Growth, dynamics, and distribution of a population of the brook lamprey Lampetra planeri in a South Swedish stream

Abstract

Size and structure of a South Swedish population of Lampetra planeri larvae were studied during 5 yr. Population size fluctuated considerably within the studied section of stream with a general decline. The fluctuations were positively and strongly correlated (multiple R2= 0.85) with the population density at the beginning of each analysed period, while poorly correlated with such variables as heavy precipitation and temperature. Several factors suggest the entire larval population drifts downstream: fluctuations in the studied stream section, increasing mean size downstream, and incongruity in longitudinal distribution in surveys, performed with a 5‐yr interval. Growth, estimated both in caged larvae and from length frequency data, occurred mainly in autumn. High density in cages reduced the growth rate of larvae.