Melanosuchus Research Articles

Mercury biomagnification in the food web of Agami Pond, Kaw-Roura Nature Reserve, French Guiana

Freshwater ecosystems are among the most important ecosystems worldwide, however, over the last centuries, anthropogenic pressures have had catastrophic effects on them. Mercury (Hg) is one of the main environmental contaminants which globally affect ecosystems and particularly freshwater wildlife. While Hg originates from natural sources, anthropogenic activities such as agriculture, biomass combustion, and gold mining increase its concentrations.Gold mining activities are the main drivers of Hg emission in tropical ecosystems and are responsible for up to 38% of global emissions. Once in its methylated form (MeHg), mercury biomagnifies through the trophic chain and accumulates in top predators. Due to the toxicity of MeHg, long-lived predators are even more subjected to chronic effects as they accumulate Hg over time.In the present study we quantified Hg contamination in two top predators, the Black caiman Melanosuchus niger and the Agami heron Agamia agami, and in their prey in the Kaw-Roura Nature Reserve in French Guiana and evaluated the biomagnification rate in the trophic chain.Our results show that despite a TMF in the range of others in the region (4.38 in our study), top predators of the ecosystem present elevated concentrations of Hg. We have found elevated Hg concentrations in the blood of adult Black caiman (2.10 ± 0.652 μg g−1 dw) and chicks of Agami heron (1.089 ± 0.406 μg g−1 dw). These findings highlight the need to better evaluate the potential impact of Hg in freshwater top predators, especially regarding reprotoxic effects.

Blood Biochemical Reference Intervals of Black Caimans (Melanosuchus niger) and Spectacled Caimans (Caiman crocodilus) in the Brazilian Amazon Region.

Reference intervals for physiologic parameters, crucial for assessing the health status of animals, have been documented for various crocodilian species across the globe. Nonetheless, the establishment of plasma biochemical reference intervals specific to Amazonian crocodilians remains incomplete. In an effort to address this gap, we procured blood samples from 65 black caimans (Melanosuchus niger) and 58 spectacled caimans (Caiman crocodilus) during the period of September-December 2019 within the Anavilhanas National Park in the Brazilian Amazon region We aimed to define reference intervals for 11 key plasma variables measured, namely glucose, triglycerides, total cholesterol, calcium, magnesium, sodium, potassium, albumin, total protein, uric acid, and urea. In general, the determined blood reference intervals aligned closely with those established for other crocodilian species. Some specific measurements, such as total cholesterol, sodium, and magnesium, exhibited distinct variations based on the species. Furthermore, female black caimans showcased elevated cholesterol levels compared with their male counterparts. Within the spectacled caimans, disparities related to sex were evident solely in the case of electrolytes sodium and potassium, with males demonstrating higher levels compared with females. These reference intervals not only provide data for assessing potential fluctuations in the health of wild or captive Amazonian crocodilians but also hold value for veterinary management.

Conservation implications of tourism and stress for Amazonian caimans

AbstractEcotourism is a strategy for biodiversity conservation, but it involves possible negative effects on animal health and welfare. Large predators such as crocodilians are one of the great public attractions sought after for tourist interactions. Interactions with wild animals and humans can hyperstimulate the hypothalamic‐pituitary‐adrenal axis in the short term, in the case of crocodilians showing an increased corticosterone level, which is indicative of physiological stress. Between September and December 2019, we simulated interactions between tourists and Amazonian crocodilians at Anavilhanas National Park in Central Amazonia, Brazil to evaluate the effects of handling and use of photographic flashes on black caiman (Melanosuchus niger) and spectacled caiman (Caiman crocodilus) on circulating corticosterone and lactate. Corticosterone levels increased 1.7‐fold during handling and 2.7‐fold when exposed to photographic flashes in black caiman but not in spectacled caiman. Increased corticosterone concentrations in black caiman were characterized by an increase caused by handling and were more intense after flashes than in controls, but the combination of handling and flash had no effect. During handling in simulated tourist interactions, anaerobic respiration increased lactate in black caiman but not in spectacled caiman. The effect of simulated tourist interactions with Amazonian crocodilians was dependent on the handling and especially on flash use in black caiman. The results can assist management, conservation programs, and public policies, especially in programs based on tourism interaction with Amazonian crocodilians.

