Quantifying the probability of invasive carp introduction via freshwater diversions: Arrival Assessment

Abstract

The Mississippi River is host to multiple species of invasive carp, including bighead, silver, and black carp, which have been linked to negative ecological impacts upon introduction to a waterbody. Most of the rivers emptying into the Gulf of Mexico are hydrologically separated from the Mississippi River by seawater and have historically been considered safe from an invasion of carp attempting to traverse coastal waters due to their intolerance of seawater salinity levels. However, there is growing concern that freshwater diversions of the Mississippi River into brackish or saltwater systems could reduce salinity to a level that allows entrained carp to navigate freshwater plumes to uninvaded rivers. To help quantify this risk, we conducted an Arrival Assessment that estimates the number of invasive carp that will enter a receiving waterbody through a single freshwater diversion event. A case study using the Bonnet Carré Spillway is presented here to illustrate how water managers and spillway operators can derive predictions for a specific spillway and how mitigative steps can be taken to target the most influential parameters and help reduce the number of carp that pass. The findings of this case study suggest that, for an average spillway opening event, the number of invasive carp that pass through the Bonnet Carré Spillway is higher than many water managers may be willing to accept. This Arrival Assessment serves as the first of three components within a broader, forthcoming quantitative risk assessment that will also consider the number of carp that survive (Survival Assessment) to reach a suitable, uninvaded river for reproduction and population sustainment (Establishment Assessment) and determine the magnitude and uncertainty of the risk of introduction to uninvaded waters downstream from a freshwater diversion that forms a hydrological connection to a source waterbody inhabited by invasive carp.