Revista de Biología Tropical, ISSN: 2215-2075, Vol. 71(S4): e57274, diciembre 2023 (Publicado Nov. 01, 2023)

Characteristics and spatial identification of Antillean manatee (Trichechus

manatus manatus Sirenia: Trichechidae) strandings in Guatemala

Oscar Machuca-Coronado1*, 2 https://orcid.org/0000-0001-9413-914X

Ester Quintana-Rizzo3, https://orcid.org/0000-0002-8957-0506

Tannia Sandoval4, https://orcid.org/0000-0002-4951-100X

M. Fabiola Corona-Figueroa5, 6, https://orcid.org/0000-0003-2227-2974

Heidy Amely Garcia1, https://orcid.org/0000-0002-2392-6768

1. Fundación Defensores de la Naturaleza, Ciudad de Guatemala, Guatemala; machuca.oscarhugo@gmail.com

(Correspondence*); hgarcia@defensores.org.gt

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

3. Emmanuel College, Department of Biology, Boston Massachusetts, USA; tetequintana@comcast.net

4. Consejo Nacional de Áreas Protegidas, Izabal, Guatemala; tanniavs28@gmail.com

5. Centro de Datos para la Conservación, Centro de Estudios Conservacionistas, Universidad de San Carlos de

Guatemala, Guatemala; fabioco112@gmail.com

6. El Colegio de la Frontera Sur, Departamento de Sistemática y Ecología Acuática, Quintana Roo, México;

fabioco112@gmail.com

Received 26-VIII-2023. Corrected 25-I-2023. Accepted 11-IV-2023.

ABSTRACT

Introduction: Marine mammal strandings can be used to determine the impacts of anthropogenic activity on

the species survival, population health, and levels of environmental pollution in ecosystems. In addition, these

data can help design conservation and management strategies as well as identify priority areas for the species.

The West Indian manatee (Trichechus manatus) is listed as endangered throughout its range. In Guatemala, it

is distributed along the Caribbean coast. Anthropogenic activities appear to be having a direct pressure on the

species, affecting the status of the population.

Objective: The general purpose of this study was to analyze the 30 years of documented manatee stranding

reports available for Guatemala. Two specific objectives were defined to: 1) conduct a spatial analysis of manatee

strandings to identify the areas of high stranding concentration, and 2) determine whether there were sex differ-

ences in the number of strandings.

Methods: Characteristics and areas of concentration of manatee strandings were described along the Caribbean

coast between 1992 to 2022. Sites with the highest probable density of strandings were identified using a Kernel

density analysis. We compared the number of stranding events that occurred in each protected area that included

manatees in their management plans and each municipality of Izabal. We determined whether there were sex dif-

ferences in the number of stranded manatees. We use the potential biological removal to estimate the maximum

number of manatees that can be removed from the population due to anthropogenic causes without negatively

impacting species survival.

Results: Forty-three manatee stranding events were recorded throughout the species’ range in Guatemala (48

total individuals). The sites with the highest predicted density of strandings were Santo Tomás de Castilla bay,

followed by Lake Izabal (including the limits of the Refugio de Vida Silvestre Bocas del Polochic) and Parque

Nacional Río Dulce. The majority of the cases were registered in protected areas (60 %). Estimates of potential

https://doi.org/10.15517/rev.biol.trop..v71iS4.57274

SUPPLEMENT • MANATEES

2Revista de Biología Tropical, ISSN: 2215-2075 Vol. 71(S4): e57274, diciembre 2023 (Publicado Nov. 01, 2023)

INTRODUCTION

Understanding animal strandings helps

attain information about endangered aquatic

species that are hard to see on the surface.

Stranding data provides critical information on

the species’ life history, population health, envi-

ronmental contamination levels, and general

impacts of anthropogenic activities on mari-

ne ecosystems (National Oceanographic and

Atmospheric Administration [NOAA], 2019).

It is one of the primary sources of evidence

biological removal were equivalent to less than one manatee per year, which was exceeded by the annual average

of stranded manatees recorded (three manatees).

Conclusions: Anthropogenic activities cause mortality of manatees in this region, despite the implementation of

protected areas. Poaching was identified as the main cause of manatee mortality in Guatemala. The implementa-

tion of management strategies focused on minimizing threats to the species, based on the application of environ-

mental legislation and environmental awareness, is essential. The creation and implementation of a protocol for

the stranding of marine mammals on the Caribbean coast of Guatemala is necessary, in order to obtain standard-

ized records of these events and conduct rescue efforts and releases when possible.

Key words: marine mammals; mortality; conservation; poaching; protected areas.

RESUMEN

Características e identificación espacial de los varamientos del manatí antillano

(Trichechus manatus Sirenia: Trichechidae) en Guatemala

Introducción. Los registros sobre varamientos de mamíferos marinos pueden utilizarse para determinar los

impactos de la actividad antropogénica en la sobrevivencia de la especie, la salud de las poblaciones y los niveles

de contaminación ambiental en los ecosistemas. Además, estos datos pueden utilizarse para diseñar nuevas estra-

tegias de conservación y manejo en las áreas prioritarias para la especie. El manatí antillano (Trichechus manatus

manatus) está catalogado en peligro de extinción en todo su rango de distribución. En Guatemala, se distribuye

a lo largo de toda la costa caribeña. Las actividades antropogénicas están ejerciendo una presión directa sobre la

especie, afectando el estado de las poblaciones.