Incidence and characteristics of crocodilian incidents on humans in Brazil in the period 2000–2022

Brazil has the largest diversity of crocodilians in the world, with six species present in the country. Considered as opportunistic generalist predators, these animals occupy the top of the food chain in river ecosystems. Anthropic actions result in an impact both on habitats and on the behaviour of the crocodilians, in addition to facilitating the encounter between humans and crocodilian species. In this study, we evaluated the characteristics of alligator incidents on humans in Brazil during the years 2000–2022. We used online platforms for scientific articles and news, collecting information about the victims, the species involved, and the locality of occurrence. We found 86 records of incidents, of which 18 resulted in the victim's death. The Amazon biome encompass the highest number of incidents, and the black caiman Melanosuchus niger was the species involved most. Most incidents (n = 35) occurred with people who were fishing or on boats. Considering the size of the country's population, alligator incidents on humans in Brazil can be considered rare, but they should not be overlooked. The advancement of activities that degrade the environment, causing imbalances, can cause an increase in the likelihood of encounters and, consequently, incidents, which usually generates critical medical problems and negative consequences for the populations of these animals. Keywords: Alligator, attack, bite, Caiman, Melanosuchus

Insights on the use of dolphins (boto, Inia geoffrensis and tucuxi, Sotalia fluviatilis) for bait in the piracatinga (Calophysus macropterus) fishery in the western Brazilian Amazon

In the Amazon Basin, the use of the pink dolphin or boto (Inia geoffrensis) for bait in the piracatinga (Calophysus macropterus) fishery was first detected in the year 2000. Since then, this artisanal fishery has become more prevalent as it requires only a few hours of work per night and provides immediate cash earnings. It is thus an attractive addition to (or replacement for) traditional fishing. Previous reports have noted the use of botos as bait, but stated that the most common bait used are caimans (Melanosuchus niger, Caiman crocodilus). Estimates of the number of dolphins killed based on fish landings have been proposed and an apparent decrease in sighting/survival of an artificially-marked boto population was observed. Although stocks/population estimates, trends and actual numbers of hunted dolphins are unknown, the conservation impacts of this activity are of concern. Between October 2010 and November 2011, research was conducted within an area with serious conflicts between dolphins and fishermen as well as intense fishing for piracatinga, i.e. in the lower Japurá River, on the border with the Mamirauá and Amanã Sustainable Development Reserves, where both boto and tucuxi (Sotalia fluviatilis) are used for bait. One-hundred and fifty-seven monitoring surveys were carried out in eight key communities, confirming 114 piracatinga fishing events through direct monitoring and incognito surveys of fishing gear (gaiolas). Empirical evidence of the activity in gaiolas comprised pieces of bait, carcass remains, piracatinga provoked vomits and dolphin fished carcasses. Of those, 31.2% (n = 35) involved cetacean bait (91.4% I. geoffrensis, 8.58% S. fluviatilis), 68.7% (n = 77) caiman bait (96% M. niger, 4% C. crocodilus), and two fishing events used both types. These percentages may be higher/lower in other areas within and outside the Reserves. Given the increasing trend of the piracatinga fishery, the authors believe that precautionary measures for the conservation of Amazonian dolphins are urgently needed. Development of practical short-term solutions (e.g. offal-baited fish traps) and multispecies management together with law enforcement, incentives and educational programmes could allow the future transition of riverine communities from the piracatinga fishery to sustainable, higher income activities.

