275
Free-ranging manatees were captured for the first time in Brazil, in the state of
Ceará, using a small mesh, 200-m long, 7-m-deep seine net launched from a specially designed 10-m long vessel. Six manatees were captured and monitored by
satellite telemetry between May 2012 and April 2013 (Petrobras 2014). Home range
of four animals were estimated and varied from 41.33 km
2
(female with calf) to
155.56 km
2
(adult male). The studied animals did not use the estuaries of the area.
Areas up to 5 m deep were used by the majority of the monitored individuals. Only
the adult male used regions with up to 10 m deep. At the time of this writing, four
manatees had been captured (two previously captive females with their native
calves) in the coast of Alagoas state.
In order to monitor manatees at lower costs, a group of researchers recently
developed satellite transmitters with GPS locator in Brazil, that use the Globalstar
system and a SPOT Messenger module; a VHF transmitter is also part of the hardware. Tests conducted with captive manatees demonstrated good buoyancy of the
housing, transmission mechanism and GPS location, with excellent precision of
received coordinates. The use of lower cost materials available in the national market should turn the technology more accessible to users in South America (Borges
et al. 2016).
11.4 Abundance
To estimate T. manatus abundance in South America is not an easy task. The species
occurs mainly in riverine dark waters that, associated with their evasive behavior,
makes their detection a challenge.
In Colombia, Arévalo-González et al. (2014) estimated manatee abundance in
Ciénagas de Paredes through boat surveys, side-scan sonar surveys and interviews
in 2002 and 2010. By boat survey, the maximum number of simultaneous sightings
was 17. Using SSS and Distance sampling, a population of 12 manatees was estimated to occur in Los Pozos.
In Suriname, Pool (2012) indicated two manatee abundance estimates for the
country: 500–600 (Duplaix and Reichart 1978) and 200–300 with a maximum of
500–600 at best (Wassink 1997). However, no details are presented on these studies’
methods.
In Brazil, Lima (1997) and Luna (2001) proposed manatee abundance in northeastern and northern region, respectively, based on interviews. Despite the unusual
method, without accuracy, these estimates were the only available in the country for
years.
More recently, Alves et al. (2016) conducted aerial surveys from Canárias Island,
on the mouth of Parnaíba river (Piauí) to São Francisco river mouth, covering
2,590 km
2
, using strip transect method. Through a Bayesian approach, the authors
estimated manatee abundance as 1,104 animals (CI 95%: 485–2,221), an inaccurate
result that could be improved with additional efforts in a smaller spatial scale.
11 West Indian Manatee Trichechus manatus in South America…
Free-ranging manatees were captured for the first time in Brazil, in the state of
Ceará, using a small mesh, 200-m long, 7-m-deep seine net launched from a specially designed 10-m long vessel. Six manatees were captured and monitored by
satellite telemetry between May 2012 and April 2013 (Petrobras 2014). Home range
of four animals were estimated and varied from 41.33 km
2
(female with calf) to
155.56 km
2
(adult male). The studied animals did not use the estuaries of the area.
Areas up to 5 m deep were used by the majority of the monitored individuals. Only
the adult male used regions with up to 10 m deep. At the time of this writing, four
manatees had been captured (two previously captive females with their native
calves) in the coast of Alagoas state.
In order to monitor manatees at lower costs, a group of researchers recently
developed satellite transmitters with GPS locator in Brazil, that use the Globalstar
system and a SPOT Messenger module; a VHF transmitter is also part of the hardware. Tests conducted with captive manatees demonstrated good buoyancy of the
housing, transmission mechanism and GPS location, with excellent precision of
received coordinates. The use of lower cost materials available in the national market should turn the technology more accessible to users in South America (Borges
et al. 2016).
11.4 Abundance
To estimate T. manatus abundance in South America is not an easy task. The species
occurs mainly in riverine dark waters that, associated with their evasive behavior,
makes their detection a challenge.
In Colombia, Arévalo-González et al. (2014) estimated manatee abundance in
Ciénagas de Paredes through boat surveys, side-scan sonar surveys and interviews
in 2002 and 2010. By boat survey, the maximum number of simultaneous sightings
was 17. Using SSS and Distance sampling, a population of 12 manatees was estimated to occur in Los Pozos.
In Suriname, Pool (2012) indicated two manatee abundance estimates for the
country: 500–600 (Duplaix and Reichart 1978) and 200–300 with a maximum of
500–600 at best (Wassink 1997). However, no details are presented on these studies’
methods.
In Brazil, Lima (1997) and Luna (2001) proposed manatee abundance in northeastern and northern region, respectively, based on interviews. Despite the unusual
method, without accuracy, these estimates were the only available in the country for
years.
More recently, Alves et al. (2016) conducted aerial surveys from Canárias Island,
on the mouth of Parnaíba river (Piauí) to São Francisco river mouth, covering
2,590 km
2
, using strip transect method. Through a Bayesian approach, the authors
estimated manatee abundance as 1,104 animals (CI 95%: 485–2,221), an inaccurate
result that could be improved with additional efforts in a smaller spatial scale.
11 West Indian Manatee Trichechus manatus in South America…