Fish and Aquatic Conservation

an artwork of River herring

Fish illustration by Laury Zicari, USFWS, Retired

River Herring:
Alewife and Blueback Herring

Our Scientific Name

Alosa pseudoharengus (alewife)
Alosa aestivalis (blueback herring)

By the Numbers

We both are 10 to 12 inches long, and weigh 0.5 pounds.

How to Identify Us

We look alike, and are often lumped together as “river herring” but we are really two different species. We are silvery in color with a single black spot just behind our eye, and alewife have a larger eye. We have sharply-angled bony scutes on our belly that feel like a saw. Alewives are grey-green and blueback herrings are blue-green on our dorsal (back) sides. We are thin or compressed from side to side, but long from our dorsal to ventral (belly) sides, and we both have a forked tail.

Why We Matter and What's Been Happening

We are food for many other animals, including other fishes, that people like to eat: striped bass, bluefish, weakfish, cod, haddock, halibut and tuna. Seals, birds and otters eat us. We are even eaten by whales! In the past, we were an important food for people, too.

Our Status

Our numbers became so low we were almost endangered, but we are beginning to recover in a few rivers. Government agencies are working to prevent overfishing out at sea, and are removing obstacles, like dams, so we can migrate back to our home rivers to spawn new generations of alewife and blueback herring.

did you know image
  • Alewives and blueback herring spawn in freshwater but spend most of their life at sea.

  • They don’t jump like salmon, but they can swim very fast in short bursts to pass through rapids.

  • They migrate from the ocean back to their home rivers in spring, where they were hatched to spawn.

  • Alewife and blueback herring use the same rivers, but alewife migrations happen earlier.

  • Alewives prefer to lay their eggs at night in slow moving water.

  • Blueback herring prefer spawning over rocks in fast-moving water during daylight.
  • River herring runs used to turn some rivers “silver” each spring when they migrated by the millions upstream. They are abundant now only in rivers where they can reach good spawning habitat.
  • Females produce 60,000 to 350,000 eggs, but only a few young fish survive to spawn 3 to 5 years later. The rest get eaten by other fish and animals.
  • Alewife is the preferred bait for lobstermen. Helping the alewife will help local lobstermen by providing them with fresh, cheap and better quality bait.
  • Rivers and lakes with alewife and blueback herring tend to grow larger sport fish like smallmouth bass, largemouth bass, trout and landlocked salmon.

More about Us image

image of river herring caught by biologists in the Connecticut River

These river herring were caught by biologists in the Connecticut River during annual fish surveys. The alewife (top) has a slightly larger eye than the blueback herring (bottom).

The "River Herring" Life Cycle

a diagram of the River Herring life cycle, showing from spawning to eggs to adults to migration to fresh water and ocean

When rivers begin warming in spring, adult alewife and blueback herring migrate up our rivers to spawn. Alewives run first and begin spawning when water temperatures are 51°F followed by bluebacks, which begin spawning when water temperatures reach 57°F. Spawning is very stressful and makes them vulnerable to being eaten. Adults that survive spawning head back to the ocean to recover and prepare for their next spawning season. Depending on water temperature, their eggs hatch in just 3-6 days. The young fish stay in freshwater until they grow large enough to start their journey in late-summer and fall to the estuary where the salt and freshwater mix, and then slowly out to sea where they join large schools of other alewives or blueback herring migrating along the Atlantic Coast. They stay in the ocean until they become adults at 3-5 years of age, and then return to their home river to spawn.

two maps of the East Coast of the USA, showing the ranges of species are found, on left for the alewife and on right for the blueback

Many coastal rivers along the East Coast supported huge river herring runs. They were so abundant that the fish were used for fertilizer, to feed hogs, as well as salted or roasted in smoke houses so they could be eaten over many weeks.

a dam blown up to restore river for fish

After a hundred fifty years, river herring can now migrate up the Rappahannock River in Virginia to their historic limit to spawn. Removing the Embrey Dam opened up the river to more fish which is helping to restore river herring.

How you can help statement: Get to know me, if you don’t already. Help make me visible to people who don’t have the chance to see me by sharing your stories about me. Get involved in efforts to help conserve my habitat and maintain my populations into the future.