Objetivos. El objetivo general de este estudio fue analizar 30 años de información sobre los eventos de varamiento

de manatíes en Guatemala. Dos objetivos específicos fueron definidos: 1) realizar un análisis espacial sobre las

áreas con mayor concentración y densidad de varamientos de manatíes, y 2) determinar diferencias en el número

de manatíes varados con base en datos sobre el sexo.

Métodos. Se describieron las características y áreas de concentración de varamientos de manatíes registrados

de 1992 a 2022, en la costa caribeña. Se identificaron los sitios con mayor densidad probable de varamientos

utilizando el análisis sobre densidad de Kernel. Se comparó el número de eventos de varamientos ocurridos en

cada área protegida y municipio de Izabal donde se distribuye la especie. Se determinaron diferencias en la edad,

sexo, y causa de muerte en los varamientos. Además, se utilizó la eliminación biológica potencial para estimar

el número máximo de manatíes que pueden ser removidos de la población debido a causas antropogénicas, sin

afectar negativamente la supervivencia de la especie.

Resultados. Se registraron 43 eventos de varamiento de manatíes en todo el rango de distribución de la especie

en Guatemala (48 individuos en total). Los sitios con mayor densidad prevista de varamientos fueron en la Bahía

Santo Tomás de Castilla, seguido del Lago de Izabal (incluyendo los límites del Refugio de Vida Silvestre Bocas

del Polochic) y el Parque Nacional Río Dulce. La mayoría de los eventos se registraron en áreas protegidas (60

%). Las estimaciones sobre la eliminación biológica potencial fueron equivalentes a menos de un manatí por año,

sobrepasando la media anual de manatíes varados (tres manatíes).

Conclusiones. Las actividades antropogénicas causan mortalidad en los manatíes distribuidos en la región, a

pesar de la creación de áreas protegidas. La cacería ilegal fue identificada como la principal causa de muerte de los

manatíes en Guatemala. Es fundamental la implementación de estrategias de manejo enfocadas en minimizar las

amenazas hacia la especie, teniendo como base la aplicación de la legislación y conciencia ambiental. Es necesario

crear e implementar un protocolo de varamiento de mamíferos marinos en la costa caribeña de Guatemala, para

obtener registros estandarizados sobre este tipo de eventos y realizar rescates y liberaciones cuando sea posible.

Palabras clave: mamíferos marinos; mortalidad; conservación; cacería ilegal; áreas protegidas.

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 71(S4): e57274, diciembre 2023 (Publicado Nov. 01, 2023)

regarding the effect of human activities such

as vessel strikes and fishery interactions

on aquatic mammals (Van der Hoop et al.,

2013). The data is also extremely valuable for

informing management and policy decisions

(Geraci et al, 2005).

Spatial analysis of stranding data can be

helpful for recognizing patterns. For example,

identifying areas with a high concentration of

strandings can depict the interaction between

a species and human activities if strandings

occur in areas of high vessel traffic (Bedriñana-

Romano et al., 2021). Spatial patterns can also

help enhance surveillance and monitoring pro-

grams and predict carcass deposition during

mortality events (Norman, 2008). This is extre-

mely important in the case of endangered spe-

cies, where the death of one individual could

significantly impact the population’s health

(Onens et al., 2022).

The Antillean manatee (Trichechus mana-

tus manatus) is one of the subspecies of the

West Indian manatee, and it is classified as

endangered throughout its range (Diario de

Centro América [DCA], 2021; Quintana-Rizzo

& Reynolds, 2010; Self-Sullivan & Mignucci-

Giannoni, 2008). Manatee hunting is prohibited

by the Presidential Agreement of 1981 (DCA,

1981), which is still in effect. Further, Article 80

of the General Law on Fisheries and Aquacultu-

re prohibits the intentional capture or hunting

of threatened or endangered marine mammals

(Ministerio de Agricultura, Ganadería y Ali-

mentación, 2002).

Poaching has significantly reduced diffe-

rent manatee populations throughout their

distribution, including those in Central Ame-

rica (Machuca-Coronado & Corona-Figueroa,

2019; Ruiz Valladares et al., 2008). Interestingly,

in this region, Belize has the largest population

of Antillean manatees, estimated to be around

1 000 individuals (O’Shea & Salisbury, 1991;

Quintana-Rizzo & Reynolds, 2010), while the

neighboring country of Guatemala has only

approximately 150 manatees (Quintana-Rizzo

& Reynolds, 2010). Although Guatemala has a

small coastline, an average of 50 manatees were

sighted per survey of the entire Atlantic coast

during aerial surveys conducted between 1992

and 2014 (Quintana-Rizzo, 1993, Quintana-

Rizzo, 2005; Quintana-Rizzo & Machuca-Coro-

nado, 2008; Quintana-Rizzo et al., 2023).

