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Home , Ecology, Local extinction, Overexploitation, Population ecology, Wildlife conservation

8

John D. Reynolds and Carlos A. Peres

There’s enough on this planet for everyone’s needs, but not enough for everyone’s greed. Gandhi

Exploitation involves living off the or , such that wild , , and their products are taken for purposes ranging from to medicines, shelter, and fiber. The term harvesting is often used synonymously with exploitation, though harvesting is more appropriate for farming and , where we reap what we sow. In a that seems intent on liquidating natural , overexploitation has become the second most important threat to the survival of the world’s , mam- mals, and plants (see Figure 3.8). Many of these are threatened by subsistence in tropical , though others are also threatened in temperate and arc- tic regions by hunting, fishing, and other forms of exploitation. Exploitation is also the third most important driver of freshwater fish events, behind the ef- fects of loss and (Harrison and Stiassny 1999). Thus, while problems stemming from habitat loss and degradation quite rightly receive a great deal of attention in this book, conservationists must also contend with the specter of the “empty ” and the “empty .” We begin this chapter with a brief historical context of exploitation, which also pro- vides an overview of some of the diverse reasons people have for using wild popula- tions of plants and animals. This is followed by reviews of recent impacts of exploita- tion on both target and nontarget species in a variety of . To understand the responses of , we then review the theory behind . The chap- ter ends with a consideration of the culture clash that exists between people who are concerned with management and people who worry about extinction risk.

History of, and Motivations for, Exploitation Humans have exploited wild plants and animals since the earliest , and most contemporary aboriginal remain primarily extractive in their daily quest for food, medicines, fiber, and other biotic sources of raw materials to produce a wide 250 Chapter 8

range of utilitarian and ornamental artifacts. Modern once formed dense clusters along 3,000 km of the Brazil- hunter-gatherers in tropical , at varying ian Atlantic forest, and the species sustained the first stages of transition to , still exploit a large major trade cycle between the new Portuguese colony number of and populations. By definition, and European markets. It was exploited relentlessly from these species have been able to coexist with some back- 1500 to 1875, when it finally became economically extinct. ground level of human exploitation. However, the ar- Since the advent of synthetic dyes, the species has been chaeological and paleontological evidence suggests that used primarily for the manufacture of high-quality violin premodern peoples have been driving other species to bows, and Pau-Brasil specimens are currently largely con- extinction since long before the of recorded fined to herbaria, arboretums, and a few small protected history. Human colonization into previously unexploit- areas (Dean 1996). These examples suggest that even ed islands and has often coincided with a some of the most abundant populations can be driven to rapid wave of extinction pulses resulting from overex- extinction in the wild by exploitation. Exploitation of both ploitation by novel consumers. Mass extinction events of locally common and rare species thus needs to be ade- large-bodied in , parts of , North quately managed if populations are to remain demo- and , , and several archipela- graphically viable in the long term. gos have all been attributed to post-Pleistocene human People exploit wild plants and animals for a variety overkill (Martin 1984; McKinney 1997). These are rela- of reasons, which need to be understood if management tively well documented in the fossil and subfossil record, is to be effective. There may be more than food and but many more obscure target species extirpated by money involved. The recreational importance of hunting human exploitation will remain undetected. and fishing in developed countries is well known. For In more recent times, extinction events induced by ex- example, hunting creates more than 700,000 jobs in the ploitation have also been common as European settlers U.S. and a nationwide economic impact of about $61 bil- wielding superior technology expanded their territorial per year, supporting nearly 1% of the entire civilian frontiers and introduced market and sport hunting. The labor force in all sectors of the U.S. economy (LaBarbera death of the last Passenger Pigeon (Ecopistes migratorius) 2003). Over 20 million hunters in the U.S. spend nearly in the Cincinnati in 1914 provided a notorious ex- half a billion days afield in pursuit of , and fees ample of the impact that humans can have on habitats levied to game hunters finance a vast acreage of conser- and species. The Passenger Pigeon probably was the vation areas in (Warren 1997). most numerous in the world, with estimates of 1–5 The importance of exploitation as a recreational activ- billion individuals (Schorger 1995). Hunting for sport ity is not restricted to wealthy countries. For example, in and markets, combined with clearance of their nesting reef in Fiji, capture rates are highest with spears (Bucher 1992), had significant impacts on their or nets, and while these techniques are used when fish numbers by the mid-1800s, and the last known wild are in short supply, the rest of the people adopt a birds were shot in the Great of the U.S. at more leisurely pace with less efficient hand-lines, using the end of the century. After that, it was simply a ques- the extended time for social and recreational purposes tion of which of the birds in would survive the (Jennings and Polunin 1995). Cultural and religious prac- longest, and “Martha” in Cincinnati “won.” tices are often important. For example, feeding taboos The decimation of the vast bison in North Amer- switch on or off among hunters in tropical forests accord- ica followed a similar time-line, but here hunting for meat, ing to availability of alternative prey species (Ross 1978; skins, or merely recreation, was the sole cause. In the Hames and Vickers 1982). The fate of some endangered 1850s, tens of millions of these animals roamed the Great species is closely bound to religious practices, as in the Plains in herds exceeding those ever known for any other case of the babirusa wild pig, Babyrousa babyrousa, in Su- mega-, but by the century’s close, the bison was lawesi. This species is consumed heavily in the Christian- all but extinct (Dary 1974). Following an expensive popu- dominated eastern tip of , but rarely consumed lation recovery program, both the plains (Bison bison bison) over the Muslim-dominated remainder of the island and bison (Bison bison athabascae) are currently clas- (Clayton et al. 1997). sified by the 2003 IUCN Red List as Lower Risk/Conser- vation Dependent, although the wood bison is listed as endangered by the U.S. Act and Ap- Impacts of Exploitation on pendix II of CITES. Target Species An example that is lesser known is the extirpation of monodominant stands of Pau-Brasil (Caesalpinia echi- Many of the best-known impacts of exploitation on pop- nata) from eastern Brazil, a source of red dye and hard- ulations involve cases of direct targeting, whereby hunt- wood for carving that gave Brazil its name. Pau-Brasil ing, fishing, , and related activities are selective, Overexploitation 251

aimed at a particular species. In this section we present where once this is depleted. This is clearly shown in a examples from major ecosystems in both temperate and mahogany study in Bolivia where the smallest trees tropical areas. felled are about 40 cm in diameter, well below the legal minimum size (Gullison 1998). At this size, trees are in- Tropical terrestrial ecosystems creasing in volume at about 4% per year, whereas real TIMBER EXTRACTION Tropical is driven pri- mahogany price increases have averaged only 1%, so marily by frontier expansion of subsistence agriculture that a 40-cm mahogany increases in value at about and large-scale development programs involving im- 5% annually, slowing down as the tree becomes larger proved infrastructure and access. However, animal and (Figure 8.1). In contrast, real interest rates in Bolivia in plant declines are typically preceded by hunt- the mid-1990s averaged 17%, creating a strong econom- ing and logging activity well before the coup de grâce of ic incentive to liquidate all trees with any value regard- complete deforestation is delivered. Approximately 5.8 less of resource . The challenges and prospects million ha of tropical forests are logged each year (Food of sustainable in the Tropics are discussed in and Agriculture 1999; Achard et al. 2002). more detail in a case study by Pinard and colleagues in Tropical forests account for about 25% of the global in- Case Study 6.2 dustrial wood production, worth U.S.$400 billion or about 2% of the global gross domestic product (World SUBSISTENCE HUNTING Humans have been hunting Commission of Forests and in tropical forests for more than 100,000 years, but con- 1998). Much of this logging activity opens up new fron- sumption has greatly increased over the last few decades. tiers to wildlife and nontimber resource exploitation, and Exploitation of (the meat from wild animals) by catalyzes the transition into a dominated by tropical forest dwellers has increased due to larger numbers slash-and-burn and large-scale agriculture. of consumers, changes in hunting technology, scarcity of al- Few studies have examined the impacts of selective ternative sources of , and because it is often a pre- logging on commercially valuable timber species, and ferred food. Recent estimates of annual hunting rates are comparisons among studies are limited because they 25,850 tons of wild meat in Sarawak (Bennett 2002), often fail to employ comparable methods that are re- 73,890–181,161 tons in the Brazilian Amazon (Peres 2000a), ported adequately. The best case studies come from the and 1–3.7 million tons in Central (Fa et al. 2001). most valuable timber species that have already declined in much of their natural geographic distributions. For in- stance, the highly selective logging of broadleaf ma- 25 hogany (Swietenia macrophylla) is driven by the extraor- dinarily high value of this species on international Minimum harvestable 20 size with value markets. These conditions make it lucrative for loggers ) % to pay royalty payments as well as high transportation ( Bolivian real y t costs of reaching remote areas. Selective log- i 15 interest rates v

i fpo t

ging of mahogany and other prime timber species affects c Biological u

the forest by creating canopy gaps and causing severe d 10 o r

collateral damage due to construction of roads and skid P Financial trails, particularly in the case of mechanized operations. 5 One of the major obstacles to implementing a sustain- able forestry sector in tropical countries is the lack of fi- 0 nancial incentives for producers to limit offtakes to sus- 0 40 80 120 160 tainable levels and invest in (see Essay 8.1 DBH (cm) by Steve Ball for an example involving East African blackwood). Economic logic dictates that trees should be Figure 8.1 of Bolivian mahogany trees as a felled whenever their rate of timber volume increment of size expressed as tree diameter at breast height (DBH). Financial productivity is equivalent to size increments drops below the prevailing interest rate (Pearce 1990). combined with a 1% real increase in price. Trees equal to or Postponing exploitation beyond this point would incur smaller than 40 cm in DBH have no commercial value, but at an opportunity cost because profits from logging could this size they increase at 5% in value per year. To maximize be reinvested at a higher rate elsewhere (see Chapter 5 their profits, loggers should fell trees at a size when the finan- for a full discussion of economic discounting). This is cial productivity drops below the prevailing interest rate, which in Bolivia was 17% in 1989–1994. The discrepancy be- particularly the case where systems are un- tween the interest rates and tree growth rate provides a stable, and where there are no disincentives against min- strong incentive to overexploit. (Modified from Gullison ing the resource capital at one site and moving else- 1998.) 252 Chapter 8

