*Dirección para correspondencia

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Abstract

The American crocodile, Crocodylus acutus, is widely distributed in the  American neotropics. It is endangered throughout most of its range and is listed as  vulnerable by the International Union for the Conservation of Natural Fauna and Flora (IUCN) and on Appendix I of the Convention for the International Trade in Endangered Species of Wild Flora and Fauna (CITES). Despite this listing, there are few published reports on population status throughout most of its range. We investigated the status of the C. acutus, at several locations along the Pacific coast of Costa Rica. We carried out spotlight and nesting surveys from 2007-2009 along the Costa Rican Pacific coast in four distinct areas, coastal areas of Las Baulas (N=40) and Santa Rosa (N=9) National Parks and the Osa Conservation Area (N=13), and upriver in Palo Verde National Park (N=11). We recorded crocodile locations and standard environmental data at each observation. Encounter rates, population structure, distribution within each area and data on successful nesting (presence of hatchlings, nests, etc) were determined. We attempted to capture all crocodiles to record standard morphometrics. A total of 586 crocodiles were observed along 185.8km of survey route. The majority of animals encountered (54.9%) were either hatchlings (<0.5m) or juveniles (0.5-1.25m). The average non-hatchling encounter rate per survey for the Pacific coast was 3.1 crocodiles/km, with individual encounter rates ranging from 1.2 crocodiles/km to 4.3 crocodiles/ km in Las Baulas National Park and the Osa Conservation Area respectively. Distribution of size classes within the individual locations did not differ with the exception of Santa Rosa and Las Baulas National Parks, where hatchlings were found in water with lower salinities. These were the first systematic surveys in several of the areas studied and additional work is needed to further characterize the American crocodile population in Costa Rica.

Key words: American crocodile, Crocodylus acutus, Costa Rica, encounter rates, population surveys, size class distribution.


Resumen

El cocodrilo americano, Crocodylus   acutus,  se encuentra ampliamente distribuido en el neotrópico Americano y hay pocos estudios publicados sobre el estado de sus poblaciones en la mayor parte de su rango de distribución. Investigamos  el  estado  del  Cocodylus  acutus  en  varias ubicaciones a lo  largo de la costa del Pacífico de Costa Rica. Se realizaron muestreos nocturnos y de anidación a lo largo de la Costa Pacífica de Costa Rica en cuatro áreas en particular desde 2007-2009,’áreas costeras en los Parque Nacionales de Las Baulas (N=40) y Santa Rosa (N=9), y en el Área de Conservación de la Osa (N=13) y en el curso alto del Parque Nacional de Palo Verde (N=11). Se registraron datos de la ubicación de los cocodrilos y datos ambientales estándar en cada observación. Se determinó la tasa de encuentros, estructura de la población, distribución dentro de  cada área y evidencia de anidación exitosa (presencia de neonatos,  nidos, etc.). Intentamos capturar todos los cocodrilos para registrar información morfométrica estándar. En total, se  observaron 586 cocodrilos a lo largo de 185.8km de ruta de muestreo. La mayoría de los animales encontrados (54.9%) fueron neonatos (<0.5m) o juveniles (0.5-1.25m). La tasa promedio de encuentros por muestreo de no-neonatos en la costa del Pacífico fue de 3.1 cocodrilos/km; con rangos de encuentro de individuos de entre 1.2 a 4.3 cocodrilos/km en el Parque Nacional de Las Baulas y el Área de Conservación Osa. La distribución por clases de tamaño no varió, a excepción de los Parques Nacionales de Santa Rosa y Las Baulas, donde se encontró a los neonatos en aguas con bajas salinidades. Estos fueron los primeros muestreos sistemáticos en varias de las áreas estudiadas y son  necesarios trabajos adicionales para  caracterizar las poblaciones de cocodrilo Americano en Costa Rica.

Palabras clave: cocodrilo Americano, Crocodylus acutus, Costa Rica, promedio de encuentros, distribución por clases de tamaño.

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Crocodilians  are  keystone  species  that play an important role in biodiversity and maintenance  of  ecosystems  (Mazzotti  et  al. 2009, Thorbjarnarson 2010). Effective management plans are critical to continued existence  of  crocodile  populations  and  should consider factors ]]> Crocodylus acutus (Cuvier 1807), is the most widely distributed of the New World crocodilians (Thorbjarnarson 2010). This species ranges from the extreme Southern tip of Florida, throughout the Caribbean and along the Pacific and Caribbean coasts of Central and Northern South America ]]> et al. 2006, Thorbjarnarson 2010). Crocodylus acutus is considered a coastal species, inhabiting lagoons and estuaries, areas with lower salinities and can also be found inland along major rivers and land-locked lakes (Kushlan & Mazzotti 1989a, Platt & Thorbjarnarson 2000, Thorbjarnarson et al. 2006, Mazzotti et al. 2009, Cherkiss et al. 2011). Crocodylus acutus can also be found in marine habitats (full-strength sea water) along offshore islands and atolls (Platt & Thorjarnarson 2000).