Drivers of human–black caiman (Melanosuchus niger) conflict in Indigenous communities in the North Rupununi wetlands, southwestern Guyana

AbstractRecovering populations of large carnivores impact the people that live alongside them, sometimes leading to conflict and lethal retaliation. One such carnivore, the black caiman (Melanosuchus niger) has been implicated in the destruction of fishing equipment, depredation of livestock and pets, and attacks on humans. In order to understand how various stakeholder groups are affected by the negative impacts of living alongside caiman, and their resulting attitudes and behaviors towards caiman, we conducted semistructured interviews in seven Indigenous communities in southwestern Guyana from November 2017 to October 2019. We used logistic and ordinal regression to identify demographic indicators of fishing behavior and factors that are associated with negative attitudes and antagonistic behavior. Loss of pets in addition to an effect of gender, rather than competition overfishing resources (as hypothesized) may drive conflict between Indigenous communities and black caiman. We propose site differences, such as ecotourism may affect attitudes about and behavior towards caiman. The presence of impacts on communities and retaliatory behavior indicates that human–wildlife and wildlife–human impacts involving black caiman may be a concern for the recovery of the species' populations, and the communities that coexist with them.

Structure and Chemical Composition of ca. 10-Million-Year-Old (Late Miocene of Western Amazon) and Present-Day Teeth of Related Species.

Molecular information has been gathered from fossilized dental enamel, the best-preserved tissue of vertebrates. However, the association of morphological features with the possible mineral and organic information of this tissue is still poorly understood in the context of the emerging area of paleoproteomics. This study aims to compare the morphological features and chemical composition of dental enamel of extinct and extant terrestrial vertebrates of Crocodylia: Purussaurus sp. (extinct) and Melanosuchus niger (extant), and Rodentia: Neoepiblema sp. (extinct) and Hydrochoerus hydrochaeris (extant). To obtain structural and chemical data, superficial and internal enamel were analyzed by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (SEM-EDS). Organic, mineral, and water content were obtained using polarizing microscopy and microradiography on ground sections of four teeth, resulting in a higher organic volume than previously expected (up to 49%). It is observed that both modern and fossil tooth enamel exhibit the same major constituents: 36.7% Ca, 17.2% P, and 41% O, characteristic of hydroxyapatite. Additionally, 27 other elements were measured from superficial enamel by inductively coupled mass spectrometry (ICP-MS). Zinc was the most abundant microelement detected, followed by Pb, Fe, Mg, and Al. Morphological features observed include enamel rods in the rodent teeth, while incremental lines and semiprismatic enamel were observed in the alligator species. The fossil enamel was in an excellent state for microscopic analyses. Results show that all major dental enamel’s physical, chemical, and morphological features are present both in extant and extinct fossil tooth enamel (>8.5 Ma) in both taxa.

Relationships between stable isotopes and trace element concentrations in the crocodilian community of French Guiana.

Trace elements in the blood of crocodilians and the factors that influence their concentrations are overall poorly documented. However, determination of influencing factors is crucial to assess the relevance of caimans as bioindicators of environmental contamination, and potential toxicological impact of trace elements on these reptiles. In the present study, we determined the concentrations of 14 trace elements (Ag, As, Cd, Cr, Co, Cu, Fe, Hg, Pb, Mn, Ni, Se, V, and Zn) in the blood of four French Guiana caiman species (the Spectacled Caiman Caiman crocodilus [n = 34], the Black Caiman Melanosuchus niger [n = 25], the Dwarf Caiman Paleosuchus palpebrosus [n = 5] and the Smooth-fronted Caiman Paleosuchus trigonatus [n = 20]) from 8 different sites, and further investigated the influence of individual body size and stable isotopes as proxies of foraging habitat and trophic position on trace element concentrations. Trophic position was identified to be an important factor influencing trace element concentrations in the four caiman species and explained interspecific variations. These findings highlight the need to consider trophic ecology when crocodilians are used as bioindicators of trace element contamination in environmental studies.

