Black Caiman

[Dark Jaguar]

Summary of Diet study with Stomach content of Black caiman and Spectacled caiman from Cuniã Lake - Amazon - Brazil.

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From the study  ( Characterization of the diet of Melanosuchus niger (Spix, 1825) and Caiman crocodilus (Linnaeus, 1758) in the Resex Lago do Cuniã, Rondônia )

http://portal.amelica.org/ameli/jatsRepo...149014.pdf

ABSTRACT:

The aim of this study was to characterize the diet of male individuals of Melanosuchus niger and Caiman crocodilus in a lake at the Reserva Extrativista do Lago do Cuniã, Rondônia. We collected guts of the animals in November/2016, rainy season, provided by the local Cooperative (COOPCuniã). Caimans abdominal cavities were opened and their stomach were removed, after the gut contents were stored in 70% alcohol, and food items were analyzed. We analyzed 82 stomachs, 42 of M. niger and 40 of C. crocodilus. Food items such as fragments of birds, amphibians, crustaceans, insects, and plant material were ingered by the species studied. However, the most representative items in the diet of M. niger and C. crocodilus were fishes from the Characifomes and Siluriformes order of no commercial importance.

STUDY AREA:

Study area with indication of Caniã Lake, Rondônia, Brazil.

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Cuniã Lake is an important protected area located in the Cuniã Lake Extractive Reserve (RESEX Cuniã), which has over 140 species of fish, supports local fisheries subject to an environmental management plan and other activities of sustainable use of natural resources such as the capture and killing of caimans. With a surface area of 18,000 ha, Cuniã Lake  is located in the lower part of the Madeira River, and comprises a complex of approximately 60 lakes and canals, which are interconnected during the flood season of the river, housing large areas of aquatic macrophytes, submerged litter, marginal trunks and being one of the few floodplain lakes of large size with turbid waters, promoting a great structural complexity, which contributes to the great animal biodiversity in the area.

Cuniã Lake presents the population of caimans with the number of males higher than the number of females. The Cooperative of Resex (COOPCuniã) was founded in April 2011 in order to market the products of RESEX. The Resex Cuniã produces flour, açaí, Brazil nuts and explores the management of some species of fish and two species of caimans, C. crocodilus and M. niger. The cooperative is managed by a group of managers who are responsible for activities within and outside the RESEX, but the objective of all the activities of the cooperative is to ensure the fulfillment of its mission: "carry out the management of resources with a focus on sustainability". The production model followed in the RESEX is of the harvesting type, authorized in 2011 by IBAMA for the purpose of population control.

RESULTS:

A total of 82 stomachs, 42 M. niger and 40 C. crocodilus stomachs were analyzed. The average length and mass of M. niger were 1.8 ± 0.1 m and 17.0 ± 5.5 kg, and of C. crocodilus were 1.7 ± 0.1 m; 19.0 ± 5.0 kg, respectively. Both species ingested a total of 14 food items, varying in items of animal origin,such as bird fragments, fish fragments, amphibians, crustaceans and insects and items of plant origin such as Brachiaria sp. (IAi = 0.20) and feathers (IAi = 0.11) were the most ingested by C. crocodilus while for M. niger the most important items were Brachiaria sp. (IAi = 0.39), Characiformes sp 1 (IAi = 0.19) and Loricariidae (IAi = 0.17; ).

Figure 4: Dietary items of M. niger and C. crocodilus in Resex Lake Cuniã, Rondônia. A: Fish skeleton of the Siluriformes Order. B: bones and epidermis of anuro. C: feathers. D: Brachiaria sp. with presence of nematoides.