Populations of C. acutus were severely depleted throughout the range during the 20^th century due to ]]> et al. 2006). As a result, C. acutus was placed on the United States Endangered  Species  Act  (1975)  and  Appendix  I of  the  Convention  on  International Trade  in Endangered Species of Wild Fauna and Flora (CITES) in 1979 and is currently recognized as vulnerable by the International Union for the Conservation of Nature and Natural Resources  (IUCN)  Red  Book  (Baillie  et  ]]> .  2004). The Florida population was down listed from endangered  to  threatened  in  2007  (Mazzotti et al. 2007, Federal Register 72: 13027 2007). Availability  of  survey  data  for  C.  acutus  is poor throughout much of its range with the exception  of  the  Florida  population  (Ogden 1978, Dunson 1982, Gaby et al. 1985, Kushlan 1988, Kushlan & Mazzotti 1989a, Kushlan & Mazzotti 1989b, Mazzotti 1999, Mazzotti & Cherkiss 2003, Thorbjarnarson et al. 2006).

Establishing the status and ecology of C. acutus in Costa Rica is recognized as a high priority by the IUCN ]]> C. acutus throughout its range was further recognized as a moderate priority (Thorbjarnarson 2010).  The population of C. acutus in Costa Rica is considered one of the largest, with reports of healthy populations throughout the country (Ross 1998). However, suitable coastal habitat is more disjunct along the Pacific coast, which has resulted in a series of smaller, isolated populations of C. acutus ]]> et al. 2006). This makes the estuary system of the Pacific coast of Costa Rica an ideal place to study metapopulation structure of crocodiles. In Costa Rica, the Tempisque (2.28-11.1 crocodiles/km) and Tarcoles (10-35 crocodiles/ km) rivers support very large, dense populations  of  C.  acutus  (Motte  1994,  Sanchez  et al. 1997, Sanchez 2001). While the status of the Tempisque River population is considered stable ]]> et al. 1997, Abadia & Orjuela 1998, Sanchez 2001). Metals and organochlorine pesticides have been found in measurable quantities in crocodiles scutes from the Tempisque and Tarcoles rivers (Rainwater et al. 2007). This shows that crocodiles accumulate environmental contaminants that are found in the Central Pacific region (Fuller et al.  ]]> C. acutus for management and conservation.

The primary objective of this study was to conduct population assessments in several estuaries, rivers and ]]> Crocodylus acutus are hypothesized to live in isolated populations in small estuaries with minimal contact occurring  between  distant  habitats. The  data obtained during surveys were used with an ongoing study examining the genetic structure of crocodile populations in Pacific Costa Rica. Understanding linkages between these potential metapopulations is crucial in developing management plans for C. acutus within Costa Rica.
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Materials and Methods

Study Area: We conducted spotlight surveys of C. acutus in four areas on the Pacific coast of Costa Rica (2007-2009) including Las Baulas  National  Park  ]]>

Las  Baulas  National  Park  (LB),  located in the ACT, was formed in 1990 and includes three beaches (Playa Ventanas, Playa Grande and Playa Langosta), two estuaries (Tamarindo and San Francisco) and extends 20km offshore. The Tamarindo Estuary is one of the largest mangrove swamps in dry Central America (Spotila & Paladino 2004) covering 440ha and was listed on the Ramsar list of wetlands of international importance ]]> et al. 2004). This brackish coastal environment is home to five species of mangrove trees, numerous bird and mammal species and the American crocodile.

