Measuring the Growth Rate in Three Populations of Larval Lampreys with Mark–Recapture Techniques

The growth rate of larval lampreys (ammocoetes) is of critical importance for scientists and managers seeking to better understand, control, and protect lamprey populations. To date, measurements of ammocoete growth have often relied upon indirect methods (e.g., length frequency), but direct measurements of growth rate in wild populations are rare. Lamprey ammocoetes in three streams were individually marked with visible implant elastomer and were subsequently recaptured. Ammocoete growth was variable among sites and among sample events (from −0.035 to 0.18 mm/d; from −0.0022 to 0.012 g/d), and maturation to the juvenile or adult stage was estimated to take 4–10 years, with some animals possibly requiring more time. American Brook Lampreys Lethenteron appendix grew 0.13 mm/d or 0.0055 g/d on average, whereas the growth of Sea Lampreys Petromyzon marinus was variable, with ammocoetes experiencing significantly higher mean growth at one site (0.12 mm/d; 0.0025 g/d) than at the other site (0.032 mm/d; 0.00039 g/d). These estimates provide support for the generally long growth periods of ammocoetes but also suggest that variability plays a wider role even within populations. The variability in growth rate may provide ammocoetes with a highly flexible life history, allowing them to exploit habitats under a variety of conditions potentially encountered during development. Received June 16, 2016; accepted October 12, 2016 Published online December 12, 2016