Year: 1998
Type: dissertation
Abstract: The proximity of the speciose South American continent to\nTrinidad and Tobago ensures that these islands have a rich and\ndynamic fauna. According to the equilibrium theory of island\nbiogeography (MacArthur & Wilson 1967), these islands should\nbe subjected to frequent immigrations from the nearby\ncontinent, and these additions will, in response, fuel local\nextinctions to maintain a balance of species richness. The\naquatic habitat is further impacted by man's activities,\n(Government of Trinidad and Tobago 1962; Government of\nTrinidad and Tobago 1976b) which have the potential to amplify\nthe natural rates of immigration and extinction. Despite the\npossible consequences, the effects of this disturbance on the\nfish fauna have not been studied. A survey of the islands'\nfreshwater fishes was therefore carried out to investigate the\nnatural spatial and temporal dynamics of local fish\ncommunities, and the effects of anthropogenic perturbations,\non these. These baseline data can be used as a benchmark to\naddress some of the problems that are threatening the fish\ndiversity of Trinidad and Tobago.\nThe fish fauna of Trinidad and Tobago is diverse. Total\nspecies richness was estimated at between 37 and 40.\nFour\nzoogeographic zones were recognised. A zone of Antillean\nfishes included Tobago and the north coast of Trinidad. A\nzone of recent colonising South American fauna existed along\nthe south coast of Trinidad. The rest of Trinidad contained a\nrelict South American fauna dating back to the time when\nTrinidad was still part of the mainland. Included here was a\ncentrally located zone of unstable fauna at risk of local\nextinction.\n\nThe fish fauna was temporally dynamic due to frequent\ncolonisation and extinction events. Examination of the\nhistoric record showed that observed species richness varied\nfrom 38 to 43 between the mid 1950s and the present. During\nthis time there were 15 introductions and 12 local\nextinctions. A conservative estimate was that a new species\nwas recorded for Trinidad almost every three years. The\ngeographic distribution of species also showed temporal\nchanges which indicated a natural tendency of the fauna to\nvary over time.\nHuman interference, particularly the introduction of exotic\nfish species and long-term habitat alteration, has affected\nspecies diversity. Forty seven percent of the new\nintroductions and 43% of the extinctions were human-introduced\nexotics. About four fifths of sites in Trinidad, and almost\none fifth of the sites in Tobago, were either perturbed or\npolluted. Polluted rivers coincided with areas of high\nurbanisation and industrial development in the west and\nsouthwest of Trinidad.\nSeveral effects of human interference on the fauna were\nrecorded. Almost 8% of the sites examined contained one of\nthe three exotic species still extant on the island. At each\nof these sites, the exotic species accounted for between 1.3%\nand 80.4%, by number, of the fish caught. Some of the effects\nof habitat disturbance on individual sites were increased\nfrequency of diseases, extirpation of species, changes in\nspecies richness and other diversity measures, and the\neventual regression of the fish community to opportunistic\nspecies (r-strategists).\nThe potential of two fishes, Poecilia reticulata and Astyanax\nbimaculatus, as indicator species was examined. Astyanax\nshowed better potential as an indicator of habitat quality as\nit was not found in depauperate communities, typical of\nseverely disturbed habitats, and its proportional abundance\nand biomass were negatively affected by pollution. Poecilia\npopulations, on the other hand, were found to be insensitive\nto habitat quality when the above-mentioned criteria were\nused. They did, however, have a high frequency of diseased\nindividuals at polluted sites.\nOne of the aims of conservation is to protect that portion of\nbiodiversity most at risk of extinction, the rare species\n(Rabinowitz 1986). Over 70% of freshwater fish species found\nin Trinidad and Tobago were classified as rare in these\nislands. This fact, in addition to the loss of diversity\nrecorded for some sites indicates that the implementation of a\nmanagement strategy for the conservation of the freshwater\nfish fauna of Trinidad and Tobago is imperative. The\nmanagement strategy should focus on the amelioration and\nprotection of aquatic habitats since at least 80% of the rare\nspecies had either a restricted geographic distribution or\nnarrow habitat specificity. Additionally, protection from\noverexploitation should be offered to commercially important\nspecies with only small populations. Finally, a minimum\nsample size of 35 sites, spread over different zoogeographic\nareas, is recommended for estimating species richness for\nmonitoring, an intrinsic part of any management strategy.
Author: Dawn A. T. Phillip
Language: English
Subfield: Nature and Landscape Conservation
Field: Environmental Science
Domain: Physical Sciences
SDG: Life below water
Open Access status: green
OpenAlex ID: W1595695143