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Sea Lamprey

Petromyzon marinus

Illustration used with permission by NOAA Great Lakes Environmental Research Laboratory

Common name: Sea lamprey, lamprey eel

 

Scientific name: Petromyzon marinus (Petromyzon means “sucker of stone” and marinus means “of the sea”)

 

Classification: Sea lampreys are one of the most primitive of all vertebrate species alive today. They have remained largely unchanged since the Paleozoic Era (340 million years ago), and survived through at least four major extinction events.

 

They are chordates, meaning they have a spinal cord protected by vertebrae. However, they are also jawless and have a cartilaginous “skeleton”, like sharks. On the fish “tree of life”, lamprey show up earlier than cartilaginous fishes like sharks, and well before the creatures you might picture when someone mentions “fish”. Compared to fishes like trout and herring, lamprey lack many of the features we associate with fish, namely a bony skeleton and jaws filled with teeth, but also scales, paired fins, and gill covers. Even eels have the above features that lampreys lack, but due to their similar body shapes, lampreys are sometimes inaccurately called "lamprey eels”. 

 

Range: Native to the north Atlantic Ocean, including the Atlantic coast of North America from the Gulf of St. Lawrence to the St. Johns River in Florida and the Atlantic Coast of Europe and the Mediterranean Sea. 

 

Sea lamprey have also colonized all five Great Lakes, rapidly becoming invasive. They likely became established after the Welland Canal was completed, and widespread populations now overwinter and reproduce in tributaries throughout the Great Lakes basin. 

 

Identification: The long, cylindrical body of an adult sea lamprey is generally brownish-tan with mottled dark markings, but may also have greenish hues. Newly transformed juveniles are grayish blue dorsally fading to silvery white on their sides and belly, which is a typical pattern of marine countershading. Prior to spawning, males develop a very pronounced rope-like ridge on their back. All sea lamprey have two small dorsal fins, and 7 small gill openings on either side of their head set behind their eyes.

 

Their most distinctive feature, however, is the disc-shaped, suction-cup mouth ringed with small, sharp teeth that act as a rasp along with a file-like tongue. The lamprey is parasitic, and uses this suction cup mouth to latch onto fish to feed. 

 

Anadromous adults are commonly 24 to 32 inches (min. adult size about 18 inches). Maximum reported size is 47 inches. Ammocoete larvae are typically 4 to 5 inches, and about 5 to 8 inches by the time they enter the sea as transformants. Landlocked lamprey are smaller on average, with adults only reaching a maximum of 24 inches in length. 

 

Life history: Lamprey are anadromous across their native range, though they can live solely in freshwater in areas where they have been introduced (and become invasive). However, even these landlocked lamprey exhibit some form of diadromy, living in the open water as juveniles and ascending streams to spawn. Sea lamprey have a complex life cycle which consists of four stages - eggs, filter feeding larvae, parasitic juveniles, and spawning adults.

 

Sea lamprey begin life as blind, worm-like larvae (ammocoetes) that hatch from eggs in gravel nests in tributaries and drift downstream with the current. When they locate suitable habitat – typically silty or sandy stream bottoms and banks in slower-moving stretches of water – they burrow in and take up residence. They may stay in this larval form from 3-17 years, but usually transform after about 5 years into miniature adults (transformants). 

 

The transformants head to sea in the summer and fall, where they stay for about 12-18 months, and up to 2 years. During this time, they grow rapidly by parasitizing other fish. During the winter and early spring, mature adults stop feeding and begin to congregate in estuaries. Then, they enter freshwater spawning habitat in late spring and early summer, or whenever the water temperatures reach at least 40 degrees F (though spawning itself doesn’t usually start until the water is at least 50 degrees). Spawning streams are located by following pheromones released by ammocoetes living in those waters. Suitable spawning sites usually consist of rocky riffle areas that are shallow with fairly swift current, with substrate that is mostly gravel and some sand. There, they build distinctive nests (redds) that consist of a gravel depression accompanied by a downstream pile of rocks, which the lamprey picks up using its oral disk and moves into place. The male and female spawn just upstream of the nest, and the fertilized eggs (as many as 100,000) drift downstream and lodge in the gravel. The adults then stir up sand which cements the sticky eggs in place. Though each pair may spawn multiple times over the course of a few hours to days, lamprey are semelparous, and die shortly after spawning. The eggs incubate for a few weeks before hatching, starting the cycle over again. 