ESSAY 8.1 East African Blackwood Exploitation Steve M. Ball, Mpingo Conservation Project n The Miombo woodlands, which vation and rural development activities cover a large swath of southern Africa, in Tanzania. In largely deforested areas are a highly species-diverse these can succeed by focusing on - and the mammalian requires fpo-hi res wood and -catchment issues, but large ranges. Thus, large contiguous this approach is unlikely to succeed in areas of land must be protected for con- southeastern Tanzania where forest servation of to be effective. cover currently exceeds 70%. However Even if the system were new laws allow for villages to take well maintained, fragmentation would ownership of local forest resources if have a significant impact on the they can produce a viable management integrity of the conserved areas. Com- plan for the forest. This includes tenure munity-based conservation could fill rights over even high-value timber the gap, providing buffer zones and trees, such as East African blackwood, corridors between reserves, but the which were previously government- need adequate incentive. reserved species. License fees for felling The East African blackwood (Dalbergia timber could significantly increase vil- melanoxylon) has the potential to do this. lage income, giving local people an The tree gets its name from its beauti- incentive to look after their natural ful dark heartwood, which is inky black resource assets. Once schemes are well in the best-quality timber. The wood is established, rural communities could used in the West to make woodwind use the promise of future income as col- instruments, especially clarinets and lateral against micro-finance loans to oboes, and locally it is a prime choice for increase the up-front benefits. wood carvers. It is the most valuable Figure A A mpingo, an African black- Simple economic analysis suggests timber growing in the Miombo wood- wood tree. (Photograph courtesy of Steve that sustainable, -based of southern Tanzania (Figure A). M. Ball.) management of East African blackwood Both the species and its habitat are offers a powerful argument to justify under threat from commercial exploita- conservation of the forest on public tion and inward migration of people as lands and to complement the protected a result of recent road improvements. ulations. Villagers generally know areas system, providing income in The blackwood’s high economic value, when illegal logging is taking place and buffer zones and corridors between its status as Tanzania’s national tree, and could apprehend suspects, but they reserves. However, it will be important its cultural significance both in the West have no incentive to do so because all to work with the suppliers of musical and in Tanzania make it an ideal flag- hardwood timbers remain the exclusive instrument manufacturers, and avoid a ship species to justify conservation of property of the government. Intentional significant increase to their costs. If the habitat (Ball 2004). are also thought to prevent regen- these challenges can be met, blackwood Current exploitation levels are prob- eration and facilitate heart-rot in adult could be used as an economic key to ably unsustainable, with at least 50% of trees. Plantations are not an option conserve—as managed areas—large trees being felled illegally without a because of their high costs, uncertain tracts of Miombo woodland. This license. Local forestry officials who return, and long rotation time (black- would not happen through a system of depend on logging companies for wood is estimated to take 70–100 years forest reserves, but rather with a more transport into the do not have suf- to reach timber size). inclusive strategy of sustainable ficient resources to enforce existing reg- Community-based forest manage- exploitation of the region’s natural ment is now a major theme of conser- resources. n

Hunting rates are already unsustainably high across large tainable hunting occurred initially in Asia, is now sweeping tracts of tropical forests, averaging six times the maximum through Africa, and is likely to move to even the remotest sustainable rate in Central Africa, for example (Figure 8.2). parts of the Neotropics. This pattern reflects human demo- Consumption by both rural and urban communities is graphics in different continents: There are 522 people per often at the end of supply chains that are hundreds of kilo- km2 of remaining forest in South and , 99 in meters long, and that extend into many previously inacces- Central-, and 46 in Latin America. sible areas (Milner-Gulland and Bennett 2003). The rapid Subsistence game hunting affects the of acceleration in tropical forest due to unsus- tropical forest assemblages, as revealed by vil- Overexploitation 253

11 of useful plants or plant parts used by different aborig- fpo ine groups throughout the Tropics. For example, the Waimiri-Atroari Indians of central Brazilian Amazonia 10 make use of 79% of the tree species occurring in a single ) ] 1-ha terra firme (upland) forest plot (Milliken et al. 1992), 1 – 9 and out of the ≥16,000 species of angiosperms in India, 6000 are used for Ayurvedic or other traditional medi-

r cine, and over 3000 are officially recognized by the gov- y

/ 8 g ernment for their medicinal uses. k [ d

e Exploitation of NTFPs often involves the systematic t c a r

t 7 removal of reproductive units from the population, but x e t

a the level of mortality in the exploited population de- e m

h pends on the method of extraction and whether vital s

u 6 b ( parts are removed. Traditional NTFP extractive practices, g o

L for either subsistence or commercial purposes, are often 5 considered to comprise a desirable, low-impact econom- ic activity in tropical forests compared to alternative forms of involving structural , such 4 45 67 8 91011as selective logging and shifting agriculture (Plotkin and Log (p roduction [kg/yr–1]) Famalore 1992). As such, the exploitation of NTFPs is usually assumed to be sustainable and is viewed as a Figure 8.2 Hunting rates are unsustainably high across large promising compromise between the requirements of bio- tracts of tropical forests as seen in the relationship between total extraction and total production of game meat through- diversity conservation and those of extractive communi- out the Congo and Amazon basin (solid and open symbols, ties under varying degrees of market integration. respectively) by mammalian taxa. The solid line indicates A recent study of Brazil nuts (Bertholletia excelsa) ques- where extraction equals production; the dashed line indicates tions the standard assumptions about sustainability of exploitation levels at 20% of production, considered to be NTFPs (Peres et al. 2003). Brazil nuts are the base of a sustainable for long-lived taxa. Taxon symbols are as follows: (squares), (triangles), (circles), major extractive industry supporting over half of the trib- rodents (inverse triangles), and other taxa (diamonds). (Modi- al and nontribal rural population in many parts of the fied from Fa et al. 2002.) Brazilian, Peruvian, and Bolivian Amazonia, either for their direct subsistence value or as a source of income. This wild seed crop is firmly established in domestic and lage-based kill profiles in Neotropical (Jerozolimski and export markets, has a history of over 150 years of com- Peres 2003) and African forests (Fa and Peres 2001). This mercial exploitation, and is one of the most valuable non- can be seen in the composition of residual game stocks at timber extractive industries in tropical forests anywhere. forest sites subjected to varying degrees of hunting pres- Brazil nuts have been widely held as a prime example of sure where overhunting often results in faunal a sustainably extracted NTFP, yet the persistent collection collapses, mainly through declines and local of B. excelsa seeds has severely undermined the patterns of large-bodied (Bodmer 1995; Peres 2000a). of seedling of Brazil nut trees. This has dras- tically affected the age structure of many natural popula- NONTIMBER FOREST PRODUCTS Nontimber forest products tions to the point where persistently overexploited stands (NTFP) are biological resources other than timber that will succumb to a process of senescence and demograph- are taken from either natural or managed forests (Peters ic collapse, threatening this cornerstone of the Amazon- Associates, Inc. 1994). Examples of exploited products (of whole plants ian extractive economy (Peres et al. 2003; Figure 8.3). G 3e or plant parts) include fruits, nuts, oil seeds, latexes, Nevertheless, the concept of sustainable NTFP extraction es of Conservation G .eps resins, gums, , spices, dyes, ornamental is now so deeply entrenched into national resource use 1 size plants, and raw materials and fiber such as Desmoncus policy that extractive reserves (or their functional ana- 0 climbing palms, bamboo, and . Forest wildlife and logues) have become one of the fastest growing cate- bushmeat can also be considered as a prime NTFP, but gories of protected areas in tropical forests (Fagan et al. for a number of reasons they will be treated as a distinct 2005). The implicit assumption is that traditional meth- category. ods of NTFP exploitation have little or no impact on for- The socio-economic importance of NTFP extraction to est ecosystems and tend to be sustainable because they indigenous peoples cannot be underestimated. Many have been practiced over many generations. However, ethnobotanical studies have catalogued the wide variety virtually any type of NTFP exploitation in tropical forests 254 Chapter 8

(A) noisseurs have been reluctant to replace the natural pau- 160 rosa fragrance by synthetic substitutes, and the last unex- ploited populations of pau-rosa remain threatened. The 120 same could be argued for a number of NTFPs for which the exploitation by destructive practices involves a lethal ) m

c 80 insult to whole reproductive individuals, such as the ex- ( H

B traction of fruits and palm-hearts in many arborescent D 40 palms. For example, in the Iquitos region of Peru, the fruits of Mauritia flexuosa palm trees, a long-lived forest emergent, are often collected only once by felling whole 0 reproductive adults (Vasquez and Gentry 1998). (B) Enthusiasm for NTFPs in community development 50 5 fpo and conservation partly results from unrealistic studies re- 40 porting their high economic value. For example, Peters et al. (1989) reported that the net present value of fruit and 30 s 10 latex extraction in the Rio Nanay of the Peruvian Amazon e l i n e

v was $6,330/ha, assuming a 5% discount rate and that 25% u j 20 f o 5 of the crop was not taken. This is in sharp contrast with a % 10 30-month study in Honduras that measured the local 3 value of , construction and craft materials, and med- 0 Unharvested Light Moderate Persistant icines extracted from the forest by 32 Indian Seed level (Godoy et al. 2000). The combined value of consumption and sale of forest goods ranged from U.S.$18 to Figure 8.3 Relationships between historical levels of Brazil U.S.$24 per hectare per year, at the lower end of previous nut collection and mean tree size, expressed in terms of DBH, estimates (between U.S.$49 and U.S.$1,089 per hectare per cm (A); and percentage of juvenile trees (B) in different popu- year). NTFP extraction thus cannot be seen as a solution lations. Numbers above bars indicate the number of popula- for rural development and in many studies the potential tions studied throughout the Brazilian, Bolivian, and Peruvian Amazon. (Modified from Peres et al. 2003.) value of NTFPs is exaggerated by the assumption of un- realistically high discount rates, unlimited market de- mands, availability of transportation facilities, and ab- will have an ecological impact. The exact extent and mag- sence of product substitution. nitude of this impact depends on the accessibility of the What, then, is the impact of NTFP extraction on the resource stock, the floristic composition of the forest, the dynamics of natural populations? How does the impact and intensity of extraction, and the particular vary with the history of plants and animals? Are cur- species or plant part under exploitation (Peres and rent extraction rates truly sustainable? These are all 2003). questions that could steer a future research agenda but Few studies have quantitatively assessed the demo- the demographic viability of NTFP populations will de- graphic viability of nontimber plant products. A boom in pend on the species’ ability to recruit new adults either the use of homeopathic remedies sustained by over-col- continuously or in sporadic pulses while being subject- lection of therapeutic and aromatic plants is threatening at ed to repeated exploitation. least 150 species of European wild plants and driving sociates, Inc. Temperate terrestrial ecosystems G many populations to extinction (TRAFFIC 1998). Com- f Conservationmercial Biology exploitation of the pau-rosa or rosewood tree FORESTRY According to one assessment, only 22% of the G ps (Aniba rosaeodora), which contains linalol, a key ingredient world’s original forest cover remains in large, relatively 1 ze 0 in fine perfumes, involves a destructive technique that al- natural ecosystems, or so-called “frontier forests” most invariably kills the tree. This species has conse- (Bryant et al. 1997). These remaining frontier forests are quently been extirpated from virtually its entire geo- predominantly classed as either boreal (48%) or tropical graphic range in Brazilian Amazonia (Mitja and Lescure (44%), with only a small fraction (3%) remaining in the 2000). Chanel Nº5® and other perfumes made with pau- temperate zone. However, much like tropical forests, rosa fragrance gained an enormous international market most of the frontier forests in mid to high latitude re- decades ago after being popularized by Hollywood stars gions are also increasingly threatened by logging and like Marilyn Monroe, but the number of processing plants agricultural clearing (World Resources Institute 1998). in Brazil fell from 103 in 1966 to fewer than 20 in 1986, due The overall impact of different sources of structural to the dwindling resource base. Yet French perfume con- disturbance generated by modern forestry in the temper- Overexploitation 255

