Revista de Biología Tropical, ISSN: 2215-2075, Vol. 71(S4): e57273, diciembre 2023 (Publicado Nov. 01, 2023)

Long-term spatiotemporal distribution, abundance, and priority areas for

manatees and calves (Trichechus manatus Sirenia: Trichechidae) in Guatemala

Ester Quintana-Rizzo1*; https://orcid.org/0000-0002-8957-0506

Oscar Machuca-Coronado2, 3; https://orcid.org/0000-0001-9413-914X

Heidy Amely Garcia3; https://orcid.org/0000-0002-2392-6768

1. Emmanuel College, Department of Biology, Boston MA 02115 USA; tetequintana@comcast.net (Correspondence*)

2. Asociación Guatemalteca de Mastozoólogos, Guatemala City, Guatemala; machuca.oscarhugo@gmail.com

3. Fundación Defensores de la Naturaleza, Guatemala City, Guatemala; machuca.oscarhugo@gmail.com;

hgarcia@defensores.org.gt

Received 20-X-2022. Corrected 03-I-2023. Accepted 21-IV-2023.

ABSTRACT

Introduction: The Antillean manatee (Trichechus manatus manatus) is an endangered species found throughout

the Caribbean, and the coastal waters of Central and northeastern South America. Their low numbers are the

result of a variety of human-related pressures. A small population of manatees has been identified in Guatemala;

however, their spatial and temporal dynamics remain unclear.

Objective: To examine long-term trends in the spatiotemporal distribution and abundance of manatees in

Guatemala. This included identification of priority areas for manatees including the presence of calves, assessing

whether distribution areas are inside protected areas, and studying the relationship between manatee sightings

and human activities.

Methods: Nine years of standardized aerial surveys were conducted along the Atlantic coast (1992, 2005-2008,

2010-2011, 2014, 2022). Quantitative approaches to detect priority areas, specifically the Kernel density estima-

tion and the Getis-Ord Gi* statistic, were used in the spatiotemporal analysis. A Spearman rank correlation

analysis tested for significant correlations between human activities, coastline topographies, and manatee num-

bers along coastline segments. Manatee abundance across years, survey sections, and protected areas were also

examined.

Results: A total of 293 sightings and 518 manatees were observed including 476 adults (92 %) and 42 calves

(8 %). Manatees were most frequently observed as solitary individuals (60 %). Most manatee (61 %) and calf

(68 %) sightings occurred inside protected areas where several priority areas were identified. The two priority

areas were Refugio de Vida Silvestre Bocas del Polochic (Bocas del Polochic) and Refugio de Vida Silvestre Punta

de Manabique, which were identified as important manatee habitats in 1992. Bocas del Polochic had the highest

manatee abundance of all protected areas (p < 0.05). However, a shift in manatee distribution was recorded in

2014, although the cause is unclear. No annual significant differences in manatee abundance were found over

time (p = 1.0), but significant differences in abundance were detected between survey sections and protected

areas (p < 0.05). Manatee numbers had positive significant correlations with ecological and human parameters.

The highest correlation was between manatees and rivers (p < 0.01), and the weakest correlation was between

manatees, motorboats, and fishing nets (p < 0.01).

Conclusions: The results indicate that the local manatee population remained relatively stable for over 20 years,

although changes in overall distribution were noted. It is unclear if the changes are temporary or permanent. As

a sentinel species, manatee distribution shifts can be used as early warnings about the health of the environment

and can depict current or potential impacts on individual- and population-level animal health.

Key words: Antillean manatee; mammal; conservation; endangered species; Central America.

https://doi.org/10.15517/rev.biol.trop..v71iS4.57273

SUPPLEMENT • MANATEES

2Revista de Biología Tropical, ISSN: 2215-2075 Vol. 71(S4): e57273, diciembre 2023 (Publicado Nov. 01, 2023)

INTRODUCTION

Identifying spatiotemporal patterns of

distribution and abundance is important for

understanding the status of a population. This

information can be used to identify areas of

importance and to evaluate the effectiveness of

established protected areas since animals must

utilize or concentrate in those areas if they have

conditions that are important for their survival

(e.g., food resources, habitat characteristics,

etc.; Roberts et al., 2021). Spatiotemporal infor-

mation is also useful for identifying wheth-

er anthropogenic activities impact animals,

particularly when their habitat overlaps with

these activities as it does in coastal environ-

ments (Halpern et al., 2008). Understanding

these complex interactions is crucial for the

design and implementation of an effective con-

servation management plan (de Souza et al.,

2021; Yoccoz et al., 2001).

The Antillean manatee (Trichechus mana-

tus manatus, Linnaeus, 1758) is an endangered

species found throughout the Caribbean, and

in the coastal waters of Central and northeast-

ern South America (Self-Sullivan & Mignucci-

Giannoni, 2008; Quintana-Rizzo & Reynolds,

2010). Their low numbers are the result of

RESUMEN

Distribución espacio-temporal a largo plazo, abundancia y áreas prioritarias para manatíes

y crías (Trichechus manatus Sirenia: Trichechidae) en Guatemala

Introducción: El manatí antillano (Trichechus manatus manatus) es una especie en peligro de extinción que se

encuentra en todo el Caribe y las aguas costeras de Centro América y noreste de América del Sur. Su bajo número

es el resultado de una variedad de presiones relacionadas con los humanos. Se ha identificado una pequeña pobla-

ción de manatíes en Guatemala; sin embargo, su dinámica espacial y temporal sigue sin estar clara.

Objetivo: Examinar las tendencias a largo plazo en la distribución espacio-temporal y la abundancia de los mana-

tíes en Guatemala. Esto incluyó la identificación de áreas prioritarias para los manatíes y las crías, la evaluación

de si las áreas de distribución se encuentran dentro de áreas protegidas y el estudio de la relación entre los avista-

mientos de manatíes y las actividades humanas.

