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7.2: Overharvesting

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  • People have always hunted, collected, trapped, or otherwise harvested the food and other natural resources they need to survive. When human populations were small, at least relative to the abundance of their resources, and collection methods were relatively unsophisticated, people could sustainably harvest and hunt wildlife in their local environments. However, as human populations have increased, and roads have provided access to previously remote areas, our impact on the environment has escalated. At the same time, our methods of harvesting have become dramatically more efficient. Guns are now used instead of blowpipes, spears, or arrows, while networks of wire snares indiscriminately catch animals of all types, even young and pregnant females. Populations of species that mature and reproduce rapidly can often recover quickly after harvests and can thus be exploited sustainably; however, species that are slow-maturing and slow-reproducing cannot sustain current harvest levels. Consequently, many species are threatened due to overharvesting, the unsustainable collection of natural resources (Maxwell et al., 2016). Overharvesting may take on many forms, including hunting, fishing, logging, and gathering of plants and animals for medicine, captive collections, subsistence, commerce, or recreation purposes (Figure 7.8).

    Fig_7.8.jpg
    Figure 7.8 Overharvesting in Sub-Saharan Africa at scale: Over 60% of species that are threatened by overharvesting are also threatened (directly and indirectly) by logging. Nearly 30% of all species are threatened by fishing, and 10% by hunting and trapping. Source: IUCN, 2019, CC BY 4.0.

    The Bushmeat Crisis

    Bushmeat harvesting is one of Africa’s most prominent overharvesting concerns (see Box 4.1). Bushmeat—wild sources of protein obtained on land by hunting and collecting birds, mammals, snails, and caterpillars—provides much of the protein in people’s diets in large parts of Africa. For example, in Nigeria and Cameroon, 12,000 tonnes of bushmeat—two tonnes obtained from bay duiker (Cephalophus dorsalis, NT) alone—are sold at markets in the Cross-Sanaga rivers region each year (Fa et al., 2006). Similarly, more than 9,000 primates are killed annually for a single market in Côte d’Ivoire (Covey and McGraw, 2014); people from Central Africa harvest an astonishing 5.3 million tonnes of mammalian bushmeat annually (Fa et al., 2002). Usually seen as a conservation challenge in Africa’s tropical forests, the bushmeat crisis also impacts savannah regions (reviewed in Lindsey et al., 2013). For example, bushmeat hunters, numbering between 1.500 and 2,000, remove over 600,000 kg of herbivore biomass from Botswana’s Okavango Delta each year, despite the region’s protected status and importance for ecotourism sectors (Rogan et al., 2017).

    The massive wildlife declines caused by the bushmeat crisis are also threatening ecosystem services, food security and people’s livelihoods.

    Outside influences play a prominent role in the harvesting pressure associated with the bushmeat crisis. In Section 5.2, we discussed neocolonialism, where jobs associated with land-grabbing industries are frequently reserved for migrant labourers. Poorly paid and with limited rights, migrant labourers are often forced to turn to local natural resources to fulfil their basic needs (Thibault and Blaney, 2003). The impact of these migrant labourers on the local environment is massive compared to traditional (and many other local) peoples that prioritise sustainability. For example, immigrants working at logging concessions in the northern parts of the Republic of the Congo hunt 72% of all bushmeat harvested in the region (Poulsen et al., 2009). The increased commercialisation of bushmeat also poses challenges (Lindsey et al., 2013); for example, in the broader Congo Basin, commercial hunters are exploiting bushmeat at scales 27 times that of the area’s traditional peoples (Fa et al., 2016). In addition to hunting for local markets, illegal exports also play an important role. For example, more than 50 tonnes of wild fish and bushmeat enters France from Africa each week (Chaber et al., 2010); similar amounts were also estimated for airports in Switzerland (Wood et al., 2014).

