COS 83-8 - Vulnerability of migratory shrimp to the interaction of drought and water extraction in Puerto Rico: The importance of examining temporal dynamics

Wednesday, August 9, 2017: 10:30 AM
B110-111, Oregon Convention Center
Jessica C. Chappell1, S. Kyle McKay2, Jason K. Christian3, Mary C. Freeman4 and Catherine M. Pringle1, (1)Odum School of Ecology, University of Georgia, Athens, GA, (2)Warnell School of Forestry and Natural Resources, University of Georgia, Athens, GA, (3)College of Engineering, University of Georgia, Athens, GA, (4)USGS Patuxent Wildlife Research Center, Athens, GA

Watershed connectivity is crucial to the life history of many aquatic organisms. To this end, ecologists have developed a variety of connectivity indices to quantify the effects of dams and other infrastructure on migratory organisms with different life histories. Although rivers are temporally dynamic, connectivity is typically calculated as a static condition. Here, we examine the role of intra- and inter-annual variations in connectivity for three watersheds of the El Yunque National Forest (EYNF), Puerto Rico: Espiritu Santo, Mameyes, and Blanco. These tropical rivers host a variety of amphidromous taxa that require both freshwater and estuarine ecosystems to complete their life cycle. Connectivity for these species, like other diadromous taxa, requires movement both upstream and downstream past potential barriers. We focus on freshwater shrimps, given their important roles as consumers and significant impacts on stream ecosystem processes. Using gaged discharge data from the last 60 years, we examine how fluctuations in longitudinal riverine connectivity have been influenced by municipal water withdrawals associated with low-head dams. We determine longitudinal connectivity by calculating shrimp passage rates upstream and downstream past water intakes and then applying a previously developed index of connectivity.


Longitudinal connectivity varies temporally, to varying extents, in all three rivers. Annually, connectivity tends to be lower in the dry season, when low rainfall results in low stream discharge and municipal water use can result in diminished connectivity between headwater streams and the ocean for extended periods of time. As just one example, water withdrawal data obtained from the Puerto Rico Aqueduct and Sewage Authority (PRASA) indicate that in 2015, a severe drought year, the Espiritu Santo River experienced near zero connectivity over a two-month period (between June 5 and August 15). Natural seasonal fluctuations in longitudinal connectivity are thus magnified by water withdrawals during droughts. This could indicate shrimp populations and other migratory biota are vulnerable to freshwater demands. In instances outside of the EYNF, where dams have been operating for decades without any spillway discharge (resulting in zero conductivity), native shrimps have been completely extirpated. Balancing social and ecological water needs poses an increasing challenge given predictions of more frequent, severe drought. By translating streamflow dynamics into variation in connectivity for migratory shrimp, we may be able to help managers better understand ecological consequences of water allocation decisions during drought.