ate and boreal zones may depend on the spatial scale and stages are present at any one time, the requirements of intensity of disturbance, the history of analogous forms nearly all species can be met somewhere (although see of natural disturbance, the groups of consid- examples in Chapter 7 on the negative effects of habitat ered, and whether forest ecosystems are left to recover fragmentation). Furthermore, clear-cutting may only be over sufficiently long intervals following a disturbance used when and where absolutely necessary. Other ex- event such as commercial thinning or . The ploitation methods include thinning and partial cutting, patterns of landscape-scale human disturbance in these each with different effects on wildlife habitat. Land- forests can be widely variable in intensity, duration, and scape-level decisions to maximize the biodiversity value periodicity, and are often mediated by economic incen- of the forest may include allocating different portions of tives to cut timber from high-biomass old-growth forests, the total area to successively longer rotations, ranging rather than natural regrowth or fast-growing tree planta- from 50 years for short-lived species up to 300 years for tions on a long rotation cycle. late-successional habitat. The expanding frontier of commercial forestry into hitherto remote, roadless wildlands often results in high HUNTING Large mammals, small game, and waterfowl levels of forest conversion and fragmentation of remain- are also major targets in temperate countries, where ing stands, with significant impacts to forest wildlife. A re- recreational hunting can be a popular sport across a view of 50 studies in Canadian boreal forests on the effects large section of the constituents. Annual culls of large of postlogging on wildlife conclud- ungulates have been rather successful in North America, ed that large impacts are universal when native forests are as shown by population , in both controlling pop- replaced by even-aged stands of rapidly-growing nonna- ulations and stocking the freezer of the average hunter. tive tree species (Thompson et al. 2003). Loss of special White-tailed deer (Odocoileus virginianus), the most com- , such as snags containing nest cavities and large mon and widespread of wild ungulates in the U.S., in- decaying woody debris, is particularly important in the creased from fewer than 500,000 around the turn of last decline of forest species depending on those structures century, to about 30 million today. Deer are among the (McComb and Lindenmeyer 1999). Unlogged boreal most heavily hunted species in the U.S., with some 5 coniferous forests within protected areas in Finland, million killed by over 10 million hunters every year, gen- where population trends of land birds have been excep- erating about 20 billion dollars in hunting-related rev- tionally well documented, are extremely important to the enue in 2001 (U.S. Fish and Wildlife Service 2002). In native old-growth avifauna, such as the Siberian Jay Texas alone, it is estimated that the white-tailed deer (Perisoreus infaustus) and the hole-nesting Three-toed population numbered more than 3.1 million in 1991 in (Picoides tridactylus), which have declined in spite of heavy hunting , and approximately areas under timber extraction (Virkkala et al. 1994). In- 474,000 animals were shot by hunters in that year. Resi- deed, logging is often considered to be the most important dent birds and small to mid sized mammals frequently threat to species in boreal forests (Hansen et al. 1991; Im- hunted or trapped for sport are often referred to as beau et al. 2001). Some 50% of the red-listed Fennoscandi- “small game.” These may include game birds such as an species are threatened because of forestry (Berg et al. quail, pheasant, partridge and grouse, rodents and lago- 1994). Forests actively managed for biodiversity could morphs such as squirrels, rabbits, and hares, and even support 100% of the species occurring in Washington carnivores such as coyotes and raccoons. The effects of state, whereas timber management on a 50-year rotation different hunting strategies upon populations of the at the landscape level could support a maximum of 87% most popular game bird in the U.S., the bobwhite quail, and a mode of 64% of the species potentially occurring in have been simulated showing that maximum yields can forests (Carey et al. 1996). be sustained from annual capture rates of about 55% In summary, many of the detrimental impacts of for- (Roseberry 1979). Hunting at such high rates, however, est management on biodiversity are associated with the little room for error in calculated bag quotas be- large-scale structural simplification of the ecosystem at cause it depresses the following populations by all forest levels, age-class truncation, and other conse- 53% below unexploited levels. quences of intensive intended to in- Ducks, geese, and swans are gregarious and often mi- crease the yield of the desired forest component. gratory species that also attract enormous attention from A reduction of this impact often involves modern game hunters. As such, the establishment of annual wa- principles of ecological forestry (Seymour and Hunter terfowl hunting regulations is a complex procedure 1999), which may include a partial removal of the stand, shared by various governmental levels and private or- often in a patch mosaic using relatively small clear-cut ganizations, involving thousands of wildlife sizes so that each stage of forest development is repre- and habitat managers under the jurisdiction of wildlife sented somewhere in the landscape. As long as most agencies. For example, retrieved duck and goose har- 256 Chapter 8

vests during 2001 were 19.4 million in the U.S. and will save wild stocks, as many of the fish that are reared, Canada, down by 6.6% on the total numbers bagged in such as and trout, are fed with meal derived from the previous year (Martin and Padding 2002). In the U.S. wild fish! Indeed, stocks of many wild fishes have con- alone, in 2001, this involved annual sales of 1.66 million tinued to decline. Recent surveys of 232 stocks showed a federal duck stamps to 1.59 million hunters who collec- median decline of 83% over the past 25 years (Hutchings tively spent nearly 15 million hunter-days in pursuit of 2000, 2001; Hutchings and Reynolds 2004). A stock of At- waterfowl. Needless to say, seasonal hunting license fees lantic cod (Gadus morhua) off eastern Canada, which once and leases of private hunting areas generate welcome seemed absolutely limitless, has undergone a decline of cash used for both population management and for pro- 99.9%, since the 1960s, leading to a designation of “en- tection of habitats against other forms of land use. dangered” under the Canadian Species at Risk Act (Com- The relatively orderly use of wildlife in North America mittee on the Status of Endangered Wildlife in Canada is not necessarily the rule for all temperate regions. Illegal 2003). This decision is not an isolated case; several other use and commercialization of wildlife continue to generate species of commercially exploited fishes have been listed a substantial clandestine traffic—even for species that are recently as threatened with extinction (Musick et al. 2000; fully protected on —in several mid- to high-latitude IUCN 2003). These developments show that some fish- countries ranging from Chile to Russia. The problem usu- eries concerns are moving from the traditional focus on ally lies not in the regulations, which are often already ex- sustainability into the realm of extinction risk (Reynolds tensive and strict, but rather in lack of law enforcement et al. 2002; Dulvy et al. 2003). that is often attributed to weak institutional capacity. Concerns about extinction risk in the sea are most acute for those targeted species that have combinations of traits Aquatic ecosystems that make them most susceptible to capture, and biologi- MARINE ECOSYSTEMS The impacts of marine fisheries on cally least productive (Reynolds et al. 2002; Dulvy et al. target species are well known. Roughly three-quarters of 2003). For example, the marine species that are most likely the world’s are considered to be fully fished or to be targeted are those that occupy shallow acces- overexploited (Food and Agriculture Organization 2002). sible to fishing gear, those that form dense shoals in pre- Since the 1990s global catches have leveled off for the first dictable places, or those that are most valuable. If a species time in , despite continuing advances in has one or more of these characteristics in combination capture technology (Figure 8.4). Exploitation of aquatic with long generation times, the results can be hazardous animals now seems to be following the pattern that oc- to the health of the population. The Chinese bahaba (Ba- curred in many terrestrial ecosystems long ago, with re- haba taipingensis) is a fish that meets many of these criteria liance on hunting of wild animals being supplemented (Sadovy and Cheung 2003). It is a huge species of croaker by the captive rearing of domestic stock, through aqua- (family Scienidae), which may exceed 2 m in length (Fig- culture (see Figure 8.4). No one should delude them- ure 8.5). It has traditionally been caught along its coastal selves into thinking that the move toward fish farming range from Shanghai to Hong Kong. This species has been

120 ) s

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l 9 9 1 i 80 9 8 1 6 9

m 8 3 1

( 9 8 1 0 9 s 60 8 1 7 9 n 4 7 1 9 o 7 1 9 1 T 40 7 1 8 9 6 1 Figure 8.4 Trends in global fisheries. 5 9 6 1 The gray portion of the bars indicate 2 9 20 6 1 capture fisheries and the black portion 9 9 5 1 6 9 of the bars indicate aquaculture. (From 5 1 3 9 Hart and Reynolds 2002, based on data 5 1 0 0 9 5 1 from FAO 2000; corrected for misre- 9 porting of capture fisheries of China by 1 Watson and Pauly 2001.) Year Overexploitation 257

great before the International Whaling Commis- sion’s moratorium on commercial whaling in 1986. The white abalone (Haliotus sorenseni) has been hit particu- larly hard. Ranging from California to Baja California, white abalone densities in some locations during the early 1970s were estimated at 1,000–5,000 per acre (Laf- ferty 2003). Commercial and recreational capture re- duced its numbers to less than one per acre by the 1990s. In May 2001 this species became the first marine mollusc to come under the U.S. Endangered Species Act, with an estimated population in the wild of only about 3,000 in- dividuals. Most remaining animals are restricted to deep waters beyond the reach of fishing (Lafferty et al. 2003). While the abalones’ value and accessibility provided the fpo-hi res motive and the means for overexploitation, it has also suffered from an additional problem: the . This is the whereby per capita fitness de- clines as a population becomes smaller (see Chapter 12). The ensuing can cause populations to become more vulnerable as they become increasingly rare, po- tentially spiraling to extinction. In the case of abalone, the Allee effect arises through the need for individuals to be within 1 m of each other for a male’s to reach a female. Biologists have had some success with artificial fertilization in captivity, with the intention of rearing abalones for release into the wild.

