Recognizing gape limitation and interannual variability in bluehead chub nesting microhabitat use in a small Virginia stream

Abstract

Understanding the reproductive microhabitat requirements of keystone species such as the gravel mound nesting bluehead chub Nocomis leptocephalus can be useful for whole-community management. Nocomis have been shown to be microhabitat specialists, but no study has accounted for interannual variability in microhabitat use or for the possibility that substrate choices are constrained by mouth size. Our goals were to quantify the spawning microhabitat requirements of bluehead chub in the North Fork Roanoke River, Virginia, USA. Specifically, we sought to (1) account for gape limitation of nesting chubs when quantifying substrate size preference and (2) to examine interannual variability in their nesting microhabitat preferences. In June 2012 and 2013, we measured pebbles on chub nests and determined the gape limit as the largest measured pebble. With the gape limit as a ceiling for measurable particles, we compared substrate used by chubs to randomly selected particles adjacent to each nest. Depth and velocity were also measured at nests during both years and compared to random points near nests. Patterns in microhabitat selection differed between years. Chubs exhibited substrate size preference in 2012, but not 2013. The mean size difference in 2012 was approximately 3 mm but we do not consider this biologically meaningful. This stands in contrast with other studies showing large mean differences in preferred and available substrate. We suggest that the gape limitation of adult male Nocomis imposes a restriction on usable nesting substrate, causing observed significant differences between preferred and available substrate sizes. Current velocities used by chubs were significantly slower than paired measurements in 2013, but did not differ in 2012; depth preference did not differ between years. Differences in velocity preference likely represent adjustment to the above-average instream flow conditions of 2013. This study demonstrates the importance of examining interannual variability in fish spawning habitat requirements.

Nesting microhabitat comparison of Central stoneroller and Bluehead chub: potential inference for host-switching by nest associates

“…leptocephalus, Nagle & Simons 2012). Quantitative nesting microhabitat descriptions of several Nocomis species have been presented (Lobb & Orth 1988;Maurakis 1998;Wisenden et al 2009;Peoples et al 2014), including for the Roanoke/New River form of Bluehead chub in the present study (Bolton et al 2015). A more thorough understanding of Campostoma nesting habitat requirements across a larger geographic extent will yield better insight into the reproductive ecology of these species, and by extension their nest associates.…”

“…Nocomis are generally highly selective for current velocity at nesting sites (Lobb & Orth 1988;Maurakis 1998;Wisenden et al 2009). However, Bolton et al (2015) noted that in small streams, Bluehead chub nested in slower-than-average microhabitats during years of high flows, but exhibited little current velocity preference during spawning seasons with low instream flow such as in 2014.…”

“…To assess stoneroller spawning microhabitat selectivity, we compared microhabitat variables at stoneroller nests to paired, randomly chosen points approximately 5 m upstream from each nest (sensu Wisenden et al 2009;Bolton et al 2015). Hereafter, we refer to these measurements as 'unused.'…”

A survey of macroinvertebrates colonizing bluehead chub nests in a Virginia stream

“…). Nests were found at the upstream end of pools, and were located primarily within one meter of the stream bank, in stream sections with an average depth of 0.267 § 0.0119 m. The rocks within the nests were usually between 8 and 16 mm in size, most likely because that was the size of rock that most easily fit in the male chub's mouth (Bolton et al 2015). Substrate in most of the areas around the nests appeared to be qualitatively different, consisting of finer gravel, sand, and silt.…”

“…We found the nests in pairs at each site, likely because multiple males put their nests in the most suitable conditions of flow and depth located at pool tails (Sabaj et al 2000;Bolton et al 2015). Our study did not examine stream flow, presence of riffles and pools, or other environmental conditions because these nest site conditions have already been studied in detail (Peoples et al 2011;Bolton et al 2015). We sampled the nests by first measuring the depth of the water at the nest location and two diameters of the nest.…”