Distribution of the Antillean manatee (Trichechus manatus manatus) as a function of habitat characteristics, in Bahı́a de Chetumal, Mexico

doi:10.1016/j.biocon.2004.02.023

Biological Conservation

Volume 121, Issue 1, January 2005, Pages 127-133

https://doi.org/10.1016/j.biocon.2004.02.023 Get rights and content

Abstract

The Antillean manatee Trichechus manatus manatus is considered endangered because of its reduced numbers, poor knowledge about its population status, and human modification of rivers, estuaries and coastal areas which it inhabits. Previous studies identified some elements of the habitat of manatees in the Caribbean, but few have explored quantitatively their relationship with their use by manatees, specially at a local scale. We explored the correlations between several habitat characteristics and the use of small spatial units by manatees in Bahı́a de Chetumal. Distance to freshwater sources, vegetation cover, depth, slope, salinity and shelter were sampled concurrently during 17 manatee aerial surveys, between November of 1998 and April of 2000. All variables, except shelter, were correlated with the occurrence of manatees. The distance to freshwater and depth contributed the most to multivariate Poisson and Logistic regression models and should be considered first in developing habitat models and conservation strategies for this species.

Introduction

The Antillean manatee Trichechus manatus manatus is a subspecies of the West Indian manatee that, because intensive hunting from the 16th century to the early 20th century, has strongly reduced populations (Lefebvre et al., 2001). Low scale subsistence hunting is still practiced in Mexico; but, currently, the main conservation threat in this country is the continuous change and degradation of the riverine and coastal habitats used by this species. Healthy populations of manatees in Mexico are confined to relatively isolated regions, but increasing human development pressure is a major reason of concern threatening these animals.

The characterization of manatee habitat at regional and local scales is a priority research issue for international, regional and local conservation plans for this species (USFWS, 2001; UNEP, 1995). Some habitat characteristics like the presence of freshwater sources, warm water, abundance of aquatic plants, water shallowness, shelter from wind and surf, and presence of travel corridors between areas with different characteristics, are considered important components of the general habitat of the manatees (Hartman, 1979; Powell and Rathbun, 1984; Packard and Wetterqvist, 1986; Rathbun et al., 1990; Provancha and Hall, 1991; Lefebvre et al., 2000), but few studies have been directed at quantifying their importance at smaller spatial scales.

In the Mexican Caribbean coasts, manatees are concentrated mostly in Bahı́a de Chetumal, which has been designated as a manatee natural protected area (Periódico Oficial del Gobierno del Estado de Quintana Roo, 1999). This bay along with the adjacent coast of Belize is considered one of the main areas of distribution of this species in the Caribbean Sea (O'Shea and Salisbury, 1991; Morales-Vela et al., 2000).

Bahı́a de Chetumal had been poorly studied, although recently some studies have begun to address its biological, physical and chemical features (Morales-Vela et al., 1996). Axis-Arroyo et al. (1998) conducted a small-scale study to explore the relationships between some habitat characteristics and the distribution of manatees in this area, but it covered a small geographic regions and data on manatee distribution was obtained opportunistically from multiple sources, limiting its interpretability.

The main goal of the study we report upon here was to examine the correlation between the occurrence of manatees and several habitat characteristics, at a local scale. We covered a large area in Northern Bahı́a de Chetumal, and obtained concurrent data about manatee distribution and habitat characteristics.

Section snippets

Manatee data

We used a CESSNA-182 airplane to conduct 17 aerial surveys for manatees in the Northern section of Bahı́a de Chetumal (Olivera-Gómez and Mellink, 2002). Three flights were conducted in November 1998, four in May–June 1999, five in August–September 1999, and five in April–May 2000. For each flight, we flew for about one hour over the survey area (about 1.25 h of total flight time), at an altitude of 150 m and an average speed of 180 km h⁻¹, following a series of transects parallel to the coast

Results

Manatees used less than 10% of the units in each sample period and 28% of them throughout the study. The frequency of occurrence within any particular unit was also low. The frequency distribution of the units used by manatees was modeled by negative binomial and geometric distributions.

