The Taiamã Ecological Station, a small conservation unit that protects a virtually untouched stretch of the Pantanal wetland in Brazil’s Mato Grosso state, is home to a peculiar treasure: fishing jaguars (Panthera onca). In a newly published study, a group of international researchers documents that the basic diet of the jaguar population living in this protected area comprises mainly fish and caimans. The finding is unprecedented for these big cats, which are better known for preying on terrestrial mammals.

And this isn’t the only surprise finding from the study in the journal Ecology. The abundance of fish and caimans, a small crocodilian, in the ecological station is such that it sustains the highest known density of jaguars: an estimated 12.4 animals per 100 square kilometers, or 32 jaguars per 100 square miles. And while jaguars in general are known to be solitary and territorial, the ones in Taiamã socialize, fish and hunt together — and even play with each other.

“The findings were surprising,” says study co-author Ronaldo Morato, a veterinarian and head of Brazil’s National Center for Research and Conservation of Carnivorous Mammals (CENAP). Morato says researchers began studying the Taiamã jaguars in earnest in 2011.

A jaguar catching a cachara.

This new study was prompted by lead author Charlotte Eriksson, a doctoral student at the Department of Fisheries, Wildlife and Conservation Sciences at Oregon State University. Her proposal to CENAP was to verify the hypothesis that the jaguars of Taiamã were feeding mainly on aquatic and semi-aquatic animals, and to see how this behavior contributes to the species’ high density in the area.

Managed by ICMBio, the Brazilian Ministry of Environment’s administrative arm, the Taiamã Ecological Station was created in 1981 in a part of the Pantanal where the wetland begins, with floodwaters spreading out of river channels. The reserve spans 11,555 hectares (28,553 acres) and is located in the northern portion of the biome, in the municipality of Cáceres. It comprises a fluvial island of floodplains, bordered to the south by the Paraguay River and to the north by a water channel called the Bracinho. The only way to reach it is by boat from local farms.

On the other side of the Bracinho lies another conservation unit, the Jurban Private Natural Heritage Reserve (RPPN). The latter is much larger than its state-run neighbor, at 35,531 hectares (87,800 acres). “The terrain’s characteristics helped to prevent the occupation of the area and guarantee its isolation,” Morato says.

Study co-author Daniel Luis Zanella Kantek, who heads the Taiamã Ecological Station, the small variation in water levels in the conservation unit allows the jaguars to live there during both the wet and dry seasons. “I guess this characteristic, together with a large amount of prey, enables the high density of the species. Other Pantanal areas with more variation in water levels cannot be used throughout the year,” Kantek says.

Highest density of jaguars on the planet

While there have been previous studies focused on the jaguars of Taiamã, the installation of 59 camera traps was a major boost for this latest research, mainly for quantifying the big cats. During the period when camera traps were installed, between 2014 and 2018, researchers managed to record 69 individuals. Jaguars were present in 95% of the images captured.

To study the animals’ behavior, researchers also fitted seven males and six females with GPS collars between December 2011 and April 2016 as part of other ongoing studies, and analyzed the composition of their droppings to identify what they were eating. By monitoring their movements, the researchers found that the jaguars remained within the bounds of the ecological station 96% of the time.

The number of jaguars and the data on their movements reinforce the idea that Taiamã is home to perhaps the highest jaguar density on the planet. For the Pantanal as a whole, the average jaguar density is 10.3 per 100 km2 (26.7 per 100 mi2), and in the Brazilian Amazon 10 per 100 km2 (25.9 per 100 mi2). The Taiamã figure of 12.4 is also higher than in other regions considered to have high jaguar concentrations, such as the Peruvian Amazon, the Venezuelan Llanos grasslands, and Brazil’s southern Pantanal.

Despite the large number of jaguars in the small Taiamã area, the big cats coexist without aggressive behavior or disputes over territory and food. Using movement data and camera trap images, the researchers analyzed 80 recordings of social interactions between adult jaguars, including individuals of the same sex — which indicates that their behavior is not motivated by the need to mate or care for cubs.

Two jaguars playing together, recorded by a camera trap at the Taiamã Ecological Station.

This was the case of a male identified as M2, which for two days moved around with another male, M1; eight months later, both were photographed by the same camera just five minutes apart. Two other males, known as M29 and M27, spent 30 minutes playing within sight of a camera, including rolling together, play fighting, and exchanging soft bites.