    Very few animal populations can withstand such high extraction rates. Consequently, regions dependent on bushmeat have already seen substantially wildlife declines (Lindsey et al., 2013). West Africa, where forest mammal populations are down an estimated 80%, have been hot particularly hard (Benítez-López et al., 2019). These wildlife declines also lead to reduced harvests—some hunters have seen their harvests reduced by over 80%, with impacts to wildlife notable as far as 40 km from hunters’ access points along roads from their villages (Benítez-López et al., 2017). At current exploitation rates, supplies are expected to decrease by an additional 80% within the next 50 years (Fa et al., 2003). Unless more sustainable, alternative sources of protein are found, people dependent upon bushmeat will see increased malnutrition and compromised livelihoods as bushmeat species are pushed to extinction. When that happens, families relying on bushmeat will face even worse food insecurity than that which is driving the current bushmeat crisis.

    Exacerbating the risk of food insecurity, people in the affected regions will also suffer from compromised ecosystem services as populations of predators, seed dispersers, and pollinators are reduced (Rosin and Poulsen, 2016). For example, reduced mammal populations have been linked to reduced abundance of fruits and other useful plant products available for human consumption (Vanthomme et al., 2010). Some areas are already suffering from “empty forest syndrome”—a condition where a forest appears to be green and healthy, but is practically devoid of animals, and in which ecological processes have been irreversibly altered such that the forest’s species composition will change over subsequent decades (Nasi et al., 2011; Benítez-López et al., 2019). The bushmeat crisis is thus a major concern to people concerned about biodiversity and/or human well-being.

    Overfishing

    Pressure on biodiversity in aquatic environments is also increasing as people continue to harvest fish, sea turtles, dolphins, shellfish, and manatees for meat at increasing rates. Modernised fishing methods play a major role. For example, a motorised fishing fleet that faces few restrictions has caused a 75% decline in fish populations at Ethiopia’s Lake Tana in recent years (de Graaf et al., 2004). Also, in the marine environment, motorised fleets and enormous factory ships can now spend months at sea where they catch fish to sell at local and global markets (Ramos and Grémillet, 2013; Pauly et al., 2014). Some estimates suggest that wild-caught seafood could be virtually absent by 2050 if current exploitation levels persist (Worm et al., 2006).

    For many aquatic organisms, the indirect impacts of modern commercial fishing methods outweigh direct exploitation (Figure 7.9). One example is ghost fishing, which causes thousands of animals to die each year after becoming entangled in dumped, abandoned, and lost fishing gear. Similarly, approximately 25% of fish harvests are considered bycatch—animals that are accidentally caught, injured, or killed during fishing operations. Recent declines in skates, rays, turtles, sharks, dolphins, and seabirds have all been linked to incidental deaths as bycatch (Cox et al., 2007; Carruthers et al., 2009). Seabird biologists from South Africa have been at the forefront of solving bycatch problems in recent years (Box 7.1).

    Box 7.1 Solving Seabird Bycatch Problems: From Theory to Practice

    Ross Wanless

    DST-NRF Centre of Excellence at the FitzPatrick Institute of African Ornithology,

    University of Cape Town, South Africa.

    rosswanless@gmail.com

    The global problem of seabird bycatch in fisheries—the accidental death of seabirds during fishing—is one of the biggest threats to pelagic seabirds (Croxall et al., 2012). Ironically, it is both one of the easiest and one of the most challenging problems to solve. How so? Simple technical fixes to stop birds from getting snagged on fishing gear and drowning can work amazingly well, but fishermen must be convinced to use them.

    Techniques for preventing bycatch break down into two basic approaches. The first approach is to prevent access to the danger point (the baited hook or the cables that birds strike). Fishing only at night eliminates up to 80% of the problem, but still jeopardises nocturnal foragers and diurnal species during a full moon. Another option is bird-scaring lines (Figure 7.A) consisting of a mainline flown from the stern of a boat with hanging streamers that scare birds away from danger areas behind the vessel. The second approach, primarily used in longline fishing, is to remove the risky gear (baited hooks) as quickly as possible; essentially this involves adding weights to lines to sink them faster. It has reduced seabird bycatch on some fisheries by 90–95%.

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    Figure 7.A Bird-scaring lines (in orange) keep a variety of albatross, petrels, and gannets at a safe distance from the baited hooks deployed off a trawler off South Africa. Photograph by BirdLife South Africa Albatross Task Force Programme, CC BY 4.0.

