Abstract

Aquasis, a non-profit organization, based in Ceará state, is a member of the Brazilian Northeastern Stranding Network. From 1992 to 2006, Aquasis reported strandings of the Antillean manatee (Trichechus manatus manatus), a critically endangered species in Brazil, at Ceará and a small portion of north of Rio Grande do Norte states. All the rescued neonates were taken to the Aquasis´ Marine Mammal Rehabilitation Center to be fed and medicated, and were transferred to the Aquatic Mammals Center (CMA) to complete the rehabilitation period. Carcasses and remaining bones were collected and necropsies were performed, depending on the decomposition stage. Trends and associations were analyzed to determine patterns of manatee strandings. The variables were: Condition of specimen (alive and dead), age/size category (Marmontel, 1995), gender, cause of stranding (undetermined and anthropogenic), counties, years and months. Alive dependent calf strandings were not considered a natural cause, as Mignucci-Giannoni et al. (2000) did, since there are no specific studies in Brazil that confirm this description. Lima (1999) suggests that the association of estuary degradation and exposed coastline in Ceará and Rio Grande do Norte potentially increased the chances of dependent calves strandings. Due to the lack of scientific evidence that support this theory, the cause of these events was signed as "undetermined". Thirty seven stranding events were registered including two cases of bone remains. The number of reports had improved along the years but since 2001 there was a significant increase. There were no considerable differences between strandings of males (48,6%) and females (37,8%). Among all events, alive dependent calves were more frequent (64,8%). Considering the category "dependent calves" (n = 26), March (26,9%) and February (19,2%) were the most frequent months in the records, while for "adults" (n = 6), July (33,3%) had the biggest frequency. The event for the category "subadults" (n = 3) had an equal distribution among the months January, March and November. Anthropogenic causes related to inshore fishery activities began significantly in 2000 and were observed in six events (16,2%). Illegal bottom trawl nets were responsible for the death of three adults and one subadult, reaching 66,6% of the total. Bottom gillnets captured one subadult and one calf. Only one episode of an intentional catch of a calf was registered. Despite all conservation efforts performed by Aquasis and other institutions, there was an increase of the number of live dependent calves in Ceará and north of Rio Grande do Norte states. These efforts are not addressing the real problem of the strandings, but improving the quality of the rescue and consequently the chances of survival during the rehabilitation process. To minimize the negative effects of these events on the population, the factors involved before the strandings must be identified. Beyond the factors suggested by Lima (1999), other factors could be seasonal changes in oceanographic and meteorological characteristics in northeastern coast. Another assumption might be that the small population must be inducing an early sexual maturity on inexperienced females not able to give birth and raise a calf safely.

Acknowledgements

The authors would like to give thanks to the Aquatic Mammal Center--Governmental Institution, REMANE--Brazilian Northeastern Stranding Network, Vetnil Veterinarian Medicine Laboratories as Aquasis partner, NGO Recicriança, NGO Associação dos Amigos da Prainha do Canto Verde as a community collaborators for the close rescues.

References

1.  Lima RP. 1999. Peixe-Boi Marinho (Trichechus manatus): Distribuição, status de conservação e aspectos tradicionais ao longo do litoral Nordeste do Brasil. Serie Meio Ambiente em debate, n. 30, Ibama.

2.  Marmontel M. 1995. Age and reproduction in Female Florida Manatee. In: Population Biology of the Florida Manatee (eds O´Shea TJ, Ackerman BB, Percival HF), 98-119.

3.  Mignucci-Giannoni, et al., 2000. Manatee Mortality in Puerto Rico Environmental Management Vol. 25, No. 2, pp. 189-198