FRESHWATER ECOSYSTEMS Many freshwater taxa are sub- ject to exploitation for food and a variety of additional products. In 2000, the global estimate for all inland cap- Figure 8.5 Chinese bahaba (Bahaba taipingensis) caught as an ture fisheries was estimated at 8.8 million tons (FAO incidental by-catch by a trawler west of Hong Kong. (Photo courtesy of Cheng Tai-sing.)

popular for the medicinal properties of its . Its numbers have declined to 1% of its in the 1960s. During this time its price skyrocketed to the point where swim bladders in 2001 were worth seven times the price of gold (Sadovy and Cheung 2003). do not have enough information to say much about its popula- tion , but its large size invariably implies that it will take many years to reach maturity. This biological feature, combined with such strong economic incentives for people to catch it, have conspired to push the species to the edge of extinction. The same basic rules of for fish species apply to other taxa. For example, species of abalone along the Pacific of North America often occur in shallow waters, where they are readily accessible to divers (Figure 8.6). There has been serial depletion of these species, beginning with the most valuable and then moving on to less valuable ones (Tegner et al. 1996). Figure 8.6 White abalone (Haliotis sorenseni) underside. This is reminiscent of the pattern that occurred with the (Photograph courtesy of K. D. Lafferty.) fpo-lo res 258 Chapter 8

2002). This figure is considerably less than the estimate tics for buttons during the 1940s. How- for inland aquaculture (22.4 million tons). In many tem- ever, today several million kilograms of mussels are still perate countries, recreational fishing in fresh waters is a exported annually to Asia, where small beads are made major past-time, yielding an estimated 2 million tons of from their shells and inserted into other bivalves for the fish (Cowx 2002). In 1996 it was estimated that 35 million production of pearls. Unfortunately, mussels now face people in the U.S. spent 514 million angler-days fishing, much more critical threats from the “usual suspects” in spending U.S. $38 billion in the process (U.S. Fish and freshwater conservation: , damming, dredging, Wildlife Service 1997). Among 22 European countries, channelization, siltation, and with nonna- the number of anglers was estimated at 21.3 million tive bivalves such as the Asian clam (Corbicula fluminea) (Cowx 1998). and the zebra mussel (Dreissina polymorpha) (Strayer et The world’s salmon species illustrate the vulnerabili- al. 2004). These problems have led to 72% of the 297 ty of fish species that spend all or part of their life cycle in species that occur in the U.S. being considered endan- freshwater. Populations of four of the seven species of gered, threatened, or of special concern, including 21 eastern Pacific salmon and trout in the Oncorhyn- species that are extinct (Williams and Neves 2004). cus are currently listed under the U.S. Endangered Species Act. Over-fishing has contributed to severe de- clines in many populations, often in combination with Impacts of Exploitation on Nontarget habitat loss through construction of that block their Species and Ecosystems migrations, as well as degradation of spawning streams due to forest clearance and water abstraction (Lynch et al. Most hunting, fishing, and collecting activities affect not 2002). The plight of salmon species is particularly sober- only the species that are the primary targets, but also ing when one considers the enormous amount of atten- those that are taken accidentally or opportunistically. tion that has been paid to these populations by scientists Furthermore, exploitation may cause physical damage and conservationists, as well as their high economic and to the environment, and also may have ramifications for cultural significance. The most recent response of the U.S. other species through cascading interactions, phase government at the time of writing (May 2004) has been shifts in the structure of the ecosystem, and changes in the announcement of the intention to count hatchery-re- food webs. Here we discuss a few examples of how ex- leased fish as “wild” (Kaiser 2004). Thus, the hundreds of tractive activities targeted to one or a few species can millions of fish that are reared in captivity each year will drastically affect the structure and functioning of terres- elevate the population counts of many of the 27 popula- trial and aquatic ecosystems. tions of Pacific salmon and that are en- dangered. This can lead to their removal from protection Tropical terrestrial ecosystems under the Endangered Species Act and presumably, the LOGGING AND FOREST FLAMMABILITY Even logging target- discontinuation of many habitat restoration programs. ed to a single timber species can puncture the forest The decision ignores the fact that hatchery fish become canopy and increase the density of treefall gaps. This in- domesticated rapidly, showing genetic and phenotypic crease can trigger major ecological changes by increasing divergence from wild stocks (e.g., Fleming et al. 1994; light and creating a warmer and drier microclimate in the Heath et al. 2003). Furthermore, there is little evidence , which thereby affects the dynamics of plant that hatcheries enhance the viability of wild stocks regeneration, and increases forest susceptibility to fire (Myers et al. 2004). Yet the regional director of the Na- disturbance. In fact, even highly selective logging opera- tional Marine Fisheries Service, which has jurisdiction tions with modest levels of incidental damage to nontar- over salmon management, has declared that “Just as nat- get trees can generate enough structural disturbance to ural habitat provides a place for fish to spawn and to rear, greatly augment understory and dry fuel also hatcheries can do that...” Presumably, can also loads, thereby breaching the forest flammability thresh- be considered natural habitats. old (Holdsworth and Uhl 1999; Nepstad et al. 1999). Any Fish are not the only taxa exploited from fresh waters. source of ignition during subsequent severe can During the late 1800s and early 1900s millions of fresh- initiate extensive ground fires that will dramatically re- water mussels (family Unionidae and Margaritiferae) duce the functional and biodiversity value of previously were collected from freshwaters of Canada and the U.S., unburned tropical forests (Barlow and Peres 2004). Sur- primarily to make buttons from their shells (Williams et face that are at least partly induced by logging al. 1993; Helfrich et al. 2003; Williams and Neves 2004). disturbance currently threaten millions of hectares of This exploitation was rarely sustainable, due to the slow Amazonian, Mesoamerican, and Southeast Asian forests generation times of these species. Mussels were saved (Cochrane 2001; Siegert et al. 2001). Despite these unde- from major impacts of exploitation by the switch to plas- sirable direct and indirect effects, large-scale mechanized Overexploitation 259

logging operations continue unchecked in many - reduction of effective animal dispersal services can be ally dry tropical forest regions. properly understood for different plant species.

HUNTING AND LOSS OF SERVICES Successful Temperate ecosystems seedling recruitment in many flowering plants depends Higher order interactions resulting from selective ex- on seed dispersal services provided by large-bodied fru- tinction or severe population declines of large mammals givores (Howe 1984). In tropical forests, the proportion that play an important role as landscapers at the ecosys- of plant species with an endozoochorous dispersal tem scale have been documented in the temperate zone. mode (bearing seeds dispersed by an animal’s digestive (Castor canadensis) and their Eurasian congener tract) is often more than 90% (Peres and Roosmalen (Castor fiber) are prime examples of ecosystem engineers, 2002). Undispersed seeds simply fall to the ground un- which can be defined as organisms that have the poten- derneath the parent’s canopy and have a low survival tial to dramatically alter the structure and function of probability (Augspurger 1984; Chapman and Chapman ecosystems at large spatial scales. Large created 1996). For example, 99.96% of Virola surinamensis seeds by the labor-intensive stream-damming activity of that drop under the parent are killed within 12 weeks colonies create large-scale semi-permanent (Howe et al. 1985). Many studies have shown lower disturbance that drastically changes the structure and seed mortality rates caused by fungal attack or verte- of (Naiman et al. 1986; Wright brate and invertebrate seed predators are lower at et al. 2002). Beavers were once locally abundant in many greater distances from parents. However, there have parts of North America and Eurasia but their popula- been only a few studies that have examined the effects tions plummeted due to the pelt trade and habitat con- of removing seed dispersers are lower on the demogra- version in the nineteenth and early twentieth century, phy of gut-dispersed plants. Wright et al. (2000) ex- radically changing ecosystems. No one knows plored how hunting alters seed dispersal, seed preda- the precise extent of these changes but it is clear that tion, and seedling recruitment for two palms (Attalea beaver damming activity has profound effects on the butyraceae and Astrocaryum standleyanum) in Panama. of wetland systems (Naiman et al. They found that where hunters had not reduced mam- 1994), the dynamics of shifting successional mosaics of mal numbers, most seeds were dispersed away from the aquatic patches (Johnston and Naiman 1990), and ulti- parent palms, but were subsequently eaten by rodents. mately the of other wetland Where hunters had reduced mammal abundance, few species including waterfowl (McCall et al. 1996). Beavers seeds were dispersed, but these tended to escape rodent are now making a gradual comeback in many parts of . Thus, seedling density increased by 3–5-fold North America (although they were exterminated by at heavily hunted sites compared to unhunted sites. In 1700 and are yet to be reintroduced in many parts of Eu- contrast, Asquith et al. (1999) demonstrated that recruit- rope including Britain) but they often continue to be per- ment of Hymenaea courbaril required scatterhoarding of ceived as a nuisance requiring controversial measures of their large seeds by agoutis (Dasyprocta sp.), and re- population control. cruitment rates of many plant species that produce very In temperate terrestrial ecosystems, large mammals large seeds cached by rodents is likely to be very low in that once had profound large-scale effects on the struc- heavily hunted areas. ture of plant communities but have been hunted to near Studies examining seedling recruitment under differ- extinction in historic times include bison, , and ent levels of hunting pressure (or abundance of large-bod- . Joel Berger and colleagues (2001) demonstrated ied seed dispersers) reveal very different outcomes. At the a cascade of ecological events that were triggered by the community level, seedling density in overhunted forests of grizzly bears (Ursus arctos) and wolves can be indistinguishable, greater, or less than that in the (Canis lupus) from the Yellowstone ecosystem. These in- undisturbed forests (Dirzo and Miranda 1991; Chapman clude large increases in the population of a riparian-de- and Onderdonk 1998; Wright et al. 2000), but the conse- pendent herbivore, the moose (Alces alces), the subse- quences of increased hunting pressure to plant regenera- quent alteration of riparian vegetation structure and tion is likely to depend on the target species. In persist- density by herbivory, and the coincident re- ently hunted Amazonian forests, where large primates are duction of Neotropical migrant birds in the affected wil- either driven to local extinction or severely reduced in low communities, including riparian specialists such as numbers, the probability of effective dispersal of large- Gray Catbirds (Dumetella carolinensis) and MacGillivray’s seeded plants ingested primarily by these frugivores can Warblers (Oporornis tolmiei). decline by more than 60% compared to nonhunted forests Where large predators (wolves, bears) have been re- (Peres and Roosmalen 2002). However, more conclusive moved through predator control programs, or other evidence is required before the importance of the loss or forms of direct persecution, ungulate populations can 260 Chapter 8

