Population regulation and response to drought in speckled chub, Macrhybopsis aestivalis

Authors: Christopher W. Hoagstrom, Stephen R. Davenport, James E. Brooks, David L. Propst

Year: 2013 (xlv)

Abstract

A population of Macrhybopsis aestivalis (speckled chub) in the Pecos River, New Mexico, was regulated at the adult life stage for 15 consecutive years and, although stable in most years, crashed in 2003 near the end of a multi-year drought when the combination of modal discharge, discharge flashiness, and peak discharge were least favorable. Availability of swift-water habitats (used by longer individuals) and forage were presumably limiting. Recruitment, on the other hand, was normally unrelated to stock because the pelagic-broadcast spawning strategy was (apparently) well suited for the flashy flow regime of the unfragmented study area. Also, life-stage habitat segregation and a short (~2-year) maximum lifespan precluded intra-cohort competition. Nevertheless, recruitment declined following the population crash, but even abnormally low recruitment was adequate to fuel a population recovery under non-drought conditions in 2004. Identification of the population-limiting life stage reveals that (1) conditions favorable for recruitment (i.e., flow regime, unfragmented river reaches) should be conserved to maintain compensatory response that buffers stressed adult populations and (2) maintaining adult habitat is a primary conservation concern.