Preliminary Findings for a Relationship between Instream Flow and Shoal Chub Recruitment in the Lower Brazos River, Texas

Abstract

Seasonal flow pulses in rivers facilitate spawning, dispersal, and early life stage survival of many fish species. To evaluate the effectiveness of current flow standards to sustain threatened fish populations, we investigated the relationship between hydrology and recruitment of the Shoal Chub Macrhybopsis hyostoma, a broadcast‐spawning minnow in the Brazos River, Texas. From March 2013 to March 2014, we collected metalarval and juvenile Shoal Chub bimonthly at night using arrays of stationary drift nets. Otoliths were examined to estimate age, and the relationship between hatch date and discharge was analyzed. Shoal Chub recruited under both base‐flow and pulse‐flow conditions, including intervals of increasing, decreasing, and stable discharge. However, hatch dates of surviving fish indicated greater levels of recruitment during flow pulses, particularly on the rising limb. Greatest recruitment occurred during flow pulses of a magnitude defined as two per season according to the method of hydrological analysis adopted by the state's environmental flow program. Our findings imply that the state's current environmental flow standards for the lower Brazos River may be insufficient to sustain Shoal Chub populations and additional research on this issue is warranted. Received October 11, 2015; accepted March 30, 2016 Published online July 28, 2016

Extreme drought causes fish recruitment failure in a fragmented Great Plains riverscape

“…Exceptions are species such as silver chub that live up to age 3 (based on our data) and thus might be able to persist despite the loss of a single year class. Our work supports recent findings that pelagic-broadcast spawning fishes likely recruit most strongly during some system-specific intermediate flow magnitude compared with extreme low flows (e.g., Pennock et al, 2017;Rodger et al, 2016), whereas crevice-and substrate-spawning fishes benefit from prolonged low flows (Perkin, Gido, Cooper, et al, 2015).…”

“…Pelagic-benthic spawning fishes such as emerald shiner (and perhaps silver chub) are extirpated from reaches upstream of dams in the Arkansas and Ninnescah rivers (Pennock et al, 2018;Perkin, Gido, Costigan, et al, 2015) and are frequently absent from the same fragments of river as pelagic-broadcast spawning fishes (Perkin, Gido, Cooper, et al, 2015;Starks, Rodger, King, & Skoog, 2018). Our work supports recent findings that pelagic-broadcast spawning fishes likely recruit most strongly during some system-specific intermediate flow magnitude compared with extreme low flows (e.g., Pennock et al, 2017;Rodger et al, 2016), whereas crevice-and substrate-spawning fishes benefit from prolonged low flows (Perkin, Gido, Cooper, et al, 2015). In fact, even benthicspawning species such as red shiner and sand shiner that successfully recruited in the Arkansas and Ninnescah rivers during 2011 and 2012 are extirpated in other regions of the Great Plains where habitat isolation and drought jointly affect riverscapes for one or more years (Falke et al, 2011;Matthews & Marsh-Matthews, 2007).…”

“…Previous research in the Great Plains has demonstrated fish diversity loss caused by interactions between spawning mode, habitat isolation, and low flow disturbance (Perkin, Gido, Cooper, et al, 2015;Worthington et al, 2018). The ERH is contingent on disturbances causing either adult mortality prior to reproduction (e.g., Durham, Wilde, & Pope, 2006) or failed recruitment after reproduction (e.g., Rodger, Mayes, & Winemiller, 2016) at a pace more rapid than the duration of the disturbance. Perkin, Gido, Costigan, et al (2015) presented the ecological ratcheting hypothesis (ERH) that postulates population extirpations brought on by low flow disturbances in small, isolated habitat patches are reinforced by barriers to recolonization even after drying disturbance subsides.…”

“…Perkin, Gido, Costigan, et al (2015) presented the ecological ratcheting hypothesis (ERH) that postulates population extirpations brought on by low flow disturbances in small, isolated habitat patches are reinforced by barriers to recolonization even after drying disturbance subsides. The ERH is contingent on disturbances causing either adult mortality prior to reproduction (e.g., Durham, Wilde, & Pope, 2006) or failed recruitment after reproduction (e.g., Rodger, Mayes, & Winemiller, 2016) at a pace more rapid than the duration of the disturbance. Increases in the application of the ERH (Kerezsy, Gido, Magalhães, & Skelton, 2017;Perkin, Gido, Costigan, et al, 2015;Schumann, Haag, Ellensohn, Redmond, & Graeb, 2018) suggest that additional research on the mechanisms causing population extirpation during drought events is necessary for understanding ecological consequences of extreme low flow events in highly fragmented riverscapes.…”

Characteristics of the natural flow regime paradigm explain occurrence of imperiled Great Plains fishes

“…However, the importance of other months of the year or the broader suite of hydrologic indices has not been rigorously quantified to the extent that flow-ecology relationships exist. A recent study on the Brazos River, Texas, USA (Rodger et al 2016), assessed the relationship between flow magnitude and recruitment for a single species, Shoal Chub Macrhybopsis hyostoma, and results from that study were used to develop flow recommendations (Texas Instream Flow Program 2018). However, such recommendations do not exist for the majority of river segments or fish species in the Great Plains, aside from a few notable exceptions (Wilde and Durham 2008, Durham and Wilde 2009, Wilde and Urbanczyk 2013.…”