Blueback herring (Alosa aestivalis)

Synonyms: Pomolobus aestivalis

Common Names: River herring, blueback shad, glut herring, big-eye herring

Description:

Blueback herring (Alosa aestivalis) is a small, silvery, herring-family fish native to the Atlantic coast of North America, where it lives in the ocean and swims up rivers to spawn [1][2]. It becomes a problem when people move it inland ? stocked or released into reservoirs and lakes, and reaching the Great Lakes through canals ? where it does not belong and harms native fish [1]. MISIN tracks it because, in inland waters such as the Great Lakes, it eats the eggs and young of native fish and strips out the tiny zooplankton those young fish need [1].

Identification:

Blueback herring is a slender, silvery fish about 5 to 12 inches long, with a deep bluish-green back and a row of hard, saw-toothed scales (called scutes) along the belly that feel sharp if you run a finger along them [1]. It looks almost identical to the closely related alewife, and even biologists mix the two up; the surest difference is the color of the lining inside the belly cavity ? dark gray to black in blueback herring, pale or silvery in alewife ? along with blueback's smaller eye [1]. In its native Atlantic range it is most noticeable in spring and early summer, when adults crowd up coastal rivers and streams to spawn; in inland lakes it lives out in deep, open water [1].

At-a-glance cues:

1. Slender, silvery fish 5 to 12 inches long with a bluish-green back [1]
2. A row of hard, saw-toothed scales (scutes) along the belly [1]
3. Dark gray-to-black lining inside the belly cavity (pale or silvery in the look-alike alewife) [1]
4. Spawns in rivers and streams in spring to early summer [1]

Habitat:

Blueback herring is native to the Atlantic coast of North America, from Nova Scotia south to Florida [1][2]. It is anadromous ? it spends most of its life in the ocean and moves into freshwater rivers and streams to spawn [1]. It is not native to inland waters: it has been introduced into reservoirs and lakes across the southeastern and mid-Atlantic states as forage for sport fish, and it has spread into the Great Lakes, reaching Lake Ontario by 1995 through the New York canal system [1][3]. In these inland lakes and reservoirs it lives in deep, open water [1].

Reproduction:

People are the main reason blueback herring turns up where it doesn't belong. It is stocked into reservoirs as food for game fish, and anglers spread it by dumping leftover live bait; once it is in a connected waterway, it spreads on its own through canals and locks between lakes and rivers [1]. Because it spreads largely by bait buckets and waterway connections, the key to stopping it is never moving live fish or bait between waters [1].

For its life cycle: adults spawn in spring and early summer, releasing large numbers of eggs in rivers and streams, and the young drift and grow in open water [1]. Landlocked inland populations tend to be smaller and shorter-lived than the sea-run fish [1].

Impact and Damage:

Blueback herring is not a hazard to people, but where it is introduced inland it damages native fisheries by disrupting the food web [1]. It feeds heavily on zooplankton ? the tiny floating animals that young native fish depend on ? and can wipe out the larger kinds, shifting the whole plankton community [1]. It also eats the eggs and larvae of native fish [1]. In some reservoirs its arrival lined up with drops in popular game fish such as largemouth bass and walleye, and in the Great Lakes it competes with native fishes and may set back the recovery of species such as cisco and lake trout [1].

It is worth noting that this is a native fish that is harmful only when moved out of place: along the Atlantic coast, where it belongs, blueback herring is itself in decline and a species of conservation concern [2]. The "invasive" problem is strictly about inland waters where people have introduced it [1][2].

Similar species:

Alewife (Alosa pseudoharengus) is nearly identical to blueback herring ? the two are so alike that they are often lumped together as "river herring," and even biologists misidentify them by appearance a fair share of the time. The most reliable differences are the lining of the belly cavity (dark gray to black in blueback herring, pale or silvery in alewife) and the eye, which is smaller in blueback herring and larger in alewife [1].

Monitoring and rapid response:

Signs to watch for:

1. Schools of small, silvery, bluish-green-backed herring with sharp belly scutes in inland lakes or reservoirs where they were not before [1]
2. Spawning runs of small herring up tributary rivers and streams in spring to early summer [1]
3. Catches of "river herring" in waters connected to the Great Lakes or to stocked southern reservoirs [1]

What you can do:

1. Never move live fish or bait between water bodies, and never dump a bait bucket into a lake or river ? this is the main way blueback herring spreads [1]
2. Do not use blueback herring or unknown "river herring" as live bait, and do not release leftover bait fish [1]
3. Drain water from your boat, livewell, and gear between trips, and do not carry water or fish from one water body to another [1]
4. Learn to tell it from alewife ? check for the dark belly-cavity lining ? so you can report it accurately [1]
5. Lake and fishery managers can monitor open-water and tributary catches and track spread along connected waterways [1]

When to call a professional:

1. A suspected new inland population ? report it to your state fisheries agency and to MISIN so managers can confirm it and respond [1]
2. For chemical control options, contact a licensed applicator or your local cooperative extension office.

Report sightings to MISIN. Help track this species' spread by submitting observations through the MISIN web site or the MISIN mobile app (Android, iOS, Windows, and macOS). Photos at multiple angles paired with a precise GPS location are the most valuable data for confirming new occurrences and triggering rapid-response review.

Credits:

1. U.S. Geological Survey, Nonindigenous Aquatic Species (NAS) Database. Alosa aestivalis (blueback herring). nas.er.usgs.gov
2. U.S. Fish & Wildlife Service. Blueback Herring (Alosa aestivalis). fws.gov
3. Center for Invasive Species and Ecosystem Health (Bugwood / invasive.org). Blueback herring (Alosa aestivalis). invasive.org

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