There are anthropogenic activities that

have put direct pressure on manatees. In Gua-

temala, the recognized threats are poaching

for meat consumption, bycatch, entrapment

and hooking in fishing gear, vessel collisions,

and habitat deterioration and contamination

(Herrera et al., 2004; Machuca-Coronado &

Corona-Figueroa, 2019). Despite efforts to

address cases of local manatee strandings,

quantified information and an analysis of how

each threat affects the manatee population

are scarce or nonexistent. Thus, the general

purpose of this study was to analyze the 30

years of documented manatee stranding reports

available for Guatemala. The specific objectives

were to: 1) conduct a spatial analysis of manatee

strandings to identify the areas of high stran-

ding concentration and 2) determine whether

there were sex differences in the number of

strandings. The information was used to eva-

luate the role of protected areas in conserving

the species. We also used the potential biologi-

cal removal (PBR) approach to determine if the

level of human-caused mortality in the manatee

population could be sustained while allowing

the population to recover. The PBR approach

is suited to data-poor situations (Punt et al.,

2020). The study results are expected to stren-

gthen the management of protected areas and

bring attention to cases of stranded manatees.

The evidence can be used to promote the crea-

tion of an aquatic mammal stranding network

and to help regulate anthropogenic activities in

the Caribbean of Guatemala.

MATERIALS AND METHODS

Study area: The study area included the

state of Izabal, which encompasses the distri-

bution area of the Antillean manatee in Gua-

temala. The state is bordered on the north by

the Caribbean Sea, and on the east by the Gulf

of Honduras (Arrivillaga & Baltz, 1999; Ixquiac

et al., 2008). It includes five municipalities: El

4Revista de Biología Tropical, ISSN: 2215-2075 Vol. 71(S4): e57274, diciembre 2023 (Publicado Nov. 01, 2023)

Estor, Livingston, Morales, Los Amates, and

Puerto Barrios (Fig. 1). Izabal has remnants

of warm subtropical and very humid tropical

forest, wetland areas, mangrove forests, estua-

ries with patches of submerged vegetation,

secondary forests, areas of intensive agricul-

tural cultivation (e.g., oil palm, cattle pastu-

res, banana, pineapple, cardamom, etc.), urban

centers, beaches, and port areas (Suárez, 2011;

Yáñez-Arancibia et al., 1999).

There are four designated protected areas

within the study area, which include manatees

as a conservation element of their management

plans (Machuca-Coronado & Corona-Figue-

roa, 2019). Those protected areas are: (1)

Refugio de Vida Silvestre Bocas del Polochic

(RVSBP; total area 207.60 km2: 143.60 km2

terrestrial and 64.00 km2 aquatic zones; Fun-

dación Defensores de la Naturaleza [FDN],

2003), (2) Parque Nacional Río Dulce (PNRD;

total area 165.90 km2: 93.92 km2 terrestrial and

71.98 km2 aquatic zones; Consejo Nacional de

Áreas Protegidas [CONAP], 2019), (3) Área de

Uso Múltiple Río Sarstún (AUMRS; total area

475.82 km2: 437.93 km2 terrestrial and 37.89

km2 aquatic zones; Fundación para el Eco-

desarrollo y la Conservación [FUNDAECO],

2009), and (4) Refugio de Vida Silvestre Punta

de Manabique (RVSPM; total area 1,519 km2:

492.89 km2 terrestrial and 1,025.89 km2 marine

zones; Fundación Mario Dary Rivera [FUN-

DARY] et al., 2006) (Fig. 1).

Manatee stranding records: Information

on live and dead manatee stranding events

was compiled in two ways. First, we obtai-

ned records documented by the government

(CONAP) and non-government (FDN and

FUNDAECO) organizations in Izabal. Second,

we obtained data on manatee strandings in

national museum collections, and grey lite-

rature (e.g., unpublished reports, newspaper

articles, theses, and social media). Stranding

records were stored in a database that included

the following data points: year of the stranding,

stranding location, geographical coordinates

(when available), name of the organization

or person who made the report, manatee sex,

manatee age class, cause of death if known

(poaching, bycatch, boat impact), and whether

the stranding occurred within a protected area.

In some cases, it was impossible to record

all of these data points, due to the degree of

decomposition of the carcasses or due to lack

of record by the stranding response personnel.

Data compiled in technical reports generated

by CONAP and non-government organiza-

tions were considered “verified.” The data was

classified as “unverifiable” when obtained from

unofficial sources or non-technical reports

(e.g., communication with fishermen or tour

operators). 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).

Data analysis: Descriptive statistics (ave-

rage and standard deviation) were used for

stranding events that occurred over the years

inside protected areas and municipalities. Per-

centages of manatee strandings based on sex,

age class, and cause of death were calculated. To

determine whether there were sex differences

in the number of stranded manatees, we used

a chi-square test in R statistical software (R

Core Team, 2021). The spatial analysis inclu-

ded two components. First, to assess whether

there are concentrated areas where strandings

occur, a Kernel density plot was created, which

estimated the probability density function of a

stranding along the coast. The Kernel density

analysis was performed using a raster with cells

of 1 km2 size on the minimum convex polygon

(MCP) using ArcGIS Pro 3.0.0. The MCP is

the smallest possible convex polygon encom-

passing all the known locations of manatee

strandings (Hayne, 1949). Spatial Kernel den-

sity is a non-parametric method that measures

the local spatial clustering of a point pattern,

visualized by a continuous estimated surface

density layer distributed through and between

all points (Worton, 1989). Second, we com-

pared the concentration of stranded manatees

and the number of stranding events between

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 71(S4): e57274, diciembre 2023 (Publicado Nov. 01, 2023)

Fig. 1. (1) Study area and general overview of the region. Location of Trichechus manatus manatus stranding events between

1992 and 2022 along the Caribbean coast of Guatemala, including (2) protected areas and (3) municipalities. Protected

areas are A) Refugio de Vida Silvestre Bocas del Polochic (RVSBP), B) Parque Nacional Río Dulce (PNRD), C) Área de Uso

Múltiple Río Sarstún (AUMRS); and D) Refugio de Vida Silvestre Punta de Manabique (RVSPM).