Population Ecology and Human Disturbance Effects on Two Caiman Species in the Southern Brazilian Amazon

Although caiman populations are being conserved in some protected areas, they face threats related to human pressure, which may ultimately influence their distribution, abundance, and behavior. In this study, we investigated the population ecology (encounter rate, size structure, sex ratio, and injury frequency) and the effects of human disturbance on Melanosuchus niger and Caiman crocodilus populations in Cantão State Park, southern Brazilian Amazon, Central Brazil. We assessed human pressure on both populations, testing the human disturbance–abundance and human disturbance–size structure relationships. We sampled waterbodies within (lakes) and adjacent to (river) protected areas via nocturnal surveys and captures. Human pressure in the river was assessed and categorized via transects with low, medium, and high levels of disturbance. Our results indicate that C. crocodilus was more abundant than M. niger, with populations of both species mainly composed of juvenile males. We also observed that injuries were more prevalent in juveniles and males. Human disturbance negatively affected C. crocodilus abundance, but no effect was found for M. niger. We found no significant effect of human disturbance on size structure for either species; however, the response for each species differed. Snout–vent length (SVL) decreased with increasing human pressure level in the C. crocodilus population, whereas M. niger showed a greater SVL at higher human pressure levels. Our results suggest that human disturbance related to boat traffic, pollution, riverine population, land use, and human activities negatively influence crocodilian populations in their distribution through a distance–abundance relationship. Additionally, the proximity of settlements and accessibility to protected areas are factors related to human disturbance and should be considered in government decisions and the management of protected areas by environmental agencies. Our results improve our understanding caiman population responses to human disturbance.

Human-wildlife conflicts with crocodilians, cetaceans and otters in the tropics and subtropics.

Conservation of freshwater biodiversity and management of human-wildlife conflicts are major conservation challenges globally. Human-wildlife conflict occurs due to attacks on people, depredation of fisheries, damage to fishing equipment and entanglement in nets. Here we review the current literature on conflicts with tropical and subtropical crocodilians, cetaceans and otters in freshwater and brackish habitats. We also present a new multispecies case study of conflicts with four freshwater predators in the Western Amazon: black caiman (Melanosuchus niger), giant otter (Pteronura brasiliensis), boto (Inia geoffrensis) and tucuxi (Sotalia fluviatilis). Documented conflicts occur with 34 crocodilian, cetacean and otter species. Of the species reviewed in this study, 37.5% had conflicts frequently documented in the literature, with the saltwater crocodile (Crocodylus porosus) the most studied species. We found conflict severity had a positive relationship with species body mass, and a negative relationship with IUCN Red List status. In the Amazonian case study, we found that the black caiman was ranked as the greatest ‘problem’ followed by the boto, giant otter and tucuxi. There was a significant difference between the responses of local fishers when each of the four species were found entangled in nets. We make recommendations for future research, based on the findings of the review and Amazon case study, including the need to standardise data collection.

Physiological stress response in free-living Amazonian caimans following experimental capture.

When captured, free-living crocodilians respond by hyperstimulation of the hypothalamic-pituitary-adrenal (HPA) axis, which triggers a cascade of downstream events of physiological stress. We examined these responses in two unstressed, and stressed Amazonian caimans, Caiman crocodilus and Melanosuchus niger. Plasma corticosterone levels increased in both stressed caiman species. In M. niger, the levels of this hormone increased 5.2-fold compared with the basal range values, while in C. crocodilus this was only 1.7-fold. After stress, M. niger needed more than 6 h to return its corticosterone levels to basal range values, whereas in C. crocodilus just 0.5 h was enough. Downstream events were characterized by an increase in glucose levels, which is associated with corticosterone increments. Excessive muscle activity resulted in increased plasma lactate content in both species. Lactate levels were also related to plasma calcium concentration, possibly due to the buffering capacity for preventing lactic acidosis. Clearance of excessive lactate load was faster in M. niger (0.5 h) than in C. crocodilus (more than 6 h). Although both caiman species respond in the same way to capture, the amplitude and duration of activation of the HPA axis are different. M. niger may be potentially more sensitive to acute stress than C. crocodilus. On the other hand, C. crocodilus needs more time to recover from the lactic acid load. Our experiment provides a useful diagnostic tool for management and conservation programs, as well as evaluating the impacts of tourism and recreational capture on caimans in the Amazon.