Also noteworthy were the recordings of jaguars fishing together. Images showed two adult males and a female with her oldest offspring catching fish. It’s not yet clear whether this behavior suggests cooperation between the cats or whether they simply tolerate being close to each other.

“This does not mean that there is no social hierarchy that determines priority in access to resources among jaguars, as occurs with other carnivores, especially during the period of more scarcity,” says study co-author Carlos Peres, biologist and professor of conservation ecology at the University of East Anglia, U.K.

A fish-rich diet

The researchers’ theory is that the abundance of fish and caimans as prey has enabled a large number of jaguars to live in the Taiamã Ecological Station. Even though they have smaller home ranges than jaguars elsewhere, and these rangers overlap, the animals don’t end up competing for food. Instead, they live together and display behaviors that are unusual for the species.

“It is surprising because of the extremely high proportion of aquatic and semi-aquatic vertebrates eaten throughout the year, which even allowed for clear changes in the socio-ecology of jaguars in the area under study. Similarly, brown bears [Ursus arctos] in Alaska and British Columbia [Canada], which consume large amounts of fish during salmon migration, can also congregate in small areas and dispute access to that resource,” Peres explains.

The 138 fecal samples that the researchers collected from the Taiamã jaguars indicated that their diet was composed mostly of reptiles (55%), primarily caimans (Caiman yacare); fish (46%); and mammals (11%), mostly capybaras. Camera trap images showed the jaguars catching a wide range of fish, from thorny catfish (Doradidae spp.) and pacu (Piaractus mesopotamicus), to red-bellied piranhas (Pygocentrus nattereri) and tiger catfish (Pseudoplatystoma fasciatum).

“Although jaguars in Taiamã consume more aquatic reptiles than has ever been observed, it is fish consumption that makes this population truly unique,” the authors write in their study. “As far as we know, this is the most piscivorous diet of any large felid and among the most for any terrestrial hypercarnivore,” an animal whose diet consists of more than 70% meat.

Study co-author Manoel dos Santos Filho, a professor and researcher in ecology and conservation at Mato Grosso State University (Unemat), jaguars are very skilled in aquatic environments and commonly feed on prey in this environment, like fish and caimans. “This type of prey is common at the Taiamã Ecological Station. As it is a virtually flooded environment with few areas of dry land, these animals, especially in the rainy season, hunt virtually in the water,” he says.

Registro de onças pescando juntas na Estação Ecológica de Taiamã. Jaguars fishing together at the Taiamã Ecological Station.

Conservation status

Jaguars are classified globally as near threatened on the IUCN Red List, the only species in the big cat genus Panthera that’s not in one of the threatened categories. In Brazil, however, they’re considered a vulnerable species. Their global population is estimated at 173,000 individuals, with Brazil home to around 86,000. In the Pantanal alone there are thought to be 4,000 jaguars.

Habitat loss and fragmentation resulting from the expansion of farms and livestock pasture, as well as mining, hydroelectric plants and roads, pose the main threats to the species. “Revenge hunting” by ranchers who kill jaguars thought to be preying on their livestock is also common.

The Pantanal jaguars are known as canguçu, the Indigenous Tupi word for “big-headed jaguar.” They are generally bigger and stronger than jaguars found elsewhere, with males growing to 140 kilograms (310 pounds) and females 90 kg (200 lbs).

Citations:

Eriksson, C. E., Kantek, D. L., Miyazaki, S. S., Morato, R. G., Dos Santos‐Filho, M., Ruprecht, J. S., … Levi, T. (2021). Extensive aquatic subsidies lead to territorial breakdown and high density of an APEX predator. Ecology. doi:10.1002/ecy.3543

Morato, R. G., Stabach, J. A., Fleming, C. H., Calabrese, J. M., De Paula, R. C., Ferraz, K. M., … Leimgruber, P. (2016). Space use and movement of a neotropical top predator: The endangered jaguar. PLOS ONE, 11(12), e0168176. doi:10.1371/journal.pone.0168176

Banner image by Daniel Kantek.

This story was reported by Mongabay’s Brazil team and first published here on our Brazil site on Dec. 7, 2021.