León David Olivera-Gómez

Gentle Giants in Dark Waters: Using Side-Scan Sonar for Manatee Research

Abstract: Manatees are tropical marine mammals that live in a wide variety of aquatic habitats ranging from coastal marine areas to freshwater lakes and rivers located hundreds of kilometers inland. All manatee species are currently characterized as Vulnerable by the International Union for Conservation of Nature (IUCN), primarily due to anthropogenic causes (i.e. poaching, habitat destruction, pollution, collisions with boats) and all of the environments they live in present challenges to biologists and wildlife managers. Tropical freshwater systems are especially difficult to work in because they are generally tannin-stained or turbid and water clarity is very restricted. Locating manatees and observing their behavior in these environments is extremely difficult and is a major limiting factor in determining population parameters. We summarize the use of sonar technology as an aid to detect and study manatees in these freshwater systems. First, by a summary of what has been attempted before our efforts, followed by presenting the various ways we have used this technology in the past 6 years to 1) detect manatees, 2) characterize manatee habitat in ways that would not be possible otherwise, 3) identify mother-calf pairs, and 4) assist in manatee captures. Finally, we discuss the advantages and limitations of using this technology for manatee conservation and research and present directions in which we believe future work can be directed, such as the determination of manatee abundance via distance sampling surveys using side-scan sonar and the use of one of the latest developments in acoustic technology, dual-frequency identification sonar.

SEASONAL PREVALENCE OF ANTIBODIES TO LEPTOSPIRA INTERROGANS IN ANTILLEAN MANATEES FROM A LANDLOCKED LAKE IN TABASCO, MEXICO

Abstract Factors that alter the dynamics of ecologic systems can influence transmission of infectious diseases and may lead to decreases in natural populations. Leptospirosis is a cosmopolitan disease of zoonotic importance that affects most mammals. At the southern Gulf of Mexico, Antillean manatees (Trichechus manatus manatus) inhabit highly variable environments, with extended floods during the rainy season and drought conditions during the dry season that affect food availability and the thermal environment for manatees. We tested for changes in prevalence and titers of antibodies to 12 serovars of Leptospira interrogans in manatees between dry and rainy seasons. We determined titers for L. interrogans through microscopic agglutination tests (MAT) from 10 manatees, six during the dry season (DS), and six during the rainy season (RS) in Laguna de las Ilusiones, a landlocked lake hosting a population of about 20 manatees. All individuals were antibody positive (titers ≥100) to at least one serovar. The serovars bataviae, bratislava, canicola, and icterohaemorrhagiae had overall prevalences ≥50%; bataviae, bratislava, and canicola had prevalences ≥50% during both seasons. Serovars icterohaemorrhagiae and pyrogenes had prevalences ≥50% during DS and pomona, tarassovi, wolfii, and autumnalis during RS. Significant differences in prevalence between seasons were found for pomona, tarassovi, and autumnalis. Titers of tarassovi, wolfii, autumnalis, and bataviae were significantly higher during RS. There was a high prevalence of L. interrogans during the RS independent of high availability of plant foods, coinciding with the epizootiology of the bacteria that are endemic to tropical regions. Another factor possibly influencing prevalence is high anthropogenic pressure at the lake, causing an increase in potential sources of infection. Because of possible cross-reaction in MAT, further research is needed on the molecular discrimination of serovars in animals in the lake.

Genetic Diversity and Structure From Antillean Manatee (Trichechus manatus manatus) in the Southern Gulf of México: Comparison Between Connected and Isolated Populations

Antillean manatees (Trichechus manatus manatus), a subspecies of the West Indian manatee, is listed as endangered species in the Red List of Threatened Species of the International Union for Conservation of Nature. The aims of this research were to survey on the possible regional genetic structure in the southern Gulf of Mexico and to compare genetic status of a landlocked population in Laguna de las Ilusiones (IL) with individuals from localities with no barriers to displacement and breed (open population [OP]). We analyzed 45 manatee skin samples collected from different locations in Tabasco (n = 38, including 19 from IL), Veracruz (n = 3), Campeche (n = 2), and Chiapas (n = 2). The genomic DNA was isolated and PCR amplifications were performed for each sample using 28 microsatellite loci, previously designed for West Indian manatees and described as polymorphic for this species. Two clusters (k = 2) were identified by STRUCTURE. The analysis of both a priori populations (IL and OP) indicate that the global values of FST and RST (FST=0.049, RST=0.077) were significant. The HE for IL was 0.38 ± 0.03 and for OP was 0.49 ± 0.01. The average number of alleles NA for IL was 2.21 ± 0.09 and for OP was 2.32 ± 0.09. The overall inbreeding coefficient was FIS=−0.013 for analyzed populations. Genetic diversity was low. The IL population had slightly lower genetic diversity compared with OP, which could be explained by isolation of that small group, so conservation plans for IL should be considered as priority.