Interannual reproduction and recruitment dynamics of Flathead Chub Platygobio gracilis in Fountain Creek, Colorado, USA.

Authors: Matt* Haworth, Kevin Bestgen

Year: 2015 (xlvii)

Abstract

Stream ecosystems of the North American Great Plains are threatened by widespread flow regulation, alteration of thermal and sediment regimes, establishment of non-native biota, and habitat loss. These changes have driven the loss or decline of many fish species, including small-bodied pelagic-spawning cyprinids, a guild thought to be particularly susceptible to flow regulation. Thus, conservation of this guild requires an understanding of their specific life histories, particularly the relationships between reproduction, recruitment, and flow regime. We measured seasonal presence and abundance of egg, larval, and juvenile life stages of Flathead Chub, Platygobio gracilis, over two reproductive seasons in the southwestern portion of their range (Fountain Creek, Colorado, USA) to relate effects of hydrology and water temperature on reproduction and subsequent recruitment. Spawning was most affected by water temperature as initiation and peak of reproduction was consistent between study years despite different seasonal flow conditions. Back-calculation of hatching dates from juvenile chub otoliths revealed survival and recruitment was most affected by high magnitude or frequent flow spikes caused by convective storm runoff. Downstream displacement or mortality of eggs and recently-hatched larvae by flow spikes caused reduced abundance of juveniles hatched just prior to or during these events. Our results demonstrate that investigations focused on a single early life stage are insufficient to evaluate factors limiting the persistence of Flathead Chub, and possibly other pelagic-spawning cyprinids, as stream flow and temperature conditions had varying effects on separate but interrelated early life stages. Life history investigations that encompass all early development stages will provide managers with information necessary to benefit both reproduction and recruitment of small-bodied pelagic-spawning cyprinids in regulated streams systems, and aid in the conservation and recovery of an imperiled guild of North American stream fishes.