Flow and water temperature affect reproduction and recruitment of a Great Plains cyprinid

Abstract

Conservation of stream fishes requires an understanding of how their reproduction and recruitment are affected by environmental conditions. Flow regulation and habitat loss in North American Great Plains streams threaten many native fishes, including pelagic-broadcast spawning cyprinids. Pelagic-broadcast spawning by flathead chub (Platygobio gracilis), a species declining throughout much of its extensive range, began after temperatures exceeded 15 °C in Fountain Creek, Colorado (USA), despite different annual flows. Alternatively, streamflow patterns controlled recruitment of juveniles because high-magnitude summer flows (spikes) reduced abundance of larvae hatched just prior to or during such events. Juvenile recruitment was highest for larvae hatched just after summer flow spikes occurred or during stable base flow periods. Understanding environmental conditions suitable for reproduction as well as subsequent recruitment should inform conservation actions, especially in flow-altered streams, and improve prospects for persistence of imperiled Great Plains cyprinids, including flathead chub.

Changes in biological communities of the Fountain Creek Basin, Colorado, 2003–2016, in relation to antecedent streamflow, water quality, and habitat

“…Conversely, the small number of streams that still experience a natural flow regime in this region still have largely intact biological communities (Bestgen and others, 2017). Two aspects of streamflow that have been shown to negatively influence the persistence, growth, and population dynamics of stream biota are increased stream intermittency and augmented peak streamflow (both frequency and magnitude) (Durham and Wilde, 2006;Perkin and others, 2015;Haworth and Bestgen, 2017). These results suggest that the persistence of streamflow is a major driver of biological community dynamics in prairie streams of the western Great Plains and in plains streams that transition from the Rocky Mountains.…”

“…To quantify ecologically relevant daily maximum streamflow, a threshold of 20 cubic meters per second (706.29 cubic feet per second) was used as proposed by Haworth and Bestgen (2017) in a study of age-0 FHC (that is, individual FHC in their first year of life) growth and survival in Fountain Creek. Streamflow exceeding this threshold was shown to decrease growth, and therefore, survival of age-0 FHC because better thermal conditions exist at streamflow levels below the 706.29 cubic feet per second threshold.…”

“…The number of daily maximum streamflow values that equaled or exceeded this value from May through August was found to be important to the growth and survival of age-0 FHC. To apply this value at other streamgages in the FCB, the percentile of this streamflow value was determined at site 8, the same study site used by Haworth and Bestgen (2017). This threshold value was the 98th percentile of daily average streamflow values from 2003 to 2016.…”

“…Age and growth analysis of FHC in FCB near site 8 found that individuals less than or equal to 6 cm total length in the fall were likely hatched that year and are of the age-0 year class (Haworth and Bestgen, 2016). These annual estimates of age-0 FHC were compared to patterns of peak flow days (in the sense of Haworth and Bestgen, 2017; see the discussion on peak streamflow).…”

“…These results indicate that, although the ARD is not widespread in the FCB, its population is not changing, but the FHC population is declining and the explanatory variables (avg240 and Lbcap) for these decreasing FHC_CPUE trends are related to streamflow regime shifts and habitat changes. A recent study reports that greater occurrences of peak flow days (greater than 98 percent of daily average discharge) can reduce growth and survival of age-0 FHC (Haworth and Bestgen, 2017). The analysis in this report examined this relationship at sites 6 and 8 from 2003 to 2016 and found that, if there are greater than 25 peak flow days from May to August, there is a decline in age-0 FHC (that is, FHC less than 6 cm total length) that year ( fig.…”