Assessment of the Effects of High Summer Water Temperatures on Shovelnose Sturgeon and Potential Implications of Climate Change

Abstract

Rivers worldwide have experienced changes through habitat modifications and are likely further exacerbated with the onset of climate change. The coupling of these anthropogenic disturbances has reduced the ability of river ecosystems and associated biota to adjust. The aforementioned human-induced habitat perturbations coupled with high summer river temperatures have been associated with an increased frequency of fish kills. Recently, shovelnose sturgeon Scaphirhynchus platorynchus have experienced numerous events of excessive summer mortality in rivers across the USA. During the summer of 2012, multiple fish kills occurred on the lower Des Moines River. During one of these events, we collected numerous dead or dying shovelnose sturgeon (N = 132) to explore factors causing mortality. Water temperatures were exceedingly high (29–35°C), while dissolved oxygen levels varied between 4 and 10 mg L−1. Based on population simulation modelling, only ~14% mortality would need to occur to reduce the reproductive potential below sustainable levels, which was likely exceeded. The results of our controlled experiment demonstrate that the high temperature in the Des Moines River was likely the mechanism initiating mortality. Future climate projections indicate that increases in temperature on the Des Moines River are possible; thus, the population may be at risk in the future. Through our microchemistry investigation, immigration from the Upper Mississippi River appears to be common and may be a source population to the Des Moines River. Despite immigration, the influence that these mortality events have on the Upper Mississippi River is unknown. Thus, proactive management efforts are needed to ensure sustainability of this population. Copyright © 2014 John Wiley & Sons, Ltd.