IMPACTS OF NON-NATIVE FISHES ON THE FISH COMMUNITY AND THE FISHERY OF THE CIÉNAGA GRANDE DE SANTA MARTA ESTUARY, NORTHERN COLOMBIA Jenny Leal-Flórez DAAD Cover: 1. Fisherman with cast net in Ciénaga Grande de Santa Marta, Colombia. Photo: INVEMAR 2001 2. The introduced fish Nile tilapia. Photo: INVEMAR 2001 3. Ciénaga Grande de Santa Marta, Colombia. Photo: STS073-760-32, Nasa 1995 4. The introduced fish snakeskin gourami. Photo: C. Mergus 2005, http://www.aquanostalgie.com/Poissons/trombinoscope2.php 5. Children at a fish market in Ciénaga Grande de Santa Marta, Colombia. Photo: INVEMAR 2001 IMPACTS OF NON-NATIVE FISHES ON THE FISH COMMUNITY AND THE FISHERY OF THE CIÉNAGA GRANDE DE SANTA MARTA ESTUARY, NORTHERN COLOMBIA Jenny Leal-Flórez A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor in Natural Sciences (Dr. rer. nat.) Faculty of Biology and Chemistry (FB 2) UNIVERSITY OF BREMEN Bremen, December 2007 DAAD ADVISORY COMMITTEE Referees: Prof. Dr. Ulrich Saint-Paul (University of Bremen, Center for Tropical Marine Ecology, Germany) Prof. Dr. Karsten Reise (CAU University of Kiel, Alfred Wegner Institute for Polar and Marine Research, Germany) Examiners: PD. Dr. Broder Breckling (University Bremen, Germany) PD. Dr. Holger Auel (University of Bremen, Germany) Members: Doctorate student Tilman Alpermann (University of Bremen, Alfred Wegner Institute for Polar and Marine Research, Germany) Diploma student Christoph Driemel (University Bremen, Germany) A mis padres María Teresa y Orlando A mis hermanos Orlando y Ervin To my friends TABLE OF CONTENTS PRESENTATION ......................................................................................................... i ABSTRACT .................................................................................................................. iii ZUSAMMENFASSUNG .............................................................................................. vi RESUMEN .................................................................................................................... x SECTION I: OVERVIEW .......................................................................................... 1 1. INTRODUCTION ............................................................................................... 3 1.1. ESTABLISHMENT OF INTRODUCED SPECIES IN AQUATIC ECOSYSTEMS.................................................................................................. 3 1.2. IMPACTS OF SPECIES INTRODUCTIONS ON AQUATIC ECOSYSTEMS ................................................................................................ 6 1.3. FISH INTRODUCTIONS IN NEOTROPICAL ESTUARIES ........................ 10 1.4. RESEARCH TOPICS AND HYPOTHESES .................................................... 12 2. STUDY AREA: The estuary Ciénaga Grande de Santa Marta (CGSM) ............ 15 2.1. LOCATION AND DESCRIPTION .................................................................. 15 2.2. HUMAN INTERVENTION AND THE INTRODUCTION OF NON-NATIVE FISHES IN CIENAGA GRANDE DE SANTA MARTA ................................ 17 2.3. THE NATIVE FISH COMMUNITY IN CIENAGA GRANDE DE SANTA MARTA .............................................................................................. 19 3. GENERAL METHODOLOGY .......................................................................... 22 3.1. DATA COLLECTION .............................................................................. 22 3.2. DATA ANALYSIS ................................................................................... 23 4. GENERAL RESULTS AND DISCUSSION ...................................................... 26 4.1. ECOLOGICAL IMPACTS OF NILE TILAPIA .............................................. 26 4.2. ECONOMIC IMPACT OF NILE TILAPIA ..................................................... 29 4.3. IMPACT OF SNAKESKIN GOURAMI .......................................................... 30 5. CONCLUDING REMARKS .............................................................................. 32 6. SOME COMMENTS ON MANAGEMENT ..................................................... 37 SECTION II: PUBLICATIONS ................................................................................ 40 7. ROLE OF NILE TILAPIA IN THE LONG TERM VARIATIONS OF ABUNDANCE AND SPECIES COMPOSITION OF THE NATIVE ICHTHYOFAUNA IN A CARIBBEAN ESTUARY (Submitted Manuscript) .................................................................................... 42 8. DOES NILE TILAPIA AFFECT THE FEEDING HABITS OF THE NATIVE ICHTHYOFAUNA OF A TROPICAL ESTUARY? - THE CASE OF THE CIENAGA GRANDE DE SANTA MARTA ESTUARY, COLOMBIA (Submitted Manuscript) .................................................................................... 