Métodos: Se realizaron nueve años de censos aéreos estandarizados a lo largo de la costa atlántica (1992, 2005-

2008, 2010-2011, 2014, y 2022). En el análisis espacio-temporal se utilizaron métodos cuantitativos para detectar

áreas prioritarias, específicamente la estimación de la densidad Kernel y el estadístico Getis-Ord Gi*. Un análisis

de correlación de rangos de Spearman probó correlaciones significativas entre las actividades humanas, las topo-

grafías costeras y el número de manatíes a lo largo de los segmentos de la costa. También se examinó la abundan-

cia de manatíes a lo largo de los años, las secciones de estudio y las áreas protegidas.

Resultados: Se observaron un total de 293 avistamientos y 518 manatíes, incluidos 476 adultos (92 %) y 42 crías

(8 %). Los manatíes se observaron con mayor frecuencia como individuos solitarios (61%). La mayoría de los

avistamientos de manatíes (61 %) y crías (68 %) ocurrieron dentro de áreas protegidas donde se identificaron

varias áreas prioritarias. Las dos áreas prioritarias fueron el Refugio de Vida Silvestre Bocas del Polochic (Bocas

del Polochic) y el Refugio de Vida Silvestre Punta de Manabique, que fueron identificados como importantes

hábitats para manatíes en 1992. Bocas del Polochic tenía la mayor abundancia de manatíes de todas las áreas pro-

tegidas (p < 0.05). Sin embargo, se registró un cambio en la distribución del manatí en 2014, aunque la causa no

está clara. No se encontraron diferencias significativas anuales en la abundancia de manatíes a lo largo del tiempo

(p = 1.0), pero se detectaron diferencias significativas en la abundancia entre las secciones de estudio y las áreas

protegidas (p < 0.05). El número de manatíes tuvo correlaciones positivas significativas con parámetros ecológicos

y humanos. La correlación más alta fue entre los manatíes y los ríos (p < 0.01), y la correlación más baja fue entre

los manatíes y las lanchas motoras y las redes de pesca (p < 0.01).

Conclusiones: Los resultados indican que la población local de manatíes se mantuvo relativamente estable

durante más de 20 años, aunque se observaron cambios en la distribución general. No está claro si estos cambios

son temporales o permanentes. Como especie centinela, el cambio en la distribución del manatí se puede utilizar

como advertencia temprana sobre la salud del medio ambiente y puede representar los impactos actuales o poten-

ciales en la salud animal a nivel individual y poblacional.

Palabras clave: manatí Antillano; mamífero; conservación; especies amenazadas; Centroamérica.

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 71(S4): e57273, diciembre 2023 (Publicado Nov. 01, 2023)

human-related pressures including poaching,

habitat loss, entanglement in fishing/shrimp

nets, chemical contamination, and watercraft

collisions (Jiménez, 2002; Lefebvre et al., 1989;

Reynolds & Powell 2002; U.S. Fish & Wild-

life Service, 2001). Poaching, specifically, has

caused an extensive reduction in manatee pop-

ulations throughout most of the species’ range

(Lefebvre et al., 1989).

A small population of manatees has been

identified in Guatemala. The most recent popu-

lation estimate is 150 manatees (Quintana-Riz-

zo & Reynolds, 2010). Poaching resulted in the

death of 20 manatees between 2003 and 2016.

A more comprehensive update details 48 deaths

between 1992 and 2022, although this num-

ber includes undetermined causes of mortal-

ity (Machuca-Coronado et al., 2023). Different

mechanisms exist to protect the species, such as

The National Strategy for the Conservation of

the Manatee, whose objectives are to monitor

and protect manatees, manage and protect their

habitat, and promote the cultural and ecological

value of the species throughout its range in the

country (Herrera et al., 2004). Their recom-

mendations include collecting long-term data

on population distribution and identifying the

effects of anthropogenic activities on manatees

and their habitats. There are also protected

areas including the “Biotopo para la Conser-

vación del Manatí Chocón-Machas”. This is

the first protected area for manatees in Latin

America (Lefebvre et al., 1989), although it is

mostly terrestrial (Consejo Nacional de Áreas

Protegidas [CONAP], 2022).

Marine protected areas (MPAs) can be

effective tools for the conservation of species

at risk. The protection of manatees could result

in the protection of many aquatic organisms.

This is because aquatic mammals typically

live in large areas where, if effective protection

measures are established, numerous other spe-

cies could be conserved and protected, as well

as the ecosystem itself (Hooker & Gerber,

2004; Quintana-Rizzo et al., 2021; Roberts et

al., 2021). However, ensuring the effective-

ness of MPAs requires a thorough understand-

ing of species distribution, abundance, and

habitat relationships (Hunt et al., 2020). In

simple terms, it requires knowing where ani-

mals are distributed, what areas are impor-

tant to them and why, how many animals are

there, and how they are negatively impacted by

human activities.

In the case of aquatic mammals, imple-

menting effective protective measures poses

a challenge. They typically have long-range

movements, are hard to see at the surface, and

have long lives, which bolster the need for

multi-year studies. Some field techniques are

better suited for the challenge. Aerial surveys

can cover large areas in short periods, allowing

for the observation of animals from above and

the simultaneous examination of human activi-

ties. They have been widely used to determine

manatee abundance, distribution, and habitat

use in the Wider Caribbean, and are one of

the most suitable field methods for monitoring

sirenian populations in the world (e.g., Edwards

et al., 2007; Garrigue et al. 2008; Hagihara et al.,

2018; Morales et al., 2000; Olivera-Gomez &

Mellink, 2002, Olivera-Gomez & Mellink, 2005).

