Spawning ecology of the American brook lamprey, Lampetra appendix

We observed spawning American brook lamprey, Lampetra appendix, in coldwater streams in Minnesota to assess various aspects of their spawning behavior and spawning habitat requirements. Spawning occurred during April and May, at water temperatures ranging from 8.7 to 15.5 degrees C. Average adult lamprey length and mass differed significantly among streams, but there were no significant differences in length or mass between males and females. Overall sex ratio was 1: 1, although one stream had significantly more males than females and one stream held significantly more females. Lampreys spawned in groups of 2 - 14 individuals, averaging 4.2 adults per nest across all streams. Nests were constructed in gravel and cobble substrate just upstream of riffles, spaced at an average density of three nests m(-2). The typical nest was 16 cm in diameter in water 31 cm deep with a bottom current velocity of 14 cm s(-1), and was excavated to a depth of 4 cm below the stream bottom; however, some nest characteristics varied significantly in a few streams. Nests were larger in streams with larger spawning groups, deeper water, and slower current velocities. American brook lamprey exhibited spawning behaviors and spawning habitat requirements similar to those of other species of lamprey in North America.