Distribuição espacial e status do peixe-boi marinho, Trichechus manatus manatus, (Sirenia: Trichechidae) no litoral leste do Estado do Ceará

Abstract

The Antillean manatee, Trichechus manatus manatus, is a mammal with an herbivorous diet and costal distribution in rivers, estuaries and inshore waters of the Brazilian Tropical Zone. In Ceará State, the species may found in the outer most ends of its western and eastern sectors. In the eastern sector there ar e no Marine Conservation Units to ward off impacts to the environment and the manatee population, such as urban development, tourism and occupation of beaches and mangrove forests. Manatees have been classified by the International Union for Nature Conservation as a “vulnerable spec ies” and included on the Official List of Endangered Species of the Brazilian Fauna. A ccording to the Brazilian Institute for the Environment, it runs an extremely high risk of extinction in the near future. The objectives of this Thesis have been to determine the spatial distribution and patterns of usage of the living area, choice of the most appropriate methodology for population monitoring and mapping of feeding grounds and freshwater sources likely to used by the animals. The database was obtained by means of aerial surveys from June, 2003 to October, 2004, making up a 24-hour monitoring effort during 11 overh ead flights, as well as nautical surveys pe rformed from August, 2003 to November, 2004, making up a 157-hour monitoring effort during 10 voyages. Of the two prospecting techniques, the aerial one was less prac tical because of water turbidity, which made it difficult to identify and count manatee specimens, whereas the nautical one, because of its nearness to the targets, proved to the most efficient. The status of the Antillean manatee population was evaluated through the following parameters: (a) habitat conservation, with emphasis on territory maintenance; (b) access to freshwater sources and areas suitable for feeding and reproduction; (c) yielding of optimum environmental conditions for parental care. The threatened extinction in the studied area is related to factors such as decreasing of food and freshwater sources, silting-up of the Jaguaribe River, by-catch by trawl and gillnet fishing. The worrying outcome of such a scenario is likely to result in a reduction of the habitat size; increase in the straying of newborns plus an increase in adult mortality rates. The Picos region, specially the Cajuais sandbank, was defined as a High Density Zone, which displays a highly aggregate distribution because of seaweed abundance and smaller deployment of fishing boats. Among the sugges tions for lowering the extinction risks of the Antillean manatee in Eastern Ceará State, the following ones stand out; (a) development of education campaigns which deal with the main aspects of environment preservation; (b) reintroduction of specimens in zones where population decline is evident; (c) installation of Marine Conservation Units and enforcement of the pertinent management measures and (d) constant monitoring of the population in th e known habitat to determine environmental patterns which influence manatees in Icapuí county, eastern Ceará State.