In Guatemala, a 9.8-hour aerial survey

detected nine manatees along the Atlantic coast

in 1991 (Ackerman, 1991). A more compre-

hensive set of monthly aerial surveys were used

to generate the first population estimate of 53

manatees in 1992 (Quintana-Rizzo, 1993). In

2005 and 2014, regional surveys were conduct-

ed with the objective to examine the manatee

numbers in the Belize-Guatemala-Honduras

and Mexico-Belize-Guatemala regions (Quin-

tana-Rizzo, 2005a, Quintana-Rizzo, 2005b).

Annual aerial surveys were conducted between

regional surveys (Machuca-Coronado & Quin-

tana-Rizzo, 2011; Quintana-Rizzo & Machu-

ca-Coronado, 2008), but none of the studies

looked at trends in spatiotemporal patterns of

manatee distribution and abundance. They did

not examine the relationship between manatee

sightings and human activities even though

earlier studies recognized that manatees must

travel through areas of high boat traffic to move

between preferential habitats. Here we present a

comprehensive assessment of the data collected

during all of the aerial surveys conducted since

4Revista de Biología Tropical, ISSN: 2215-2075 Vol. 71(S4): e57273, diciembre 2023 (Publicado Nov. 01, 2023)

1992 and a depiction of long-term trends in the

spatiotemporal distribution and abundance of

manatees in Guatemala. Priority areas, or areas

of particular importance for conservation, for

the species were identified including the pres-

ence of calves, a determination of whether they

are using protected areas, and the co-occur-

rence of manatee sightings and human activi-

ties. The results fill a critical gap in knowledge

to ensure that the protection of this endangered

species is based on a foundation of the most

inclusive data available.

METHODS

Study area: The study area included the

entire Atlantic Coast of Guatemala, located

along the state of Izabal (Fig. 1.1). It is bordered

Fig. 1. (1) Location of the study area along the Atlantic Coast of Guatemala including (2) important geographical points,

(3) protected areas, (4) survey sections, and location of (5) manatee sightings and (6) calf sightings between 1992 and 2022.

Protected areas evaluated: A) Refugio de Vida Silvestre Bocas del Polochic, B) Parque Nacional Río Dulce, C) Refugio de Vida

Silvestre Punta de Manabique, and D) Área de Usos Múltiples Río Sarstún.

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 71(S4): e57273, diciembre 2023 (Publicado Nov. 01, 2023)

to the north by the Caribbean Sea and to

the east by the Gulf of Honduras. The study

area encompasses distinctive aquatic ecosys-

tems. Lago de Izabal is the largest freshwater

lake in Guatemala (area = 717 km2; Fig. 1.2).

It connects to the Gulf of Honduras in the

Caribbean Sea by Río Dulce. It has an average

depth of 12 m and a maximum depth of 18 m

(Arrivillaga, 2002). The southwestern part of

the lake includes the protected area “Refugio de

Vida Silvestre Bocas del Polochic” (Bocas del

Polochic, Fig. 1.1). This RAMSAR site is a wet-

land of great ecological importance, providing

food for more than 250 species of birds, both

resident and migratory (Fundación Defensores

de la Naturaleza, 1997). Midway between the

lake and the sea is Río Dulce, a tidal river that

broadens into a large and shallow area (4.5 m

depth) known as El Golfete (Brinson et al.,

1974). Both Río Dulce and El Golfete are part

of a protected area called “Parque Nacional

Río Dulce” (Fig. 1.3), which has terrestrial and

aquatic zones (CONAP, 2005).

The Atlantic Coast forms a semi-enclosed

bay called Bahia de Amatique. This bay includes

a complex ecosystem of coastal lagoons, marsh-

es, and swamps influenced by tides and the Río

Dulce-El Golfete riverine systems. It is part of

the protected area “Refugio de Vida Silvestre

Punta de Manabique” (Punta de Manabique), a

RAMSAR site located in the Gulf of Honduras

(Fig. 1.3). Punta de Manabique is one of the

most important ecosystems in the country as

it is composed of multiple marine, coastal, and

terrestrial areas (Yañez-Arancibia et al., 1999).

Río Sarstún is another important site, locat-

ed on the borderline between Guatemala and

Belize. Two protected areas are partially located

within this basin, the “Área de Usos Múltiples

Río Sarstún”, a RAMSAR site, located in Guate-

mala, and the Sarstoon-Temash National Park

located in Belize (Fundación para el Ecodesar-

rollo y la Conservación [FUNDAECO], 2005)

(Fig. 1.3).

Survey methods: Standardized aerial sur-

veys were selected as an efficient and cost-effec-

tive method to collect data on the distribution

and number of manatees (Reynolds et al.,

2012). In 1992, April 2005, and 2022, aerial

surveys were conducted by two observers who

sat on each side of the aircraft and maintained

their position throughout the survey. The 1992

surveys covered the center of Lago de Izabal,

although since manatees were never sighted

there, this portion of the lake was not included

in the analysis or future surveys. The May 2005,

2006-2011, and 2014, surveys involved three

observers. Two observers sat in the rear seats,

while a pilot and another observer sat in the

front seats. The front observer (EQR) was the

more experienced, participated in all surveys,

and was responsible for confirming total mana-

tee numbers. Each observer scanned an area

approximately 400 m wide (Olivera-Gomez &

Mellink, 2002, 2005). Surveys were conducted

parallel to the coast at altitudes of 150 to 200

m and at an average airspeed of 160 km/h from

a Cessna 337 or Aero Commander (1992), or

a Cessna 335 and Cessna 206 (2005-2022). A

GPS continuously recorded the survey path

during each survey.

The study area was divided into four sec-

tions: Lake Izabal, El Golfete, Livingston-Río

Sarstún, and Livingston-Río Motagua (Fig. 1.4).

