Recruitment ecology of pelagic‐broadcast spawning minnows: paradigms from the ocean advance science and conservation of an imperilled freshwater fauna

Abstract

Pelagic‐broadcast spawning is a dominant mode of fish reproduction in the oceans and is associated with Fundamental Triad (i.e. nutrient enrichment, nutrient concentration, propagule retention) and Loophole (i.e. disruption of larval competition and predation) processes that are mediated by water currents. Pelagic‐broadcast spawning is uncommon in freshwater, but is employed by an evolutionarily convergent spawning guild in rivers on the Great Plains, North America. We reviewed ecological studies of pelagic‐broadcast spawning minnows to evaluate whether Fundamental Triad and Loophole concepts explain the adaptive significance of this behaviour. Pelagic‐broadcast spawning minnows exhibit spawning periodicity dependent on floods. Nutrient enrichment, nutrient concentration and propagule retention are enhanced during flood recession. Retention is also enhanced by high fecundity and rapid development of pelagic‐broadcast propagules. Predation and competition threats are relatively low in temporary, patchily distributed nurseries present during flood recession. Extended spawning periods and diffusive spread of juveniles and adults ensure annual recruitment despite the unpredictable and often harsh conditions in rivers on the plains. Over the last century, pelagic‐broadcast spawners have suffered declines due to dewatering, flood control and sediment deprivation that disrupt natural Fundamental Triad and Loophole processes. We propose that restoration of conditions necessary for Fundamental Triad and Loophole processes to operate will be most successful at stopping decline and extinction of pelagic‐broadcast spawning minnows of the Great Plains.

Fragmentation and dewatering transform Great Plains stream fish communities

“…Our focus was on fish communities of greatest conservation need, including those with members of the pelagic-spawning reproductive guild that inhabits large Great Plains streams (Hoagstrom and Turner 2013). We selected 39 stream fragments distributed among the five basins and including all large-order (e.g., greater than fourth order; Strahler 1957, Perkin et al 2013b) stream segments historically inhabited by pelagic-spawning fishes.…”

“…In each of these categories, we divided fishes into specific guilds (Table 1). We relied primarily on Simon (1999) for species classifications, but sought to classify as many species as possible based on additional literature sources (Platania and Altenbach 1998, Eisenhour 2004, Bestgen and Compton 2007, Frimpong and Angermeier 2009, Hoagstrom and Turner 2013. Some species were excluded because of insufficient reproductive biology data.…”

“…This reproductive guild has received increased attention in recent years associated with widespread accounts of decline throughout the region (Dudley and Platania 2007, Perkin and Gido 2011, Hoagstrom and Turner 2013. Documented declines brought on by fragmentation include extirpations in upstream portions of riverscapes following impoundment construction (Winston et al 1991, Luttrell et al 1999, Wilde and Ostrand 1999 Table 1 for reproductive guild information.…”

“…Similarly, declines ensue where stream fragments are dewatered because of surface water retention or groundwater extraction (Cross et al 1985, Durham and Wilde 2009, Perkin and Gido 2011. Mechanisms driving the decline of small-bodied pelagophilic fishes include disrupted spawning cues, reduced survival of drifting progeny, insufficient habitat complexity for recruitment processes, and truncated availability and connectivity of wetted refuge habitats (Taylor and Miller 1990, Wilde and Durham 2008, Hoagstrom and Turner 2013. These findings have shifted management focus toward early life stages that are most sensitive to environmental alterations (Wilde and Durham 2008), and work considering longitudinal habitat connectivity and heterogeneity suggests natal dispersal via drift is critical for population persistence (Dudley and Platania 2007, Wilde and Urbanczyk 2013, Worthington et al 2014a.…”

Larval fish abundance in relation to environmental variables in two Texas Gulf Coast rivers

“…Flood pulses may provide spawning cues and floodplain inundation creates temporary but productive aquatic habitats for spawning and larval growth and survival (Junk et al 1989). As flood pulses recede, they leave behind shallow, low-velocity habitats that often are 'hot spots' for aquatic primary production (Bowen et al 2003;Hoagstrom & Turner 2013). Spawning during flood pulses allows larvae and their predators to disperse at low densities within a greatly expanded volume of aquatic habitat, which should reduce both predation mortality and competition for food resources (Hoagstrom & Turner 2013).…”