Sea lamprey (Petromyzon marinus)

Common Names: lamprey eel, great sea lamprey, lamprey

Description:

Sea lamprey (Petromyzon marinus) is an eel-like, jawless fish native to the Atlantic Ocean that invaded the Great Lakes through shipping canals in the early 1900s [1][2]. It attaches to other fish with a sucker-like mouth and feeds on their blood and body fluids, often killing them [2][3]. MISIN tracks it because it devastated Great Lakes fish populations and is now the target of one of the largest invasive-species control programs in the world [2].

Identification:

The sea lamprey looks like a long, narrow eel, but it is not a true eel. It is usually about 12 to 24 inches long, with a smooth, scaleless body that is blue-gray to olive-brown on the back, often with dark marbling [1][2]. It has no paired side fins and two close-but-separate fins along the back near the tail [1]. Behind each eye sits a row of seven small round gill openings instead of a single gill cover [1]. Its most striking feature is its mouth: a round sucking disc, as wide as or wider than its head, ringed with circles of sharp teeth around a rasping tongue [1][2].

Adults are easiest to see in late winter and spring, when they swim up rivers and streams to spawn [1][2]. The rest of the year you are more likely to notice their work than the animal itself ? round or oval wounds and scars on caught fish such as lake trout, whitefish, and salmon [2].

At-a-glance cues:

1. Round, jawless sucker mouth ringed with circles of sharp teeth [1][2]
2. Seven small round gill openings behind each eye ? no gill cover [1]
3. Eel-like body with no side (paired) fins and two fins near the tail [1]
4. Round or oval open wounds and ring-shaped scars on host fish [2]

Habitat:

Sea lampreys are native to the Atlantic coasts of North America and Europe and the Mediterranean Sea [1]. In the ocean they normally live as adults at sea and swim up rivers to spawn, but in the Great Lakes they complete their whole life in fresh water [1][2].

The young live burrowed in the soft sediment of clean streams and rivers, while the adults feed out in open lake water [1][2]. As parasites, their "hosts" are other fish. They attach to large-bodied fish such as lake trout, whitefish, salmon, and other species, and a single lamprey can move from host to host as it feeds [2].

Reproduction:

Sea lampreys spread into the Great Lakes by following shipping canals that bypassed natural barriers like Niagara Falls, which had long kept them out of the upper lakes [1][2]. From there they moved through connected rivers and lakes [2]. People can move them, too ? moving water, fish, or bait between water bodies risks carrying lampreys or their larvae to new waters [2].

In late winter and spring, adults swim up tributary streams, build gravel nests, spawn, and then die [1][2]. A single female can lay tens of thousands of eggs [2]. The young hatch and burrow into the soft stream bottom, where they filter-feed for several years before transforming into the parasitic adult form and moving to the lake [1][2]. Adults then feed on fish for about 12 to 18 months before returning to streams to spawn [2][3]. Because the larvae and spawning adults are concentrated in streams, that is where control efforts are focused [2][3].

Impact and Damage:

Sea lampreys are not a danger to people ? they feed on fish, not humans [2]. Their damage falls on fish and on the economies that depend on them. A single sea lamprey can kill up to about 40 pounds of fish during its 12-to-18-month feeding phase, and fewer than one in seven fish survive a sea lamprey attack [2][3].

After sea lampreys spread through the Great Lakes, native fish populations collapsed. In the upper Great Lakes, the yearly lake trout catch fell from roughly 15 million pounds to a small fraction of that within a few decades [2]. The loss rippled through commercial fishing, sport fishing, tourism, and the jobs tied to them [2]. Ecologically, by killing huge numbers of lake trout, whitefish, and other native fish, sea lampreys helped unravel the food web and contributed to the decline ? and in some cases the disappearance ? of native fishes such as several cisco species [1]. Ongoing control now holds sea lamprey numbers down by about 90 percent, but the threat remains and the work never stops [2][3].

Similar species:

A few native fish can be mistaken for the sea lamprey, but key features set it apart.

Silver lamprey (Ichthyomyzon unicuspis) is a native lamprey that also attaches to fish, but it is much smaller (usually under 15 inches) and has a single fin along its back, while the sea lamprey has two separate fins near the tail [1].

Chestnut lamprey (Ichthyomyzon castaneus) is another native parasitic lamprey, also smaller than the sea lamprey and with a single back fin and fewer, blunter teeth [1].

American brook lamprey (Lampetra appendix) is a small native lamprey that does not feed on fish at all as an adult; it has weak, poorly developed teeth and never grows to the sea lamprey's size [1].

American eel (Anguilla rostrata) is a true, jawed fish that looks eel-like but has a normal jawed mouth, a single gill cover instead of seven holes, and paired side fins ? none of which a lamprey has [1].

Monitoring and rapid response:

Signs to watch for:

1. Eel-like fish with a round, jawless sucker mouth full of teeth, especially in streams during spring spawning runs [1][2]
2. Round or oval open wounds and ring-shaped scars on caught fish such as lake trout, whitefish, and salmon [2]
3. Lampreys turning up in inland lakes or streams where they were not seen before [2]

What you can do:

1. Report any sea lamprey you find ? early reports from new waters are the most valuable [2]
2. Never move water, fish, or bait between water bodies, and never use lampreys as bait, since this can carry them or their larvae to new waters [2]
3. Clean, drain, and dry boats, trailers, and gear before moving them between lakes and rivers [2]
4. If you fish, note and report lamprey wounds on the fish you catch ? anglers' observations help managers track where lampreys are active [2]
5. For lake associations and natural area groups: share sightings with your state fishery agency, support stream barriers and monitoring, and help spread the word about not moving water or bait [2][3]

When to call a professional:

1. Sea lamprey control across streams and lakes is run by trained agencies and the Great Lakes Fishery Commission using barriers, traps, and stream treatments ? report findings to your state fishery agency rather than trying to control lampreys yourself [2][3]
2. Any sighting in a new inland lake or stream, which may trigger a rapid-response assessment [2]
3. 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 Database. Petromyzon marinus (Linnaeus, 1758) ? Species Profile. nas.er.usgs.gov
2. Great Lakes Fishery Commission. Sea Lamprey. glfc.org
3. Siefkes MJ (2017). "Use of physiological knowledge to control the invasive sea lamprey (Petromyzon marinus) in the Laurentian Great Lakes." Conservation Physiology 5(1):cox031. semanticscholar.org

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