Ichthyomyzon fossor Reighard and Cummins, 1916
Northern Brook Lamprey
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Basis for Listing
The Northern Brook Lamprey (Ichthyomyzon fossor) went undiscovered in Minnesota until 1986, when it was collected from the Blackhoof River in Carlton County and the Zumbro River in Olmsted County. It has subsequently been collected in Roseau, Lake of the Woods, Koochiching, Itasca, St. Louis, and Pine counties in the north; Dodge, Mower and Fillmore counties in the southeast; and additional populations are expected to be found. These populations represent the northwestern edge of the species' range, which is centered in the Upper Midwest. The Northern Brook Lamprey is at some risk from reduced water quality due to land use practices and from lampricide treatments of parasitic Sea Lamprey (Petromyzon marinus) (Hatch et al. in preparation). For these reasons, it was listed as a special concern species in Minnesota in 1996.
The Northern Brook Lamprey has a single, continuous dorsal fin that may or may not be divided by a shallow notch, connected to a short, round, caudal fin. Its mouth is a sucking disc, with small, poorly developed teeth. Adult length is usually less than 16 cm (6.3 in.). Adults are grayish brown dorsally, with a pale median line down the back, and lighter ventrally. The posterior portion of the tail is darker, almost black. Females tend to be slightly larger. Breeding males have a urogenital papilla, and breeding females have an enlarged, post-anal fold, with eggs often visible through the body wall. Ammocoetes, the larval form, lack eyes and are similar in coloration to adults but have a hood-like mouth instead of a sucking disc. Ammoceotes of Minnesota lampreys within the genus Ichthyomyzon are extremely difficult to confidently identify.
Adult Northern Brook Lampreys can be easily distinguished from parasitic lampreys (Chestnut Lamprey (I. castaneus) and Silver Lamprey (I. unicuspis)), which grow larger, have large sucking discs, and numerous, well developed, rasping teeth used to ingest blood from their fish hosts. Northern Brook Lampreys have few, degenerate, blunt bicuspid teeth in comparison to Southern Brook Lampreys which have somewhat more developed, unicuspid teeth (Lyons et al 2000). Furthermore, in Minnesota both species do not overlap in distribution.
The Northern Brook Lamprey uses different microhabitats during different stages of its life history. Adults are typically found over coarse substrate, sand, or gravel; in swifter waters, riffles, or runs. Ammocoetes are found burrowed in fine sediment or organic debris, in side channels or other quiet water in areas with embedded woody debris. Spawning occurs in crevices beneath rocks and boulders (Hatch et al. in preparation). The species is most commonly found in clear streams averaging 19 m (62 ft.) wide and 0.7 m (2.3 ft.) deep and usually in moderately warm water.
Biology / Life History
The Northern Brook Lamprey is a non-parasitic species. The majority of its life, 3-6 years, is spent as a blind ammocoete, partially buried in sandy substrate. Ammocoetes feed on drifting, suspended, organic detritus, algae, and bacteria, or nutrients drawn from the surrounding sediment. Transformation to adults occurs over 2-3 months in late summer or early fall. As adults, they do not feed, living instead off body fat reserves. During spring spawning, adults make a nest by displacing stones and organic material until an oval depression is formed. As many as seven or eight individuals can be involved in nest building, and they may spawn in aggregations of 10-30 individuals. Adults die a few days after spawning. Eggs hatch 12 days after fertilization, and the young are free-swimming when they hatch (Hatch, in preparation).
Hybrids of Northern Brook Lamprey and parasitic Silver Lamprey (I. unicuspis) are viable, suggesting the two species have recently diverged or are ecotypes of one species. Recent genetic research supports the latter hypothesis (Ren et al. 2016).
Conservation / Management
The apparent decline of the Northern Brook Lamprey in North America is a result of habitat degradation and incidental poisoning. Streams in which they occur should be protected from degradation by maintaining riparian buffers, avoiding contamination, and employing best management practices for timber harvest in surrounding forests. The species may also be adversely affected by lampricide treatments (TFM: 3-trifluoromethyl-4-nitrophenol) for parasitic lampreys, especially in the Blackhoof River population. Although suitable habitat is limited in North Shore streams, TFM may have eliminated populations before their discovery (J. T. Hatch et al. in preparation).
Future surveys are recommended for southeastern Minnesota streams, where the Northern Brook Lamprey have a very spotty distribution. Introductions to North Shore streams using the Blackhoof River population as donor stock should be considered, if non-lethal alternatives are developed for Sea Lamprey control in Lake Superior.
Conservation Efforts in Minnesota
Because the Northern Brook Lamprey has a highly restricted range and little is known about the Minnesota populations, information regarding its distribution, population size, life history, habitat requirements, and genetics are necessary to determine the need for monitoring and/or management. There are currently no management plans directly aimed at the Northern Brook Lamprey.
The recent inception of Minnesota’s Clean Water Legacy Program will eventually yield benefits to Northern Brook Lamprey habitats through nutrient and sediment load reductions.