San Juan River Fish Community Dynamics at Chaco Wash, New Mexico

Authors: C. Nathan Cathcart, Keith B. Gido, Mark C. McKinstry

Year: 2013 (xlv)

Abstract

Fishes in arid river systems have often adopted life history strategies favoring the opportunistic use of ephemeral habitats. Chaco Wash, a small, turbid, artificial tributary that joins the San Juan River near Shiprock, New Mexico embodies the flashy stream archetype lending itself to the opportunistic and exploratory use by fishes. To determine the extent of use at the confluence zone and upstream into Chaco Wash we performed two studies related to fish community dynamics between the San Juan River and tributary systems. First, we designed a Passive Integrated Transponder (PIT) technology study focused on razorback sucker, Xyrauchen texanus and Colorado pikeminnow, Ptychocheilus lucius to compare habitat use at the confluence of Chaco Wash and the San Juan River relative to another tributary confluence, McElmo Creek. We also conducted seasonal and annual fish sampling in 2012 and 2013 in Chaco Wash to quantify the species present and the upstream extent of their distributions. PIT antenna data suggest Chaco Wash supports relatively frequent use by both razorback sucker and Colorado pikeminnow, especially at the confluence area where an extensive backwater containing relatively deep water (> 1 m) extends over 500 m upstream into Chaco Wash. Sampling data informed us of fish community dynamics occurring seasonally and annually including early-Summer and Fall use by Colorado pikeminnow, Spring use by bluehead sucker, Catostomus discobolus and year-round use by black bullhead, Ameiurus melas. Flannelmouth sucker, Catostomus latipinnis occur primarily at sizes under 200 mm, suggesting Chaco Wash offers suitable rearing habitat. Speckled dace, Rhinichthys osculus and red shiner, Cyprinella lutrensis were the most abundant small-bodied species, peaking in abundances during early-Summer and Fall sampling. Speckled dace also appear to spawn in and around Chaco Wash. Antenna data show how differently fish, especially razorback suckers, can interpret McElmo Creek and Chaco Wash, suggesting life history mechanisms related to spawning aggregations and post-spawn movements. At the community level, the severely flashy nature of Chaco Wash apparently influences seasonal fish community patterns especially by disturbance events such as flooding from the seasonal monsoons. This study illustrates why confluences of intermittent streams and washes with mainstem rivers should not be overlooked as fish habitat, however marginal or ditch-like they appear superficially.