The effects of river channel restoration on early juvenile fishes and meiofauna of the Pecos River, New Mexico

Authors: Darrel Mecham, Christopher W. Hoagstrom, Brian Graeb

Year: 2014 (xlvi)

Abstract

Slackwater habitats function as nursery areas for early-life-stages fishes and are critical for their growth and survival. Channelization can reduce slackwater availability by reducing channel complexity. Because of this, river channel restoration efforts have become more common and have been utilized to increase slackwater availability. We compared slackwater habitat conditions, early juvenile fish density, epibenthic meiofauna density, and fish and epibenthic meiofauna assemblage composition of a recently restored reach of the Pecos River, New Mexico with unchannelized and channelized reaches. We also assessed the relationship between flow regime and estimated hatch dates of common fish species including Red shiner (Cyrpinella lutrensis), Plains killifish (Fundulus zebrinus), and Western mosquitofish (Gambusia affinis). The availability and extent of slackwater habitat was greater in unchannelized reaches and lower in the restored and channelized reaches. Densities of F. zebrinus were greatest in unchannelized reaches upstream and decreased as the river becomes more channelized downstream. G. affinis exhibited the opposite trend, showing low densities upstream in the unchannelized reaches and increasing densities in the lower more channelized reaches. Densities of C. lutrensis were highest in more perennial reaches regardless of channel morphology. Total meiofauna density was also greatest in more perennial reaches. Rotifera densities were greatest in unchannelized reaches, while Ostracoda densities were greatest in channelized reaches. Both fish and epibenthic meiofauna assemblages of the restored reach were more similar to assemblages of channelized reaches, despite temporal differences. The common fish species spawned and hatched during periods of lower discharge. We suggest that future restoration efforts should focus on maintaining sufficient base-flows in addition to physical channel restoration. Maintenance of base-flows contributes to the provision of more extensive and abundant slackwater nursery areas within the restored river channel conducive to the growth and survival of early juvenile fishes.

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