greatly increase in size, with subsequent impacts on generation times and low rates of productivity. Recent re- plant communities. White-tailed deer in the U.S. and assessments by the IUCN (2003) have led to six species of in Europe were once controlled by wolves and albatross recently being “upgraded” toward more se- , and despite annual , their numbers are verely threatened status, with fisheries by-catch playing larger than they were when controlled by native preda- a significant role in each case. These problems are not tors. The result is that their larger populations may over- confined to the Southern . For example, it has been browse forests, which can cause extensive damage in estimated that 10,000 Black-footed Albatrosses (Phoebas- some places (e.g., Väre et al. 1996 and Horsley et al. tria nigripes) may be killed each year in the central North 2003). Particularly in areas where hunting is prohibited, Pacific (Lewison and Crowder 2003). Measures adopted deer populations can become so large that most tree and to reduce mortality on seabirds include bird-scaring de- herb seedlings are consumed, which may lead to a vices, the release of baited lines from below the water change in patterns of forest succession (e.g., Horsley et surface (where albatrosses cannot reach them), use of al. 2003 and Pedersen and Wallis 2004), or to decline of heavy lines that sink immediately, and use of fish oil on rare species (e.g., Gregg 2004). Plant populations can be the surface, which dissuades seabirds from landing on slow to recover from episodes of excessive herbivory. the water. For example, a population of the rare orchid showy lady Sea are caught incidentally by longlines and slipper (Cypripedium reginae) in West Virginia lost up to trawlers. For example, it has been estimated that 20,000 95% of all stems during a 3-year period of excessive deer turtles have been killed each year in the Mediterranean browsing, from which the population took 11–12 years in longlines set for swordfish. excluder devices are to recover (Gregg 2004). Beyond effects on plants, un- now in widespread use in trawl fisheries, and these re- controlled herbivore populations can have indirect ef- duce turtle mortality by providing an exit flap that tur- fects on (Wardle and Bardgett 2004) and tles can push through, while retaining the fish. Turtles spider communities (Miyashita et al. 2004). are not the only taken as by-catch. It has been es- timated that 120,000 sea snakes are taken annually by Aquatic ecosystems prawn trawlers in the Gulf of Carpentaria, . MARINE ECOSYSTEMS Marine fisheries are estimated to There are mounting concerns about the impacts of by- have a global by-catch of roughly 27 million tons annu- catches on populations of many fish species as well. The ally, which is between one-third and one-fourth of the best-known cases involve , skates, and rays (see total marine landings (Alverson et al. 1994). This is prob- Case Study 8.1 by Julia Baum). These fishes are toward ably a conservative estimate. Most of these by-catches the seabird–turtle end of the life-history continuum. For were from trawl fisheries, followed by drift nets and gill example, the European common skate (Raja batis) does nets. Shrimp trawls, with their small mesh sizes, account not reach maturity until it is 11 years old. They used to for roughly one-third of the total by-catch, with ratios of be taken by the thousands as by-catch in prawn trawls in weight of discarded animals per weight of shrimp the Irish Sea (Brander 1981), but only six individuals caught typically about 5:1. It has been estimated that were captured by extensive government bottom fish sur- shrimp trawlers in the Australian northern prawn fish- veys between 1989 and 1997 (Dulvy et al. 2000). In this ery typically discard 70,000 individual organisms during same region, there is evidence for complete local extinc- each night of fishing. tion of one and possibly two more species. Some by-catches are threatening species with extinc- tion. All but two of the world’s 21 species of albatross are FRESHWATER ECOSYSTEMS In fisheries, it is easy to find considered threatened with extinction, and most of these freshwater equivalents of the kinds of difficulties that have been severely affected by longline fisheries in the face many marine fish species. An example of nontarget (IUCN 2003). Albatrosses, as well as fishes is the Mekong giant catfish (Pangasianodon gigas) other seabirds such as petrels, drown when they take (Figure 8.7), a species that is in a similar situation to the baited hooks as the lines are being set in fisheries aimed Chinese bahaba discussed earlier. This fish is restricted to at species such as the Patagonian toothfish (Dissostichus the Mekong River Basin in Thailand (where no individu- eleginoides). While the rate of accidental capture per hook als have been caught since 2001), Laos, and Cambodia. is very low, the potential risks are enormous when scaled Studies by Zeb Hogan and colleagues (2004) have shown up by the total fishing effort, with individual vessels that individuals can reach 3 m in length and weigh 300 often setting many thousands of hooks each day, and a kg, and are therefore extremely valuable to fishers. Fur- total of over 250 million hooks being set each year since thermore, they are migratory, thereby running a gauntlet the 1990s south of 30o South (Tuck et al. 2003). Long-lived of nets set for other species. Finally, their only spawning species such as seabirds have extremely low resilience grounds, in whirlpools and rapids in the Chiang Khong- against elevated adult mortality, due to their very long Chiang Saen region of the Thai–Laos border, are being Overexploitation 261

salmon carcasses. For example, carcass enrichment of ar- tificial streams has led to an eight-fold increase in densi- ties of macroinvertebrates, which also increased twenty- five-fold in artificially enhanced natural streams (Wipfli et al. 1998). These effects have been shown to have im- portant feedback to productivity of the streams for salmonids themselves, because juvenile salmon prey on many of these insects (Wipfli et al. 2003). Studies have also shown higher growth of riparian trees such as white spruce, (Helfield and Naiman 2002). Indeed, fpo-hi res there has been preliminary success in matching records of the sizes of salmon runs in southeastern Alaska from 1924 to 1994 with tree-ring growth in Pacific coastal - forests (Drake et al. 2002). All of these examples imply that stream ecosystems, as well as associated terrestrial components, will have been affected strongly by the many extinctions and depletions of salmon populations that have occurred in recent decades.

Biological Theory of Sustainable Exploitation The examples in the preceding sections give a flavor of the great diversity of forms of exploitation and impacts on species and ecosystems. Some of these forms of ex- ploitation, such as fisheries, hunting, and forestry in tem- Figure 8.7 Mekong giant catfish, Pangasianodon gigas, from perate countries, have been occurring under scientifical- the Mekong River. (Photograph courtesy of Zeb Hogan.) ly informed management. Because this is a chapter on “overexploitation,” most of the examples that we have chosen have not been very encouraging. In fact, species dynamited as part of a plan to enhance river navigation. and ecosystems show a wide variety of responses to ex- Conservation biologists have set up a scheme whereby ploitation. In this section we review the theory that has fishers telephone them day or night if they catch a been advanced to explain how populations and ecosys- Mekong giant catfish, which the biologists then purchase tems respond to exploitation, and tie this to manage- at market price, tag, and release away from the nets. This ment options. is a stop-gap measure, being used to save a small number Biological populations are by definition renewable, of fish while working on longer-term conservation meas- but why should we ever expect plant and animal popu- ures. The prospects for this species do not look good, and lations to be able to withstand the elevated mortality that its threat status has now been raised to “critically endan- occurs with most forms of exploitation? The key is the gered” by the IUCN (2003). ability of birth or death rates to compensate when we re- Overexploitation can also have unforeseen effects on move individuals from the population. As populations biodiversity through trophic interactions among species are reduced by exploitation, there may be reduced com- in an ecosystem. A freshwater example that is currently petition for food, territories, shelter, and a lower trans- receiving a great deal of attention involves the effects of mission rate of diseases. This can lead to greater birth reduced numbers of Pacific salmon on productivity of rates or enhanced survival. The tendency for such com- streams and their riparian vegetation in northwestern ponents of fitness to limit populations at high density is North America (e.g., Cederholm et al. 1999). All native known as (Figure 8.8). This does not Pacific salmon species die after they spawn, and their mean that populations do not experience episodes of decomposing bodies provide a large proportion of the density-independent growth, as would occur after sud- received by streams in their range. These nu- den environmental changes, for example. But the ten- trients have been acquired when the fish were growing dency of populations to fluctuate around some sort of during the marine phase of their life cycle. Experimental mean value, rather than growing indefinitely, can be at- studies have shown a variety of effects of nutrients from tributed to density dependence. 262 Chapter 8

Reproduction (A) n

o N i max t c u d o r p e

r r r o ) y fpo t N i ( l r a e t b r m o u m n f n

Mortality o o i t e a l t u a p r o a P t i p a c r e 0 P Time Equilibrium (B) Figure 8.8 Density dependence stems from relationships be- fpo tween population density and per capita rates of birth and death. The difference between these at a small is the intrinsic rate of natural increase, r, and the density at YMSY which these rates are balanced is the equilibrium population size. ) Y ( d l e i y e To understand sustainable and unsustainable levels l b Maximum a n i

of exploitation, we need to ask whether removal of indi- a t s u viduals is equivalent to “thinning” the population, there- S 0 by allowing the survivors to grow more quickly or sur- Nmax vive better, or is the removal occurring too rapidly for Population number (N) populations to compensate. Figure 8.9 (A) Logistic of a population The simplest way to ask about the ability of a popula- up to a maximum population size, Nmax. (B) Sustainable tion to compensate for elevated mortality is to start with yield, Y (surplus production) against population size for the the logistic model, which gives the number of individu- logistic case shown in (A). The maximum sustainable yield als at time t as: (YMSY) occurs at 50% of the maximum population size.

Nmax Nt =  N  − [8.1] 11+− max e rt  N0  food. The population grows slowly at first, because there are few individuals producing offspring, but growth ac-

Here Nmax is the maximum population size (Figure 8.9A). celerates up to a point where the animals start running This is often called the “,”Sinauer orAssociates, equilibri- Inc. out of food, whereupon growth stops. In the real world, c. um population size. None of these Gtermsroom 3eis meant to populations will be buffeted by changing environmental imply that populations remain stable,Principles but they of Conservation convey Biologyconditions, interactions with their predators, and so on. Gro0809.eps on Biology the idea of some sort of average size over a given period These can cause population fluctuations, cycles, or crash- G 100% of size of time. N0 is the initial number of individuals.01.17.05 The pa- es. But the logistic is still a reasonable “default” option, rameter r is the intrinsic rate of natural increase, that is, conveying the essence of the potential for density-de- the difference between per capita birth and death rates at pendence. Specific details of the biology of species will small population sizes where there is no density depend- determine whether the initial upward slope and final de- ence. For many species we may want to substitute bio- due to density dependence are steeper, shallower, mass for number of individuals, as in the case of fisheries, or occur sooner or later than shown here. in which case we often see the terms B substituted for N. The growth rate of this population before exploitation Figure 8.9A shows the classical population growth can be considered its surplus production, g(N), and is rate that matches the logistic equation. This is the sort of given as:  N  trajectory that we would expect, for example, if we put a gN()=− rN1  [8.2] few Daphnia into a tank of water with as  Nmax  Overexploitation 263

This indicates, sensibly, that as the number of individu- High quota als, N, approaches the maximum population size, Nmax, there is no growth, and even more sensibly, that growth MSY quota stops when the population size is zero. YMSY

