The Complex Business of Sustainable Exploitation of Wildlife

For millennia, humans have been exploiting other living organisms for food, shelter, and survival. Historical overexploitation of wildlife led to extinctions of the moa, dodo, passenger pigeon, and Steller's sea cow, among many other species. And as modern human populations have burgeoned and our tools for exploitation increased in efficiency, so, too, has our ability to take more from ecosystems than nature can sustain, leading to population crashes such as the Atlantic cod and great whales and the extirpation of large carnivores in many regions where they once roamed. Overexploitation is one driver of species extinction and biodiversity loss, and recognition that it can have catastrophic impacts has led to a focus on how to achieve “sustainable” exploitation. As interest and scientific sophistication in this complex research area grow, intriguing questions are being explored. Despite progress from technological advances and decades of study, many unknowns continue to hamper our understanding of what level of exploitation is sustainable and how best to establish such limits. An Atlantic cod harvester retrieving an experimental Norwegian style cod pot, off Fogo Island, Newfoundland, in 2016. Atlantic cod stocks collapsed in 1992 in Canadian waters, and a moratorium was put in place, although a small fishery has since resumed. Photograph: Phillip Meintzer Sustainable exploitation lies along a continuum of human attitudes toward nature, describe Georgina Mace and John Reynolds in the 2001 book Conservation of Exploited Species. That continuum begins with strict preservation of nature on one end to “take it all now and leave nothing for the future” on the other, an attitude they call “hit-and-run.” Between these two extremes lies sustainable exploitation, a concept that comes from population modeling theory. The premise: A certain number of individuals can be removed without compromising the long-term viability of their source population because of density dependence. Populations generally do not grow exponentially but are kept in check by intrinsic and extrinsic factors around a limit called their carrying capacity. As the population density rises, individuals become overcrowded, which puts food, shelter, and other limited resources in shorter supply, affecting the total numbers of individuals via reproduction or survival. Theoretically, moderate human exploitation reduces population density enough that individuals are less crowded so that food and habitat are no longer limited. That allows individuals to reproduce at their maximal rate. Sustainable exploitation aims at this numerical “sweet spot” to remove neither too few nor too many individuals from the population at a point along the curve where reduced densities mean they reproduce more quickly than they would without exploitation. Fisheries researchers formalized this idea in the 1930s in the concept of maximum sustainable yield. Since then, the concept has often been at the center of exploitation debates. Exploiting at the maximum sustainable yield was at first widely endorsed in part because of the idea's elegant simplicity—at least in theory. In practice, though, nature and the human ability to sustainably exploit living organisms are more complex than single-species models in an unchanging environment. Whether to set targets for exploited populations at the maximum sustainable yield—the ecological knife's edge at the top of the curve, at which the relative benefits versus costs are maximized—or at more conservative but still efficient levels of exploitation is one of many subjects of ongoing debate. So, too, is the question of whether the goal is to sustain populations, species, ecosystems, or human communities. Battles over these goals have long consumed researchers, resource managers, and fishing and hunting interests. In examinations of the challenges of sustainable exploitation and the limits to both knowledge and control, sharks are a prime example. The exploitation of sharks and their close relatives, the rays and chimeras, remains a contentious issue. Poorly regulated fisheries combined with large numbers of sharks and rays taken incidentally as the by-catch of other fisheries mean that many populations, such as angel sharks and sawfish, are overfished. Some face a threat of extinction. Tens of millions of the class Chondrichthyes are captured each year, fueled by a global trade in shark products including flesh, liver, and fins. The widespread practice of shark “finning,” in which fins are sliced off and the fish left to die, shown here in Mbour, Senegal, is both wasteful and inhumane. But researchers say a moratorium on all species is unwarranted, with many shark species being sustainably caught. Photograph: Sebastián Losada. Shark fin is a delicacy in some Asian cultures. But the traditional harvesting of fins—by chopping them off the live animal, which is then tossed back into the sea to suffocate or bleed to