BIODIVERSITY OF FRESHWATER FISHES OF TRINIDAD AND TOBAGO, WEST INDIES Dawn Arlene Teresa Phillip A Thesis Submitted for the Degree of PhD at the University of St. Andrews 1998 Full metadata for this item is available in Research@StAndrews:FullText at: http://research-repository.st-andrews.ac.uk/ Please use this identifier to cite or link to this item: http://hdl.handle.net/10023/2832 This item is protected by original copyright BIODIVERSITY OF FRESHWATER FISHES OF TRINIDAD AND TOBAGO, WEST INDIES Dawn Arlene Teresa Phillip Thesis submitted for the degree of Doctor of Philosophy University of St Andrews October 1998 Declaration: (i) I, Dawn A.T. Phillip, hereby certify that this thesis, which is approximately 30,000 words in length, has been written by me, that it is the record of work carried out by me and that it has not been submitted in any previous application for a higher degree. Date: Cf3·/0 ·/ol Signature of candidate: (ii) I was admitted as a research student in October 1995 and as a candidate for the degree of ph.D. in October 1996; the higher study for which this lS a record was carried out in the University of St Andrews between 1995 and 1998. Date: 1d"1"'/~ Signature of candidate: (iii) I hereby certify that the candidate has fulfilled the conditions of the Resolution and Regulations appropriate for the degree of ph.D. in the University of St Andrews and that the candidate is qualified to submit this thesis in application for a higher degree. Date: 11.. t u ·9 ~ Signature of supervisor: In sUbmitting this thesis to the University of St Andrews I understand that I am giving permission for it to be made available for use in accordance with the regulations of the University Library for the time being in force, subject to any copyright vested in the work not being affected thereby. I also understand that the title and abstract will be published, and that a copy of the work may be made and supplied to any bona fide library or research worker. Date: '15'" /0./01... Signature of candidate: 1 BIODIVERSITY OF FRESHWATER FISHES OF TRINIDAD AND TOBAGO, WEST INDIES Abstract The proximity of the speciose South American continent to Trinidad and Tobago ensures that these islands have a rich and dynamic fauna. According to the equilibrium theory of island biogeography (MacArthur & Wilson 1967), these islands should be subjected to frequent immigrations from the nearby continent, and these additions will, in response, fuel local extinctions to maintain a balance of species richness. The aquatic habitat lS further impacted by man's acti vi ties, (Government of Trinidad and Tobago 1962; (Government of Trinidad and Tobago 1976b) which have the potential to amplify the natural rates of immigration and extinction. Despite the possible consequences, the effects of this disturbance on the fish fauna have not been studied. A survey of the islands' freshwater fishes was therefore carried out to investigate the natural spatial and temporal dynamics of local fish communities, and the effects of anthropogenic perturbations, on these. These baseline data can be used as a benchmark to address some of the problems that are threatening the fish diversity of Trinidad and Tobago. The fish fauna of Trinidad and Tobago is diverse. Total species richness was estimated at between 37 and 40. Four zoogeographic zones were recognised. A zone of Antillean fishes included Tobago and the north coast of Trinidad. A zone of recent colonising South American fauna existed along the south coast of Trinidad. The rest of Trinidad contained a relict South American fauna dating back to the time when Trinidad was still part of the mainland. Included here was a centrally located zone of unstable fauna at risk of local extinction. 2 The fish fauna was temporally dynamic due to frequent colonisation and extinction events. Examination of the historic record showed that observed species richness varied from 38 to 43 between the mid 1950s and the present. During this time there were 15 introductions and 12 local extinctions. A conservative estimate was that a new species was recorded for Trinidad almost every three years. The geographic distribution of species also showed temporal changes which indicated a natural tendency of the fauna to vary over time. Human interference, particularly the introduction of exotic fish species and long-term habitat alteration, has affected species diversity. Forty seven percent of the new introductions and 43% of the extinctions were human-introduced exotics. About four fifths of sites in Trinidad, and almost one fifth of the sites in Tobago, were either perturbed or polluted. Polluted rivers coincided with areas of high urbanisation and industrial development in the west and southwest of Trinidad. Several effects of human interference on the fauna were recorded. Almost 8% of the sites examined contained one of the three exotic species still extant on the island. At each of these sites, the exotic