Factors affecting larval sea lamprey growth and length at metamorphosis inlampricide-treated streams

Larval sea lampreys Petromyzon marinus in seven lampricide-treated streams were studied to assess the effects of density and abiotic factors on growth , length at metamorphosis, and age at metamorphosis. Support for density-de pendent growth was not found in these streams. A linear relationship betwee n total length and age was found for all populations. The daily growth of l arvae in lampricide-treated streams was similar to that of populations that were never exposed to lampricide. Furthermore, the growth of stocked resid ual populations did not increase following a lampricide-induced reduction i n larval density. Differences in growth and length at metamorphosis among t hese streams were accounted for by abiotic factors. Larval growth was highe st in streams with an annual water temperature around 8 degreesC, moderate discharge (0.5-2.0 m(3)/s), and high conductivity (>300 muS). Length at met amorphosis, on the other hand, was inversely related to conductivity, annua l discharge, and annual mean temperature. A model of age at metamorphosis b ased on larval growth and length at metamorphosis, both as functions of wat er temperature, showed that age at metamorphosis was lower for populations showing linear growth with age (typically low-density populations) than for those showing compensatory growth with age (typically high-density populat ions).