 

Diet: In their larval form, lamprey filter-feed on algae, detritus and microscopic organisms that live in the streambed. Once they transform into juveniles, however, they become parasitic. The juveniles latch onto fish with their oral disks and use their rough tongues to rasp away the fish's flesh so it can feed on its host's blood. Lamphredin, an anticoagulant, is secreted to prevent the host from healing. In the Atlantic Ocean, they are known to parasitize Atlantic cod, Atlantic herring, haddock, pollock, red hake, sturgeons, Atlantic mackerel, swordfish, and basking sharks. One lamprey can kill about 40 pounds of fish every year, which is why they have been so detrimental to Great Lakes fish populations. 

 

Ecological importance: Sea lamprey have a bad reputation because of their role in the decimation of fish populations in the Great Lakes. However, in Maine and other parts of their native range, sea lamprey do not feed while in freshwater and pose no risk to freshwater fish populations. Instead, they transport valuable marine nutrients into river ecosystems and provide important forage for predators and scavenger animals that range from eagles to coyotes to caddisfly larvae. They also serve as habitat architects while constructing their nests. As they pick up rocks from the bottom, compacted silt is loosed and washed away, creating ideal breeding grounds for Atlantic salmon and trout and improving overall stream health. Additionally, salmon, fallfish, common shiners, and brook trout are able to make use of abandoned lamprey nests for their own eggs.

 

Notes on invasive lamprey: Sea lamprey invaded the Great Lakes in the 1830s, following the construction of the Welland Canal. Prior to the canal’s existence, Niagara Falls served as a natural barrier to their migration. Within a decade, lamprey had gained access to all five Great Lakes, where they began predating on the lakes' commercially important fishes, including trout, whitefish, perch, and sturgeon. Their success in the Great Lakes can be attributed to hundreds of stream miles of excellent spawning and larval habitat, the abundance of host fishes at the time of invasion and a lack of natural predators. Within a century, the trout fishery had collapsed, largely due to the lamprey's unchecked proliferation. Today, the Great Lakes Fishery Commission coordinates control of sea lampreys in the lakes, which is conducted by the U.S. Fish and Wildlife Service and Fisheries and Oceans Canada. Field biologists set up barriers and traps in the streams that feed the lakes to prevent the lamprey's upstream movements, and apply special chemicals, called lampricides, that target lamprey larvae but are harmless to other aquatic creatures.

 

Cultural importance: Sea lamprey were used as food by Native Americans and later by some immigrants, particularly those from Eastern Europe. There are some people who still eat sea lamprey today, but much fewer than in the past. 

 

Threats: Most historic runs were lost due to the construction of dams and pollution. Lampreys are able to ascend falls, as long as they are not too steep and high, by clinging to the rocks with their oral discs to rest between bursts of swimming. Similarly, they can use the same method to ascend fishways, but are blocked by dams that do not include fish passage structures. 

 

Restoration efforts: Currently, there are no concerted efforts that specifically target sea lamprey, however the removal of dams and installation of fishways has helped restore historic runs of lamprey in rivers throughout New England. At least two studies in Maine in the last decade indicate that dam removals, while usually aimed at restoring endangered species like Atlantic salmon, benefit both the lamprey and the ecosystems they reside in. It is important to look at projects like these as part of a whole-ecosystem approach to restoration, since no one species exists in a vacuum. 

 

Fishery: Lampreys were considered a delicacy in Europe during the middle ages and there are historic accounts of a robust fishery in the Connecticut and Merrimack Rivers of New England. Today though, this is little more than a memory. Some lamprey are used to supply the needs of biological laboratories, where they can be used in cancer research because of their simple circulatory systems. Larvae are caught to be used as bait in the Susquehanna River and perhaps elsewhere along the mid-Atlantic coast.

 

The lamprey has never been of any commercial importance in the Gulf of Maine. The average fisherman might not even see one in a lifetime. There is one company that operates out of Pembroke, Maine that sells lamprey, but these specimens are primarily meant for educational purposes rather than eating. 

 

Sources:

 

https://oceanservice.noaa.gov/facts/sea-lamprey.html

https://portal.ct.gov/deep/fishing/freshwater/freshwater-fishes-of-connecticut/sea-lamprey

https://nas.er.usgs.gov/queries/factsheet.aspx?SpeciesID=836

https://www.fws.gov/species/sea-lamprey-petromyzon-marinus

https://cybrary.fomb.org/fgom.cfm?Petromyzon_marinus.htm

https://gulfofme.com/all-sea-life/kr3l0ehwe81ionb3kovbyz1ta4umms

https://www.nrcm.org/nrcm-creature-feature/sea-lamprey/

What a Long, Strange Fish It's Been

Sea lamprey, dam removal, and habitat restoration

https://atlanticsalmonrestoration.org/resources/fact-sheets/sea-lamprey-petromyzon-marinus

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