Great Lakes Environmental Assessment and Mapping Project

Sea lamprey

Sea lamprey mouth
Sea lamprey mouth (Photo: T. Lawrence, GLFC)

The sea lamprey (Petromyzon marinus) is a primitive, jawless fish native to the Atlantic Ocean. It is considered one of the most detrimental invasive species to enter the Great Lakes.  It parasitizes lake trout, non-native salmon, lake whitefish, lake herring, rainbow trout, burbot and walleye.

  • Sea lamprey invaded Lake Ontario in the early 19th century via locks and ship canals from the St. Lawrence River. It's range expanded to Lake Erie and throughout the Great Lakes following improvements to the Welland Canal.  
  • Sea lamprey is an “anadromous” fish, meaning it spawns in rivers or streams, spends its juvenile phase in one of the Great Lakes (or, in its native range, the ocean), then returns to its natal river or stream as an adult to spawn.
  • Part of the sea lamprey’s life cycle is spent feeding parasitically on the blood of host fishes. The lamprey uses its distinctive suction cup mouth, sharp teeth, and rasping tongue to attach to a prey fish, pierce its skin, and feed on blood and other bodily fluids,
  • A sea lamprey can kill up to 40 pounds of fish during its 12-20 month parasitic phase.  In the 1940s and 1950s, sea lamprey contributed profoundly to the collapses of lake trout, whitefish, and chub populations.
  • The sea lamprey’s aggressive feeding behavior and its freedom from natural predators contributed to its success in the Great Lakes.


Sea lamprey control efforts

Today the Great Lakes are home to a very successful sea lamprey control program. The program is administered by the Great Lakes Fishery Commission (GLFC) in cooperation with Fisheries and Oceans Canada (DFO) and the U.S. Fish and Wildlife Service (USFWS).

Ongoing control efforts have reduced sea lamprey populations in most areas by ninety percent using the following measures:

  • Lampricide: The lampricide TFM (3-trifluoromethyl-4-nitrophenol) is used to kill larval sea lampreys in their spawning tributaries. The lampricide has little or no impact on other fish or wildlife.
  • Barriers: Barriers are used to block upstream migration of spawning sea lampreys. Most barriers are constructed to allow other fish species to migrate normally.
  • Sterile male release: Male sea lamprey are trapped during their upstream migration, sterilized, then re-released to compete with spawning males and reduce the reproductive success of female lampreys.
  • Assessment: Monitoring is an important tool used to identify high priority areas and determine the best times for sea lamprey control. Collection of population data is critical for continued success managing sea lamprey in the Great Lakes.

Despite the controls in place, sea lampreys are still prevalent enough in the Great Lakes to prevent a full recovery of the lake trout population. The GLFC calls sea lamprey control “the cornerstone of fisheries management - without sea lamprey control, stocking would be futile and fisheries rehabilitation would be fruitless.”


Mapping sea lamprey distribution as a Great Lakes stressor

We used estimates of the number of spawning adults entering tributaries to spawn as a proxy for the distribution and relative abundance of parasitic young lampreys in the Great Lakes.1



We estimated the lake area most affected by parasitic sea lampreys using an exponential decay model with the assumption that 10% travelled as far as 100 km from their natal river, and only 1% dispersed as far as 150 km.

Spatial distribution of sea lamprey as a stressor in the Laurentian Great Lakes (Inset: Northern Lake Michigan).

Data Sources: 

1. Estimates of parasitic sea lamprey adults entering spawning tributaries were provided by the Great Lakes Fishery Commission.