A (Fish) Tale of Two Herring

BARNSTABLE – Many are gathering at rivers and ponds across Cape Cod to watch the herring “run” through their annual migration.

River herring are known for their ability to return to the same freshwater body they spawned in to breed, even after a year out at sea.

But some nature observers are not aware that what they’re looking at may be two different species.

Alewives and Blueback Herring, though incredibly similar in appearance, are in fact slightly different.

It is believed that Alewives spawn before Bluebacks, usually when the water temperature is around 41 to 50 degrees.

Both species have an expected lifespan of up to 10 years, however a high rate of predation usually means that less than 1 percent of juveniles make it back to sea from their spawning grounds.

As a foodstuff, these species are invaluable to many predatory birds, land and marine mammals, and some commercially important species of other fish.

Their role in local ecosystems has been described as “invaluable” by local scientists, but human-caused disturbances have furthered the river herrings’ decline.

Once at sea, many are caught in commercial ocean trawlers fishing for a different type of herring.

Massachusetts and other coastal states declared a moratorium on harvesting river herring in 2005, and in 2009, NOAA’s National Marine Fisheries Service listed alewife and blueback as “species of concern.”