FISH ABUNDANCE AND COMMUNITY COMPOSITION IN NATIVE AND NON-NATIVE LITTORAL AQUATIC PLANTS AT LAKE IZABAL, GUATEMALA By CHRISTIAN ALBERTO BARRIENTOS A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2005 Copyright 2005 by Christian Alberto Barrientos To God, who provides all wisdom and judgment. ACKNOWLEDGMENTS I first thank my advisor, Dr. Mike Allen, for his guidance and willingness to do research in Guatemala. I also thank my committee members, Dr. William Haller and Dr. Daniel Canfield. I really appreciate Patrick Cooney and Maritza Aguirre’s help and support on this project, in the field and by email. Special thanks go to Dr. Mark Brenner who, on one of his research trips to Petén, encouraged me to pursue a higher education level.. Thanks also go to my parents, Jorge and Alicia Barrientos, who provided logistical and moral support. Most importantly, my parents were always there for me. Partial funding for this research was provided by the Wildlife Conservation Society, Mesoamerican Program, especially thanks to Archie Carr III. Funding was also provided by the Fulbright Scholarship and the University of Florida. Last, but not least, I thank my wife Corina and my two daughters Ana Isabel and Ana Cris, who came with me from Guatemala to Gainesville, Florida. iv TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................................................................................. iv LIST OF TABLES............................................................................................................. vi LIST OF FIGURES .......................................................................................................... vii ABSTRACT..................................................................................................................... viii INTRODUCTION ...............................................................................................................1 METHODS ..........................................................................................................................4 Study Site......................................................................................................................4 Habitat Characterization ...............................................................................................6 Fish Sampling ...............................................................................................................6 Analyses........................................................................................................................7 RESULTS ..........................................................................................................................12 Habitat Characterization .............................................................................................12 Fish Population Comparisons.....................................................................................12 Low PAC Analysis .....................................................................................................13 Low & High PAC Analysis ........................................................................................14 Hydrilla Analysis........................................................................................................15 DISCUSSION....................................................................................................................25 MANAGEMENT IMPLICATIONS .................................................................................32 APPENDIX A BLOCK NETS SUMMARY AT LAKE IZABAL ....................................................34 B WATER LEVELS AT LAKE IZABAL.....................................................................36 LIST OF REFERENCES...................................................................................................37 BIOGRAPHICAL SKETCH .............................................................................................41 v LIST OF TABLES Table page 1 Block net distribution among treatments .................................................................10 2 Physicochemical variables measured at Lake Izabal ...............................................17 3 Taxonomic family and scientific name of fish collected in block nets in Lake Izabal. Mean fish biomass across all treatments.. ....................................................19 4 Taxonomic family and scientific name of fish collected in block nets at Lake Izabal. Plant species and percent area covered (PAC) are located at the top of each column..............................................................................................................20 5 Fish metrics for treatments with low percent area coverage (PAC) including the no plants treatment. ..................................................................................................21 6 Fish metrics for six treatments included in the high versus low PAC comparison..22 7 Hydrilla data set were treatments are different percent area coverage (PAC). ......23 8 Taxonomic family and scientific name of fish observed in the local market at El Estor, Izabal, Guatemala. .........................................................................................24 9 Block nets summary at Lake Izabal (June-July/2004). ..........................................34 vi LIST OF FIGURES Figure page 1 Location of Lake Izabal in Guatemala. ....................................................................11 2 The relation between plant biomass and percentage area coverage.........................16 3 Fish total length (TL) distribution across all treatments. .........................................18 4 Water levels at Lake Izabal 2003-2004....................................................................36 vii Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science FISH ABUNDANCE AND COMMUNITY COMPOSITION IN NATIVE AND NON-NATIVE LITTORAL AQUATIC PLANTS AT LAKE IZABAL, GUATEMALA By Christian Alberto Barrientos December 2005 Chair: Micheal S. Allen Major Department: Fisheries and Aquatic Sciences I evaluated effects of the coverage of five aquatic plant species on fish community structure and abundance in Lake Izabal, the largest lake in Guatemala, which was recently invaded by a non-native aquatic plant Hydrilla verticillata. The objectives were to assess how hydrilla influenced littoral fish community composition and abundance. Fish were sampled from monotypic beds of five plant species including bulrush Scirpus carrizo, chara Chara phoetida, eelgrass Vallisneria americana, Illinois pondweed Potamogeton illinoensis, hydrilla Hydrilla verticillata, and areas with no plants. Bulrush, hydrilla and eelgrass were found in different densities and were sampled in low (<25%) and high (>75%) percent area coverage (PAC). Fish were sampled using block nets (0.01-ha) treated with rotenone in each plant type and PAC (N = 5 block nets per treatment) during June and July of 2004. Hydrilla had higher aquatic plant biomass relative to native species of the same PAC. Fishes from the family Cichlidae (7 species) viii had the highest species richness and highest biomass across all habitats sampled. Total fish species richness was 24, which ranged from 12-15 species and was similar across plant types in the littoral zone. Fish density did not differ significantly among plant types, but fish biomass was significantly different (P=0.01) among plant types with the hydrilla containing the highest fish biomass (186 kg/ha). Fish biomass was higher (P=0.02) in high PAC levels of hydrilla and bulrush than in eelgrass at either low or high PAC. Biomass of mojarra Cichlasoma maculicauda, which support the most important subsistence fisheries in the lake, was significantly different (P=0.01) among treatments and had the greatest biomass in hydrilla. Results of this study show that hydrilla provides suitable habitat for fishes in the littoral areas of Lake Izabal. Areas with hydrilla contained significantly greater biomass of fish compared to native plants or no-plants areas. Although hydrilla may cause problems for lake access and other uses, it is not likely detrimental to Lake Izabal fish community composition or total fish biomass, at levels of growth and coverage found in 2004. ix INTRODUCTION Excessive growth of aquatic macrophytes has caused serious problems in many lakes throughout the world (Canfield et al. 1985). Lake Izabal, Guatemala, has recently been colonized by Hydrilla verticillata, a non-native submersed plant. The hydrilla in Lake Izabal was first reported by anglers in 2000, and perhaps entered the system with hurricane Mitch in 1998. The plant is currently too widespread to be eradicated from the lake (Haller 2002). Hydrilla can quickly colonize and dominate systems where it is introduced because it grows rapidly, tolerates low light conditions, and inhabits water depths exceeding four meters (Langeland 1996). Light is often the most limiting factor prohibiting submersed plant growth (Canfield et al. 1985). Arrivillaga (2002) noted that 3 % of the Lake Izabal was covered by hydrilla in 2002, but the plant could potentially cover 10-15% in the dry season when light penetrates into deeper waters, due to increased water clarity. Allen and Tugend (2002) found that areas with dense macrophytes coverage (100 %) had lower