6Revista de Biología Tropical, ISSN: 2215-2075 Vol. 71(S4): e57274, diciembre 2023 (Publicado Nov. 01, 2023)

protected areas and between municipalities, by

using a chi-square test in R statistical software

(R Core Team, 2021).

We used the potential biological remo-

val (PBR) to estimate the maximum num-

ber of animals that could be removed from

the Guatemalan manatee population (due to

anthropogenic mortality) without affecting the

optimal population size (Wade, 1998). The U.S.

Marine Mammal Protection Act developed the

PBR statistic for managing the impacts of fis-

hing on marine mammal populations. PBR is

calculated as:

Nmin × 1/2Rmax × Fr

Where Nmin is the estimate of the mini-

mum population size of the stock, 1/2Rmax is

one-half the maximum theoretical or estimated

rate of population growth, and Fr is the reco-

very factor which is selected depending on the

species conservation status (lower values for

poorer conservation status) and varies from

0.1 to 1 (Wade, 1998). To calculate the PBR for

the Guatemalan population, we used the most

recent population estimate of 150 manatees

(Quintana-Rizzo & Reynolds, 2010). Additio-

nally, a PBR for 70 % and 40 % of this popula-

tion were calculated since those percentages are

within the range of older population estimates

(Quintana-Rizzo, 1993). We used the minimum

(0.04) and maximum (0.08) growth rates pre-

viously described or suggested for West Indian

manatees (Marsh et al., 2011; National Marine

Fisheries Service [NMFS], 2016; Runge et al.,

2004) after Galves et al. (2022). A Fr equal to 0.1

was used because this is the value expected for

endangered species or stocks that are declining

(Taylor et al., 2000; Wade, 1998).

RESULTS

A total of 48 manatee individuals were

recorded in 43 stranding events from 1992 to

July 2022 (Table 1; = 1.07, SD = 0.33). Of the

48 manatees, 96 % (N = 46) were dead animals

and only two were live animals (4 %, all female

orphan calves). The age group was determined

for 46 manatees; 61 % were adult manatees (n

= 28), 26 % calves (N = 12), and 13 % juveniles

(N = 6). Sex was determined for 24 manatees

(50 %). No significant difference was found

in the percentage of male and female manatee

strandings (χ2 = 0.050, d.f. = 1, p = 0.818).

Cause of death was determined in 65 % of the

stranded manatees (N = 30), due to the degree

of decomposition of the carcasses or lack of

record in some cases. Poaching was the main

cause of mortality (70 %, N = 21), followed by

entanglement in fishing gear (hereafter referred

to as bycatch) (17 %, N = 5) and boat collisions

(13 %, N = 4; Fig. 2). Entanglement in fishing

nets was recorded in six separate events. Of

these events, three were recorded in the RVSBP

(two dead adult manatees and one live calf),

two in the PNRD (two dead manatee calves),

and one in Lake Izabal (one dead adult mana-

tee). The highest number of stranding events

were reported in 2015 and 2020, with a total of

6 stranded manatees each year (Fig. 3). Since

Guatemala has not implemented a protocol for

marine mammal stranding, there were no stan-

dardized records of stranding. Consequently,

there were no recorded reports of manatee

stranding events during the following years;

1993-2002, 2006, 2010, 2012, and 2017 (Fig. 3).

Stranding events were recorded throug-

hout the distribution range of manatees in

Guatemala (Fig. 1). The Kernel analysis showed

that the highest predicted density of strandings

occurred in the Santo Tomás de Castilla bay

and surrounding waters. The second highest

predicted stranding density was the southern

corner of Lake Izabal including the limits of the

protected area RVSBP, and a third, less dense

area, was in the southern section of the protec-

ted area PNRD (Fig. 4).

Of the 43 stranding events, 65 % (N = 28)

occurred inside protected areas (AUMRS: =

1.33, SD = 0.58; PNRD: = 1.00; SD = 0.00;

RVSBP: = 1.00; SD = 0.00; RVSPM: = 1.00;

SD = 0.00) involving 29 individual manatees.

In protected areas, no statistically significant

differences were found among the number

of stranding events (χ2 = 3.43, d.f. = 3, p =

0.330) and the number of manatees stranded

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 71(S4): e57274, diciembre 2023 (Publicado Nov. 01, 2023)

Table 1

Chronological records of Trichechus manatus manatus strandings in Guatemala from 1992 to 2022. Date is reported as year,

month, and day when available.