A survey of the entire study area generally took

a day, however in cases of unfavorable weather

conditions some surveys were conducted over

two days. A given section of the survey area

was fully surveyed on the same day. Each sight-

ing was considered to be independent because

it was impossible to determine whether the

manatees moved to different sections of the

survey area on different days. When manatees

were sighted, the aircraft circled to obtain the

most accurate count (number of individuals)

possible (Lefebvre & Kochman, 1991). Mana-

tees within close proximity of one another

and displaying similar behavior were grouped

as one sighting. For each sighting, individuals

were classified as adults or calves. Calves were

defined as smaller animals up to 1/3 of the adult

size (Hartman, 1979) and closely associated

with a larger manatee (Irvine, 1982; Reynolds

& Wilcox, 1994). One or more manatees were

considered a group (Morales-Vela et al., 2000).

6Revista de Biología Tropical, ISSN: 2215-2075 Vol. 71(S4): e57273, diciembre 2023 (Publicado Nov. 01, 2023)

Observers recorded the number of manatees

(calves and non-calves) and the location of each

sighting. For each section of the survey area,

environmental conditions such as the percent-

age of cloud cover and water surface conditions

were estimated and recorded by the observers.

To ensure that visibility was acceptable for effi-

cient spotting of manatees, surveys were con-

ducted only when sustained winds were < 10

knots and surface conditions scored ≤ 3 on the

Beaufort wind scale.

Data analysis: The data were divided into

two sets based on the available survey effort

(e.g., total kilometers) at the time of the analy-

sis. Data with no survey effort (DNS) included

surveys conducted in 1992 and April 2005.

Data with survey effort (DWS) included sur-

veys conducted from May 2005 on.

Manatee groups: size, calf presence, and

sighting distance from shore. Group size across

years were examined using a two-tailed Krus-

kal–Wallis test, and multiple Mann-Whitney U

post hoc tests were used to compare differences

between years. The 2-tailed statistical tests were

conducted using the SPSS 28.0.1.1 package

(2021) at a significance level of 0.05. The per-

centage of groups with calves inside and outside

of protected areas was reported as descriptive

statistics (mean ± standard error). Distance of

manatee sightings and calf sightings from shore

were calculated in ArcGis Pro 3.0.0.

Spatial distribution: two metrics were

used to quantify the spatial distribution of

manatees and identify priority areas: (1) a

hotspot analysis, and (2) Kernel density esti-

mation (Roberts et al., 2020). The first metric

allows the use of DWS data as sightings per unit

effort, and therefore, the evaluation of sections

with uneven coverage. Thus, statistically, a pri-

ority area was defined by this study as one that

was identified as either a “hot spot” or “cold

spot”, which are areas of statistically significant

spatial clustering (see Hotspot analysis), or an

area where the manatee density is more than

85 % of the estimated density in a given year

(see Kernel density analysis).

A Hotspot analysis tests for statistically

significant spatial clustering using the Getis-

Ord Gi* statistic (Getis & Ord, 1992), which

determines the spatial clustering of grid cell

values that are higher (hot spot) or lower (cold

spot) than is expected by random distribution.

The study area was divided into 4 km x 4 km

grid cells resulting in 246 cells. A 4 km width

was chosen because it covered the survey flight

path, the meandering sections of the study

area, and the mouths of large and medium

rivers flowing into the coastline (also referred

to as secondary rivers). Medium and large riv-

ers were defined based on the contribution of

their streams as >10 to 100 m3/s and > 100 to

500 m3/s, respectively (Spillman et al., 2000).

Within each grid cell, the total number of man-

atees and the total length of survey tracks were

calculated. If no sightings occurred in a grid cell

that was surveyed, the grid cell was attributed a

value of zero, but the cell was considered part

of the survey effort. A spatial map was created

at three levels of confidence (99 %, 95 %, and

90 %), and all clusters that were within the 90 %

confidence level were considered hot spots or

cold spots.

The second metric used was the Kernel

density estimation to identify core activity areas.

This nonparametric method estimates density

curves, where each observation is weighted by

the distance from a central value or core, also

named kernel, generating a smoothed surface

that describes a likely distribution at a given

time (Worton, 1989). The analysis allows the

use of data regardless of effort (e.g., both DNS

and DWS), and thus, the examination of tem-

poral patterns across the 8 years of surveys. A

buffer with a 4 km extension over the coastline

was created to include river mouths and delimit

the analysis boundaries. The 4 km extension

is of a similar size to one side of the grid cells

used in the Hotspot analysis. Predicted density

rasters were generated using a cell size of 1 km2.

All spatial analyses were conducted using Arc-

Gis Pro 3.0.0.

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Relationship between sightings, coastline

features, and human activities: A Spearman

rank correlation analysis tested for signifi-

cant correlations between human activities,

coastline features such as rivers, and manatee

numbers per segment (Alves et al., 2013) in

the study area and in each protected area.

This correlation analysis was chosen due to

the non-linear nature of relationships and the

non-normality and heteroscedasticity of most

distributions (Alves et al., 2013). The coastline

was divided into 4 km segments for a total of

122 segments. For each analysis and segment,

the occurrences of five ecological and human

parameters were examined: (1) manatee num-

bers, (2) fishing activity (fishing nets), (3) tour-

ism activity (transiting motorboats, kayaks), (4)

commercial traffic (merchant or cargo ships),

and (5) rivers. Fishing activity was recorded

during the 2006-2008 and 2010 surveys, and

tourism activities were recorded during the

2006-2011 surveys by the left rear observer.

Since the final sample size of the commercial

traffic parameters was small and confined to

a specific area, we only reported descriptive

statistics. The fifth parameter was based on

cartographic and bibliographic analyses and it

included the presence of large/medium size riv-

ers in each segment. These are secondary rivers

as sections of the coast such as El Golfete and

Río Sarstún are part of the main rivers. Thus,

for the correlation between manatees and riv-

ers, one protected area was excluded from the

analysis (Area de Usos Múltiples Río Sarstún)

because no secondary rivers flow into the por-

tion of the main river (Río Sarstún) that was

surveyed. All analyses were performed using

SPSS 28.0.1.1 package (2021) at a significance

level of 0.05.

