Population status of the American crocodile, Crocodylus acutus (Reptilia: Crocodylidae) and the spectacled caiman, Caiman crocodilus (Reptilia: Alligatoridae) in the Costa Rican North Caribbean

Along the Costa Rican Caribbean shoreline, it is possible to find two species of crocodilians, the American crocodile (Crocodylus acutus) and the spectacled caiman (Caiman crocodilus). This region can be divided geographically into three subregions: North, Central, and South Caribbean. We conducted this research in the North Caribbean, between October 6, 2018 and August 31, 2019. Specifically, we worked in the area lying between the Jalova Station of the Tortugero National Park (TNP) and Agua Dulce Lake situated in the northern tip of Machuca Island, at the mouth of the Colorado River inside the Barra del Colorado National Wildlife Refuge (BACORE), which includes other connecting wetlands as well (Sierpe River, Samay Lake). Overall, this study area had an approximate extension of 408 km2 characterized by large, wide and deep canals, as well as wetlands, meanders, and adjacent lakes. The sampling was performed along 10 segments that varied in length from 7.5 km up to 29.49 km, located in the nearby zones of TNP and BACORE. In these zones, nightly counts were carried out using dazzling lamps. Individuals of C. acutus and C. crocodilus were classified into eight and six body size classes, respectively (both with 50 cm intervals). A relative abundance of 0.55 crocodiles and 1.37 caimans per linear kilometer was estimated during these spotlight surveys. The capture of 39 caimans let us to estimate a ratio of 30 males to 9 females (3.3:1 M:F). In stark contrast, only 1 male and 1 female crocodile were captured. A total of 85 C. acutus and 205 C. crocodilus were observed. Regarding the number of caiman sightings in the TNP, a statistically significant difference was found (Χ2=5.62, p≤0.05) for the distribution by sizes between the zones of BACORE and TNP, whereas no such difference was found for C. crocodilus sightings (Z=–1.22, p≥0.222). Some segments had a higher probability of caiman occurrence than did others in the surveys performed during the monitoring period (X2=8.36, p≤0.05), especially the Jalova-Sierpe River, Caño Negro-Tortuguero, and Tortuguero-Samay Lake (Tortuguero subarea) segments. Ninety percent of the sightings occurred in the BACORE zone, and this was significantly different (Χ2=7.34, p≤0.026) from the studied subareas. The number of crocodile sightings in the Colorado River segment was significantly different and higher than the other segments (X2=7.28, p≤0.05). There was a significant statistical difference among the sizes in all areas of study (X2=5.529, p≤0.026). The abundance of C. acutus and C. crocodilus in the north Caribbean part is lower than in the central Caribbean part of Costa Rica, where this species could use the resources available in more urbanized areas.

Factors influencing the occurrence of negative interactions between people and crocodilians in Mexico

Negative interactions between people and crocodilians have increased worldwide, but in Mexico there have been few systematic reports and no rigorous evaluation of this problem. We compiled information on negative interactions between people and the spectacled caiman Caiman crocodilus and American crocodile Crocodylus acutus from the Worldwide Crocodilian Attack Database for 1993–2018, and we investigated interactions in greater depth, through interviews with people in La Encrucijada Biosphere Reserve. We examined the relationship between the occurrence of negative interactions between people and C. acutus and the species' nesting season and abundance, and presence records. In Mexico, the frequency of negative interactions increases when anthropogenic activities occur close to nesting sites (< 30 km) and during the nesting season (February–September). In La Encrucijada, following negative interactions with crocodiles, the local inhabitants killed 30 crocodiles measuring > 2.5 m long in 2011–2012. The frequency of negative human–crocodilian interactions was not correlated with the abundance of crocodilians but was correlated with the number of presence records of crocodiles. Strategies to minimize these interactions include warnings at nesting sites, increased monitoring of anthropogenic activities during the nesting season, and management of nests to prevent them being destroyed by people.

American crocodiles (Crocodylus acutus) as restoration bioindicators in the Florida Everglades

The federally threatened American crocodile (Crocodylus acutus) is a flagship species and ecological indicator of hydrologic restoration in the Florida Everglades. We conducted a long-term capture-recapture study on the South Florida population of American crocodiles from 1978 to 2015 to evaluate the effects of restoration efforts to more historic hydrologic conditions. The study produced 10,040 crocodile capture events of 9,865 individuals and more than 90% of captures were of hatchlings. Body condition and growth rates of crocodiles were highly age-structured with younger crocodiles presenting with the poorest body condition and highest growth rates. Mean crocodile body condition in this study was 2.14±0.35 SD across the South Florida population. Crocodiles exposed to hypersaline conditions (> 40 psu) during the dry season maintained lower body condition scores and reduced growth rate by 13% after one year, by 24% after five years, and by 29% after ten years. Estimated hatchling survival for the South Florida population was 25% increasing with ontogeny and reaching near 90% survival at year six. Hatchling survival was 34% in NE Florida Bay relative to a 69% hatchling survival at Crocodile Lake National Wildlife Refuge and 53% in Flamingo area of Everglades National Park. Hypersaline conditions negatively affected survival, growth and body condition and was most pronounced in NE Florida Bay, where the hydrologic conditions have been most disturbed. The American crocodile, a long-lived animal, with relatively slow growth rate provides an excellent model system to measure the effects of altered hydropatterns in the Everglades landscape. These results illustrate the need for continued long-term monitoring to assess system-wide restoration outcomes and inform resource managers.