Date No. manatees Age class /sex Municipality Protected area* Cause of stranding

1992/03/01 1 NA/NA Livingston PNRD Boat impact

2003 1 Adult/NA Livingston PNRD Unverifiable

2004 1 Adult/NA El Estor Bycatch

2004 1 Juvenile/NA El Estor Poaching

2005/05/25 1 Adult/NA Puerto Barrios RVSPM Poaching

2005/06/18 1 Juvenile/male Livingston PNRD Unverifiable

2005/09/20 1 Adult/NA El Estor Poaching

2005/10/20 1 Juvenile/NA El Estor RVSBP Poaching

2007/05/10 1 Adult/female El Estor RVSBP Bycatch

2007/12/05 1 Calf /male El Estor RVSBP Unverifiable

2008 2 Adults/NA Livingston AUMRS Poaching

2008/07/12 1 Calf/female El Estor RVSBP Orphan

2008/08/11 1 Adult/NA Livingston Poaching

2009/06/08 1 Calf/NA El Estor RVSBP Poaching

2009/06/10 1 Adult/female El Estor RVSBP Poaching

2009/07/20 1 Adult/NA El Estor Poaching

2009/10/01 1 Adult/NA El Estor RVSBP Unverifiable

2011/07/01 1 Calf /male Livingston PNRD Boat impact

2013 1 NA/NA El Estor Poaching

2013/01/23 1 Adult/NA El Estor RVSBP Bycatch

2013/08/09 1 Juvenile/female Puerto Barrios RVSPM Unverifiable

2014/05/05 1 Calf/NA Los Amates Unverifiable

2015/04/06 1 Adult/female Livingston AUMRS Poaching

2015/07/01 5 1 adult/female

3 adults/NA

1 calf/NA

Puerto Barrios Poaching

2016/06/01 1 Adult/NA El Estor Unverifiable

2016/07/24 1 Adult/NA Puerto Barrios RVSPM Poaching

2018/07/19 1 Adult/female Livingston AUMRS Poaching

2018/07/31 1 Adult/female Puerto Barrios RVSPM Poaching

2019/10/13 1 Adult/male El Estor Unverifiable

2020 1 Calf/NA Puerto Barrios RVSPM Unverifiable

2020/02/15 1 Adult/male Livingston PNRD Boat impact

2020/02/27 1 Juvenile/male El Estor Unverifiable

2020/05/06 1 Adult/male Puerto Barrios Unverifiable

2020/05/13 1 Juvenile/male El Estor RVSBP Unverifiable

2020/06/14 1 Calf/NA Livingston PNRD Bycatch

2021/07/21 1 Calf/female Livingston Orphan

2021/11/13 1 Calf/male Puerto Barrios RVSPM Unverifiable

2021/12/09 1 Adult/NA Livingston PNRD Poaching

2022/02/04 1 Adult/male Los Amates Unverifiable

2022/04/29 1 Calf/male Livingston PNRD Unverifiable

2022/05/05 1 Calf/male Livingston PNRD Bycatch

2022/07/12 1 Adult/male Puerto Barrios Boat impact

2022/07/14 1 Adult/male Puerto Barrios RVSPM Unverifiable

NA = Not available. * PNRD (Parque Nacional Río Dulce); RVSPM (Refugio de Vida Silvestre Punta de Manabique); RVSBP

(Refugio de Vida Silvestre Bocas del Polochic); AUMRS (Área de Uso Múltiple Río Sarstún).

8Revista de Biología Tropical, ISSN: 2215-2075 Vol. 71(S4): e57274, diciembre 2023 (Publicado Nov. 01, 2023)

(χ2 = 0.231, d.f. = 3, p = 0.510). Regardless of

location, the stranding events of two protected

areas combined included the highest propor-

tion of the strandings in the study area (42 %).

Those protected areas were RVSBP and PNRD

(stranding events in each: 21 %, N = 9; stranded

manatees N = 9).

In municipalities, significant differences

were found in the number of stranding events

(X2 = 11.7910, d.f. = 3, p = 0.0081) and the

number of manatees stranded (χ2 = 11.50, d.f. =

3, p = 0.009) among them. The highest number

of stranding events were recorded in El Estor

(39 %, N = 17; = 1.00; SD = 0.00), followed by

Livingston (33 %, N = 14; = 1.07; SD = 0.27),

Puerto Barrios (23 %, N = 10; = 1.17, SD =

0.58), and Los Amates (5 %, N = 2; = 1.00,

SD = 0.00). The percentage of stranded mana-

tees in each municipality was 35 % (N = 17)

in El Estor, 31 % (N = 15) in Livingston, 29 %

Fig. 2. Trichechus manatus manatus strandings based on age class, sex, and cause of mortality for each municipality and

protected area on the Caribbean coast of Guatemala.

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 71(S4): e57274, diciembre 2023 (Publicado Nov. 01, 2023)

(N = 14) in Puerto Barrios and 4 % (N = 2) in

Los Amates (Fig. 2).

The mean annual verified mortality for

years with reported sightings was three mana-

tees, with three yearly events directly resulting

from anthropogenic causes. The estimated PBR

for a population of 150 manatees is 0.6 if the

growth rate is 0.08 and 0.3 if the growth rate

is 0.04. The PBR decreases for smaller popu-

lations of manatees (Table 2). Therefore, in all

cases, the PBR was equivalent to one manatee.

This PBR was exceeded in each reported year.

