DOI: 10.6073/pasta/effdcb7caf8e4470eb1aa9fdf903aefd
title: 2004 Estuarine Fish Sampling - Managing freshwater inflow to estuaries in northeast Puerto Rico

description: Historical data are often one of the only resources for documenting and assessing causes of environmental change, particularly in developing regions where funding for ecological studies is limited. In this study, previously unpublished data from a 1977 year-long study of the fish community of the Espiritu Santo estuary are presented. This dataset is among the oldest and most extensive surveys of a Caribbean island estuarine fish community. A comparison of these historical data with data collected in June and July 2004 using identical sampling methods allowed description of potential long-term changes in the fish community, identification of vulnerable species, and assessment of potential drivers of change. Results strongly suggest a decline in species richness and abundance in the Espiritu Santo estuarine fish community, with greater declines in freshwater-tolerant than marine or euryhaline species. Declines in freshwater inflow to the estuary, due to large-scale upstream water abstractions for municipal use, have increased since the initial 1977 survey. This is the first study to examine long-term change in the fish community of a tropical island estuary. Additional research and conservation efforts are needed to understand mechanisms of change and to protect Caribbean island estuarine fish communities. Chapter 2 (isotope and gut content data): The contribution of riverine-derived organisms and organic matter to four fishes along the salinity gradient in two Puerto Rican estuaries, the Espiritu Santo and Mameyes, was examined via stable isotope and gut content analyses. Stable isotope analyses indicated that riverine organic matter potentially contributed as much as 69% of the diet of one (caitipa mojarra, Diapterus rhombeus) of four fishes sampled. In contrast, riverine organic matter was of little direct importance to the three other fishes, tarpon snook (Centropomus pectinatus), ground croaker (Bairdiella ronchus), and white mullet (Mugil curema) contributing less than a third of their assimilated material even in the estuariesâ€™ upper reaches. Gut content analysis of estuarine fishes demonstrated that several species of pelagic or omnivorous fish consume riverine-derived organisms, specifically juvenile migratory freshwater shrimps, during their residence in the estuary. Freshwater shrimps were frequently encountered (in 37 and 39% of guts examined) and composed an average of 18 and 22% of gut content material of omnivorous fishes sampled in the Espiritu Santo and Mameyes estuaries, respectively. To our knowledge, this is the first study to examine the contribution of riverine subsidies to a Caribbean island estuary. Given increasing demand for water resources on tropical islands and the importance of diadromy in these systems, there is a need for additional research on this topic to better inform water management decisions.
 
 Support for this work was provided by grants BSR-8811902, DEB-9411973, DEB-9705814 , DEB-0080538, DEB-0218039 , DEB-0620910 , DEB-1239764, DEB-1546686, and DEB-1831952 from the National Science Foundation to the University of Puerto Rico as part of the Luquillo Long-Term Ecological Research Program. Additional support provided by the University of Puerto Rico and the International Institute of Tropical Forestry, USDA Forest Service.