63 9. HAS THE ACCIDENTAL INTRODUCTION OF NILE TILAPIA ECONOMICALLY BENEFITED THE FISHERY OF THE CARIBBEAN ESTUARY CIENAGA GRANDE DE SANTA MARTA– COLOMBIA? (Submitted Manuscript) .................................................................................... 85 REFERENCES ............................................................................................................ 103 ACKNOWLEDGMENTS ........................................................................................... 116 APPENDICES .............................................................................................................. 121 A. TERMINOLOGY ......................................................................................................... 123 B. NON-NATIVE FISHES ....................................................................................... 125 C. NATIVE FISHES ......................................................................................................... 127 D. ABBREVIATIONS ...................................................................................................... 133 PRESENTATION PRESENTATION In 1958 Charles S. Elton published one of the most important works in Ecology: “The Ecology of Invasions by Animals and Plants”. With this work he placed the cornerstone to the foundations of what is known today as invasion ecology. His book called the attention of the scientific community to a problem that nowadays is considered as one of the main threads to biodiversity. I acknowledged the problem of species introductions in 1997. I was part of an interdisciplinary team that was assessing the status of the aquatic resources in some flood plains within the lower basin of the River Magdalena, the largest and most important river in Colombia. At that time, the Nile tilapia (Oreochromis niloticus) was one of the most important fishes for the local fishery. Some of the fishermen with whom I had the chance to talk during my work blamed the “Lora”, as the Nile tilapia is called in the region, for the reduction of the native Bocachico (Prochilodus magdalenae), the most important species for the local fishery. According to them, the “Lora” was feeding on the Bocachico’s fry and food. They did not know that Nile tilapia is a mouth brooder that feeds mainly on phytoplankton and detritus. So they could have confused the tilapia fry in its mouth with that of the native fish. This comments of the fishermen, however, caught my attention and I started to look for the pathway and reason of the introduction of this fish in these ecosystems. I found out that the government agency in charge of fisheries management introduced the Nile tilapia into the lagoons because it was considered a good alternative of livelihood for the fishermen, since the main native fish populations were in decrease. I asked if there was a previous study on the possible impacts of this fish on the ecosystem, but I was told that it was not necessary, since they believed that this fish could not cause any problem. I was very surprised and became interested in helping to change this mentality of worrying only for today’s problems when managing our resources. The project of which my work became part was abruptly interrupted due to lack of funds and I was unable to return to that region. Some years after that experience, I decided to start my PhD. Searching for a topic I heard of the “boom” of Nile tilapia in Ciénaga Grande de Santa Marta (CGSM), the most i PRESENTATION important estuary in the north of Colombia. Since I had maintained an interest in species introductions, I decided to study the impacts of the non-native fishes on that ecosystem. I counted with the support of the Institute for Marine and Coastal Research (INVEMAR), in Santa Marta, which provided me a database with several types of information from periods before and after the introduction of the non-native fishes in the ecosystem. This was a golden chance that seldom occurs in the field of invasion ecology, since it is very rare to find information of the time before the introductions. Therefore I have written my Doctoral thesis on the following topic: Impacts of non-native fishes on the fish community and the fishery of the Ciénaga Grande de Santa Marta estuary, Colombia. The study focuses on the impacts of two introduced fishes, Nile tilapia (Oreochromis niloticus) and snakeskin gourami (Trichogaster pectoralis), and has been organized in two main sections. The first is a general overview of the study and consists of several chapters providing an introduction (chapter 1) to the research problem on a global and regional scale, as well as the research topics and hypotheses, a description of the study area (chapter 2), a general methodology (chapter 3), general results and