Manatee abundance: Abundance was mea-

sured as density (Krebs, 2014) or the number of

manatees per square kilometer to account for

incomplete surveys (e.g., the entire study area

was not surveyed but individual surveyed sec-

tions were fully covered) and an unequal num-

ber of surveys per section. Periods of circling

were excluded from this and all other analytical

calculations. DWS data were used to examine

manatee abundance across years, survey sec-

tions, and protected areas using a non-paramet-

ric Kruskal-Wallis test. Years with incomplete

coverage (e.g., 2010 and 2022) of the study

area were excluded from this analysis. Multiple

Mann-Whitney U post hoc tests were used to

compare differences in abundance using the

SPSS 28.0.1.1 package (2021) at a significance

level of 0.05. Boundaries of the protected areas

were extracted from the World Database of

Protected Areas (United Nations Environment

Programme World Conservation Monitoring

Centre & International Union for Conservation

of Nature [UNEP-WCMC & IUCN], 2021).

RESULTS

Distribution of sightings: A total of 293

sightings were recorded between 1992 and

2022. This included 518 manatees, 476 adults

(92 %) and 42 calves (8 %) (Table 1). Of the 293

sightings, 17 % included groups with calves.

Further, 61 sightings were part of the DNS

data and 232 sightings were part of the DWS

data. Manatees were most frequently observed

as solitary individuals (63 %), but a group of

12 individuals was sighted on one occasion.

This large group included a calf. Calves were

typically sighted in groups of 3 ± 0.30 (stan-

dard error) while the mean group size for all

manatees, regardless of age class, was 2 ± 0.09

(Fig. 2). Significant differences in group size

were found among years (H = 18.02, d.f. = 8,

p = 0.02). Group size was smaller in 2005 than

in 2007, 2014 (p < 0.05); it was also smaller in

2006 than in 2007 and 2014 (p < 0.05). How-

ever, group size was not significantly different

between 2005 and 2006, and among all other

years (p > 0.05).

Analysis of sighting distribution from

shore showed that manatees were most fre-

quently sighted at distances ranging from 0.02

km to 2.6 km from the coast. Survey areas are

depicted in Figure 1.3. Manatees were most fre-

quently sighted at distances ranging from 0.02

km to 2.6 km from the coast. The mean and

median distances from shore were 6.5 km and

5 km, respectively, followed by a continuous

8Revista de Biología Tropical, ISSN: 2215-2075 Vol. 71(S4): e57273, diciembre 2023 (Publicado Nov. 01, 2023)

decrease in the sighting frequency toward open

waters (Fig. 2).

Spatial distribution: Manatees were sight-

ed throughout the study area, but they were

unevenly distributed (Fig. 1.3, Fig. 1.4). Most

manatee and calf sightings occurred inside

protected areas (60 % and 68 %, respectively).

Half of the groups with calves were observed in

Bocas del Polochic, but in the overall Lago de

Izabal, 82 % of groups with calves were sighted.

No calves were observed in the coastal waters

from Rio Sarstun to Rio Motagua.

A series of priority areas were identi-

fied and all occurred inside protected areas.

This included three hot spots or areas of high

clustering and two cold spots or areas of low

clustering (Fig. 3). A hot spot was detected in

the protected area Punta de Manabique while

a large cold spot and two large hot spots were

detected in Lago de Izabal (Fig. 3). In Lago

de Izabal, one of the hot spots overlapped by

approximately 1.5 km2 with the protected area

Bocas del Polochic. This protected area also

overlapped with the cold spot by more than 50

km2. A small cold sport was identified in the

north side of Parque Nacional Río Dulce in El

Golfete. No hot or cold spots were identified in

other protected areas.

The location, number, and extension of

predicted core activity areas for manatees var-

ied across years (Fig. 4). However, some general

patterns emerged. Lago de Izabal is a priority

area for manatees as one or more core activity

areas were detected there in each of the nine

years of surveys. Within the lake, the southern

corner, which covers the entire aquatic zone

of Bocas del Polochic and Punta Chapin, was

Table 1

Total number of manatees (including adults and calves) sighted per month, protected area, and survey section between 1992

and 2014 along the Atlantic coast of Guatemala.

Year Month

No. of manatees

in study area No. of manatees in protected areas No. of manatees

in survey sections

Total Adults Calves RVSBP PNRD AUMRS RVSPM 1234

1992 January 15 13 2 8 1 0 0 14 1 0 0

March 28 24 4 19 0 0 0 21 0 7 0

April 15 13 2 7 4 2 1 7 4 2 2

May 15 15 0 3 2 0 1 3 2 0 10

2005 April 39 36 3 14 6 0 6 22 6 2 9

May 49 43 6 15 2 0 8 35 2 2 10

2006 July 27 26 1 21 4 0 NS 21 4 2 NS

October 53 48 5 8 7 0 10 25 7 6 15

2007 January 52 48 4 13 6 0 7 39 6 0 7

March 38 35 3 5 7 2 20 8 7 2 21

2008 February 40 39 1 11 12 0 NS 28 12 0 NS

2010 May 26 23 3 26 NS PC PC 26 NS PC PC

2011 March 52 48 4 14 7 1 5 40 3 7 2

2014 May 45 43 2 4 7 0 10 20 14 1 10

2022 August 24 22 2 1 5 NS NS 19 5 NS NS

Total 518 476 42 169 70 5 68 328 76 31 86

Range 12-53 12-48 0-6 4-26 0-7 0-2 0-10 3-40 0-14 0-7 0-21

Percentage 100% 92% 8% 54% 22% 2% 22% 63% 14% 6% 17%

PC = poor conditions, NS = no surveyed. RVSBP = Refugio de Vida Silvestre Bocas del Polochic, PNRD = Parque Nacional

Río Dulce, RVSPM = Refugio de Vida Silvestre Punta de Manabique, and AUMRS = Área de Usos Múltiples Río Sarstún.