*This image is copyright of its original author

DISCUSSION:

The fish were the most consumed item by both species studied in Lake Cuniã. C. crocodilus and M. niger ingested a total of 14 food items, however C. crocodilus consumed a greater variety of invertebrate items while M. niger ingested more items from the vertebrate group.
Crocodilians are generalist predators, feed on a variety of animal prey and their diet can vary according to species, habitat, prey availability and environmental conditions such as temperature and water levels. The species M. niger and C. crocodilus feed mainly on insects (coleoptera), spiders, crabs, molluscs and vertebrates such as fish, birds, reptiles and mammals.

Approximately 82% of food items recorded in the diet of M. niger and C. crocodiles in this study are the same as those recorded for these species in the Amazon and Venezuelan Llanos. The high incidence of fish in the diet of the species is according to previous information and may be related to the fact that the animals analyzed are males, considering that they use the aquatic habitat more frequently when compared to females, which in the reproductive period go through long incubation periods of the eggs on land. Studies of Da Silveira and Magnusson, in the archipelago of Anavilhanas, Amazonas, point to a higher proportion of fish consumed by C. crocodilus in lakes of the region, and this result is probably related to the higher availability of fish, lower depth and current in this environment which increases the vulnerability of prey to crocodilians when compared to lotic environments, which present greater depth and current.

Preliminary researches has suggested that M. niger may ecologically affect C. crocodilus. However, although both species use similar food items in their diets, the research cannot indicate the existence of trophic competition, considering that it is necessary to evaluate the structural complexity, presence of microhabitats of Lake Cuniã and availability of prey for the analyzed species. We highlight the higher consumption of fish by the caiman species studied, so management and conservation measures of regional ichthyofauna are important to maintain the survival and prevalence of M. niger and C. crocodilus and promote other sources of income for communities living in Resex Cuniã.

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Summary of Diet study with Stomach content of Black caimans in the Peruvian Amazon.


From the study ( Feeding Ecology of the Black Caiman (Melanosuchus niger) in Manu National Park, Peru )

https://www.researchgate.net/publication..._Park_Peru

ABSTRACT:

During 1992  and 1994, eighty eight individuals of the endangered species Black  Caiman (Melanosuchus niger )  were captured in an oxbow lake in Manu National Park located in the Peruvian rainforest. Stomach contents and body dimensions were collected and recorded from the captured animals. A total of 15 items among invertebrates and vertebrates were found in the stomachs. Snails  (Pomatia  spp) and fish were the main items of the diet composition. The category snails was the most abundant in the stomachs of juvenile black caimans while the category fishes was the most common in the stomachs of adult animals. Vertebrates such as frogs, birds and mammals were found in few stomach  content samples. The results of the statistical and descriptive analyses indicated that there was a significant effect of ontogeny on diet composition. Also significant seasonal differences were recorded in the composition of the diet suggesting that black caimans modify their feeding behavior according to changes in prey ocurrence.

The study of habitat distribution in the study area allowed the determination of natural habitats like oxbow lakes, river margins and flooded floodplains that host a high diversity of organisms that represent prey items for the Black Caiman. The conservation of this species that has been heavily exploited in the past should consider the protection of  ist natural habitat in Amazonia.


STUDY AREA:

Cocha Cashu lies in the Manu National Park area and is located in the Western Amazonian Floodplain of the Rio Manu, Peru. Cocha Cashu is a shallow oxbow lake located within large old-growth stands of pristine tropical lowland rain forests. The weather in the area follows a cyclic pattern with the strong period of rain occurring between January and April (Terborgh et al.1985). Precipitation is scarce between July and September and the rainy season starts in October. The rains are frequent and sometimes on a daily basis from November to December. Annual mean precipitation for Cocha Cashu is about 2080 mm. The lake has an approximate area of 20ha, a perimeter of 4 km, and a maximum depth of 2.95 m  (Otte 1978, Herron 1985, Terborgh et al. 1985)

Figure  1.  Geographic location of the study area in Manu National Park, Peru.

