Ichthyomyzon gagei Hubbs and Trautman, 1937
Southern Brook Lamprey
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Basis for Listing
The geographic range of the southern brook lamprey is centered in the southern United States. It was unknown in Minnesota waters until 1985, when it was taken from a small tributary of the St. Croix River (Cochran 1987). As of 2008, the species had been collected from 31 sites in the St. Croix River and its tributaries in Carlton, Chisago, Kanabec, Pine, and Washington counties. The southern brook lamprey was listed as a special concern species in Minnesota in 1996 because of its very limited range in the state, the fact that it is disjunct from the contiguous southern populations and represents either a new species or a relict of the southern populations, and because of the vulnerability of its habitat to degradation.
The southern brook lamprey has a single dorsal fin that is divided into 2 lobes. Its mouth is a sucking disc with circumoral teeth that are bicuspid, distinguishing it from the northern brook lamprey (Ichthyomyzon fossor). The southern brook lamprey also has an oral disc that is narrower than its head and it reaches a maximum length of 16 cm (6.3 in.), which distinguishes it from the chestnut lamprey (I. castaneus). Adult southern brook lampreys are grayish or tan above and lighter below. Ammocoetes, the larval form, lack eyes, have a hood-like mouth instead of a sucking disc, and lateral line pores that are darker than their background (Hatch et al. in preparation).
The southern brook lamprey uses different microhabitats during different portions of its life history. Adults are found in very clear, small to large streams and rivers, with swift, permanent flow over sand and gravel riffles. Ammocoetes (larvae) are found burrowed in fine sediment or organic debris in areas with embedded woody debris, usually in lower gradient stream segments, and sometimes in silt pockets behind obstructions in main channels. Southern brook lampreys tend to be found where water is shallow, less than 1 m (3.3 ft.) deep, and may be found in waters cool enough to support trout. Spawning is associated with gravel substrate at the head of riffles and may occur in crevices beneath rocks and boulders. Frequent ecological associates include common shiners (Luxilus cornutus), longnose dace (Rhinichthys cataractae), hornyhead chubs (Nocomis biguttatus), johnny darters (Etheostoma nigrum), and mottled sculpins (Cottus bairdi) (Hatch et al. in preparation).
Biology / Life History
The southern brook lamprey is a non-parasitic species. It spends the majority of its life, 3-4 years, as an 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, southern brook lampreys do not feed. During spring, adults make an oval depression in the substrate by displacing stones and organic material with their oral discs, into which they spawn. They may spawn in aggregations of as many as 40 individuals. The spawning period is brief (< 1 week) and adults die a few days thereafter (Hatch et al. in preparation).
Conservation / Management
Although the southern brook lamprey population in Minnesota is apparently healthy, it is limited in range and highly disjunct from the southern population. This makes the population especially vulnerable to impacts such as habitat degradation. Additional research needs for the southern brook lamprey include Minnesota life history studies, genetic analysis, and identification of habitat guilds.
Conservation Efforts in Minnesota
More information about the southern brook lamprey's distribution, population size, genetics, and habitat requirements in Minnesota are necessary to better conserve this species. Lyons et al. (1997) found the species to be much more widespread in Wisconsin than just the St. Croix drainage, and this could be the case in Minnesota as well.