    Despite clear harm to seabirds caused by fisheries and the simple, effective fixes at hand, implementing these mitigation measures has been patchy at best in most fisheries where seabird bycatch occurs. There are some exceptions, and it is useful to examine what elements led certain fisheries to fix the problem. A good case study is in South Africa, where BirdLife South Africa’s Albatross Task Force (ATF) demonstrated in 2006 that trawl fishing for hake (Merluccius spp.) was killing around 18,000 seabirds each year (Watkins et al., 2008). The fishery involved had Marine Stewardship Council (MSC) certification, which gives a fishery access to premium European markets on the condition that it meets environmentally friendly and sustainable metrics, including no significant bycatch impacts. This provided a powerful incentive for fleet-wide implementation of a bycatch mitigation measure; failure to do so would have resulted in a loss of certification, with catastrophic financial implications.

    Despite this strong incentive, it required another five years of work from the ATF to assess bird scaring lines and refine the design, overcome resistance to their use, and close loopholes in regulations. In 2014, the ATF published an assessment of the effectiveness of their bird scaring lines—a single measure to prevent the accidental and avoidable deaths of around 10,000 albatrosses and large numbers of other species. When used correctly, the system eliminated 90–95% of seabird bycatch (Maree et al., 2014). Why did it take so long for the fleet to adopt this measure, despite it costing almost nothing, requiring no skill or time to use, and posing no meaningful operational problems? And why have identical fishing industries in many other countries failed to follow suite?

    The answer is complex. ATF teams are present in South Africa (and now also in Namibia), providing sustained pressure and constant presence. South Africa had standing legislation, yet compliance from the South African fleet was initially minimal (and remains less than perfect today). MSC certification certainly created an enabling environment (Wanless and Maree, 2014) and incentive to drive change, yet it took more than that to change the entire fleet. Constant lobbying from BirdLife and regular dialogue from deck to boardroom were also critical ingredients. A legislative framework that provides some hope of censure against non-compliant vessels meant that there was internal pressure within the industry to “tow the line”—pun intended. Ultimately, widespread change became possible when there was a credible, independent observer program to verify deck practice and give teeth to agencies when addressing non-compliance.

    Fig_7.9b_Robertson-2.jpg
    Figure 7.9 (Top) Discarded fishing gear, such as this ghost net, poses an entanglement hazard to marine wildlife. Photograph by Tim Sheerman-Chase, https://www.flickr.com/photos/tim_uk/
2692835363, CC BY 2.0. (Bottom) A wandering albatross (Diomedea exulans, VU) that was a victim of bycatch, the accidental catching of non-target species during fishing operations. Photograph by Graham Robertson, CC BY 4.0.

    The impact of traditional medicine

    Africa has a long history of sustainable use of traditional medicines. Unfortunately, as the number of people living in Africa has increased, so has the demand for traditional medicine. Today, harvesting for traditional medicine is putting unsustainable pressure on species exploited for this purpose (Williams et al., 2014). One prominent example is vultures: the demand of vulture body parts, believed to bestow clairvoyant abilities, is driving massive vulture population declines across Africa (see Box 4.4). The growth in traditional medicine markets in East Asian countries such as China, Thailand, Cambodia, and Vietnam exacerbates these problems. For example, as tigers (Panthera tigris, EN) and rhinoceros have become scarce in Asia, Asian traditional healers are increasingly targeting African predators and rhinoceros to satisfy their market demands. Another group of species threatened by the Asian traditional medicine trade is sea horses (Hippocampus spp.). Due to population declines from overharvesting, sea horse exports from Kenya and Tanzania to East Asia have halved over recent years; yet, more than 600 kg of dried sea horses (over 254,000 individuals) continue to be exported annually (McPherson and Vincent, 2004). Exploitation for Asian traditional medicine markets has already pushed the western black rhinoceros (Diceros bicornis longipes, EX) to extinction. In a similarly perilous position is the northern white rhinoceros (Ceratotherium simum cottoni, CR); with only two non-reproductive females left in the world, this species is now considered committed to extinction (see Section 8.3; Box 11.4). A group of species sought after by both African and Asian traditional medicine markets is pangolins, thought to be the most heavily poached animals on Earth. For example, between 2012 and 2016, more than 20 tonnes of African pangolin scales (involving up to 30,000 animals) were seized during law enforcement operations across the region (Andersen, 2016). The problem is also getting worse: authorities intercepted 13 tonnes of scales in Singapore in 2019, all from a single shipment believed to travel from Nigeria to Vietnam (Geddie, 2019). With such a large active operational scale, it comes as no surprise that all four African pangolin species are now threatened with extinction (IUCN, 2019).