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STOMACH CONTENT COLLECTION:

During three consecutive years, eighty-eight individuals of the endangered species Melanosuchus niger (Black Caiman) were captured in Cocha Cashu. Small caimans were captured at nighttime from a boat  by catching the animal by hand at the neck, while large animals were capture using a lace placed on the neck of the animal and rapidly tightened (Vasquez 1981). For all individuals of  Black  Caiman  we  measured   total  lenght,  snout-vent length,  head  length,  weight,  and determined the sex for each individual. The caimans were marked by cutting off one of the caudal crest scales following a binary code according to Vasquez (1981). Stomach contents were collected using the stomach flushing method (Webb et al. 1982). The collected stomach content samples were preserved in ethanol. The caimans were released to their habitat immediately after investigation.


HABITAT IDENTIFICATION:

The habitat determination was done from a composite Synthetic Aperture Radar image  taken by a side looking airborne during 1993 by a NASA’s AIRSAR mission over the area of the Manu River.


RESULTS:

Diet Composition

About 15 different remnants of invertebrates and vertebrates were found as stomach contents. Snails (Pomatia spp) and various fish species  were the main items observed in the diet. Snails were more abundant in juvenile caimans and fish in the adult animals. Vertebrates such as frogs, birds, and mammals were also eaten by Black Caimans (Table 1). The most numerous item found in the diet, independent of the caiman size, were snails, mainly Pomatia spp., which are very abundant at the Cocha Cashu lake  and constitute an important  food supply for  other vertebrates such as fishes, wading birds, and aquatic mammals.


CAIMAN SIZE AND DIET COMPOSITION:

The diet composition  had a strong positive and significant relationship with size classes of Black Caimans (r = 0.887; df = 1; p < 0.003). Therefore, the results of  MDS analysis clearly suggests that the diet composition changes as Black Caimans grow older. There was a tendency to increase the frequency of fish with increasing size class. The opposite tendency was observed for snails and aquatic beetles. For the rest of the prey items there was no clear tendency.
Table 1. Diet composition items according to different size classes of Black Caimans in Cocha Cashu, Manu National Park, Peru. Numbers are mean number of the diet items. The numbers in parenthesis are the sample sizes (number of stomachs analysed).

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SEASONAL VARIATION OF THE DIET:

The results  of  a  post-hoc multivariate  test suggested  that  there were significant  seasonal differences in the diet composition of Black Caimans  (Pillai Trace F = 3.736; df = 4, 166; p = 0.006. Some individuals of Black Caiman had significantly more snails, spiders, aquatic beetles, and other insects in their stomachs during the wet season than during the dry season.


HABITAT DISTRIBUTION:

The floodplain area  along the Manu River offers a  variety of habitat conditions for Black Caimans (Figure 3). Oxbow lakes like Cocha Cashu are one of the most important habitats, because they provided a mix of open water and well protected lake shores were adult females build their nests. This habitat undergoes an annual transition from low to high water levels which also means that the lake is either isolated from or connected with the main river channel of the Manu River. As it was observed from the seasonal variation of diet composition the seasonality in the habitat also determines the availability of different preys.
During the rainy season the floodplain of the Manu River offers a large area were caimans are moving easily between adjacent flooded areas and take advantage of a broader variety of prey items. The main river banks are also habitat for black caimans, but mainly for larger size animals.

CONCLUSIONS:

The results from both, descriptive statistics and multivariate ordination analyses, indicate a significant effect of ontogeny on diet composition. There was a clear tendency in diet change with caiman age and growth.
The significant seasonal differences in the diet composition suggest that Black Caimans adjust their feeding behavior according to changes in prey abundance and occurrence. Although Black Caimans are top predators, they depend on both, invertebrates and vertebrates to satisfy their energetics needs during their development.

The conservation of this heavily hunted species has to consider the protection of natural areas such as lakes, cochas, and rivers containing a high diversity and abundance of organisms at various trophic levels. Also, experiments aimed to monitor controlled harvesting in protected areas are urgently needed for developing realistic management plans for Black Caimans in the Amazon. Reply