The cumulative frequency of the units used exhibited an asymptotic trend as the number of surveys increased. Permuting 50 times the order of the 17 surveys and using a simple quadratic function to fit the data,

Discussion

Among the variables included in our study, the distance to freshwater sources was the most consistently correlated with the frequency of occurrence of manatees. This was clearly seen when we analyzed data from the Western and Eastern coasts separately. On the East coast, only distance to freshwater sources was significantly correlated with the occurrence of manatees. Shallowness and flatness of this coast and its low cover of aquatic plants might account for the lack of other correlations (

Acknowledgements

This study was supported by financial aid of Save the Manatee Club and Wildlife Conservation Society, and by a student fellowship of the Consejo Nacional de Ciencia y Tecnologı́a CONACYT, México to the first author. CICESE and ECOSUR-Unidad Chetumal provided logistic support. We want to thank specially our local guide Daniel Rovelo, as well as Cecilia Flores and Adriana Olivera, and a number of colleagues who worked as volunteers during fieldwork. We also thanks to Horacio de la Cueva, Robert

References (28)

A.O. Nicholls
How to make biological surveys go further with generalized linear models
Biol. Cons.
(1989)
B. Morales-Vela et al.
Distribution and habitat use by manatees (Trichechus manatus manatus) in Belize and Bahı́a de Chetumal, Mexico
Biol. Cons.
(2000)
J. Axis-Arroyo et al.
Variables asociadas con el uso de hábitat del manatı́del Caribe (Trichechus manatus), en Quintana Roo, México (Mammalia)
Rev. Biol. Trop.
(1998)
D.W. Bayley et al.
Mechanisms that result in large herbivore grazing distribution patterns
J. Range Manag.
(1998)
L.C. Colmenero-Rolón et al.
Distribución de los manatı́es, situación y su conservación en México
An. Inst. Biol. Univ. Nal. Autón. Méx. Ser. Zool.
(1986)
C.J. Deutsch et al.
Radio-tracking manatees from land and space: tag design, implementation, and lessons learned from long-term study
Mar. Tech. Soc. J.
(1998)
D.S. Hartman
Ecology and behavior of the manatee (Trichechus manatus) in Florida
Am. Soc. Mammalog., Special Publ.
(1979)
D.A. Hill et al.
Gross and microscopic anatomy of the kidney of the West Indian Manatee, Trichechus manatus (Mammalia: Sirenia)
Acta Anat.
(1989)
L. Lefebvre et al.
Status and biogeography of the West Indian manatee
L.W. Lefebvre et al.
Characterizing manatee habitat use and seagrass grazing in Florida and Puerto Rico: implications for conservation and management
Pacific Cons. Biol.
(2000)

N.S.R. Maluff

Renal anatomy of the manatee, Trichechus manatus (Linnaeus)

Am. J. Anat.

(1989)

J.C. Moore

The range of the Florida manatee

Quart. J. Florida Acad. Sci.

(1951)

Morales-Vela, B., Olivera-Gómez, L.D., Ramı́rez-Garcı́a, P., 1996. Conservación de los manatı́es en la región del...

B. Morales-Vela et al.

Radiotagging manatees in Mexico

Sirenews (Newsletter of the IUCN/SSC Sirenia Specialist Group)

(1995)

Cited by (41)