Survey sections: (1) Lago de Izabal, (2) El Golfete, (3) Livingston-Río Sarstún, and (4). Livingston-Río Motagua.

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 71(S4): e57273, diciembre 2023 (Publicado Nov. 01, 2023)

consistently identified as a core activity area,

although this pattern shifted to the northern

shoreline of the lake in 2014 and continued

in 2022 (Fig. 4). Another core activity area

was detected inside Punta de Manabique, near

Bahia La Graciosa. In Parque Nacional Río

Dulce, a core activity area was identified but

only in half of the nine years of surveys (Fig. 4).

Correlations of coastal features and

human activities: For the entire study area, the

Spearman rank correlation analysis identified

significant correlations between manatees and

ecological and human parameters (Table 2). The

first and highest positive significant correlation

was found between manatees and rivers (rs =

0.67, p < 0.01). A similar significant correla-

tion was detected in the inshore protected areas

(Bocas del Polochic and Parque Nacional Río

Dulce) with the highest correlation (rs = 1.00)

being between manatees and rivers of a pro-

tected area (Bocas del Polochic). Additionally,

Fig. 2. Frequency distribution of group sizes of manatees and their distance from shore in Guatemala.

Table 2

Spearman correlation (rs) between numbers of manatees, selected coastal features, and human activities in the study area and

individual protected areas.

Parameters Study area Protected Areas

RVSBP PNRD RVSPM AUMRS

Coastal features (rivers) rs = 0.67, p < 0.01* rs = 0.99, p < 0.01* rs = 0.52, p < 0.01* NA rs = -0.07, p = 0.75

Fishing nets rs = 0.04, p = 0.40 rs = -0.06, p = 0.54 rs = 0.27, p < 0.05 NA NA

Tourism activity

Motorboats rs = 0.07, p < 0.05* rs = 0.19, p < 0.05* rs = 0.19, p < 0.05* rs = -0.15, p = 0.59 rs = 0.14, p = 0.15

Kayaks rs = -0.40, p = 0.26 rs = 0.06, p = 0.48 rs = -0.15, p = 0.87 rs = -0.31, p = 0.26 rs = -0.06, p = 0.54

10 Revista de Biología Tropical, ISSN: 2215-2075 Vol. 71(S4): e57273, diciembre 2023 (Publicado Nov. 01, 2023)

Fig. 3. Hotspots and cold spots of manatees based on sightings per unit effort. Additional details of the study area are shown

in Figure 1.

Fig. 4. Interannual variation in core activity areas of manatees in Guatemala between 1992 and 2022 using Kernel estimates.

Each section of the study area was surveyed except in 2008 (no survey: Livingston-Río Motagua), 2010 (no survey: El Golfete;

poor weather conditions: Livingston-Río Motagua, Livingston-Río Sarstún), and 2022 (no survey: Livingston-Río Motagua,

Livingston-Río Sarstún).

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 71(S4): e57273, diciembre 2023 (Publicado Nov. 01, 2023)

manatee sightings were weakly positively corre-

lated with the presence of motorboats (p < 0.01)

in these two protected areas and with fishing

gear (p < 0.05) in Parque Nacional Rio Dulce

(Table 2). No other correlations were found for

the entire study area or in the protected areas.

Commercial traffic in the form of mer-

chant or cargo ships was only observed in the

Livingston-Río Motagua section. Within this

section, the commercial traffic happened near

the Santo Tomas de Castilla port where 10

cargo ships were observed during surveys. A

total of eight manatees were sighted in this area.

Manatee abundance: Manatee abundance

was estimated for the entire study area, each

surveyed section, and each protected area.

For a given survey, the mean abundance was

0.10 ± 0.01 manatees/km2 (range = 0.05 – 0.26

manatees/km2) and the overall mean calf abun-

dance was 0.01 ± 0.002 manatees/km2 (range =

0.00 – 0.03 calves/km2). No annual significant

differences in manatee abundance were found

among 2015 (May), 2006, 2007, 2008, 2011, and

2014 (H = 0.82, d.f. = 6, p = 0.99) or the years

with complete surveys of the study area.

Manatee abundance was significantly dif-

ferent among sections surveyed and among

protected areas (p < 0.01). In the first case, no

statistical difference in manatee abundance was

found between Lago de Izabal and Livings-

ton – Río Motagua (U = 9.28, p = 0.06). Mean

abundance was 0.18 ± 0.02 manatees/km2 in

Lago de Izabal and 0.10 ± 0.02 manatees/km2

in Livingston – Río Motagua (Fig. 5). However,

manatee abundance was significantly different

between Lago de Izabal and El Golfete (U =

12.20, p = 0.006) and between Lago de Izabal

and Río Sarstún (U = 15.20, p < 0.001). Further,

manatee abundance was not statistically differ-

ent among El Golfete and the two more coastal

sections (Livingston – Río Sarstún, Livingston –

Río Motagua; p > 0.05). In these three sections,

mean abundance varied between 0.06 and 0.10

manatees/km2 (Fig. 5).

In the case of the protected areas, Bocas del

Polochic (Lago de Izabal) had the highest man-

atee abundance (1.52 ± 0.03 manatees/km2) of

all protected areas (p < 0.05; Fig. 5). Manatee

abundance was not statistically different among

the other three protected areas (p > 0.10).

DISCUSSION

This study comprises the largest effort to

quantify and correlate the distribution of mana-

tees along the Atlantic coast of Guatemala,

yielding important insights into the local status

of the species. Our results show that manatees

were nonuniformly distributed along the sur-

veyed area with most sightings being recorded

in protected areas (60 %).

