Ichthyomyzon gagei Hubbs and Trautman, 1937
Southern Brook Lamprey
Basis for Listing
The geographic range of the Southern Brook Lamprey (Ichthyomyzon gagei) 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). The species has since been collected at several localities but remains restricted to the St. Croix River and its tributaries in Carlton, Pine, Kanabec, Chisago, 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 two lobes. Its mouth is a sucking disc with circumoral teeth that are bicuspid, distinguishing it from the Northern Brook Lamprey (Ichthyomyzon fossor), which has small, poorly developed teeth. 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.). 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). Ammoceotes of Minnesota lampreys within the genus Ichthyomyzon are extremely difficult to confidently identify.
Adult Southern 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. Southern Brook Lampreys have few, poorly developed, non-functional, unicuspid teeth in comparison to Northern Brook Lampreys which have few, degenerate, blunt, bicuspid teeth (Lyons et al 2000). Furthermore, in Minnesota both species do not overlap in distribution.
The Southern Brook Lamprey uses different microhabitats during different stages 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 bairdii) (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, living instead off body fat reserves. 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).
Southern Brook Lamprey and Chestnut Lamprey have been observed spawning together in the same nests in the St. Croix River system (Namekagon and Yellow rivers, WI), and samples from the adults and eggs were preserved for genetic analysis; however, there has been no funding available to run the analyses (J. Lyons, personal communication).
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 it 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 may be the case in Minnesota as well.
The recent inception of Minnesota’s Clean Water Legacy Program will eventually yield benefits to Southern Brook Lamprey habitats through nutrient and sediment load reductions.