Want to model a species niche? A step-by-step guideline on correlative ecological niche modelling
2021, Ecological Modelling
The use of correlative ecological niche models has highly increased in the last decade. Despite all literature and textbooks in this field, few practical guidelines exist on the correct application of these techniques. We present here a step-by-step guideline explaining best practices for calculating correlative ecological niche models considering their conceptual and statistical assumptions and limitations. We divided the modelling process into four stages: 1) data collection and preparation; 2) model calculation; 3) model evaluation and validation; 4) and model application. Based on ecological niche theory, we review the concepts of ecological niche and how they can be modelled; classes of correlative models; modelling software; selection of study area; data sources for species records and environmental variables; types of species records and their influence on correlative models; errors in species records; minimum number of species records and environmental variables; effects of prevalence, sampling design, biases, and collinearity between variables; model calculation; model projection to different scenarios in time and space; ensemble modelling; model validation; classification, discrimination and calibration metrics; calculation of null models; analysis of model results; and model thresholding. This guideline is expected to help potential users to obtain better results when using correlative ecological niche models.
Inferring spatial and temporal behavioral patterns of free-ranging manatees using saltwater sensors of telemetry tags
2015, Mammalian Biology
Diving or respiratory behavior in aquatic mammals can be used as an indicator of physiological activity and consequently, to infer behavioral patterns. Five Antillean manatees, Trichechus manatus manatus, were captured in Chetumal Bay and tagged with GPS tracking devices. The radios were equipped with a micropower saltwater sensor (SWS), which records the times when the tag assembly was submerged. The information was analyzed to establish individual fine-scale behaviors. For each fix, we established the following variables: distance (D), sampling interval (T), movement rate (D/T), number of dives (N), and total diving duration (TDD). We used logic criteria and simple scatterplots to distinguish between behavioral categories: ‘Travelling’ (D/T ≥ 3 km/h), ‘Surface’ (↓TDD, ↓N), ‘Bottom feeding’ (↑TDD, ↑N) and ‘Bottom resting’ (↑TDD, ↓N). Habitat categories were qualitatively assigned: Lagoon, Channels, Caye shore, City shore, Channel edge, and Open areas. The instrumented individuals displayed a daily rhythm of bottom activities, with surfacing activities more frequent during the night and early in the morning. More investigation into those cycles and other individual fine-scale behaviors related to their proximity to concentrations of human activity would be informative.
Meeting the giants: The need for local ecological knowledge (LEK) as a tool for the participative management of manatees on Marajó Island, Brazilian Amazonian coast
2013, Ocean and Coastal Management
O Conhecimento Ecológico Local (CEL) tem sido bastante utilizado como uma fonte de informação confiável para o desenvolvimento de pesquisas sobre a ecologia de peixes-boi. Com base nesta abordagem, o presente estudo avaliou o nível de conhecimento sobre o peixe-boi dos pescadores locais da costa leste da Ilha de Marajó, no litoral da Amazônia brasileira, que apresenta uma zona de simpatria e hibridização entre as especies de peixes-boi marinho e amazônico. A maioria dos entrevistados (70%) tinha um alto nível de conhecimento em relação a esses mamíferos, e forneceram informações confiáveis para o mapeamento da ocorrência de peixes-boi na área de estudo, incluindo a identificação dos hábitats e áreas mais adequadas para sua ocorrência (tais como: hábitos alimentares, áreas preferenciais e registros de avistamentos). Os desafios enfrentados pela pesca, assim como o entendimento de demais questões relativas aos desafios da região amazônica mostra a relevância dos dados apresentados nessa pesquisa. E este estudo reforça o valor de tais informações repassadas pelos pescadores, e de como pode-se associa-las ao saber científico como uma ferramenta eficaz para a gestão participativa de peixes-boi ao longo da costa amazônica brasileira.
Local ecological knowledge (LEK) has been widely used as a source of reliable information for the development of research on the ecology of manatees. Based on this approach, the present study evaluated the level of knowledge related to manatees among the local fishermen on the east coast of Marajó Island on the Brazilian Amazonian coast, which represents a zone of sympatry and hybridization between marine and Amazon species of manatees. Most of the interviewees (70%) displayed a high level of knowledge with regard to these mammals, and provided reliable information for mapping of the occurrence of the manatees within the study area, including identifying the habitats and areas that are most appropriate for their occurrence (based on their eating habits, preferred areas and records of sightings). The challenges faced by fishers as well as knowledge of other issues related to the challenges present in the Amazon region demonstrate the relevance of the data presented in this study. Furthermore, our findings reinforce the value of such information provided by fishermen, and demonstrate how it can be associated with scientific knowledge as an effective tool for the participatory management of manatees along the Brazilian Amazonian coast.
Aerial survey of manatees, dolphins and sea turtles off northeastern Brazil: Correlations with coastal features and human activities