species accounted for between 1.3% and 80.4%, by number, of the fish caught. Some of the effects of habitat disturbance on individual sites were increased frequency of diseases, extirpation of species, changes in species richness and other diversity measures, and the eventual regression of the fish community to opportunistic species (r-strategists). The potential of two fishes, Poecilia reticulata and Astyanax bimaculatus, as indicator species was examined. Astyanax showed better potential as an indicator of habitat quality as it was not found in depauperate communi ties, typical of severely disturbed habitats, and its proportional abundance and biomass were negatively affected by pollution. Poecilia populations, on the other hand, were found to be insensitive 3 to habi tat quality when the above-mentioned cri teria were used. They did, however, have a high frequency of diseased individuals at polluted sites. One of the aims of conservation is to protect that portion of biodiversity most at risk of extinction, the rare species (Rabinowitz 1986). Over 70% of freshwater fish species found in Trinidad and Tobago were classified as rare in these islands. This fact, In addition to the loss of diversity recorded for some sites indicates that the implementation of a management strategy for the conservation of the freshwater fish fauna of Trinidad and Tobago is imperative. The management strategy should focus on the amelioration and protection of aquatic habitats since at least 80% of the rare species had either a restricted geographic distribution or narrow habitat specificity. Additionally, protection from overexploitation should be offered to commercially important species wi th only small populations. Finally, a minimum sample size of 35 sites, spread over different zoogeographic areas, is recommended for estimating species richness for monitoring, an intrinsic part of any management strategy. ACKNOWLEDGMENTS I wish to express my sincere gratitude to my supervisors, .Aru1e Magurran, Mary AIkins - Koo and Indar Ramnarine for their support and guidance. Special thanks to .Aru1e and Mary for their encouragement and for sharing their vast knowledge with me. It has been an honour to work with you. John Agard and Azad Mohammed provided advice on water chemistry. Azad and Azeena Mohammed carried out some of the more difficult chemical analyses. I am indebted to Prof. Kenny for leaving the original data sheets and maps from his fish survey at my disposal, and for the timely publication of his memoirs. I would also like to express gratitude to the numerous persons who have helped in the field: among them, Maurice, Mark, Raj, Darryl, Pooran, Brain, Berry and Carl. Special thanks to Maurice for taking care of us, and for his patience with me. Credit must also be given to the members of the UWI Biological Society, Celeste and Natasha for volunteering your help in sorting the endless numbers of fish collected. Credit must be given to my family for the sacrifices they have made so that I could take advantage of this opportunity. To the gang at the University or the West Indies, Karen (H&D) , Claire, Camille, Leona, Bhola, and those already mentioned, thanks for the support, company, food, good times and laughter. Thanks as well to the E­ floor crew at the University of St Andrews, especially my office mates Sian, lain, Jon and Helda. Special appreciation to Sian who has been so helpful (And now, the end is near ... ). Thanks Jeff for your patience; explaining statistics to me is not an easy task. To Imelda and Nene who have shared their home in St Andrews with me for seven months, much appreciation is given. Finally, I would like to acknowledge the Darwin Initiative for providing the financial support for the project, and the Institute of Marine Affairs in Trinidad, for granting me study leave. CONTENTS Page Abstract 1 Chapter 1: Introduction 4 Background 6 Objectives 10 Chapter 2: Methodology Study area 13 Drainage systems 15 Climate 16 Selection of sampling sites 17 Frequency of sampling 17 Field techniques 17 Laboratory methods 22 Chapter 3: Estimation of species richness Introduction 26 Methods of estimating species richness 27 Methods 33 Results 36 Discussion 39 Chapter 4: Spatial patterns Introduction 41 Methods 44 Results 49 Discussion 52 CONTENTS CONT'D Page Chapter 5: Temporal patterns in species richness Introduction 57 Methods 59 Results 60 Discussion 65 Chapter 6: Pollution Introduction 69 Methods 70 Results 74 Discussion 77 Chapter 7: Summary and future research 83 References 90 Appendices 4 CHAPTER 1. Introduction In recent years there has been increasing interest in environmental issues growing out of the realisation that the state of the environment is of fundamental importance to the quality of human existence. We depend on our environment (physical and biological) for ecosystem services (United Nations Environment Programme 1995) water, food, clothing, shelter, medicine, in short, for life.