What do adult black caiman (Melanosuchus niger) actually eat?

AbstractThe black caiman (Melanosuchus niger) is one of the largest predators in South America, yet we know little about adult diets. We studied stomach contents of adults in Guyana and found the largest individuals target mammals instead of fish and males exhibit cannibalism, a behavior never recorded for this species previously.

Science and conservation of Amazonian crocodilians: a historical review

Abstract Crocodilians represent one of the oldest extant vertebrate lineages. They have co‐existed with humans throughout the Amazon basin for thousands of years, often having a strong cultural and economic influence on people's lives. Shifts in the socio‐economic and political reality of the Amazon basin during the last century have led crocodilian populations to face large variations in their numbers according to different levels of exploitation and strategies for their conservation. This article reviews the scientific knowledge obtained between 1945 and 2019 on the biology, conservation and management for the four Amazonian crocodilian (caiman) species (Caiman crocodilus, Melanosuchus niger, Paleosuchus palpebrosus and Paleosuchus trigonatus). It provides a general overview on past and current population status and research efforts involving caimans in the Amazon basin and discusses perspectives for the future. The most significant studies on the ecology, genetics and management strategies are examined in more detail and this information is contextualized to provide an overview of the most relevant findings that might explain caiman population trends over the last 75 years. Systems for sustainable management in the Amazon basin have been discussed for the past 20 years, but remain rarely applicable. It is necessary to develop new ways to maintain healthy caiman populations through innovative management programmes. Sustainable harvesting of wildlife has been shown to promote conservation targets, especially those initiatives based on community co‐management. In this article, we propose some general guidelines for future management schemes, in the expectation that the information provided by the scientific community will be considered fully without political agendas determining the priorities.

Responses of crocodilians to construction of a hydroelectric dam on the Madeira River in the Brazilian Amazon

The spillways of the Santo Antônio Hydro-electric Dam on the Madeira River in Brazilian Amazonia were closed in November 2011, inundating more than 100 km of river and reducing the annual fluctuations in water level. We surveyed the crocodilians in the affected area for two years before and for eight years after dam filling in order to evaluate the effects of the dam on the size structure of the population, the distribution of each species, and the detectability of individuals to interpret changes in apparent density. Our methodology was probably not appropriate to evaluate trends in population characteristics of Paleosuchus palpebrosus or P. trigonatus, but there was little evidence of an effect of the dam on the numbers of Caiman crocodilus and Melanosuchus niger in the area, and the distributions of all caiman species along the river changed only slightly after the dam was constructed. However, the proportions of small C. crocodilus and large M. niger detected in surveys increased eight years after dam filling. Despite having detectable effects on some population characteristics, the dam does not appear to represent a threat to the persistence of the species in the area if deforestation along the banks of the reservoir can be avoided.

Characterization and Shelf Life of Semi-preserve Black Caiman (Melanosuchus niger) Meat

Some conservation methods can add value to the product involved, especially those that involve meat derivatives. To take advantage of the raw materials available in the Amazon region, a semi-preserve using the meat of black caiman (Melanosuchus niger) was elaborated and evaluated for 90 days. The product was prepared using a curing brine of 4% acetic acid and 5% sodium chloride (NaCl), tail meat and back strap (sirloin), and was maintained at a controlled temperature of 5 °C for 30 d., with subsequent addition of flavoring brine (olive oil or Brazil nut oil), seasoning and soy lecithin for emulsification. The product was pasteurized at 70 °C/20 min and stored at 25 °C/90 d. The proximate composition, pH, acidity index, total volatile base nitrogen (TVBN), were determined. In the microbiological analysis for Salmonella sp., total coliforms and E. coli were within the standards required by current Brazilian legislation. The results of the physical-chemical analyses showed that the product had remained stable during the 90 d. of storage at room temperature (25 °C), and the pH values confirm that the immersion in acetic acid and sodium chloride in the proposed concentrations were enough to promote the reduction of pH and thus maintain the stability of the product.