2013, Biological Conservation
Citation Excerpt :
Furthermore, these few records may be due to lack of sampling within the estuaries, which are ecosystems using for reproduction and parental care of manatees (Hartman, 1979; Lima et al., 2011), or detection difficulty related smaller size. The presence of manatees in shallow coastal waters, generally with less than 12 m depth, seems to be related to the availability of food sources (Hartman, 1979; Olivera-Gómez and Mellink, 2005; Rodas-Trejo et al., 2008; Langtimm et al., 2011). Furthermore, these are often shallow sheltered sites that allow animals to spend less energy in respiratory intervals (Smethurst and Nietschmann, 1999; Bacchus et al., 2009).
The objective of the present study was to analyze the distribution of manatees, dolphins and sea turtles off northeastern Brazil through aerial surveys, relating them to specific habitats and human activities, with emphasis on marine protected areas (MPAs). Surveys were conducted between January and April 2010 at 150 m altitude and 140 km h⁻¹, using two independent observers. Strip transects were flown in a zigzag pattern. Transects covered 4026 km in more than 27 flight hours. A total of 36 sightings of manatees (Trichechus manatus manatus, 41 individuals), 28 of dolphins (Delphinidae, 78 individuals, including 10 Sotalia guianensis) and 256 of sea turtles (Cheloniidae, 286 individuals) were recorded. Manatees and sea turtles displayed solitary habits, while dolphins were commonly seen in groups. Manatees were positively correlated with sea turtles, probably due to their preference for sheltered shallow habitats with favorable conditions for foraging and resting. Furthermore, manatees showed a positive relationship with mangrove estuaries, and medium-sized coastal cities probably due to the intense urban development in many estuarine areas. Manatees and sea turtles were also positively correlated with boats, showing a severe threat for these species. Density of manatees was significantly higher within MPAs with preserved mangrove estuaries than in non-protected areas, while dolphins and sea turtles were observed in high densities MPAs with coral reefs. The elevated density of these organisms shows the vital importance of protecting and adequately managing unique ecosystems to ensure a sustainable future for the populations of severely threatened species.
An index of risk of co-occurrence between marine mammals and watercraft: Example of the Florida manatee
2013, Biological Conservation
Citation Excerpt :
Based on these analyses, distance to seagrass appeared to be an important environmental covariate that influenced the distribution of manatees. This was consistent with previous studies on this species, all of which found a positive relationship between manatee observations and presence of vegetation (Axis-Arroyo et al., 1998; Jiménez, 2005; Olivera-Gómez and Mellink, 2005). However, our study represents the first attempt to predict probability of occupancy of manatees as a function of seagrass availability while accounting for imperfect detection due to observer bias (Fig. 2).
Collisions between wildlife and vehicles represent a large source of mortality for many species. To implement effective protection zones, it is important to identify areas in which wildlife–vehicle collisions are likely to occur. We used statistical models to derive an index of risk of co-occurrence between manatees and boats. Our statistical models were used to predict the distribution of both manatees and boats, while accounting for observer-specific detection probabilities. Models used aerial survey data and we found that both environmental and temporal covariates influenced manatee and boat distributions. Moreover, the probability of detecting manatees varied substantially with the weather and among observers. To our knowledge, this is the first time that manatee distribution is modeled as a function of key environmental and seasonal covariates, while accounting for imperfect detection of manatees. We computed an index of risk of co-occurrence by multiplying the probability of manatee occupancy by the expected boat density and occupancy to identify areas where manatee–boat collisions are likely to occur. This analytical framework emphasizes the importance of accounting for imperfect detection, and how modeling distribution of both organisms and vehicles as a function of key covariates can help improve predictions of risk of collisions. Risk of collision metrics can then be used in designing protection zones.
Reproductive success of Antillean manatees released in Brazil: implications for conservation
2022, Journal of the Marine Biological Association of the United Kingdom

View all citing articles on Scopus

Distribution of the Antillean manatee (Trichechus manatus manatus) as a function of habitat characteristics, in Bahı́a de Chetumal, Mexico

Abstract

Introduction

Section snippets

Manatee data

Results

Discussion

Acknowledgements

Biol. Cons.

Biol. Cons.

Variables asociadas con el uso de hábitat del manatı́del Caribe (Trichechus manatus), en Quintana Roo, México (Mammalia)

Rev. Biol. Trop.

Mechanisms that result in large herbivore grazing distribution patterns

J. Range Manag.

Distribución de los manatı́es, situación y su conservación en México

An. Inst. Biol. Univ. Nal. Autón. Méx. Ser. Zool.

Radio-tracking manatees from land and space: tag design, implementation, and lessons learned from long-term study

Mar. Tech. Soc. J.

Ecology and behavior of the manatee (Trichechus manatus) in Florida

Am. Soc. Mammalog., Special Publ.

Gross and microscopic anatomy of the kidney of the West Indian Manatee, Trichechus manatus (Mammalia: Sirenia)

Acta Anat.

Status and biogeography of the West Indian manatee