DISCUSSION

This study compiles data on manatee

strandings over 30 years throughout the species

distribution range in Guatemala. It represents

the country’s most extensive and complete

summary of manatee strandings. The results

show that a significant number of strandings

occurred in particular areas of the coast, inclu-

ding protected areas, and that a large percenta-

ge of the strandings involved the poaching of

adult males.

Fig. 3. Number of Trichechus manatus manatus strandings (live and dead) and number of individuals per sex identified from

1992 to July 2022. * = years with no stranding reports.

10 Revista de Biología Tropical, ISSN: 2215-2075 Vol. 71(S4): e57274, diciembre 2023 (Publicado Nov. 01, 2023)

Predicted density of stranded manatees.

The predicted density of stranded manatees

was highest in Santo Tomás de Castilla bay and

surrounding waters, as well as in the southern

corner of Lake Izabal. In both locations, mana-

tee carcasses with harpoons or wounds on the

body consistent with hunting processes were

recorded. Poaching was the leading cause of

death in these places (> 55 % of stranded

manatees). These areas are in close proximity

to municipal markets where there is evidence

of an illegal market for manatee meat (Ruiz

Valladares et al., 2008). In Santo Tomás de

Castilla bay, the Kernel density area of high

concentration of stranded manatees (0.019 to

0.030 manatees/km2) included the clustering of

nine manatees that were part of five stranding

events. Two events involved the poaching of

six manatees, including a calf. The other cau-

ses of mortality were unverifiable. In this bay,

groups of manatees are commonly observed

(T. Sandoval, pers. obs.), possibly due to the

presence of aquatic vegetation and seagrass

patches (Arrivillaga & Baltz, 1999; Ixquiac et

al., 2008; MacDonald, 2011; Yáñez-Arancibia

et al., 1999). However, Santo Tomás de Castilla

bay is a vulnerable area for manatees due to the

commercial vessel traffic of port Santo Tomás

de Castilla. This medium-sized commercial

port is located in the southwestern part of the

Fig. 4. Predicted Kernel density of stranded Trichechus manatus manatus along the Caribbean coast of Guatemala.

Table 2

Potential biological removal for the population of Trichechus

manatus manatus in Guatemala using both maximum

(0.08) and minimum (0.04) estimated growth rates based

on Marsh et al. (2011), NMFS (2016), and Runge et al.

(2004).

Population size

estimates*

Potential Biological Removal

Growth rate = 0.08 Growth rate = 0.04

60 0.24 0.12

105 0.40 0.21

150 0.60 0.42

* Based on (Quintana-Rizzo, 1993; Quintana-Rizzo &

Reynolds, 2010).

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 71(S4): e57274, diciembre 2023 (Publicado Nov. 01, 2023)

bay. The vessel traffic in this area includes oil/

chemical tankers, container ships, bulk carriers,

general cargo, and crude oil tankers. Vessels as

large as 244 m have entered the bay and port

(Marine Traffic, 2022).

The other area with a high predicted stran-

ding density of manatees was the southern

corner of Lake Izabal, including the area within

the limits of a protected area (RVSBP). Kernel

density analysis projected strandings in the cen-

ter of Lake Izabal. However, only one stranding

was recorded at approximately 6.5 km from

the coast, and it could be a case of a carcass

transported by currents to the deep waters of

the lake. All other stranding events were within

1.5 km from shore. In the southern corner of

Lake Izabal, 37% (N = 16) of the total stranding

events were recorded, representing the highest

concentration of strandings in the entire cou-

ntry. This is worrisome as RVSBP has been

identified as a priority area for the manatees in

Guatemala (Quintana-Rizzo, 1993, Quintana-

Rizzo, 2005; Quintana-Rizzo & Machuca-Coro-

nado, 2008; Quintana-Rizzo et al., 2023), and

poaching was the leading cause of death within

this protected area (60 %, N = 3), followed by

bycatch (40 %, N = 5). Since the sex of most

of the manatees poached is unknown (N = 11,

52 %), there is no clear evidence of a sex-bias

in manatee poaching. However, in another

study, some hunters recognized that female

manatee meat is softer and has a better flavor

(Del Valle, 2002).

The highest mortality cases involved adults

(eight out of 15 identified by age-class) and

males (five out of eight identified by sex). Simi-

lar sex- and age-biased poaching mortality has

been observed in other wildlife populations

(Archie & Chiyo, 2012; Ginsberg & Milner-

Gulland, 1994; Jones et al., 2018). From a

demographic standpoint, age- and sex-biased

poaching mortality is expected to bear fitness

consequences in a population (Ginsberg &

Milner-Gulland, 1994). The PBR suggests that

this mortality is indeed having an effect on the

Guatemalan manatee population. Furthermore,

removing adult individuals from a population

could lead to a more significant reproductive

investment by young adults, with potentially

detrimental consequences on their overall sur-

vival (Ginsberg & Milner-Gulland, 1994). In

Guatemala, poaching continues to be a signifi-

cant challenge in spite of the fact that manatees

are protected by the Fisheries and Aquaculture

law, Decreto 80-2002, which declares that it is

illegal to hunt any endangered marine mammal

and that the fine for breaking this law is high for

the socio-economic status of the average person

living in Izabal (approximately USD $1 055.00

– USD $10 555.00). However, effective law

enforcement is problematic and generates con-

flict between the authorities and residents as

there are no alternatives for the sustainable use

of natural resources.

Protected areas, management,

and conservation.