Spatiotemporal distribution and priority

areas: Our results agree with other studies that

found that manatees tend to be located in areas

near freshwater sources (Alvarez-Alemán et al.,

2017; Castelblanco-Martínez et al., 2018; Fave-

ro et al., 2020; Lefebvre et al., 2001; Marsh et

al., 2001; Olivera-Gomez et al., 2022; Powell &

Rathbun, 1984; Rathbun et al., 1990), with shal-

low waters (Hartman, 1979; Olivera-Gomez &

Mellink, 2005), close to shore (Olivera-Gomez

& Mellink, 2005), where aquatic vegetation

(Arrivillaga & Baltz, 1999; Poll, 1983; Yañez-

Arancibia et al., 1999) known to be part of

the species diet (Allen et al., 2018; Alves et al.,

2013; Hurst & Beck, 1988) exists, and where

there is minimum motorboat traffic and little

to no coastal human development. Priority

areas were identified in the southern corner of

Lago de Izabal, from Punta Chapin to Bocas

del Polochic, and the innermost corner of

Punta de Manabique (Bahia de Amatique). The

southern corner of Lago de Izabal has been an

important area for manatees for nearly 30 years

(Machuca-Coronado & Quintana-Rizzo, 2011,

Machuca-Coronado & Quintana-Rizzo, 2014;

Quintana-Rizzo, 1992), although a shift in

manatee distribution occurred in 2014. Within

the southern corner, manatees clustered in

small groups (1-2 manatees) in the northern

section and in large groups (up to 8 manatees)

in the southern section (Punta Chapin). A high

percentage of sightings that included calves was

also reported there (50 %) and in coastal waters

12 Revista de Biología Tropical, ISSN: 2215-2075 Vol. 71(S4): e57273, diciembre 2023 (Publicado Nov. 01, 2023)

of the lake (82 %). This distribution may reflect

habitat requirements specific to this social unit

or demographic group (Gannon et al., 2007).

The southern corner of the lake is probably

the most protected section for manatees of Lago

de Izabal and the entire Atlantic coast, but the

area is not free of human activities and inter-

actions. Illegal gillnets of up to 4 km long are

commonly sighted there (H. A. Garcia personal

communication). An orphaned manatee was

entangled in one of those nets in 2014. The calf

was rescued from the net but died after a failed

rehabilitation attempt (Machuca-Coronado &

Quintana-Rizzo, 2014). Further, changes in

land use and development have altered anthro-

pogenic nutrient inputs resulting in an increase

of raw sewage, strip mining flow, and agricul-

tural fertilizers into the lake (Obrist-Farner

et al., 2019). This has negatively impacted the

water quality and overall health of the ecosys-

tem. In the southern corner, water quality was

classified as medium and good based on the

National Sanitation Foundation Water Quality

Index (a 100-point scale from excellent, good,

medium, bad, to very bad; Aguirre Cordón et

al., 2006). The lake has also started to undergo

cultural eutrophication, which contributes to

frequent harmful algal blooms, the proliferation

Fig. 5. Relative abundance of manatees for years 2005-2022 with survey effort of the entire study area, each section, and

protected areas in Guatemala. Note: * = only one section was completed; thus, mean was not calculated, ** = no aerial surveys

were conducted. RVSBP = Refugio de Vida Silvestre Bocas del Polochic, PNRD = Parque Nacional Río Dulce, RVSPM =

Refugio de Vida Silvestre Punta de Manabique, and AVMRS = Área de Usos Múltiples Río Sarstún.

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 71(S4): e57273, diciembre 2023 (Publicado Nov. 01, 2023)

of invasive species such as Hydrilla verticillata,

and a decline in fish abundance (Obrist-Farner

et al., 2019). Additionally, predictive models

indicate that the temperature of the coastal

surface waters will increase by 2 – 5 °C by

2100 and that this will be a biological stressor

that could alter or harm the aquatic ecosystem

(Marchese, 2015).

The 2014 shift in manatee distribution

could have been caused by multiple factors.

Since manatees are considered sentinel species

of the overall health of the ecosystem (Bonde et

al., 2004; Bossart, 2011), distributional changes

could be used as early warnings about current

or potential negative impacts on individual-lev-

el and population-level animal health; Bossart,

2011). Those warnings could help identify

environmental stressors that could ultimately

affect human health associated with the oceans

(Bossart, 2011). The fact that a similar pattern

was observed in 2022 suggests that the change

in manatee distribution is permanent, and

future studies will help to determine this. A

multispecies approach could be useful in this

case since other species like macroinvertebrates

are also biological indicators of an aquatic eco-

system in stress (Roldán-Pérez et al., 2016).

Protected areas do not appear to be equally

important for manatees as indicated by differ-

ences in the number, location, and temporal

presence of priority areas. For example, the

innermost section of Punta de Manabique is a

priority area but its extension and persistence

varied over time. No priority areas were iden-

tified in Área de Usos Múltiples Río Sarstún

while they were only detected in some years

in Parque Nacional Río Dulce. There is a high

presence of human activities in the former.

The demand for land leases in mangrove areas

has increased considerably in Parque Nacional

Río Dulce, which saw the construction of large

tourist complexes (Arrivillaga, 2003). Parque

Nacional Río Dulce is one of two coastal areas

in the entire country where the transforma-

tion of mangrove areas by coastal develop-

ment and tourist infrastructure is more evident

(Arrivillaga, 2003). Notably, we recorded the

highest number of motorboats (64 %) and

kayaks (68 %) there along the entire Atlantic

coast. Manatees that use this area must navigate

through a busy intersection of fast-moving ves-

sels, kayaks, and fishing gear. They appear to

stay within the coastal waters as suggested by

their high proportion of sightings (80 %) within

a kilometer from the coast. Females with calves

must pay attention in this busy environment for

the safety of the calf, and few appear to remain

there as suggested by the small percentage of

calf sightings (6 %) in this protected area.