Influence of sex, size and trophic level on blood Hg concentrations in Black caiman, Melanosuchus niger (Spix, 1825) in French Guiana

Mercury (Hg) is a contaminant that is impacting ecosystems worldwide. Its toxicity is threatening wildlife and human populations, leading to the necessity of identifying the most affected ecosystems. Therefore, it is essential to identify pertinent bioindicator organisms to monitor Hg contamination. In this study, we determined the stable carbon (δ13C) and nitrogen (δ15N) isotope ratios in the red blood cells (RBCs), and the total Hg concentration in total blood of 72 Melanosuchus niger in French Guiana. The goals of our study were to assess the level of Hg contamination in total blood of Black caimans and to further investigate the influence of individual traits (i.e., sex, size/age, diet) on Hg concentrations. Mercury concentration in total blood of Black caimans ranged from 0.572 to 3.408 μg g−1 dw (mean ± SD is 1.284 ± 0.672 μg g−1 dw) and was positively correlated to individual body size and trophic position (δ15N). We did not find any sexual or seasonal effects on Hg concentrations in the blood. The use of blood of M. niger is relevant to determine Hg concentrations within the population and suggests that this species can be used as a bioindicator for environmental contamination. In addition, our results emphasize trophic position as a major source of Hg variation and further suggest that it is essential to take trophic position (δ15N) into account for future studies.

Home range and habitat use of two sympatric crocodylians (Melanosuchus niger and Caiman yacare) under changing habitat conditions

Abstract We used radio-telemetry to record how Caiman yacare (Cy) and Melanosuchus niger (Mn) responded to the intrusion of the Maniqui river into Cedral Lagoon in the Bolivian Amazon. Nine M. niger and 3 C. yacare were followed between December 2015 and May 2016. Both species showed a gradual reduction in mean monthly range from December (19.96 ha Mn and 1.74 ha Cy) to May 2016 (0.08 ha Mn and 0.24 ha Cy). Habitat use was fairly constant throughout the months for both species, Melanosuchus niger used mainly open swampy forests and Cyperaceae Marshes, while C. yacare used more islands and flooded grasslands. This study shows that both species of caimans responded to changes in depth and vegetation types, as their habitat as a whole was changed by river intrusion.

Near-complete phylogeny of extant Crocodylia (Reptilia) using mitogenome-based data

AbstractSpecies of the order Crocodylia are mostly large, predatory and semi-aquatic reptiles. Crocodylia, the closest living relatives of birds, first appeared in the Late Cretaceous period. In the present study, the complete mitochondrial (mt) genomes of 19 Crocodylia species, including two species (Melanosuchus niger and Caiman yacare) that have not been previously sequenced for mitogenomes, were processed through Illumina sequencing to offer genetic resources and compare with the mitogenomes of Crocodylia species reported previously. In addition, a high-resolution phylogenetic tree of nearly all current recognized species of Crocodylia is constructed based on mitogenomic data. Phylogenetic analyses support monophyly of three families: Alligatoridae (four genera: Alligator, Caiman, Melanosuchus and Paleosuchus), Crocodylidae (three genera: Crocodylus, Mecistops and Osteolaemus) and Gavialidae (two genera: Gavialis and Tomistoma). The tree topology is generally similar to previous studies. Molecular dating suggests that the first split within Crocodylia date back to the Upper Cretaceous (approx. 86.75 Mya). The estimated time to the most recent common ancestor (TMRCA) of Alligatoridae is 53.33 Mya and that of Crocodylidae and Gavialidae is 50.13 Mya, which might be closely linked to climate changes during the Late Palaeocene and Early Eocene. Additionally, this study proves that the diversification rate within Crocodylia began to increase from the Late Eocene (about 36 Mya) and two diversification peak periods of Crocodylia (0–10 Mya and 10–20 Mya) are disclosed, which is roughly consistent with the estimated crocodylian species richness through time. Combining all these clues, we can suggest that climate fluctuation may have played a decisive role in the speciation of Crocodylia.