Although protected areas have manage-

ment plans and the legal basis to protect mana-

tees and natural resources, more than half of

the cases of strandings were reported within

those areas (N = 28; 65 %). All types of morta-

lity were identified, but poaching was again the

leading cause of mortality. Eleven cases of poa-

ching were registered in all four protected areas

combined. Further, bycatch was identified in

RVSBP and PNRD, but mortality due to motor-

boat collisions was only reported in PNRD.

This protected area is one of the sites with the

highest tourism records in the country (Ins-

tituto Guatemalteco de Turismo [INGUAT],

2015). Watercraft collisions are among the

leading causes of anthropogenic mortality for

manatees in other habitats in Florida (Lightsey

et al., 2006), Puerto Rico (Mignucci-Giannoni

et al., 2000), and Belize (Galves et al., 2022). In

Guatemala, studies have shown that manatee

sightings are (weakly) positively correlated with

the presence of motorboats (Quintana et al.,

2023) in PNRD, suggesting the probability of

vessel collisions exists.

The variety and number of stranding cases

inside different protected areas demonstrate

that management strategies and actions have

not been sufficient for species protection. There

12 Revista de Biología Tropical, ISSN: 2215-2075 Vol. 71(S4): e57274, diciembre 2023 (Publicado Nov. 01, 2023)

is no surveillance within the protected areas to

prevent poaching. Protected areas managers

have not proven effective at preventing poa-

ching or other threats to biological diversity. In

addition, it is necessary to regulate the speed of

boats within protected areas to avoid collisions

with manatees. Although there is no national

legislation that supports the implementation of

navigational regulations, in each municipality,

the authorities must disclose to motorboat users

the current navigation guidelines. For example,

the PNRD Management Plan stipulates naviga-

tion at speeds between 9 and 18 km/h (CONAP,

2019). This aspect is important, because in this

protected area, mortality related to boats was

recorded. Indeed, the shallow, narrow waters

and interconnected channels of PNRD requi-

re high regulation (Corona-Figueroa, 2012).

Evidence shows that speed restrictions reduce

manatee deaths (Calleson & Frohlich, 2007;

Laist & Shaw, 2006).

Municipalities, management,

and conservation.

Poaching was the leading cause of manatee

death in the municipalities of Puerto Barrios, El

Estor, and Livingston. In these municipalities, it

is known that manatee poaching has occurred

for at least 20 years (Del Valle, 2001; Machuca-

Coronado & Corona-Figueroa, 2019). Groups

of hunters have been identified moving along

the coast to areas with manatee presence (inclu-

ding inside protected areas). Hunters from

Livingston and Puerto Barrios have even been

reported to travel to Belizean territory, where

hunting is also illegal. In the 1990s, there were

reports of manatee poaching in Belize that

appeared to be the result of poaching from

Guatemala and possibly Honduras (E. Quin-

tana-Rizzo pers. obs.). In August-September

1995, at least 35 manatee carcasses were found

in the Port Honduras area, Belize, in what

appeared to be a butchering site. Manatee skulls

had deep cut marks, and evidence suggests

they were shot, harpooned, or chased until

exhausted (Bonde & Potter, 1995). A year later,

a second report of poaching was documented

south of Port Honduras, where another nine

manatees were found dead (Morales-Vela et al.,

2000). In Guatemala, manatee meat is illegally

sold in the main municipal markets at a lower

price than other types of meat (Quintana-Rizzo

& Reynolds, 2010; Ruiz Valladares et al., 2008).

In this study, reports of manatee entan-

glement in fishing gear occurred inside and

outside protected areas. The use of trawl nets

in large-scale commercial fishing (nets > 4

km in length) is common in the municipali-

ties of El Estor and Livingston, even though

this type of fishing is prohibited in inner or

continental waters (Ministerio de Agricultura,

Ganadería y Alimentación, 2002). Large fis-

hing nets interrupt the movement of manatees,

mainly at the mouth of rivers; they also reduce

the available habitat for the species (Machu-

ca-Coronado & Corona-Figueroa, 2019; Ruiz

Valladares et al., 2008).

Differences in the number of reported

stranding events in each municipality are

likely related to the presence of government

(CONAP) and non-governmental organiza-

tions co-managing protected areas in the diffe-

rent municipalities. Those organizations have

taken the lead in reporting and documenting

manatee strandings. In the case of El Estor,

since 2007, FDN established a protocol to

record manatee stranding data in collaboration

with community members, fishers, and boat

captains. This collaboration was fundamental

in implementing the procedures, mainly in the

notification of cases and location of manatee

carcasses (Quintana-Rizzo & Machuca-Coro-

nado, 2008), some of which are part of this

study. These actions represent the first efforts

toward the establishment and implementation

of a stranding protocol for marine mammals in

Izabal (Quintana-Rizzo & Machuca-Coronado,

2008); however, implementation has slowed

down in recent years. In Livingston and Puerto

Barrios, the presence of CONAP is funda-

mental to registering and confirming manatee

stranding cases. Since 2010, systematic reports

of each manatee stranding have been produ-

ced. In Los Amates, the number of stranding

records is lower than in other municipalities;

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 71(S4): e57274, diciembre 2023 (Publicado Nov. 01, 2023)

this could be because the government authori-

ties of this municipality have not implemented

a stranding protocol in their work plans.