If the population in Figure 8.9A is being exploited at a ) Y steady rate, then its rate of change per unit time, dN/dt ( Low quota d l e

will be the difference between its surplus production i and the yield, Y, for a given level of exploitation: Y fpo dN  N  = rN 1−  − Y dt  Nmax  [8.3]

0 N1 NMSY N2 Nmax The population’s surplus production is the yield that can Population number (N) be removed sustainably. We can plot this property against different population sizes (Figure 8.9B). This Figure 8.10 Equilibria and population stability under con- stant quota exploitation. The arrows indicate the directions of gives us the classic dome-shaped yield curve that under- change in population size for each quota. pins all models of exploitation. This shows that the max- imum sustainable yield (YMSY) occurs at an intermediate population size, which coincides with the inflection point in the logistic curve shown in Figure 8.9A. This makes in- quota because the numbers removed are “constant” in the tuitive sense: We can take the most from a population sense of being independent of the population size. Exam- when it is at the size where it can grow most quickly. The ples include fisheries that set quotas on numbers of fish dome does not have to be symmetric; a failure of the lo- that are caught, regardless of subsequent changes in the gistic assumption can cause it to lean to the left or to the number of fish in the sea, or hunters who are given fixed right. For example, density-dependent processes such as limits that do not vary as the number of target animals , competition, predation, or disease may goes up or down over time. This may sound extreme, be- occur at smaller or larger population sizes than depicted cause common sense suggests that quotas should be ad- in Figure 8.9A (Sutherland and Gill 2001). If the curve justed according to such changes in the . And it is leans to the right, we should allow the population to re- extreme. And so was the collapse of Peruvian anchovy in main at higher numbers. the 1970s, which occurred in part because people did not fully appreciate the implications of this assumption (see Stability of exploitation the discussion later in this chapter). In theory, we have discovered how many individuals we The constant quota situation is depicted in Figure can take from the population to maximize the yield. But 8.10, where each of three potential quotas runs horizon- in practice, we will have a very difficult time taking ex- tally across the graph, implying no relationship with actly that number. For one thing, people rarely do what population size. First, consider the high-quota line. Here, they are told, and common experience suggestsSinauer Associates, that we Inc. the yield exceeds the population’s surplus production have to assume that the population will Gprobablyroom 3e be ex- capability, perhaps because of illegal hunting activity, or Principles of ploited at a higher rate than we recommend.Gro0810.eps Even the because the population’s resilience had been over esti- best-controlled fisheries and hunts are subject100% of tosize the va- mated. The arrow beneath this line shows that with con- garies of in the population estimates,01.18.05 or un- stant exploitation at this rate, the population will become foreseen circumstances such as conditions caus- extinct. Year after year the quota exceeds the popula- ing populations to behave in unpredictable ways. The tion’s ability to keep up with the elevated mortality. An question is, what happens when (not if) the population alternative that seems more sensible is the MSY quota. is exploited at a rate that differs from the one that theory However, this is a very risky target because it is impossi- suggests should be maximally sustainable? The answer ble to get precise measurements of either the surplus depends on how the exploitation rate is managed. production curve, or N. Furthermore, as we have ar- gued, even if this were possible, there is still a good Constant quota exploitation chance that we will be unable to set quotas sufficiently Our formulation implies a system of exploitation in which accurately to score a bulls eye when we shoot for the

the number of individuals removed is independent of the MSY point. If the population is at or smaller than NMSY, population size. That is, in Equation 8.3 we have subtract- the quota will exceed its surplus production and it will

ed Y from the surplus yield, rather than making Y pro- decline to zero. On the other hand, the NMSY point will portional to N. This case is typically known as constant be stable if the population is initially higher, because al- 264 Chapter 8 though the MSY quota is initially higher than surplus Very high exploitation fpo production, as the population declines it will benefit from reduced density dependence. Still, given the diffi- High exploitation MSY exploitation culty of estimating MSY with precision, such a quota is dangerous. Finally, consider the low quota example. If )

the population is initially below N it will still crash. Y

1 ( Low exploitation

However, if it is between N and N , then its production d

1 2 l e will exceed the quota, and it will grow to N2. If it is ini- i Y tially higher than N2, it will be driven down to N2 by the quota exceeding its surplus production. So N1 is an un- stable equilibrium and exploitation in that region should be avoided. In contrast, as long as we are sure the popu- lation is well above N , exploiting it with the low quota 1 0 N1 N N2 Nmax indicated would allow it to grow to a stable equilibrium MSY Population number (N) at N2. Here, finally, we have sustainable exploitation. Proportional (constant effort) exploitation Figure 8.11 Equilibria and population stability under pro- portional exploitation (also called “constant effort exploita- A much more sensible way to set exploitation targets is tion”). Here, a constant fraction of the population is removed. to tie them directly to the size of the population. In prac- The dashed lines have slopes E corresponding to different tice, this is always bound to happen to some extent, be- rates of exploitation. The arrows indicate the directions of change in population size for each scenario. cause as plants and animals become scarce, people tend to switch to alternative species or other activities, even if no one is forcing them to do so. For example, local de- ploitation rate is below the intrinsic rate of natural in- mand for game species in tropical forests tends to in- crease, r, then all equilibria are stable. For example, crease sharply when catches in the marine fishing sector whereas the high quota crashed the population under fair poorly (Brashares et al. unpublished data), and trop- the constant quota scenario in Figure 8.10, here we find ical forest hunters become heavily reliant on smaller- that if the population is initially below this removal rate, bodied game species once large-bodied species are de- it will increase to N1, and if it is above this point, it will pleted (Jerozolimski and Peres 2003). Conservationists decrease to N1. The MSY is also stable, and it still occurs and resource managers amplify this kind of common at half of the maximum population size. sense by encouraging or forcing people to reduce pres- Figure 8.12 compares the risk of extinction from ex- sures on populations that reach low abundance. So, un- ploitation based on either constant quotas or proportion- like the case of constant quota above, we have exploita- al rates for a study of the American marten (Martes amer- tion effort that is proportional to the population size. icana) in southern Ontario, Canada (Fryxell et al. 2001). In this scenario the size of the yield, Y, will be equal to The marten is a member of the weasel family (Mustel- the exploitation rate, E, multiplied by the population idae) found primarily in coniferous forests where it preys size, N: on a wide variety of small vertebrates as well as some in- vertebrates. Marten are trapped for their fur and trappers Y = EN Sinauer Associates,[8.4] Inc. Groom 3e are granted licenses for exclusive access to trapping From Equations 8.2 and 8.3 we Principlesknow that of Conservation a steady Biologygrounds. Fryxell et al. (2001) use a simulation model of Gro0811.eps state will occur between the yield and100% the of size surplus pro- data from commercial trapping from 1972 to 1991 to eval- duction when g(N) = Y. This means01.18.05 that g(N) = EN. uate effects of different types of harvest. This analysis Therefore, showed that whereas exploitation in proportion to the population size has a negligible chance of causing local  N  rN 1−  = EN [8.5] extinction, this risk becomes quite high for moderate lev-  Nmax  els of exploitation under a constant quota system that does not track the population. We can rearrange this equation to find the equilibrium population size for any rate of exploitation, as long as E Threshold exploitation is below r: The final class of exploitation strategies involves the use E NN=−max 1 [8.6] of population size thresholds to determine not only the ()r rate of exploitation but also whether exploitation should These equilibria are shown in Figure 8.11. The advantage take place at all (Lande et al. 1997, 2001). All populations of this form of management is that as long as the ex- are subject to random () variations, for exam- Overexploitation 265

1.0 ple are doing to the environment and to each other.

k Imagine you have sole access to the trout in a lake on s i your property. You will probably manage these trout r

g Constant quota quite carefully, because if you take too many, you will be n i

t 0.4 the one who suffers in future. But if the straddles

s fpo e the boundary with your neighbor, then each of you v r should only take half the number you would take if you a h

r had exclusive access. Will you both be so prudent? Un- e

v 0.2 less you get along very well with each other, probably

O not, because each person’s self-restraint can be exploited Proportional quota by the other one. Imagine the outcome if we scale this example up to the North Sea, bordered by many coun- 0.0 tries, each with thousands of fishers, all competing for 200 250 300 350 400 450 the same fish. The sea is a “common” fishing ground, Mean number of martens taken and indeed, the massive over-fishing of the past century Figure 8.12 Probability of overexploitation (local extinction) has been tragic for both fishers and their prey. in relation to mean yield of marten in commercial trapping in We can incorporate the tragedy of the into southern Ontario, Canada. The proportional quota line the scheme developed in the previous sections by assum- (black) refers to yields that track annual changes in the popu- ing that the benefits from exploitation are directly propor- lation whereas the constant quota line (gray) is based on the tional to the yield. So the dome in Figure 8.13 represents same absolute number of individuals being trapped each year regardless of population size. the benefits. Assume that the costs of exploitation are pro- portional to the effort necessary to obtain that yield. For example, in a the more days spent at sea, the ple, due to environmental variation. In the absence of ex- greater the costs of fuel and labor. This is depicted by the ploitation, they will sometimes exceed their carrying ca- straight line rising from the origin. If we ignore the costs,

pacities temporarily. We can take advantage of this by the maximum benefits will be found at EMSY, or the effort taking the entire “surplus” whenever the population is that provides the maximum sustainable yield. However, above its carrying capacity, but otherwise ceasing ex- if the goal is to maximize profits, this would lead to a ploitation completely. This would maximize the cumu- lower exploitation rate corresponding to the effort at lative yield while minimizing the chances of collapse. A which the difference between benefits and costs is maxi-

more precautionary variant on this is to remove only a mized, at EP. But the most important fundamental truth of proportion of the surplus. This is an even safer version of the proportional exploitation method outlined above because it maintains the population near its carrying ca- pacity. However, while such low rates of exploitation are fpo excellent for conservation, it is difficult to convince peo- s ple to accept such severe restrictions. t s Y o MSY Yield c

d YP Bioeconomics n Costs a ) s

t Y i C Understanding biological constraints is necessary to f e n

achieving a sustainable level of exploitation. But as we e b ssociates, Inc. ( saw earlier in the chapter, we also need to understand the d l e