    The impact of live animal trade

    Millions of non-domesticated animals are sold as pets around the world each year (Table 7.1). Given that many of these pets were originally collected in the wild, it is no surprise that the most popular species tend to be at a high risk of extinction (Bush et al., 2014). These huge numbers are magnified by the extra millions of animals needed to compensate for deaths during collection and shipping. Collection of wild animals for pets and other purposes has a massive impact of biodiversity in Africa, the world’s largest pet trade exporter (Bush et al. 2014).

    Among the most popular groups of wildlife traded are Africa’s parrots (Figure 7.10). For example, 32,000 wild-sourced African grey parrots (Psittacus erithacus, EN) were imported into the European Union in 2005 (UNEP-WCMC, 2007). Combined with habitat loss, the wild bird trade has already caused extirpations of this species in some areas of West Africa (Annorbah et al., 2015). Similarly, 82 of the 291 species of African freshwater fish known to occur in the pet trade are considered threatened with extinction (UNEP-WCMC, 2008). While it is true that collecting wild animals for the pet trade sustains many people’s livelihoods, research on harvesting of ornamental fish in Cameroon has shown that this practice is not sustainable in the long term (Brummet et al., 2010). It is therefore critical to find ways to make these practices more sustainable, for the sake of the pet collectors and biodiversity.

    Table 7.1 Examples of groups targeted in global wildlife trade, and their levels of exploitation.

    Group

    Number traded each year

    Notes

    Orchids

    250 million

    Mainly cultivated, but about 10% sourced from the wild. Illegal trade—and mislabelling to avoid regulation—a major problem.

    Succulent plants

    35 million

    Mainly cultivated, but about 15% sourced from the wild. Illegal trade remains a major problem.

    Corals

    13 million

    Collected using destructive methods; used for aquarium decor and jewellery.

    Reptiles

    7.2 million

    Mainly sourced from the wild for zoos and pet trade, but increasingly from farms. Does not include large skin trade.

    Birds

    2.3 million

    Mostly perching birds destined for zoos and pet trade. Also includes legal and illegal trade of parrots.

    Ornamental fish

    2 million

    Most originate from wild reefs, caught by illegal methods that damage the surrounding coral reef and other wildlife.

    Primates

    148,000

    Used for biomedical research, while many also destined for pets, circuses, zoos, and private collections.

    Sources: http://cites-dashboards.unep-wcmc.org, data presented as live specimens exported from 2011–2015. Data generally do not include illegal traded specimens, which are usually not reported to CITES.

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    Figure 7.10 Wild-caught African grey parrots crammed into a travel crate before export to Asia. Researchers estimate that over 60% of smuggled parrots die from stress, dehydration, and smothering during transit (Mcgowan, 2008). Because of trade-driven population declines, CITES banned all international trade in this species in October 2016. Photograph by Lwiro Primates, CC BY 4.0.

    Overharvesting of plant products

    Overharvesting is not restricted to animals and animal products. While legal and illegal timber and firewood extraction is a major source of deforestation throughout Africa, it is also an important extinction driver. In fact, logging and other forms of wood harvesting have already contributed to the extinction of at least six plant species in Sub-Saharan Africa, with an additional 116 species considered Critically Endangered in part due to these threats (IUCN, 2019). Other plant species face extinction due to exploitation for medicines, spices, fragrances, and ornaments. For example, White’s ginger (Mondia whitei)—reputed to have aphrodisiac and antidepressant properties—has been harvested to extirpation in parts of central Kenya and South Africa (Aremu et al., 2011). Similarly, harvesting rates of African blackwood (Dalbergia melanoxylon, NT)—popular for making musical instruments and fine furniture—are currently unsustainable because the tree is slow-growing, has low germination rates, and extractions are seldom offset with planting of new seeds or seedlings (Amri et al., 2009).