Palo Verde National Park (PV), located in the ACA-T, contains the valley of the Tempisque River, the ]]> 2 (Frankie et al. 2004). Twelve  different  habitats  exist  in  the  park including lagoons, freshwater and brackish swamps, mangrove forests, grasslands and dry forests (Boza & Cevo 2001). Palo Verde is an important area for resident and migratory birds and contained a large population of American crocodiles (Thorbjarnarson 2010). The Tempisque  River,  which  passes  through  the  park, is 144km long. Palo Verde ]]>

Santa  Rosa  National  Park  (SR),  located in the ACG, is on the Santa Elena Peninsula, the oldest (85 million years) and driest area of the country (Boza & Cevo 2001). SR was initially established to restore the dry forests in the area and to protect the neighboring rain forests, cloud forests and marine environments. Most of this park is on ]]>

The Osa Peninsula and areas of the ]]> C. acutus. Over 50%, approximately 20 254ha, of Costa Rica’s mangrove wetlands are found in this area. The Terraba-Sierpe National Wetland is made up of the delta of the Terraba and Sierpe Rivers and is the most extensive mangrove swamp in the country (Boza & Cevo 2001). ACOSA also has 6 986ha of evergreen, broad-leaf swamp forest that is dominated by raffia palm (Raphia taegidrea), cerillo (Symphonia globulifera) and hog plum ]]> Spondias sp.), and 822ha of freshwater, herbaceous swamps and lagoons. Open waterways and rivers also provide important habitat for C. acutus.

Crocodile Surveys: Crocodiles were surveyed in a mix of lagoons (SR, PTL, PL, PB), estuaries (LB, SR) and rivers (PV, RE, RC, RS) of different sizes and locations in Pacific ]]> Table 1). Surveys in SR were conducted in the Naranjo Estuary and the Laguna el Limbo roughly one kilometer to the South. One survey was conducted on Nancite Beach approximately one kilometer to the North. Survey lengths (Table 2) were calculated on ArcMap 9.3.1 using the start and end points of each survey as determined by GPS. Crocodiles were only counted during the survey and were not counted ]]> Table 2) with an average of 18 surveys per locality. We conducted a minimum of one and a maximum of three surveys per river or lagoon within ACOSA (Table 3) with an average of 2.2 surveys per location.

We recorded a ]]>
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Crocodile Capture: We attempted to capture all crocodiles observed using the breakaway snare method (Hutton et al. 1987, Hutton & Woodhouse 1989), snake tongs or by hand. Crocodiles were individually marked by removing caudal scutes in a numbered sequence (Mazzotti 1983, Richardson et al. 2002). This technique has been utilized in numerous studies and does not adversely ]]> et al 1985, Kushlan & Mazzotti 1989a, Jennings et al. 1991, Leslie 1997, Davis et al. 2001, Dever & Densmore 2001). We measured head length (HL; measured from the tip of the snout to the posterior edge of the supra-occipital bone), snout-vent length (SVL; measure from the tip of the snout to the posteRíor end of vent), total length (TL; measured from tip of snout to tip of tail), tail girth (TG; measured at the fourth whorl at ]]>

Data Analysis: Crocodiles were separated into four size classes: hatchlings (<0.5m), juveniles (0.5m-1.25m), sub-adults (1.25m-2.25m) and  adults  (>2.25m)  (Kushlan  &  Mazzotti 1989a). The size ]]> Tables 2 and 3). Hatchlings were not included in encounter rates due to their high mortality rate. We compared the salinity of crocodile sightings and captures within and between sites ]]>

Results

We conducted 73 crocodile surveys on the Pacific coast of Costa Rica covering 185.8km of  ]]> Tables  2  and  3).  50% of surveys were conducted in the Tamarindo Estuary of Las Baulas National Park; the remainder of the surveys were spread between Palo Verde National Park (Tempisque River), Santa Rosa National Park (Naranjo Estuary and Laguna el Limbo) and the Osa Conservation Area (Tables 2 and 3). We observed crocodiles during all surveys.

We observed a total of 763 crocodiles (586 non-hatchling; Table 2) over the Pacific coast with an average of 8 non-hatchling crocodiles per survey. The spectacled caiman, Caiman crocodilus,  was  encountered  in  ]]> C. acutus or eye shine. Over 89% (n=548) of crocodiles for which a size could be estimated or directly measured were <2.25m (reproductive size; Table 4).

The mean encounter rate over all areas was 3.1 crocodiles/km with the highest encounter rate occurring ]]> Table 2).

Las Baulas National Park (LB): We conducted 40 surveys (54.5% of total) in LB covering 70km of crocodile habitat (Table 2). ]]> Table 4). Crocodiles were not distributed in the estuary according to size class with  the  exception  of  hatchlings,  who  were only ]]>

Individuals captured ranged in size from hatchlings to adults (30.8cm-347cm). Hatchlings were 35.1±4.5cm in TL (n=31); juveniles were 76.7±28.2cm in TL ]]>

Palo Verde National Park (PV): We conducted 11 surveys (15.1% of total) on the Tempisque River covering ]]> Table 2). We observed 178 nonhatchling (4 crocodiles/km) with an average of 16.2 non-hatchlings per survey. The sex ratio of captured non-hatchling crocodiles was 2:3 (males: females).