G i of Conservation Biologyhunters’ incentives and disincentives if we are to under- Y G ps stand their impacts on the hunted, and provide manage- 1 ze ment advice to mitigate such impacts. Bioeconomic mod- 0 EP EMSY EC els incorporate the costs and benefits of exploitation. Even Exploitation effort in societies where exploitation is a necessity rather than a source of revenue, as in subsistence hunting, a cost–bene- Figure 8.13 The economics of exploitation, represented by fit framework can be very useful for understanding peo- costs that are proportional to effort, and benefits proportional ples’ behavior (see Essay 8.2 for an example). to yields. At EP the profits are maximized, at EMSY the maxi- mum sustainable yield is obtained, and at EC the costs are Open access and the equal to the benefits. Note that unlike Figures 8.10 and 8.11, the x-axis here represents fishing effort (which increases from The “tragedy of the commons” (Hardin 1968) provides left to right, corresponding to population number decreasing a powerful explanation for a lot of the damage that peo- from left to right). 266 Chapter 8

ESSAY 8.2 Using Economic Analysis to Bolster Conservation Efforts Marine Aquaria and Reefs

Gareth-Edwards Jones, University of Wales, Bangor n Advances in technology combined (I) with increased interest in marine sys- Indonesia tems have contributed to a large Sulawesi increase in American households keeping marine aquaria. As part of the large global business associated with establishing and maintaining these aquaria, approximately 350 million fish are harvested annually from the wild and sold worldwide with a value of $963 million (Young 1997). This continued wild harvest is necessary as some species of aquar- ium fish do not breed well in captiv- ity. Some of the more popular aquar- ium species are associated with coral Sulawesi Luwuk reefs, and 85% of aquarium fishes are caught from coral reefs around the Philippines and Indonesia. Catching these fishes can be an important Peleng source of income for some communi- ties, but it is increasingly happening on a large scale and there are 4000 Banggai aquarium fish collectors in the Philippines alone. A network of traders are involved in the marketing of the fish; the fish- 10 km ermen themselves may sell to local Bankulu traders who then sell to exporters and so on. There are significant Figure A (I) Map of the Banggai (II) financial gains at each step in the Archipelago of Indonesia, showing 10 marketing chain. For example, an study sites as black circles. The Bang- orange and white striped clownfish gai cardinalfish is pictured in the costs 10 cents when bought from a lower left corner. (II) Correlation be-

tween Banggai cardinalfish density s

Filipino collector, but sells for $25 or n i h

and the intensity of fishing at eight c 8 more in an American pet store (Simp- r u

separate sites in the Banggai Archipel- a e son 2001). Thus, traders in developed s

ago near Sulawesi, Indonesia. Because 2 countries typically make the largest the cardinalfish is associated with sea gains, while collectors or even the urchins, their density is expressed per m

2 / first traders make pennies. Because y m of sea urchins on the sea bed. In- t 6 i s n

the returns to collectors are so low, tensity of fishing was estimated from e there is room for conservation alter- interviews with local people. Banggai D natives to be attractive; it does not cardinalfish are caught by nets only, take as much return to exceed the so reductions in density are solely re- earnings of the people supplying the lated to fishing pressure, not to reef 4 destruction (Modified from Kolm and 1 2 3 fish. Berglund 2003.) Fishing intensity The impacts of collecting these fishes from the wild are quite varied. When using traditional netting tech- niques for catching the fish the most While traditional forms of harvesting hide. The cyanide triggers asphyxiation direct impact is a reduction in the can reduce species densities, an issue of or muscle spasm in fish, stuns them, population density of the harvested greater concern is the use of cyanide to and makes them easier to catch. These species, as shown for the Banggai catch the fish. Fishermen typically crush methods have been used since the 1950s cardinalfish (Pterapoggon kauderni) cyanide tablets in a squeeze and are believed to have quite a large in Sulawesi, Indonesia (Kolm and bottle and squirt the resulting liquid impact on fishes and the coral reefs Berglund 2003) (Figure A). into the crevices where the reef fish themselves. have tested

Sinauer Associates, Inc. Groom 3e Principles of Conservation Biology Gro0802ACaseStudy.eps 100% of size 0 Overexploitation 267 the response of 10 species of coral to would be permitted entry. While some work several issues have to be followed concentrations of hydrogen cyanide legislative backing of this nature could in parallel: lower than those typically used by fish- be beneficial, in practice it will be very ers. Eight of the coral species died hard to police. • There needs to be accurate identifi- immediately, and the other two died Alternatively, it may be possible to cation of non-cyanide caught fishes within three months. Death occurred achieve more sustainable harvest by near the point of capture. This can because the cyanide disrupted the rela- apportioning property rights to differ- be done through testing samples of tionship between the coral and its sym- ent sets of actors. Currently most fishes in export warehouses for biotic zooxanthellae. Doses as low of 50 marine fisheries are open access, and cyanide exposure. mg/L cause death of the zooxanthellae, because of this are susceptible to the so- • Fisherman need to be informed and one spray (approximately 20 cc) can called “tragedy of the commons.” In 2 about the certification scheme and kill the over an area of 5 m theory the solution to this is to allocate trained to use alternative collecting within 3–6 months. These impacts are of property rights to different groups of techniques, such as hand nets. concern as Southeast Asia has 30% of people. In the presence of property the world’s coral reefs, and these have rights, the fishermen should seek to • Fishes caught without cyanide been declining in quality due to a vari- manage their resource with a long-term should be labeled so that fish buyers ety of factors, of which perspective, as opposed to the extreme can choose to support practices that is but one. Now only 4.7% of Philippine short-term perspective that open access preserve reefs. and 6.7% of Indonesian reefs are in per- encourages (Ostrom and Schlager • Consumers should be educated fect condition and quite naturally these 1996). The allocation of property rights about the asso- are the reefs targeted by collectors. The to fishermen is on-going around the ciated with the use of cyanide for cyanide also affects fishes themselves. world; for example, the Chilean gov- catching fish. Half the poisoned fish die on the reef, ernment is offering the rights to harvest and 40% of those caught alive die before a benthic gastropod Concholepas conc- Many such certification schemes are reaching an aquarium (Simpson 2001). holepa, known locally as “loco” (Castilla currently under development around Estimates of the economics of this and Fernandez 1998). This involves the globe, particularly for food and for- practice suggest that the profitability of allocating certain areas of seabed to est products, and are easily linked to cyanide fishing to the fishermen is defined groups of local people from other management schemes such as the about $33,000 per km2 over 25 years local communities who then manage allocation of property rights. In most (10% discount rate). The direct losses to them collectively. situations certified products will cost fisheries total $40,000 per km2 and the While the theory of property rights more than non-certified products. This tourism losses can range between is simple, recent work on the Chilean is almost inevitable if, as in the case of $3,000 and $436,000 per km2 depending experience shows that the allocation of aquarium fishes, the damaging fishing on location (Cesar 1997). The nonuse property rights is not a panacea and techniques are used because they are costs of losing the are likely can lead to considerable social tension easier and cheaper than less-damaging to be larger than these direct values. between different groups in a commu- techniques. But if consumers can be nity. One important issue in all such educated about the certification Solutions? efforts relates to policing the agree- scheme, then the hope is that they This is an interesting situation where ments, as it is difficult for hard-pressed would chose to buy the more expen- poor local people are seeking to harvest officials to spot breaches of agreements sive, certified products rather than the a local resource to sell it to richer West- at sea. In the absence of official polic- cheaper alternatives. In this way the erners, but a side effect of this harvest ing, disagreements between groups combination of an efficient market is the loss of another valuable resource. about who can harvest where can economy and an educated The marketed resource is nonessential become difficult, if not violent. These can bring real benefits to the environ- to Westerners, (i.e., we could all live sorts of issues highlight the need for ment. One of the most positive exam- without a marine aquarium if we had strong, functional institutions to help ples of this comes from Home Depot® to), but we like the aquariums, and coordinate and manage any network of stores in the U.S., patronized by mil- many conservationists may argue that common property resources. While the of people each year. Home Depot® through keeping aquaria, people’s need for such institutions is clear from has begun selling and promoting certi- interests in could theory and practice, their development fied forest products, thus vastly increas- be heightened. So what should we do? can be a long and complex process ing their availability and visibility, and The solution seems to be to permit a requiring considerable effort from all due to their enormous market share, sustainable harvest of fishes caught in a involved (Ostrom 1990). reducing the costs. nondestructive manner. Attempts to A third approach to dealing with Unfortunately, research done to date achieve this can be legislative; for these issues is being tested by the on food products suggests that ulti- example the application of international Marine Aquarium Council. They aim to mately price determines consumers’ law like CITES (Convention on the set up a certification scheme whereby purchasing patterns. Generally only International Trade in Endangered Wild fish caught in traditional nets would be wealthier and more educated con- Fauna and ) to the relevant fish labeled in some way, which would sumers are prepared to pay more for species could stop all trade in these enable consumers to buy these fish in certified products. Thus if economic species. Alternatively, tighter import preference to cyanide-caught individu- means are to be used to help conserva- controls could be implemented in the als. If all consumers preferentially pur- tion, there is a need to increase the gen- destination countries (e.g., in North chased certified fishes, then the advan- eral level of education and awareness America and Europe) whereby only tage of using cyanide would disappear. in —a continuing challenge to all fish harvested to approved standards To get such a certification scheme to conservation biologists. n 268 Chapter 8 exploitation revealed by this diagram is that in open ac- Comparison of Methods for Calculating cess operations, we can expect people to join the exploita- Sustainable Yields tion until their individual costs become equal to their profits, at EC. Exploitation will proceed to this risky break- There are many ways of putting the theory of sustain- even point because people are competing with each other. able exploitation into practice, depending on what peo- The lesson from this analysis is that open-access ex- ple need to know, and how much time and money they ploitation leads to much greater rates of exploitation can spend getting the information. For example, the In- than are most profitable or safest for the long-term sur- ternational Whaling Commission uses some of the most vival of the population. This is tragic both for the re- sophisticated population models in the world to calcu- source and for consumers, because each individual is late the impacts of hunting on populations. Their catching less than they could if they had fewer competi- models need to be robust, in order to stand up to the tors. Governments often respond by providing perverse tremendous exerted by those who are “for” or subsidies (Myers 1998; Myers and Kent 2001), leading to “against” whaling. Yet, to be used effectively, these mod- lower apparent costs, and hence encouraging further els often demand a lot of information about the biology overexploitation (Repetto and Gillis 1988). The capital in- of whales that is not yet available. vested in many activities such as commercial fisheries Methods for calculating sustainable yields have been and logging operations cannot easily be converted to reviewed by Hilborn and Walters (1992), Milner-Gulland other uses, making it difficult for people to leave the and Mace (1998), Quinn and Deriso (1999), Jennings et business when times are hard. Naturally, this leads to re- al. (2001), among others. Here we give only the bare sistance against restrictions on exploitation rates. In fact, minimum needed to understand the logic of each exploitation can have a one-way ratchet effect, with gov- method and the pros and cons of using them. ernments providing aid to encourage overexploitation when populations are already low, as well as supporting Surplus production investment in the activity when times are good, to in- Surplus production models are also called surplus yield crease profits. The consequent over-capitalization leads models or simply “production” models. They are most to a one-way trip toward overexploitation. often used in fisheries. The simplest ones require very lit- tle data, thanks to an ingenious derivation by Schaefer Discounting (1954) who pointed out that if you know how yields Even when people have exclusive rights to exploit a re- have responded to different levels of exploitation effort source, they may still be tempted to exploit it heavily over time, then you could estimate the dome-shaped now, rather than conserve it for the future. This is be- yield curve shown in Figure 8.9B. Effort might be meas- cause we place a higher value on current than on future ured as number of fishing boats out each day of the year, worth. This is due to economic discounting (see Chapter but in non-fisheries contexts it could also be the number 5). Discounting can have serious implications for efforts of days spent hunting by all hunters in a given area per to restrain overexploitation of renewable resources season. The corresponding yields might be the thou- (Clark 1976). For example, suppose you could either let sands of tons of bluefin tuna (Thunnus maccoyii) caught a forest grow for 100 years, when the larger trees will by the fishery each year (or number of mallards, Anas fetch twice their current value, or chop it down now. platyrhincos, shot per year in an area). Which should you do? From a purely economic per- While this is a helpful simplification, it has several spective the most sensible thing might be to cut it now pitfalls that have led to extremely dangerous outcomes and invest the money because the interest may accumu- when this method was first applied. First, it treats each late faster than the growth rate of the standing timber. year as an independent replicate, which it will not be, This carries a rather sobering message for conserva- due to lags in the ability of the population to respond to tionists: Even with small discounting rates that are well different levels of mortality. For example, cod in the within reasonable bounds for economics, it may be eco- North Sea take about four years to reach maturity. There- nomically rational to exploit populations to extinction fore, no how much you reduce density depend- rather than leaving them to provide future returns. This ence by reducing the number of adults in any given year, may be especially true for slow-growing species such as it will take four years for the survivors to produce off- whales and hardwood trees, which take a long time to spring that become old enough to be caught. So if you accumulate value. This does not imply that conserva- double the fishing effort from one year to the next, you tionists should roll over in the face of economics, but may catch twice as many fish. But obviously this cannot merely that they will need to consider more than the eco- be due to the survivors producing twice as many young, nomic investment value of renewable resources to for- because in that second year, those young fish will only mulate cogent argues for conservation. As many of the be one year old, and not big enough to be caught. What chapters of this book make clear, this is not difficult. is really happening is that more fish are caught with a Overexploitation 269