Sperm kinematic subpopulations of the American crocodile (Crocodylus acutus)

There has been very limited use of computer assisted semen analysis (CASA) to evaluate reptile sperm. The aim of this study was to examine sperm kinematic variables in American crocodile (Crocodylus acutus) semen samples and to assess whether sperm subpopulations could be characterized. Eight ejaculates (two ejaculates/male) from four sexually mature captive crocodiles were obtained. An ISAS®v1 CASA-Mot system, with an image acquisition rate of 50 Hz, and ISAS®D4C20 counting chambers were used for sperm analyses. The percentages of motile and progressively motile spermatozoa did not differ among animals (P > 0.05) but there was a significant animal effect with regards to kinematic variables (P < 0.05). Principal component (PC) analysis revealed that kinematic variables grouped into three components: PC1, related to velocity; PC2 to progressiveness and PC3 to oscillation. Subpopulation structure analysis identified four groups (P < 0.05), which represented, on average, 9.8%, 32.1%, 26.8%, and 31.3% of the total sperm population. Males differed in the proportion of sperm in each of the kinematic subpopulations. This new approach for the analysis of reptile sperm kinematic subpopulations, reflecting quantifiable parameters generated by CASA system technology, opens up possibilities for future assessments of crocodile sperm and will be useful in the future development of assisted reproduction for these species.

Valores hematológicos de cocodrilo de Tumbes Crocodylus acutus (Cuvier, 1807) mantenidos en cautiverio en Puerto Pizarro, Tumbes, Perú

El objetivo fue determinar los valores hematológicos del cocodrilo de Tumbes (Crocodylus acutus), especie categorizada en peligro crítico de extinción por el Estado Peruano. Se realizó la recolección de muestras de sangre por punción del seno venoso localizado en la region cervical postoccipital de individuos machos separados en dos grupos etarios (15 individuos juveniles y 15 individuos sub adultos) aparentemente sanos del Centro de Acuicultura Tuna Carranza, Puerto Pizarro en Tumbes, Perú. Luego de colectar la sangre en tubos con heparina de litio, se realizaron los frotices para hemograma y se llenaron microcapilares para la determinación de hematocrito. Las muestras fueron enviadas y procesadas en el Laboratorio de Patología Clínica de Facultad de Medicina Veterinaria y Zootecnia de la Universidad Peruana Cayetano Heredia. Se obtuvieron los siguientes valores promedios: 23,56% ± 3,23 de hematocrito, 8,48 g/dL ± 2,13 de hemoglobina, 0,988 106/µL ± 4,54 de glóbulos rojos y 5,90 ± 4,27 103/µL de glóbulos blancos: 2,68 103/µL ± 1,51 de heterófilos, 1,58 103/µL ± 1,4 de linfocitos, 2,35 103/µL ± 2,4 de eosinófilos, 1,45 103/µL ± 1,71 de basófilos y 0,50 103/µL ± 0,85 de monocitos. No se encontraron diferencias estadísticas significativas entre grupos etarios.

Analysis of the population dynamics of the endangered American crocodile, Crocodylus acutus in Paramillo National Natural Park

Few studies have been conducted on the population dynamics of crocodiles, especially in the Neotropics. This is the first study to provide data on the population dynamics of the threatened American crocodile (Crocodylus acutus (Cuvier, 1807)) in Paramillo National Natural Park. Twenty-four survey routes of 22km each were studied, and a total of 733 sightings was recorded. During the study period (from October 2014 to March 2016), the population remained stable and experienced slight growth (λ=1.049±0.428). Offspring production by the adults II stage was the most sensitive contribution (17.05), whereas the permanence of this adult stage was the demographic process that contributed the most to population growth (0.653). However, an 18% decrease in adults II would jeopardise long-term population viability and lead to a high probability of quasi-extinction, with under 300 individuals over the next 30 years. Thus, despite the apparent stability of this population, we suggest that it be considered a key target for future conservation efforts. Additionally, we recommend that this species continue to be listed as endangered in Colombia and not be modified in the CITES Appendix I.

Conocimiento local sobre Crocodylus acutus (Reptilia: Crocodylidae) en la zona costera de Colima, México

Se caracterizó el conocimiento local sobre los cocodrilos por los pobladores de la zona costera de Colima, México mediante entrevistas guiadas semi-estructuradas. Cada entrevista estuvo dividida en cinco secciones: conocimiento biológico de la especie, interacción humano-cocodrilo, ataques por cocodrilos, usos y manejo y percepción general. La información se analizó mediante los porcentajes de respuesta en cada sección. Se aplicaron 30 entrevistas, 25 a hombres y cinco a mujeres. El 40 % de los entrevistados se dedican a la pesca, el 34 % son prestadores de servicios turísticos, el 10 % es comerciante, 7 % empleado de taller mecánico, 3 % acuacultor, 3 % ganadero y 3 % maestra de primaria. Aunque el total de los entrevistados conoce a los cocodrilos, menos del 50 % tiene conocimiento biológico de la especie. Sin embargo, existe interés por los entrevistados en utilizar a la especie como atractivo turístico, lo cual ayudaría a promover la conservación de los cocodrilos en la zona. Aunque la opinión de los entrevistados sobre los cocodrilos es positiva, no se detectó un sentido de apropiación del recurso. Se proponen acciones de capacitación y sensibilización en grupos organizados que trabajan en o a los alrededores de la laguna, para establecer un adecuado manejo y conservación de los cocodrilos en el área.