death, a process called “finning”—has prompted public outcry. Many environmental advocates have called for a ban of shark fishing altogether. Although calling shark finning “one of the most wasteful and inhumane ways of gathering food in the history of human civilization,” David Shiffman, a postdoctoral research fellow at Simon Fraser University, in Vancouver, Canada, says that it is feasible to trade in fins without finning—by landing the whole shark and using its flesh and organs, not just discarding it. Shiffman led a 2016 attitudes survey that found that a majority of shark researchers believe that sustainable shark fishing is possible and preferable to bans. Nicholas Dulvy, Canada Research Chair in Marine Biodiversity and Conservation at Simon Fraser University and Co-Chair of the International Union for Conservation of Nature (IUCN) Shark Specialist Group, explains that until recently, very little was known about whether any sharks were being fished sustainably. So Dulvy teamed with shark ecologist Colin Simpfendorfer, of James Cook University, in Australia, to examine global stock assessments of 65 populations of sharks and related species. Publishing their work in Current Biology (2017), they found that 39 popu­lations, representing 33 species, were being fished sustainably, based on biomass and fishing mortality data. Their analysis determined that globally, 7 to 9 percent of global shark catch comes from sharks being fished sustainably. Looking specifically at fins, the research suggested that 4000 tons of dried fins—at least 8 percent of total shark fins harvested—originate from sustainable sources. But they also noted that only 4 percent of the global trade in sharks was being directly managed, such that sustainable management was happening more by accident than by design, making even these sustainably fished but unmanaged species vulnerable to future overexploitation. When carefully managed, explains Dulvy, even slow-reproducing, long-lived shark species such as the spiny dogfish (Squalus acanthias), in which gestation lasts 2 years and individuals can live to more than 70, can be sustainably fished. A recent Marine Stewardship Council (MSC)–certified dogfish fishery on the US Atlantic coast now supplies a European market whose own dogfish stocks—used for British fish and chips, for example—have collapsed. Dulvy and Simpfendorfer's work highlighting “bright spots” in the shark fisheries provides cautious optimism. Although the 33 species they identified as sustainably fished account for a small proportion of more than 1000 shark species, they are evidence for what is unthinkable for many: that sustainable shark fishing is possible. A source of food is one reason humans exploit living creatures. But sometimes, predatory species are exploited because they are perceived as competitors for food—for livestock—or hunted purely for recreation. This is at the root of a contentious debate over the sustainable exploitation of wolves. Similar to the case of sharks, direct human-caused mortality has contributed to wolf declines across much of Western Europe, Mexico, and the United States. Once the world's most widely distributed mammal, according to the IUCN, the gray wolf (Canis lupus) has for centuries been persecuted by farmers and feared by humans, out of proportion to the danger it presents. In Wisconsin, gray wolves, a protected species, come into conflict with humans over livestock. The efficacy of predator control and sport hunting as a strategy to reduce livestock killings by wolves has been questioned in several recent studies (e.g., doi:10.1002/fee.1312). Nevertheless, it is a long-standing practice for US federal and state agencies to issue legal permits to cull wolves, explains Adrian Treves, at the University of Wisconsin–Madison. McKinley, the alpha male of High Country Wolf Pack, West Yellowstone, Montana, in 2011. In some places, wolves have long been hated by livestock owners, but in others, farmers and wolves more harmoniously coexist. Hunting quotas vary throughout the United States and Canada. Photograph: Nomadic Lass. To designate how many wolves may be culled, managers need to understand wolf population size and trajectory. Individuals are radio collared to assess population trends. In radio-telemetry studies, important information is gleaned from individuals whose radios continue to transmit as they move around the habitat, as well as from those whose collars are recovered after they die. But among collared individuals, there are nearly always individuals that disappear for unknown reasons. For these mystery wolves, it is unclear whether the radio battery died, a wolf traveled too far away to be detected, or, in some cases, the wolf was killed illegally and the radio collar destroyed by a poacher. “We always have error in our measurements. It is inevitable with science,” Treves says. In an analysis published in 2017 in the Journal of Mammalogy (doi:10.1093/jmammal/gyx052), Treves and colleagues tested the numerical