    Challenges in managing overharvesting

    One of the biggest challenges in combatting overharvesting is the non-enforcement and/or outright absence of legal controls to protect exploited species. But even where strong regulatory frameworks exist, the sheer scale of the problem poses practical challenges for effective enforcement (discussed in Chapter 12), as billions of dollars flow among participants in illegal wildlife trade, which include local people trying to make a living, professional poachers, corrupt government officials, unethical dealers, and wealthy buyers who are not concerned about how the wildlife products they use were obtained. The illegal wildlife trade has hit Africa’s megafauna particularly hard. For example, even though there has been an international ban on the ivory trade since 1989, thousands of African elephants continue to be illegally killed on an annual basis (Box 7.2). Similarly, despite a ban on rhinoceros horn trade since 1977, an increasing number of rhinoceros succumb to poaching every year (Figure 7.11). Worse yet, the illegal wildlife trade shares many characteristics and practices with the illegal trade in drugs and weapons; in some cases, the same syndicates run these various criminal enterprises (Christy and Stirton, 2015). Apprehending these criminal networks is generally very dangerous, requiring vast resources.

    Box 7.2 Conserving Elephants in the Anthropocene

    David H.M. Cumming1,2

    1FitzPatrick Institute of African Ornithology, University of Cape Town,

    Cape Town, South Africa.

    2Tropical Resource Ecology Programme, University of Zimbabwe,

    Harare, Zimbabwe.

    cummingdhm@gmail.com

    As our increasingly human-dominated planet enters a new geological era, will there still be room for Earth’s largest land mammals? Or will there be, as happened to mammoths, sabre-toothed cats, and giant sloths during the Pleistocene (see Box 8.1), another hominid-induced extinction of large mammals? Our new human-dominated era has become known as the Anthropocene (Waters et al., 2015), and the animals are, of course, Africa’s elephants.

    Elephants encapsulate the dilemmas of conserving large charismatic mammals. They are dominant ecosystem engineers that, depending on their densities, can facilitate or adversely impact species diversity and ecosystem processes (Section 4.2.1). They are also economically important to ecotourism industries and revered by many; ivory ornaments and carvings have been valued highly by many cultures past and present. But elephants are also regarded as dangerous pests by expanding small-scale farming communities, responsible for destroying crops and killing people. While retaliatory killings and habitat loss (primarily through agricultural expansion) certainly contribute to the endangerment of elephants, poaching to supply Asian markets (see Figure 12.1) is the primary cause behind massive population reductions we are currently witnessing (Wittemyer et al., 2014).

    Africa’s elephants have, in the past, been greatly exploited, first for their meat and later also for their ivory. In 1887, about 1,000 tonnes of ivory were being exported from Africa (Spinage, 1973) and, by 1900, elephant populations in many African countries had all but collapsed. In Southern Africa, for example, it was feared that they might soon go extinct. However, with effective protection, elephant populations increased twentyfold, to more than 200,000, south of the Zambezi River by the 1970s. Elsewhere, elephant numbers also recovered, and, in the mid-1970s, the continental elephant population was estimated to be more than 1 million (Table 7.B). But a rapid escalation of the illegal killing of elephants for ivory and meat soon followed, accompanied by a steep rise in the price of ivory. In response, African elephants were placed on CITES Appendix II in 1976 to control the international trade in ivory. Elephants in some Southern African countries were well protected, so numbers continued to grow. However, elsewhere poaching and illegal trade in ivory continued and, in 1989, the African elephant was placed on CITES Appendix I, which banned all international trade in elephants and elephant products. The result was a decline in the price of ivory, and recovery of many populations.

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    Figure 7.B Estimated number of elephants in West, Central, East and Southern Africa between 1979 and 2016. Source: http://africanelephantdatabase.org, CC BY 4.0.

