Population Status And Habitat Requirements Of The American Brook Lamprey In Southeastern Minnesota

American brook lamprey ammocoetes, adults, and/or their spawning redds were observed at 23 stream locations in Olmsted, Winona, Fillmore, and Houston counties in southeastern Minnesota. During 1995 and 1996, adult lamprey (147 in 1995, 54 in 1996) were observed in spawning areas between 25 April and 9 May at 13 stream locations. Spawning occurred at water temperatures ranging from 12.615.5°C, and was concentrated at the head of riffles in water < 50 cm deep with bottom current velocity < 0.2 m/sec and substrates of cobble, gravel, and coarse sand. Spawning redds averaged approximately 200 cm2 in area, were dug out to an average depth of 5 cm below the surrounding sediment level, and generally were spaced 40-70 cm apart. Typical spawning group size was 4-6 lamprey per redd. Only 42 ammocoetes were collected from 13 stream sites, preferring water depths < 50 cm, water column velocities < 0.1 m/sec, and sediment organic contents < 12%. The size range of ammocoetes collected suggests the presence of possibly three size/age classes. At 150-m-long sites where ammocoetes were collected by single-pass electrofishing, the median number of ammocoetes collected was three. Three-pass removal sampling of ammocoetes in Pine Creek produced density estimates ranging from 0-1.68 ammocoetes/100 m2 (mean = 0.63/m2). Spawning populations of American brook lampreys in most streams surveyed were small, and ammocoete abundance was low. These apparently small populations should be given greater protection and their susceptibility to decline or disappearance should be examined.