Where Have All The Herring Gone?
by Catherine Schmitt, Science Writer with the Maine Sea Grant College Program

Every spring for hundreds of years, East Coast rivers and bays filled to the brim with fish as sea-run species left the ocean and headed upstream to spawn in freshwater. But three hundred years of fishing, dam construction, and pollution have shrunk fish populations to a small fraction of their historic numbers.

Same old story, right? Not quite for the river herring, which for multiple reasons is being viewed by scientists as a model species for ecosystem-based management, an often cited, but rarely applied concept in modern resource management.

Also known as sawbellies, gaspereau, and graybacks, river herring include the alewife, Alosa pseudoharengus, and blueback herring, Alosa aestivalis, both in the shad family. They are anadromous fish: born in freshwater, they spend most of their life at sea, but enter freshwater in spring, migrating upstream (as far as 250 kilometers) to spawn in slow-moving rivers and lakes. Almost every stream from Cape Sable to Cape Cod had an annual herring run.

The alewife run begins in spring when water temperature reaches 5 to 10 degrees Celsius, which is in late March or early April south of Cape Cod, early to mid-April in Massachusetts, and late April to mid-May in Maine. Blueback herring arrive about a month later.

While two-thirds of the spawning runs along the Gulf of Maine coast had vanished by the 20th century, a few runs persisted and even experienced a rebound after the Clean Water Act mandated water pollution control. These runs, however are residual vestiges of what they used to be, says Mike Armstrong of Massachusetts Division of Marine Fisheries. “Some of these rivers had runs of 200,000 fish. Now, we bring in 20,000 fish and think that’s a good number.”

Armstrong has been working with graduate student Holly Frank and others at the University of Massachusetts to research the effects of current restoration activities by tagging and tracking herring to see if they stay in the river, and find out where they spawn. “The Ipswich River project came out of our desire to determine whether it was worth our efforts to keep taking fish out of healthy runs to stock other rivers. We’ve been doing that for ten years in the Ipswich, with no success. If stocking isn’t working, we’ll stop doing it.” Only 50 herring returned the Ipswich this spring, and 1,000 more were stocked in spawning habitat in the section of river near the Topsfield Fairgrounds. Armstrong and Frank found that about half of the alewives they tagged stayed in the river long enough to spawn, but they didn’t find any juvenile alewives in the traps they deployed at the end of the summer.

The plight of the alewives in the Ipswich River is especially dire, because water withdrawals create conditions of extremely low or even no flow in some sections of the river. Armstrong estimates that the flow this past summer was maybe five percent of normal. What’s the purpose of restoring fish if there’s no water in the river?

While this makes the Ipswich seem like a unique case, in recent years river herring declines have been occurring coast-wide. On the Connecticut River, the number of herring passing the Holyoke Dam fishway decreased from 600,000 in 1985 to 1,300 in 2003. In Rhode Island, the state’s largest run declined from 290,000 fish in 2000 to 17,000 four years later. Massachusetts’s Mattapoisett River run decreased from 200,000 to 5,000 in one year. Some parts of New Hampshire and Maine also are starting to see numbers drop.

These declines have forced states to place moratoriums on harvesting river herring; Connecticut in 2002, Massachusetts and Rhode Island in 2005, and North Carolina in 2006. In Massachusetts, where the majority of the catch is used as bait for striped bass, the recreational fishing industry was supportive of the ban.

Death By A Thousand Stabs
What caused the crash in herring numbers? The National Marine Fisheries Service cites loss of habitat due to dams and other barriers, habitat degradation, fishing, and increased predation by striped bass as reasons for the decline. Scientists admit they know very little about the species.

Some scientists and fishermen believe that alewives and blueback herring may be getting caught up with Atlantic herring, a different species. When in the ocean, river herring tend to stick together, following congregations of zooplankton, and they will mingle with schools of Atlantic herring, leading some to suspect that they, too, have been victims of the same midwater trawlers that cannibalized Atlantic herring populations the past few years.

Alewives are heavier in front than Atlantic herring and the dorsal fin is closer to the snout. They are grayish green above and silvery on their sides. These differences are difficult to discern by looking at a pile of a million fish scooped up by a giant trawler. “Bycatch is a big question,” says Theo Willis of the University of Southern Maine, “especially the winter component. If river herring spend the winter south of Georges Bank, which is where we think they go, then they might get caught by Atlantic herring trawls.”

“It’s a crapshoot,” says Armstrong, “call it death by a thousand stabs. Predation is high. Some people blame the midwater trawlers, but we don’t have a smoking gun.” What we do have is a big, black box: the Atlantic Ocean, and whatever is happening to river herring while they are there. What makes river herring different than other fish that live in the black box is their role in the ecosystem and numerous complex relationships with other species.

Poster Child For River Restoration
When herring come into rivers, they are delivering nutrients from the ocean far inland to the upper reaches of watersheds, fueling predators like eagles, osprey, mink, and otter. The 20 to 40 percent that die after spawning contribute nutrients to lakes and streams (reviews by the Maine Department of Environmental Protection have found that this input does not negatively influence water quality, perhaps because river herring are natural components of these ecosystems). This nutrient delivery is reversed as young herring leave freshwater each fall, bringing nutrients back to the sea, along the way feeding larger fish like striped bass, Atlantic cod, tuna, and bluefish, as well as seabirds, seals, and whales. The role of herring in the food web in the subject of research by Willis and his colleagues, who are analyzing the diets of herring from the St. George River estuary, in a project funded by the Northeast Consortium and Maine Sea Grant.

Some believe that river herring are valuable to Atlantic salmon restoration, because alewives run upriver at the same time as young salmon smolts are making their way downriver to the sea. The alewives provide cover for the salmon, and their larger numbers made their population more resilient to predation. Alewives are the preferred host for the alewife floater, a type of freshwater mussel that as larvae attach to alewives and hitch rides upstream. In his now-famous paper in the journal Fisheries, Ted Ames of the Penobscot East Resource Center wrote that the disappearance of river herring may have disrupted the traditional movement patterns and arrival times of inshore spawning populations of Atlantic cod, because cod are a major predator of herring. If so, the restoration of coastal populations of river herring may also be important to restoration of coastal Atlantic cod fisheries.

“River herring beg for ecosystem management. If there is a poster child, this is it,” says Armstrong, “We can’t destroy our watersheds, cut herring populations to low levels, then bring striped bass back to record numbers. Species do not exist in a vacuum.”

Now, because river herring populations are so small, they are much less resilient to predation and other threats. Another factor that makes them less resilient is a lack of age diversity. Alewives can live as long as nine years and spawn three or four times, but today’s population is mostly four and five year-olds that only spawn once. Armstrong says that having a diversity of year-classes would also provide resiliency. “If you only have one or two year-classes, and they don’t spawn, you’re finished as a run.” Armstrong and his colleagues are trying to sort out demographics, and are working with fisheries managers in other states to find long-term ways to synthesize data for the whole coast, to see if the story is the same everywhere: broken watersheds, no fish, and a focus on parts instead of the whole.