A production estimate approach to analyze habitat and weather effects on recruitment of two endangered freshwater fish

Abstract

Factors affecting the early life survival of fishes are often difficult to demonstrate because variable immigration and mortality rates coupled with noncontinuous sampling may confound estimates of mortality and bias inference to more numerous smaller individuals. The larval production estimate (LPE) method eliminates these problems by compensating catch data for size- or age-specific mortality and growth and back-calculating abundance at a predetermined size or age. Despite its utility, LPE has not been widely applied in studies of freshwater fish recruitment. We executed an LPE analysis using 10–14 mm and 15–19 mm size classes of Upper Klamath Lake’s (UKL) endangered Lost River suckers ( Deltistes luxatus ) and shortnose suckers ( Chasmistes brevirostris ) for five cohorts per year for 1995–2001. Larval survival peaked when habitat conditions included high availability of emergent macrophytes as habitat (>15 000 m3), air temperatures between 14 and 22 °C, and a low frequency of wind speeds >16 km·h–1. Age-0 juvenile suckers collected later in each year corroborated results of the LPE analysis, as most (88%) juveniles had otolith-estimated swim-up dates corresponding to early life rearing under the specified habitat conditions. Our results support the management practice of maintaining higher than natural UKL water surface elevations through the larval rearing period.