    Conservationists, and the world at large, traditionally regarded the African elephant as a single species. Recent morphometric and genetic evidence has revealed that forest and savannah elephants represent two distinct species, with forest elephants (Loxodonta cyclotis) occupying the West and Central African forests, and the larger savannah elephants (Loxodonta africana) being widespread in non-forested regions of Sub-Saharan Africa (Roca et al., 2015). The distinction has important implications for their conservation, as each of these elephant species now viewed on its own is even more sensitive to population declines (CBD, 2015).

    Since about 2006, poaching of elephants again began to escalate, in part a response to an increase in the price of ivory, poorly funded wildlife agencies, and corruption (Hauenstein et al., 2019). The scale of these killings is extraordinary. For example, an estimated 30,000 elephants were killed in 2013 alone. Forest elephants declined by about 60% (Maisel et al., 2013). While population trends for savannah elephants vary across the region, they too face increased poaching pressure (Chase et al., 2016). Due to these large-scale killings, combined with the impact of habitat loss from agricultural expansion, West Africa’s elephants are today confined to small isolated protected areas with a total population of about 17,000 (Maisel et al., 2013). Elephant population trends in East Africa vary: numbers are increasing in Uganda and Kenya, but Tanzania has lost some 60,000 elephants in the last few years. In Southern Africa, Botswana has the largest elephant population, estimated in 2014 to number at least 130,000. Neighbouring Zimbabwe has a population of 83,000 elephants, much the same number as it had in 2001. However, two of Zimbabwe’s four regional populations declined significantly between 2006 and 2014 with a loss of at least 20,000 elephants (Figure 7.C).

    Fig_7.C_Cumming-2.jpg
    Figure 7.C Savannah elephants at a waterhole in Hwange National Park. Hwange, Zimbabwe’s flagship protected area, has been a hotspot of poacher activity in recent years. By lacing waterholes and salt licks with cyanide during the dry season, poachers killed over 100 elephants here in 2013 (Cruise, 2017); several elephant poisoning events have occurred since then. Photograph by D.H.M. Cumming, CC BY 4.0.

    Global and national efforts to curb elephant poaching are currently focused on improving law enforcement on the ground, intercepting ivory shipments to Asia, closing ivory markets in Africa and Asia, and leading campaigns to reduce demand for ivory in major consuming countries in Asia, particularly in China. Importantly, while these initiatives are relieving poaching pressure on African elephant populations, they fail to address core issues relating to the interactions between people and elephants in the rural areas of Africa. A high proportion of elephant ranges lie outside protected areas where they overlap with people. Relieving continued pressures on elephants, outside as well as inside protected areas, would only happen if people who are harmed by elephants derive enough benefits from elephants and other wildlife to outweigh the direct and indirect costs of sharing land with them. Community-based natural resource management (CBNRM) projects, such as those in Namibia (Section 14.3) show that this can be achieved. Establishing secure and sustainable funding streams through payments for ecosystem services (Section 15.3), or payments for co-existing with large dangerous mammals such as elephants (Section 14.4), could extend these promising initiatives even further.

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    Figure 7.11 More than 7,200 rhinoceros were illegally killed in South Africa between 2007 and 2017. Fortunately, illegal killings have declined in recent years, thanks to massive anti-poaching campaigns and increased law enforcement efforts. Source: SADEA, CC BY 4.0.

    Now, consider a hypothetical conservationist concerned about the bushmeat crisis’ impact on biodiversity. This person may very well think that effective enforcement of a hunting ban would be the best solution to prevent further overharvesting. Unfortunately, solving complex challenges with simplistic steps runs a high risk of being counterproductive. For example, local bushmeat markets provide important contributions to food and financial security in many rural parts of Africa (van der Merwe et al., 2015). Replacing bushmeat with livestock and crops production—two primary drivers of habitat loss (Chapter 5)—also carries risks. For example, an estimated 250,000 km2 of forest will need to be converted to pastureland to replace the bushmeat trade just for the Congo Basin (Nasi et al., 2011). Clearly, there is a need for the bushmeat trade, albeit in a sustainable manner to ensure long-term viability of the local biodiversity, as well as the prosperity of the people who inhabit these areas. We delve deeper into solutions for these kinds of complex challenges from Chapter 9 onwards.

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