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American Brook Lamprey

(Lethenteron appendix)

American brook lamprey NH Conservation Status: Endangered


State Rank: Critically imperiled


Scientific Name: Lethenteron appendix


Distribution:The American brook lamprey inhabits the Great Lakes, Atlantic coastal, and Mississippi drainages from the St. Lawrence River south to North Carolina, and west to Minnesota and Arkansas. In New Hampshire, American brook lamprey populations have only been confirmed in the Oyster River watershed.


Description: The American brook lamprey is a small eel like fish, similar in appearance to a juvenile sea lamprey. Unlike the sea lamprey, the disc shaped mouth of a mature American brook lamprey contains only small teeth arranged in pairs. The mouth of the sea lamprey is filled with well developed teeth arranged in concentric rings. Immature lamprey, called ammocoetes, lack fully developed eyes or teeth and have a darker pigment than the light gray color of the adults. American brook lamprey ammocoetes are difficult to distinguish from sea lamprey ammocoetes. Behind the nostril, there is an unpigmented area which is twice the size of the nostril in the American brook lamprey and approximately the same size as the nostril in the sea lamprey.


American brook lamprey

The well-developed eye and suction cup shaped mouth indicate that this American brook lamprey is sexually mature.


Species commonly confused with:

Sea lamprey, juvenile American eel


Habitat: The American brook lamprey depends on streams and rivers with cooler temperatures, sand and gravel substrate for spawning, and areas of loose sand or silt for burrowing ammocoetes. American brook lampreys in the Oyster River are usually found in areas where the river channel meanders through open wetlands, especially in the fine sediment trapped among the wood left over from abandoned beaver dams.


Life History: Adults spawn at the head of riffle areas over coarse sand and gravel substrate. Spawn­ing adults construct small nests by moving stones with their disc-shaped mouths. After spawning, the adults die.  Following emergence from the redd, larvae (ammocoetes) drift downstream to areas of slower flow where they burrow into the sedi­ment and filter feed on organic detritus for about 5 years.  Ammocoetes pre­fer to burrow in medium to fine grained sand mixed with organic matter.


Origin: Native


Conservation/Management: American brook lamprey are vulnerable to human activities that impact free flowing, riverine and riparian habitat. In New Hampshire, the American brook lamprey is only known to exist in a small fraction of the Oyster River Watershed. Surveys indicate that the species’ distribution within the watershed has decreased since the 1980s. To avoid extirpation of the American brook lamprey from New Hampshire, it is critical that the Oyster River maintain all the properties of a healthy, free flowing river. This includes seasonally fluctuating flows, sufficient water during low flow periods, the ability for wood to enter the stream channel, and other attributes associated with intact riparian zones.


American brook lamprey

Immature American brook lampreys, called ammocoetes, have no eyes or teeth.  The white spot near the tip of the snout is larger than that of a sea lamprey ammocoete.

Groundwater: American brook lamprey ammocoetes (juveniles) depend on a steady supply of unpolluted water for filter feeding. Water withdrawals during the summer have the potential to lower the water table, increasing water temperatures and reduce dissolved oxygen levels. This may stress or cause mortalities to brook lampreys and other aquatic organisms. Low water levels also reduce the available habitat and individuals can become exposed or isolated in stagnant backwaters. Ammocoetes can be a vulnerable prey item if forced to migrate long distances to find suitable burrowing habitat. American eels and wild brook trout are examples of two predator species that may target the slow swimming juveniles. These problems would be exacerbated in natural drought years.


Fragmentation: In the fall, mature American brook lamprey begin to move toward wintering areas from which they will access spring spawning habitat. Freedom of movement, both among and between populations is important for maintaining sufficient gene flow and increasing the distribution of the species within the watershed. Therefore it is important that all road/stream crossings encountered by brook lamprey do not act as barriers to dispersal. Road/stream crossings are also sources of sedimentation due to scouring and sediment deposition from inappropriately sized culverts and bridges as well as road washouts during flood events. Increased erosion and sedimentation from stream crossings can bury ammocoete nursery habitat with road fill or wash away the fine gravel needed by adults for spawning habitat.


Riparian zone: Intact riparian habitat is essential for maintaining a healthy American brook lamprey population. Stream bank vegetation provides shading, which reduces extreme temperature fluctuations (Welsh 1991). Trees and shrubs that fall into the river also trap sediment, which brook lamprey ammocoetes are able to burrow into. In some reaches, fallen trees and the remnants of old beaver dams trap fine silt or gravel and provide the only suitable habitat among substrate otherwise dominated by clay and boulders. Riparian zone vegetation also provides a buffer against runoff from parking lots, roads, or lawns which may contain pollutants. Intact riparian areas accommodate flows at flood stage as water levels crest banks and access flood plains. This process can dissipate erosive forces. When bank armoring techniques are instituted, these erosive forces remain restricted to the wetted channel.


Impervious surfaces:Impervious surfaces and stormwater management practices throughout a watershed combine to impact river and stream habitat. The Oyster River is already above 10% impervious surface coverage, a threshold above which aquatic habitat shows clear signs of degradation. Evidence of aquatic habitat degradation may be detected in watersheds with impervious surface coverage as low as 4%. Impervious surfaces inhibit groundwater recharge by causing surface runoff, and its associated toxins and high temperatures, to flow directly into rivers and streams instead of absorbing into the ground. Reduced groundwater recharge can affect water levels during periods of little or no precipitation, when all stream flow is derived from groundwater. Stormwater management designs that drain parking lot and road runoff directly into rivers and streams have a direct effect on habitat quality. Streams receiving stormwater drain pipes become subject to flash flooding and often show signs of widening or eroding banks. Pollutants commonly found on paved surfaces, including motor oil, gasoline, and road sand/salt, are chronically washed into aquatic habitats. Stormwater that flows over hot pavement may also cause temperature spikes at the points where the stormwater drains into the stream. The use of Low Impact Development (LID) practices can reduce the effects of stormwater runoff by promoting infiltration into the ground. For more information on LID, refer to the University of New Hampshire Stormwater Center website.



  • Monitor American brook lamprey populations for evidence of further decline.
  • Encourage land protection within the Oyster River watershed that will maintain habitat quality for brook lamprey.
  • Work to reduce fragmentation in the Oyster River mainstream and tributaries.
  • Encourage zoning that protects riparian zones throughout the Oyster River watershed, regardless of stream size.
  • Review land uses and permits for development that may impact American brook lamprey populations.
  • Improve stormwater management practices and protect water quality throughout the Oyster River watershed.


See also: Wildlife Action Plan Species Profile PDF Document