implications of two types of systematic errors in radio-tracked wolf population data. Traditional radio-telemetry data analysis assumes that the distribution of mortality types from known fates are representative of those with unknown fates. However, “none of your unknown fates contain legal killing,” explains Treves. (If it were legal, it would be known.) This leads to an overestimated risk of legal killing. What is left is natural causes of death that do not involve humans and a possibility that Treves calls “cryptic poaching”—illegal killing in which the radio collar is also destroyed and never recovered. The overall conclusion of the study is that for the four US wolf populations examined, legal kills are systematically overestimated, and illegal kills are systematically underestimated. Studies from Scandinavia and Alaska also suggest that the risk of wolf poaching may be underestimated. Published government estimates may “have obscured the magnitude of poaching as the major threat to endangered wolf populations,” argue Treves and coauthors. The Wisconsin Department of Natural Resources, a funder of Treves's study, declined to comment on the study's implications when contacted by BioScience. The science and politics of calculating what culling or trophy-hunting levels are sustainable versus desirable are no less fractious a topic for carnivores in Europe. Like much of Western Europe, “Wolves were exterminated in Norway and only began reestablishing in 1999,” says John Linnell, senior researcher at the Norwegian Institute for Nature Research. “We could probably easily fit in 200 or 300 wolf packs,” says Linnell, but the Norwegian government has established a controversial target of 4 to 6. Linnell is exploring the legality of limiting this protected species to such small numbers. Further east, in Romania, where wolves were never extirpated, farmers are typically more tolerant of coexistence, explains Viorel Popescu, assistant professor of Conservation Biology at Ohio University. In Romania, “we found that there was not really a sentiment of persecution and conflict between humans and wolves and bears,” says Popescu. There, management concern centers more on trophy hunting. After 2007, when Romania joined the European Union, bears, wolves, and lynx became species of conservation concern. But the establishment of hunting quotas remained a lucrative source of income for management agencies. Popescu grew concerned that decision-making was a “closed loop,” with a lack of transparency and “zero independent oversight,” he says, in terms of how the number of animals designated for hunting was being determined. So Popescu and collaborators ran official government data through simple population-growth equations to see whether growth rates of bears, wolves, and lynx fell within biologically realistic bounds as was reported in the literature. They discovered that especially for bears, the most economically valuable trophy species, but also to a lesser extent for wolves and lynx, the growth rates reported for many Romanian counties exceeded those considered to be their biological maxima (doi:10.1111/1365-2664.12660). A wolf legally shot in January 2011 by a professional hunter with the Slovenia Forest Service in southeastern Slovenia, Central Europe, as part of the annual wolf-culling quota prescribed by the Slovenian Ministry for Environment. Photograph: Miha Krofel. Romanian researchers from the Vrancea Environmental Protection Agency and Association for Biodiversity Conservation placing a global-positioning-system collar on a tranquilized Carpathian brown bear. Photograph: Szilárd Szabó. Uncertainty as a limit to knowledge and control is also a concern with respect to recreational trophy hunting for grizzly bears in British Columbia (BC). “The biology of these bears makes them very vulnerable to management error,” says Kyle Artelle, doctoral candidate at Simon Fraser University and the Raincoast-Hakai Lab at the University of Victoria. As large carnivores, grizzly bears occur at low densities and reproduce very slowly. Females do not become reproductive until the age of 4 or 5, and there can be many years between litters of usually two to three cubs. “If you make a management error, it can be very difficult for that population to rebound,” says Artelle. Artelle is involved in surveying a population of grizzly bears in the Great Bear rainforest region in Heiltsuk territory on BC’s northern Pacific coast. Sampling with noninvasive hair-snagging stations across 22,000 square kilometers of land accessible only by boat and helicopter “is an enormous undertaking,” he says. The expense and difficulty of counting bears mean that provincial government biologists estimate total bear numbers predominantly by modeling, using landscape characteristics such as vegetation, annual precipitation, human population, and topography. The challenge: It is almost impossible to quantify how certain those estimated numbers are. 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