Individuals  ranged  in  size  from  hatchling   to   adult   (30cm-314cm).   Hatchlings were   ]]> Table 4). Crocodiles were not distributed in the river according to size class. The average salinity at all observations was 1.6ppt and did not differ between size classes (ANOVA, F=0.312, p=0.82).

]]> Santa Rosa National Park (SR): We conducted 9 surveys (12.3% of the total) in SR covering 12.1km (Table 2). A large crocodile (approximately  3.5m)  was  known  to  live  in the Nancite Estuary (Shaya Honovar, personal  communication).  This  individual  was not observed. We observed 43 non-hatchling crocodiles (3.7crocodiles/km) with an average of 4.8 non-hatchling crocodile per survey. Sex ratio of captured non-hatchling crocodiles was 1:2 (male: ]]>

Individuals ranged in size from hatchling to sub-adult (31.7cm-184.4cm). Hatchlings were 32.6±0.6cm TL (n=13); juveniles were 79.6±25.7cm  TL  (n=8);  and  subadults  were 144.0±23.5cm TL (n=5) with no adults captured.  Two  adults  (approximately  2.5m  and 3m)  were  observed  but  not  captured.  Over 60% (n=41) of ]]> Table 4).  No  hatchlings were observed in the estuary. Juveniles were  only  encountered  in  the  upper  reaches of the estuary. All size classes were observed in the Laguna el Limbo, with hatchlings only being observed in the right branch. Hatchlings were found in lower salinities than other size classes (ANOVA, F=11, p<0.001). Average salinity of the estuary and lagoon were 5.2ppt and 0.9ppt respectively.
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Osa Conservation Area (ACOSA): We conducted 13 surveys (17% of the total) in ACOSA covering 58.9km (Tables 2 and 3). We observed a total of 277 non-hatchling crocodiles (4.3 crocodiles/km). Individual encounter rates ranged from 2.9 (RS) to 14.1 (PTL) crocodiles/km with non-hatchling observations ranging from 6 (PB) to 87 (RC) with an average of 21.3 non-hatchling crocodiles per ]]>

Individuals  ranged  in  size  from  juvenile to adult (50.2-273.7cm). Juveniles were 71.6±17.1cm   TL   (n=35);   subadults   were 150.5±21.3cm  TL  (n=3);  and  adults  were 273.7cm TL (n=1).  No  observed  individuals were ]]> Table 4).


Discussion

There are few ]]> C.  acutus  from  Costa  Rica,  with  those  that have been undertaken having been conducted in Central and Northern rivers (Sasa & Chaves 1992, Bolaños et al. 1996, Porras 2004, Barrantes 2008). This study was the first to assess the population status of C. acutus in Las Baulas and Santa Rosa National Parks.
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Crocodylus acutus encounter rates on the Pacific coast of Costa Rica were comparable to  the  majority  of  other  population  surveys on C. acutus populations (Table 5). These encounter rates support the hypothesis that C. acutus populations within Costa Rica are large (Ross ]]>

The American crocodile is known to prefer habitats  of  lower  salinity  (Kushlan  &  Mazzotti 1989a, Mazzotti et al. 2007). Crocodiles in this study were encountered in water with salinities ranging from 0ppt to over 50ppt. However, most (61%) encounters occurred in water with lower salinities (0-5ppt). Hatchlings were ]]>

Crocodiles were encountered at different rates during our surveys ( Tables 2 and 3) with the highest encounter rates within the ACOSA. These values may be skewed due to the large numbers of individuals encountered in the Pejeperrito and Pejeperro Lagoons and the timing of our surveys which coincided with nesting season (Table 3). These neighboring lagoons are small in size and had large numbers of crocodiles. This is possibly due to an abundance of food, protection from ocean currents and presence of suitable nesting habitat. The highest encounter rate within the ]]> et al. 2006, Barrantes 2008). Since only a small number of surveys were conducted at each site, it is probable that the crocodile density along the Pacific coast of Costa Rica has been underestimated in this study, which has been shown during studies of other crocodiles (C. porosus; Stuebing et al. 1994). We recommend long ]]>