Serological evidence of Toxoplasma gondii infection in Melanosuchus niger (Spix, 1825) and Caimam crocodilus (Linnaeus, 1758).

Toxoplasma gondii is a protozoan with worldwide prevalence, known to affect a large variety of warm-blooded hosts. However, its ability to induce long-lasting infections in cold-blooded animals remains unclear. The most likely source of infection is through consumption of meat containing tissue cysts or by ingestion of food or water contaminated with oocysts. The current global climate change trend and the progressive degradation of natural habitats are prone to alter the distribution of ectotherm populations over a short period of time, which may favor contact between these animals and the protozoan. In association, alligator meat is considered a delicacy in many regions and its consumption has been previously related to a diversity of foodborne diseases. In that sense, we proposed in this study to search for specific antibodies against T. gondii in serum samples of two common species of alligators from the Brazilian fauna (Melanosuchus niger and Caimam crocodilus). We obtained the serum samples from 84 alligators from the Araguaia region, which were tested by agglutination assays that do not require species-specific secondary antibodies (Modified Agglutination Test – MAT; Indirect Hemagglutination Assay – IHA). From the 84 samples tested, eight (9.5%) were positive by MAT. From those, seven (87.5% of MAT+, 8.3% of the total) were also positive by IHA, reassuring a probable exposure of these animals to the parasite. Direct parasite detection in muscle fragments of one serologically reactive alligator did not yield positive results. Our results provide serological evidence that Brazilian alligators may be exposed to T. gondii and further studies should be performed to elucidate whether alligators are natural hosts of this ubiquitous protozoan parasite.

A standardised monitoring protocol for the black caiman (Melanosuchus niger)

Abstract ContextEstimating population abundance can be plagued by the violation of methodological assumptions, which can be overcome with standardised protocols. The black caiman (BC) is considered a conservation-dependent species, and previous abundance estimates are surrounded by uncertainty and flaws in the survey (e.g. different survey design and efforts) and analytical approach used (e.g. relative abundance index, which ignores imperfect detection). Its conservation status assessment demands the implementation of a standardised monitoring protocol. AimsThe protocol provides guidelines to collect and analyse data in a consistent manner to survey BC. Besides accounting for imperfect detection to produce reliable abundance estimates, the protocol aimed to be easily implemented by park rangers, and to fit field observations into a hierarchical modelling approach to assess how environmental variables affects detectability and abundance. MethodsThe protocol subdivides a 20-km transect into 10 2-km segments; each transect is surveyed four consecutive nights, starting at 1900 hours and finishing when the 20km are completed. For each caiman detected, the observers estimated head size to classify the individual by age. We tested the protocol in Ecuador during January and December 2017, and field data were analysed using N-mixture models. We compared abundance estimates derived with this protocol with commonly used relative abundance indexes. Key resultsWe surveyed 460km that resulted in 177 detections. Percentage of moonlight and distance from human settlement best explained detectability and abundance respectively. Mean detection probability was 0.14 (95% BCI: 0.1–0.18), whereas absolute abundance was 196 (95% BCI: 147–370). The overall adult to immature ratio was 1:1.3. ConclusionsThis is the first estimate of detectability and absolute abundance for BC by using a standardised survey with a clearly defined and repeatable survey and analysis methods. Relative abundance indexes did not reflect absolute abundance estimates. We recommend the use of this protocol in future surveys across the Amazon region to effectively evaluate BC conservation status. ImplicationsPopulation size cannot be estimated from relative abundance indexes; they lead to bias estimates for ignoring imperfect detection. We discourage the use of relative abundance indexes to evaluate the conservation status of this species.