desirable habitat, which typically exists further upstream, or spawn in too-crowded conditions.  Accessible habitats are often degraded: stream banks may be stripped of  vegetation and vulnerable to erosion and silt runoff, and waters may be polluted.  The net result of blocked migration routes and degraded habitats, combined with losses at the hands of human predators, is fewer alewives along the South Shore, perhaps too few to adequately serve their important ecological roles in the overall ecosystem.

Alewives are not the only diadromous fishes that use the tributaries of Long Island's southern bays:  blueback herring (also called river herring), American eel and rainbow smelt still make their way up rivers along the South Shore to reach feeding, spawning and nursery grounds.  Sea-run brook, brown and rainbow trout make spawning runs in South Shore tributaries.

All play important ecological and economic roles, and all can benefit if the impacts they face are reversed.  Given the importance of diadromous species as forage fish and life-sustaining  links between the sea and freshwater habitats, conservation of these fishes is an important part of ecosystem-based management, wherein decisions are made not just with a single species in mind, but rather with an eye to the role that species play as part of an integrated ecosystem.   

Fisheries But a Shadow of What They Once Were

Long Island's diadromous species have long been popular quarry of fishermen, who catch American eels and river herring for food for people and for bait and three trout species fished for  sport.  But sadly, since the 1970s, commercial landings of river herring in the mid-Atlantic states have since steadily declined to negligible levels in recent years. Declines  in commercial landings of American eel have been ongoing for an even longer period of time, the eel fishery today is but a shadow of what it once was. Overfishing is certainly a part of these troubling trends, but increased blockages of waterways, habitat degradation and declining water quality have also contributed to the collapse of diadromous fish stocks.  

Little Fish in a Big Pond: How Long Island's Migratory Fish Fit into the Big Picture

Perhaps the most important role of Long Island's diadromous fishes is as food for the larger predators that support Long Island's economy and recreation, and the best scientific information on this role is for river herring. Up and down the Atlantic coast, alewives and blueback herring figure prominently into the diet of fish and wildlife that capture the attention of anglers and other outdoor enthusiasts.  Some striking figures:

• In the Chesapeake Bay, nearly 80% of the diet of striped bass can be river herring during May, when the herring migrate.
• In North Carolina, 33% of the diet of striped bass can be river herring during winter, rising to 50% during the spring migration period.
• Along the Northeast coast, from New Jersey to Maine, up to 33% of the diet of striped bass can be river herring during the spring migration period.
• In the Hudson River estuary, up to 40% of the diet of bluefish can be river herring during the summer months when bluefish return to cooler northern waters.
• In Saint John Harbor, New Brunswick, the abundance of harbor seals is five times the yearly average during the peak of the alewife run.
• Reproductive success of ospreys in Connecticut and Rhode Island has been up to 50% greater than Long Island birds.  Some biologists hypothesize that the difference is due to larger river herring runs in New England. Ospreys are intimately entwined with the history of the environmental movement on Long Island, and of Environmental Defense in particular. 

These figures all show the tremendous contribution that diadromous fish can make to key wildlife species.  Indeed, some speculate that, after the stunning revival of stripers on the Atlantic coast during the 1990s, their numbers, or at least the size and quality of stripers, are compromised today because of declining forage fish populations. Others have speculated that the devastating collapse of the Atlantic cod fishery was due in part to declines in numbers of alewives, depriving the cod of an important food source.  

 

What Environmental Defense Is Doing to Help

Despite the importance of diadromous fish, their plight has received scant attention along the South Shore - until now.  Environmental Defense has teamed up with an array of local stakeholders and other concerned groups, including the South Shore Estuary Reserve office, the New York Department of Environmental Conservation, U.S. Fish and Wildlife Service, Trout Unlimited, The Nature Conservancy, local municipalities and representatives of fishing organizations, to help conserve diadromous fish along the South Shore.

The group's goals are to:

• Install a fish ladder for the first dam on the Carmans River.
• Conduct a survey of South Shore tributaries to document the presence and size of existing diadromous fish runs.  Because there are a large number of tributaries and the arrival of migrating fish can be difficult to predict, this will require recruiting members of the local community to gather information -- school groups, naturalist clubs, fishing clubs and others who spend time on the South Shore rivers and creeks.  These informal observations, along with more formal scientific information, will help determine whether proposed development projects are likely to impact diadromous fish runs.  The data will also assist in planning the next generation of restoration projects along the South Shore.

There are numerous opportunities for diadromous fish restoration projects along the South Shore.  Our efforts will focus mainly on  opening migratory pathways, which is expected toresult in the greatest changes in fish populations.  We will explore the possibility of dam removal where possible, as this not only allows migration but also restores the overall river ecosystem.  Where removal is not practical, we will work to install fish ladders or step pools to allow fish to circumvent barriers.  Additionally, we will work to improve habitat and water quality, and reform fisheries management to help diadromous fish populations increase and serve their vital ecological roles.

	For more detailed information, read the full articlE [pdf].
	For more information on diadromous fish ecology and conservation, or to share ideas and observations, please contact Jake Kritzer at jkritzer@environmentaldefense.org.