Manatee abundance including calf pres-

ence: Our manatee abundance estimates are

within the lower confidence limit of abundance

estimates reported in 1992 (Quintana-Rizzo,

1993). Nevertheless, early abundance estimates

were calculated based on Schaeffer et al. (1986)

and thus, differences in analytical procedures

could account for the observed differences.

New population modeling techniques based

on aerial survey data could provide more reli-

able population estimates (e.g., Martin et al.,

2015). However, those models require different

collection protocols than the ones used in this

survey, and observers that are trained in those

protocols. A preliminary survey was conducted

in this way, and there are plans to apply one of

those models to the results.

Mean manatee abundance was comparable

to that reported in other parts of Mesoamerica

including Bahia de Chetumal, although the

study was conducted at a different time of the

year (Morales-Vela & Olivera-Gómez, 1994).

The overall percentage of calf sightings (12 %)

and number of calves sighted (8 %) were also

comparable to other parts of Mesoamerica

(Callejas-Jiménez, 2021; Edwards et al., 2014;

Morales-Vela et al., 2000) and the Caribbean

(Alvarez-Alemán et al., 2017).

Mean manatee abundance was not signifi-

cantly different from 2005 to 2014. This repre-

sents approximately 10 years of relative stability,

which is significant for a small population of

an endangered species. Yet at least 20 mana-

tees died around the same time (2003-2016;

Machuca-Coronado & Corona Figueroa, 2019)

representing 13 % of a minimum population

14 Revista de Biología Tropical, ISSN: 2215-2075 Vol. 71(S4): e57273, diciembre 2023 (Publicado Nov. 01, 2023)

of 150 manatees (Quintana-Rizzo & Reyn-

olds, 2010). This begs the question of how the

population could appear to remain stable at this

mortality rate, which is likely underestimated.

Possible explanations include that the popula-

tion is higher than 150 manatees or that the

survey methodology does not account for the

re-sighting of individual animals (i.e., one indi-

vidual could be sighted twice in the same sur-

vey). Alternatively, or in conjunction with this,

there could be an influx of manatees moving to

and from neighboring countries such as Belize,

which has the largest manatee population of

Antillean manatees in the Caribbean (Morales-

Vela et al., 2000; O’Shea & Salisbury, 1991), and

Honduras. This influx could counterbalance

the effects of mortality. However, this assumes

that mortality remains at a sustainable rate,

which is unclear. Better population estimates

and record keeping of mortality events are

needed to understand the dynamics of the Gua-

temalan manatee population.

Conservation and management: The

identification of priority areas for manatees

should be used to better focus management

efforts in the future. This level of information

is needed to design and evaluate the effective-

ness of protected areas for the conservation of

the species. Manatee protection needs to be

strengthened by ensuring that priority areas

and critical resources (e.g., freshwater sources,

feeding areas) are given special management

consideration. It is urgent that the impact of

human activities, such as those caused by the

cultural eutrophication of Lago de Izabal, are

minimized, and controlled. Similar actions are

needed to minimize the use of fishing nets in

protected areas. Motorboat speed restrictions

need to be implemented to increase safety

for manatees traveling through and between

protected areas, considering the movement

of animals between the inshore waters of the

lake and the marine environment. This 150

km (round-trip) movement is well within the

species capabilities since manatees can con-

duct 600-km+ round-trip migrations (Deutsch

& Barlas, 2016). Manatee movements among

different parts of the coastline highlight the

importance of connectivity between protected

areas. The most effective conservation and

management actions require a comprehensive

understanding of animal movement patterns

and habitat selection as depicted by this study.

Ethical statement: The authors declare

that they all agree with this publication and

made significant contributions; that there is no

conflict of interest of any kind; and that we fol-

lowed all pertinent ethical and legal procedures

and requirements. All financial sources are fully

and clearly stated in the acknowledgments sec-

tion. A signed document has been filed in the

journal archives.

Author Contribution: E.Q.R conceived

the original idea for this manuscript. E.Q.R,

O.H.M.C, and H.A.G. expanded and agreed on

the details of the publication. All authors col-

lected data and helped secure funding for aerial

surveys and related field work. E.Q.R. (lead)

and O.H.M.C. processed and analyzed the data.

E.Q.R. lead the manuscript writing with contri-

butions to drafting, critical review, and editorial

input from O.H.M.C. and H.A.G.

ACKNOWLEDGMENTS

The study was conducted under the

research permit 042/2010 approved by the

Guatemalan Government National Council for

Protected Areas (CONAP). We would like to

thank the many agencies that provided different

types of funding and/or support (chronological

order from oldest to newest): Shell Exploration

Guatemala; Y. Fustukjian Memorial Scholar-

ship, University of South Florida to EQR; Ligh-

Hawk; CONAP; European Union and Comitato

Internationale Per Lo Sviluppo dei Popoli; Fun-

dación para el Ecodesarrollo y la Conservación;

Aviones Comerciales; Fundacion Defensores

de la Naturaleza; Fondo Nacional para la Con-

servación de la Naturaleza; and Clearwater

Marine Aquarium. Gerrit Hartman and Jose

Miguel Giron provided geographical informa-

tion system assistance. Sarah Leiter provided

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 71(S4): e57273, diciembre 2023 (Publicado Nov. 01, 2023)

helpful comments that improved the quality

of the manuscript. Jorge Cardona and Nicole

Auil helped to collect data during the 1992

and 2005 (May) aerial surveys, respectively.

Claudia Romero, Diana Ramirez, and Franklin

Herrera participated in an aerial survey. Many

people helped with field logistics including

Hans Droege, Michelle Gangaware, Charles

(Chuck) Schroll, George Simchuk, Alejandro

Berthet, Gerardo Poitevan, Enrique Escalante,

and Diana Ramirez. This work is dedicated to

the Antillean manatee.

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