It’s not something you see around here very often. Imagine a river absolutely brimming with fish, a seemingly endless ribbon of blueback herring swimming with determination against the current, their silver backs shining in the sun.

It’s a sight to behold — and if you know where and when to look, you can see it year after year here on the South Shore.

Every April our local rivers come alive as thousands of blueback and alewife herring make their annual migration from the sea to their spawning grounds in the upper reaches of the watershed. The arrival of the herring is a sure sign of spring, as it indicates that water temperatures have warmed to a cozy 51-57 degrees.

If you watch from the bridge over the South River at Veterans Memorial Park in Marshfield you are likely to see them. Go in the early morning or late afternoon and look down into the water. If the conditions are right (remember this is entirely dependent on water temperature) you will see one fish after another fiercely battling the current to make its way upstream. On some days you may only see one fish — or perhaps none at all; but on others the stream will be so choked with herring that you’ll think you could cross the river simply by walking on their backs.

River herring such as the blueback and alewife are native to the eastern coast of North America, appearing from Newfoundland to Florida’s St. John’s River. These anadromous (migratory) fish live almost exclusively in the ocean, but migrate to fresh water once each year to spawn.

Bluebacks and alewives are closely related; in fact the casual observer will have difficulty telling one from the other, as they are distinguished only by subtle differences in scale pattern. Bluebacks tend to spawn in the main stream of a river or brook, while alewives prefer headwater ponds for their mating games.

The river herring spawning season extends from April to mid-July, depending on the temperature of the water. The males arrive first, and the females are not far behind. Tens of thousands of eggs are deposited in the water, hatching over the course of the summer. While the parent fish return to the ocean shortly after spawning, the juveniles remain in their home streams until fall. Or at least the strong ones do — less than 1% of these neophyte herring survive long enough to return to the sea.

Most herring return year after year to spawn in the same watershed in which they hatched. They are guided, scientists think, by their sense of smell.

River herring are small fish, rarely exceeding 12” in length or 2/3 lb in weight. They feed on zooplankton such as the eggs and larvae of fish, insects, and other aquatic creatures. In turn, larger fish such as bluefish and striped bass, as well as gulls, terns, and other seabirds feed on the herring.

Here on the South Shore the blueback herring population far exceeds the alewife. This is probably because access to the headwater ponds that alewives prefer was blocked centuries ago by the construction of mill dams. Popular area fish runs such as French Stream in Rockland, and the North River’s First, Second, and Third Herring Brooks all contain dams that place obstacles along the path of migratory fish. While ponds such as Studley’s, Jacob’s and Old Oaken Bucket may be ideal spawning grounds for migrating alewives, our industrial advances have rendered them inaccessible.

River herring populations on the South Shore have been relatively low since Colonial times, as a result of overfishing, dams, and mill-related pollution. Thanks to stocking programs and the construction of fish ladders (which help fish climb the steeper portions of streams) however, the numbers have begun to grow. While in 1920 there were only nine active herring runs from Maine to Massachusetts, now there are more than 100 of these in our state alone. Removing inactive dams might help to increase numbers further.

River herring used to be a popular foodstuff in this area — they are said to be similar to but not as flavorful as sardines — but these days they are generally not caught for consumption. In fact, most anglers don’t go after herring at all. Small in size, bluebacks and alewives are more often used as bait to lure the larger and more palatable American shad and striped bass, which will begin their own migratory runs later this season.

Pembroke’s Town Herring Run on the aptly-named Herring Brook is another ideal site to view migrating bluebacks and alewives. If you do stop to see them, consider this: every one of those fish has fought its way upstream from the ocean. Twelve miles of North River, plus several more of Herring Brook is a considerable journey even for a canoeist or kayaker, even with the winds and tides in her favor. Imagine swimming the entire distance, and fighting the current as well.

by Kezia Bacon, Assistant Director, North and South Rivers Watershed Association
April 1997