The majority of all crocodiles encountered (54.9%)  in  each  population  were  hatchlings and juveniles. Very few large adult animals (8.1%) were observed in this study. The smallest size classes were present in the highest numbers with frequencies decreasing as TL ]]> et al. 1981, Ouboter & Nanhoe 1989). Therefore, they may be underestimated in this study. This low number of adults is consistent with the results of other studies (Webb et al. 1984, Kushlan & Mazzotti 1989a, Ouboter & Nanhoe 1989, Stuebing et al. 1994, Read et al. 2004, ]]> et al. 2011) and could be indicative of a recovering population (Ouboter & Nanhoe 1989). If hatchlings were excluded, roughly 40% of the entire coast and each of the Northern populations were composed of juveniles. Many of the sites in ACOSA were close to or greater than 50% juvenile (Table 3). Therefore, further work is needed to determine the size structure and growth rates of C. acutus in Costa Rica to better ]]>

Distribution of the American crocodile populations in Florida are known to change seasonally for nesting, feeding or to find new territories, and individuals are known to have large over lapping activity areas (Kushlan & Mazzotti 1989a). Shoreline development and other anthropogenic effects may limit ]]>

Conservation Implications: Protection of the American crocodile and coastal habitat in Costa Rica is crucial to its continued survival. The central location of these populations within the species range makes them important in their regional management. The ability of individual crocodiles to migrate long distances (Webb & Messel 1978, Kushlan & Mazzotti 1989a, Kay 2004, Read et al. 2007) illustrates the importance of protecting all potential crocodile habitat. Crocodylus acutus habitats in Costa ]]> C. acutus populations exist as metapopulations along the Pacific coast of Costa Rica. Therefore, management of the American crocodile in Costa Rica should be aimed at protecting and conserving all populations

Hunting and habitat alteration have confined C. acutus ]]> et al. 2006) including Costa  Rica.  The  largest  potential  threat  to C.  acutus  in  Costa  Rica  is  habitat  destruction and fragmentation (Thorbjarnarson et al. 2006, Thorbjarnarson 2010). Land use has increased exponentially in Costa Rica due to its growing urban ]]> et al. 1994, Daily et al. 2001). The Tarcoles River, which drains the urbanized central valley of Costa Rica, is one of the most polluted rivers  in  Central America  (Fuller  et  al.  ]]> et al. 2007, Rainwater et al. 2011). Our results indicate that the crocodile populations studied in Pacific Costa Rica are large, although they may be recovering from past reductions due to the large numbers of juveniles observed. It is important to maintain the environmental conditions necessary to ensure the continued survival of these populations.


Acknowledgments

We would like to thank everyone that helped us in the field especially Bernal Cortes, Luis Fernando ]]>

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*Correspondencia:
Laurie A. Mauger: Department of Biology, Drexel University, 3141 Chestnut St, Philadelphia, PA 19104, USA/ Department of Biology, Southern Utah University, 351 West University Boulevard, Cedar  City, UT 84720, USA. lauriecotroneo@suu.edu; lcotroneo@gmail.com
Elizabeth Velez: Kelonian Conservation Society, P.O. Box 473-3000, Heredia, Costa Rica. evbaulas@yahoo.com ]]> Michael S. Cherkiss: University of Florida Fort Lauderdale Research and Education Center, 3205 College Ave, Davie, FL 33314, USA. mcherkis@ufl.edu
Matthew L. Brien: Charles Darwin University, Casuarina 0810, Australia. crocmatt@hotmail.com
Michael Boston:  Casa Verde, 100 meters east of the Catholic Church, Puerto Jimenez, Puntarenas 8203, Costa Rica. mike@osaaventura.com
Frank J. Mazzotti: University of Florida Fort Lauderdale Research and Education Center, 3205 College Ave, Davie, FL 33314, USA. fjma@ufl.edu
James R. Spotila: Department of Biology, Drexel University, 3141 Chestnut St, Philadelphia, PA 19104, USA. spotiljr@drexel.edu

1. Department of Biology, Southern Utah University, 351 West University Boulevard, Cedar  City, UT 84720, USA; lauriecotroneo@suu.edu
2. Kelonian Conservation Society, P.O. Box 473-3000, Heredia, Costa Rica; evbaulas@yahoo.com
3. University of Florida Fort Lauderdale Research and Education Center, 3205 College Ave, Davie, FL 33314, USA; mcherkis@ufl.edu, fjma@ufl.edu
4. Charles Darwin University, Casuarina 0810, Australia; crocmatt@hotmail.com
5. Casa Verde, 100 meters east of the Catholic Church, Puerto Jimenez, Puntarenas 8203, Costa Rica; mike@osaaventura.com
6. Department of Biology, Drexel University, 3141 Chestnut St, Philadelphia, PA 19104, USA; lcotroneo@gmail.com, spotiljr@drexel.edu

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