ERDC/EL CR-12-4 "Effects of Dam Operations on Least Tern Nesting Habitat and Reproductive Success Below Keystone Dam on the Arkansas River"

This report describes Least Tern (Sternula antillarum) sandbar nesting habitat (SNH) on the Arkansas River below Keystone Dam from field and GIS measurements after the 2008 nesting season. This season was preceded by 2 years with high-magnitude, long-duration dam releases (>50,000 cfs for >3 weeks), which resulted in major habitat renewal; replacing small, low-elevation sandbars that were mostly covered with vegetation with large, completely bare, high-elevation sandbars. Habitat measurements are reported relative to hydrographs that describe Keystone Dam operations for hydropower production and flood control (based on a post-dam era of 19772008). Habitat measurements for 2008-2009 were compared to a degraded habitat dataset that was simulated in ArcGIS based on descriptions in the most recent USFWS biological opinion for the Arkansas River. TernCOLONY, an individual-based model of Least Tern reproduction, was then used to evaluate how dam operations affect ILT reproduction, given these two sets of habitat conditions, across the range of dam operations. In simulations, infrequent nest flooding mortality was observed when habitat conditions were outstanding (e.g., after the high flows of 2007-2008). Conversely, regular nest mortality due to flooding, as well as higher predation rates, resulted in low reproductive success when habitat conditions were degraded. Given this baseline understanding, three different management alternatives were simulated that were designed to reduce flooding and/or predator mortality when habitat conditions are degraded (e.g., mechanical sandbar habitat restoration, predator control, and a combination of the two). Only management treatments that included predator control components were effective at increasing regional reproductive output. Since ILT populations experience periods with excellent habitat conditions and degraded habitat conditions at the decadal scales that affect population trajectories, widespread application of this type of evaluation would be helpful to assess the persistence of regional ILT populations considered important to the ILT metapopulation. DISCLAIMER: The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. All product names and trademarks cited are the property of their respective owners. The findings of this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents. DESTROY THIS REPORT WHEN NO LONGER NEEDED. DO NOT RETURN IT TO THE ORIGINATOR.