Quantifying the ecological impacts of the 20th century trade in Amazonian furs

Scientists have long proposed that the international trade in furs and skins that took off in the 20th century led to an “empty forest” scenario in the Amazon, but no one has ever sought to actually quantify the impacts of that trade.

New research shows that, because our understanding of the resilience of Amazonian ecosystems to hunting has largely been based on studies that are temporally or spatially restricted and focused mostly on terrestrial species, it appears we might have failed to properly account for the far more drastic effects hunting has had on populations of aquatic and semi-aquatic species as well as the resulting damage to overall ecosystem health.

A study published this month in the journal Science Advances comprises the first systematic accounting of the history, scale, and repercussions of the trade in Amazonian hides throughout the 20th century. The authors of the study, an international team of scientists led by André Antunes of the Wildlife Conservation Society Brasil, compared two periods of peak exploitation — the 1930s to 1940s and the 1960s.

The team used previously unanalyzed historical documents and unpublished shipping records cataloguing the quantity and scale of the wildlife trade to determine trends in the vulnerability of different wild animal species. They found widespread collapse of giant river otter, black caiman and manatee populations in the aftermath of commercial hunting, while terrestrial animals such as collared peccaries, deer, and even jaguars were found to be much more resilient to hunting pressure during periods of peak international hide exports for the international fashion trade in the 1930s to 1940s and again in the 1960s.

These time periods were chosen because both saw a marked increase in the total harvest of all species and also because hunting incentives were strong thanks to high market prices for pelts. One noticeable difference, on the other hand, was that the rural human population in the central-western Brazilian Amazon was 68 percent larger in the 1960s than in the 1940s, according to Antunes and his co-authors, who say that it is therefore reasonable to assume that hunting activities were higher in the latter time period.

“Thus, species that disappeared from the harvest in the 1960s had presumably experienced widespread population collapse,” the authors write. “Although it cannot be proved that this was due to overhunting, the circumstantial evidence is strong, especially when considered alongside anecdotal evidence from hunters of the day.”

Conversely, greater resilience to hunting pressures on the part of species whose harvests remained steady throughout the 1960s can also be inferred, the authors add.

The 11 animal species that were the most hunted were the giant river otter, neotropical otter, black caiman, capybara, manatee, jaguar, ocelot, margay, collared and white-lipped peccary, and red brocket deer. Between 1930 and 1970, exports of hides from these animals represented some $500 million in trade for the Brazilian states of Amazonas, Acre, Rondônia and Roraima.

Based on their modeling of harvest trends, the researchers estimated that from 1904 to 1969 at least 23.3 million individual animals of some 20 different species were commercially hunted for their hides, including 13.9 million terrestrial mammals, 1.9 million aquatic and semi-aquatic mammals, and 7.5 million reptiles.

The researchers determined that several aquatic species underwent population collapse at a basin-wide scale, as peak harvest of the giant otter in the 1960s, for instance, was only 12 percent of 1930s levels and the black caiman harvest in the 1960s was just eight percent of peak production in 1943.

By contrast, terrestrial species such as red brocket deer and collared peccary showed higher harvests in the 1960s than in the 1930s, providing evidence of greater resilience to 20th century hunting activities. Meanwhile, about 180,000 jaguars were harvested in the central-western Brazilian Amazon during the fur trade, and harvest numbers remained consistent across the time period studied. Though jaguar harvest numbers peaked in 1938 at 9,000 individuals, nearly 8,000 were still harvested in 1969. Of all terrestrial mammals, the researchers found that only the white-lipped peccary showed signs of population decline at both basin-wide and local scales.

“For most of the terrestrial species we examined, our findings do not support the assumption that 20th-century commercial hunting resulted in a severe degree of defaunation at a basin-wide scale,” the researchers write, “which would have been to the large-scale detriment of ecosystem roles played by ungulates, such as seed predation and dispersal for hundreds of plant species, and top-down population regulation performed by jaguar, ocelot, and margay.”

In other words, an “empty forest” scenario may not have been the most pressing concern around over-hunting in the Amazon. Commercial exploitation of animal hides in the 20th century did lead to population collapse for affected aquatic wildlife species, however, “signaling the possibility of an ‘empty river’ phenomenon,” the researchers write in the study. “Population collapses in aquatic species attest to their high vulnerability to unregulated hunting, particularly during years of severe drought when aquatic wildlife is confined to larger waterways that are generally accessible to hunters.”

Antunes and team say that these differences in resilience are best explained in terms of access. Flooded aquatic environments make up just 12 percent of total surface area in the Amazon and are more easily accessible, while upland forest areas are much more extensive and less accessible, leaving significant areas that hunters cannot reach and providing refuges for heavily hunted terrestrial animals.

The team argues that the relative resilience of terrestrial species suggests a marked opportunity for managing, rather than criminalizing, contemporary traditional subsistence hunting in Amazonia, through both the engagement of local people in community-based co-management programs and science-led conservation governance.

“Legal regulation and management of subsistence hunting represents a tremendous conservation opportunity in Brazil and other Amazonian countries,” the researchers write. The same dynamics that led to the resilience of most terrestrial animal species during the peak of commercial hunting in the 20th century underpin indigenous and other forest peoples’ hunting strategies to this day, they argue. But increasing deforestation, fragmentation, and penetration of Amazonian forests by roads, logging, large infrastructure projects, and agricultural expansion threaten the refuge areas that allow terrestrial animal populations to remain steady despite continued hunting.

“Our suggestion that traditional subsistence hunting may represent more a management opportunity than a threat is restricted to roadless regions that remain largely forested, ideally officially protected, and where people still maintain traditional practices,” Antunes and his co-authors state.

CITATION

• Antunes, A.P., Fewster, R.M., Venticinque, E.M., Peres, C.A., Levi, T. , Rohe, F., & Shepard, G.H. (2016). Empty forest or empty rivers? A century of commercial hunting in Amazonia. Science Advances. doi:10.1126/sciadv.e1600936