Sex and age class.

Most stranding records include dead mana-

tees, and only two cases of live manatees were

recorded, both corresponding to female orphan

calves (Machuca-Coronado & Quintana-Rizzo,

2014; Quintana-Rizzo et al., 2008; T. Sandoval

personal communication July 21, 2021). Calf

strandings could be related to the poaching of

the corresponding mothers. Manatee hunters

are known to focus on adults (Ruiz Valladares

et al., 2008); however, they take the opportunity

to hunt calves when they are in the company

of their mother (Ruiz Valladares et al., 2008).

Poaching targeted to this demographic group

can directly affect the population’s stability.

Females have low reproductive rates since they

do not reach sexual maturity until 3-years of

age and produce an average of one calf every

two to four years, which means that the growth

of manatee populations is significantly slow

(Hartman, 1979; Powell, 2002; Quintana-Rizzo

& Reynolds, 2010).

Stranding records were biased towards

adult males; 63 % of the stranding events

corresponded to this demographic group. Male

manatees are vulnerable because they spend

more time moving around than females and

calves (Quintana-Rizzo & Reynolds, 2010).

This behavior pattern may increase their expo-

sure to different threats. In fact, 75 % (N = 3)

of the registered cases of boat collisions corres-

pond to male manatees. However, the relation-

ship between strandings and demographics is

likely underestimated because sex and cause

of death determination were only possible in

50 % (N = 24) and 36 % (N = 16) of events,

respectively.

Potential biological removal.

PBR has been used to calculate the spe-

cies-specific level below which human-induced

mortality must be reduced for species survi-

val (Marsh et al., 2004). If the anthropogenic

mortalities are less than the PBR, then a deple-

ted population should recover given sufficient

time (Williams et al., 2016). Our PBR estimates

were equivalent to less than one manatee per

year, which is lower than the annual avera-

ge number of stranded manatees recorded in

Guatemala over the past thirty years. As such,

anthropogenic activities affect the local mana-

tee population, although long-term studies on

population dynamics are needed to understand

the gravity of their impact.

Conservation and future

recommendations.

The success of conservation relies on key

factors, including the collection of scientific

data to understand species threats, the develo-

pment of stakeholder partnerships to address

potential threats, consistent enforcement of

regulations to protect the species, and equally

on public adherence to protection programs.

The lack of any one of these factors makes

conservation efforts more challenging and less

efficient. In Guatemala, there is a great need

to increase awareness of the threats facing

manatees and their habitat at all levels, and the

enforcement of laws is critical. Poaching was

identified as one of the main threats affecting

the local manatee population more than 30

years ago (Lefebvre et al., 1989; Quintana-

Rizzo, 1993), and this study shows that the

threat continues to be significant. If manatees

are to survive in Guatemala, developing a stra-

tegic plan to significantly reduce human-related

mortalities is crucial to their conservation and

proper management.

There is also a great need to develop and

implement a protocol for manatee strandings.

This includes performing necropsies and taking

samples of biological material. The existing

marine mammal stranding protocol for the

Guatemalan Pacific coast (WWF, 2018) could

serve as a starting point, but a protocol specifi-

cally focused on manatees must be included. In

addition, a marine mammal stranding network

needs to be established in the Caribbean area,

together with training sessions for technicians,

14 Revista de Biología Tropical, ISSN: 2215-2075 Vol. 71(S4): e57274, diciembre 2023 (Publicado Nov. 01, 2023)

park rangers, and key local people. Finally, a

reduction in anthropogenic mortality of mana-

tees can be accomplished through education

and proactive management and training of the

park rangers and other stakeholders, together

with a conservation plan that includes law

enforcement, mortality assessment, scien-

tific research, and stakeholder involvement

and cooperation.

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

followed all pertinent ethical and legal proce-

dures and requirements. All financial sources

are fully and clearly stated in the acknowled-

gments section. A signed document has been

filed in the journal archives.

Author contribution: O.H.M.C. and

E.Q.R. created the original idea for this manus-

cript, and H.A.G. expanded the details of the

publication. O.H.M.C. and E.Q.R. analyzed

the data. O.H.M.C., E.Q.R. and M.F.C.F pre-

pared the initial draft of the document. All

authors collected data, edited and revised the

manuscript, and approved the final version of

the document.

ACKNOWLEDGMENTS

We thank all the entities, technical staff,

park rangers, fishers, and community mem-

bers who oversaw the search for the stran-

ded manatees and recorded information in

each event. We appreciate Franklin Herrera’s

contribution to promoting the initiation of

records and attention to manatee strandings

in Guatemala. A special thanks to CONAP,

FDN, FUNDAECO, Autoridad para el Manejo

Sustentable de la Cuenca Hidrográfica del Lago

de Izabal y Río Dulce, and everyone who shared

the information that was used to prepare this

document. We also thank CONAP, FDN, FUN-

DAECO, Naturaceites S.A., and Fundación Pro-

tectora de Animales en Vías de Extinción, for

their participation in the rescue process of two

stranded manatee calves in 2008 and 2021. We

thank all the people who make efforts focused

on the conservation and management of the

species in Guatemala. Finally, we thank the

anonymous reviewers for carefully reading our

manuscript and for their insightful comments

and suggestions.

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