Recruitment ecology and conservation of pelagic-broadcast spawning minnows

Authors: Christopher W. Hoagstrom, Thomas F. Turner

Year: 2012 (xliv)

Abstract

Pelagic-broadcast spawning is a dominant mode of fish reproduction in the sea, but not in freshwater where suitable habitats appear to be limited. Notably, Fundamental Triad and Loophole processes that support pelagic-broadcast spawning in oceans and estuaries have analogs in rivers of the plains where pelagic-broadcast spawning minnows were historically widespread and diverse. Ecological evidence suggests these minnows are adapted to exploit a common sequence of events initiated by peak flows that invigorate nutrient flux and meso-habitat formation in unconfined, braided riverscapes. During flow recession, temporary, meso-scale nurseries are relatively abundant and patchily distributed. Drifting embryos that passively colonize these nurseries likely experience lower competition and predation risk, providing an explanation for synchronous spawning during peak-flow events, poor recruitment during base-flow periods, and population extirpation where peak flows or natural river-channel morphology are degraded. Similar to many pelagic-broadcast spawning marine fishes, pelagic-broadcast spawning minnows throughout North America occupy relatively unproductive habitats that are geographically extensive and structurally homogenous. Interestingly, pelagic-broadcast spawning minnows of the plains differ from those elsewhere. Whereas plains endemics are sensitive to impoundment, flow regulation, and river-channel degradation, pelagic-broadcast spawning minnows from the North American lowlands have benefitted from these changes, expanding their range on the plains. This contrast is consistent with patterns in the ocean that demonstrate the adaptive potential of pelagic-broadcast spawning. Further, it shows the importance of linking species life-histories and reproductive ecology with critical ecological processes to understand and conserve fish biodiversity.