doubling of effort simply because you are scooping more often available, natural mortality can be difficult to esti- adults out of the population. You are not learning much mate because scientists are usually late on the scene, with about the ability of populations to respond to lower den- exploitation well underway by the time they start collect- sities, you are simply cutting more deeply into your orig- ing data. This makes it difficult to disentangle natural inal stock of fish. The population is decidedly not in from human-induced mortality. Yield-per-recruit models equilibrium with the fishery. This dangerous assumption are the standard approach used in many temperate fish- was the downfall of the original production models eries, but developing countries in the Tropics rarely have (Hilborn and Walters 1992). The biggest collapse in the the resources to collect the growth and recruitment data history of fisheries happened to the Peruvian anchovy needed to use this technique as a management tool. (Engraulis ringens) in the early 1970s when the fishery was operating at a level that a surplus production model Full demography suggested to be safe (Boerema and Gulland 1973). For some species there has been sufficient economic A number of much more sophisticated surplus pro- value or conservation concern to lead to the production duction models have been developed since the rise and of full-blown population models. These models combine fall in popularity of the original Schaefer version (Po- information on vital rates such as births, juvenile sur- lacheck et al. 1993; Schnute and Richards 2001). While vival, age at maturity, and adult survival. These param- these require more information than the elegantly simple eters are often analyzed with models in which early version, they can get around the dangerous equilib- populations are divided into discrete classes based on rium assumption. In fact, in fisheries they have been their age or stage in the life cycle (reviewed by Caswell shown to sometimes outperform more complex models. 2001, and Lande et al. 2003). The most comprehensive models incorporate stochastic variation in parameters, Yield per recruit and quantify uncertainty in the outputs. Yield-per-recruit models were developed originally as Assessment of population growth rates is a common part of the “dynamic pool” concept in the landmark fish- practice to deduce whether populations are declining as eries book written by Beverton and Holt (1957). The dy- a result of direct exploitation, or exploitation of their namic pool refers to models that keep track of separate habitats. For example, Lande (1988) used a model to processes that add to a population, such as recruitment make a preliminary determination of whether the and growth, or that subtract from it, such as natural mor- Northern Spotted (Strix occidentalis caurina) was in tality and fishing mortality. The basic principle can be decline in the northwestern United States. This species applied to many other forms of exploitation. was suffering from overexploitation of old-growth Imagine a species that becomes more valuable as it forests, prompting potential listing under the U.S. En- ages, due to increasing size. Older fish provide more dangered Species Act. A significant meat and older trees provide more wood. If exploitation would be indicated by a population growth rate, λ, that is weak, most of the fish or trees will be big when they is significantly less than 1.0. Lande’s model was based are taken, which is good. But if we wait too long, natural on estimates of clutch size, fledgling survival probabili- mortality will have taken its toll and there won’t be as ty, the probability of successful dispersal, and survival of many individuals available to us. Yield-per-recruit mod- subadults and adults. The estimated population growth els search for the level of mortality that maximizes the rate was 0.961. However, this estimate had a high degree yield under this tradeoff between numbers and value. of uncertainty, due to uncertainty in the underlying pa- Here, a “recruit” is defined as an individual that has be- rameter estimates. When these were scaled come big enough to be captured, not in the demograph- up through the model, the estimate of λ had a confi- ic sense of an individual that has reached maturity. Once dence interval of ±0.0562. Therefore, λ could not be dis- the level of mortality has been found that maximizes the tinguished statistically from a value of 1. Further field re- yield per recruit, we can calculate the total yield that will search ensued, yielding better parameter estimates, and be obtained from a given level of mortality, if we know worse news for the , with significant population de- how many recruits are coming each year. That is how clines detected in 10 of 11 sites (Forsman et al. 1996). fishing quotas are set in many countries today (Jennings Other uses of demographic analyses are to diagnose et al. 2001). Yield in this context is measured in biomass the reasons for population declines, and also to suggest (number of fish caught in each age cohort multiplied by the likelihood of success of various management proce- that cohort’s mean weight). dures (Caswell 2001). For example, many populations of This method requires information about how the value sea turtles suffer from egg collecting, hunting of adults, (often size) of individuals increases with age, as well as an and of juveniles and adults in fisheries. Should estimate of natural mortality rates, because natural mor- conservationists concentrate on protecting eggs, juveniles tality determines the rate at which individuals die before or adults? Crouse et al. (1987) examined the effects on we have a chance to get them. While growth data are population growth rates of enhancing survival of each of 270 Chapter 8

these and other life stages in loggerhead turtles (Caretta state. Probabilities of surviving and growing from one stage caretta). They found that protection of eggs was far less to the next, as well as annual reproductive output, were cal- important to population demography than protection of culated from field studies, which showed strong density de- older life stages. This and subsequent research (e.g., pendence in these parameters. For example, seedlings (the Crowder et al. 1994, Heppell et al. 1996) contributed first stage in the model), compete with each other for light strongly to changes in conservation tactics, most notably and resources, and are also shaded out by high densities of through the adoption of mandatory turtle excluder de- adults (Silva Matos et al. 1999). Analyses showed that when vices in trawlers in the United States. Spatial analyses the correct amount of density dependence in survival and also can improve understanding of what management growth from one stage to the next were incorporated, pop- interventions may be most effective. For example, analy- ulations were predicted to be able to sustain considerably ses of the coincidence of turtle sightings and shrimp higher levels of exploitation before they become eradicated. trawling activities allows specific recommendations for area closures that can reduce bycatch mortality by avoid- Adjustments based on recent results ing larger concentrations of sea turtles in areas of lower If we can monitor either the population itself, or the num- economic importance (McDaniel et al. 2000). Finally, con- bers of individuals that are taken as a result of various tinued monitoring coupled with population modeling al- management measures, then we can adjust the quotas lows evaluation of how well management efforts are each year to take account of new information. For exam- doing, and suggestions for improvements (e.g., increased ple, in North America hunting licenses for waterfowl and compliance; Lewison et al. 2003) (Figure 8.14). mammals are allocated each year according to the health The simplest structured population models often ignore of the populations. So, if goose populations increase from density dependence. That is, the probability of surviving one year to the next, the hunting season may be extend- long enough to move from one age class (or stage) in the life ed. Box 8.1 provides an example of this method applied cycle and eventually reproducing, is kept constant as the to the setting of quotas for trapping marten in Canada. population changes in size. As we argued earlier, this as- sumption may be defendable in some situations, but be- Demographic rules of thumb cause the concept of sustainability is founded on density-de- Parameter-hungry models are useless for the vast major- pendent compensation, some people would argue that it ity of the world’s exploited species, because we usually makes little sense to ignore density dependence in exploita- lack even the most fundamental information about the tion models. A study of the edible palm, Euterpe edulis, biology of the and the activities of the people showed the value of incorporating density dependence ex- who exploit them (Johannes 1998). The cruel irony is that plicitly (Freckleton et al. 2003). This edible palm is found in it is often the species that we know least about that are in the Brazilian Atlantic forests. Edible “palm hearts” corre- most trouble from intentional or accidental exploitation. spond to the apical meristem of this species. Extraction of Most of the tropical vertebrates that are hunted for their the apical meristem kills the plant. Freckleton et al. (2003) meat fall into this category, as do most whales, sea turtles, modeled a population of edible palms divided into seven sharks, and rays. Various demographic rules of thumb stages according to size of the plant and itss reproductive have been developed that seek to overcome this problem. g n i d n

a 6

r 0 t 250 5 0 0 s 2 4 0 0 b 3 2 y 0 0 2 e 200 2 0 Figure 8.14 Projected annual strand- l 0 2 1 0 ings for Kemp’s ridley sea turtles d 0 fpo 2 i 0 0 0 based on three potential levels of r 2 150 9 0 9

s 2 compliance by shrimpers in using tur- 8 9 ’ tle excluder devices in their nets. 7 9 1

p 9 9 Black squares = compliance at 2000 100 6 9 1 9 1 m 5 9 levels, gray squares = 50% improved 9

e 1 4 9 compliance over 2000 levels, and 9 3 1 open squares = full compliance. Fluc- K 50 9 9 1 2 9 tuations in strandings reflects varia- 9 1 1 9 tion in compliance and sea turtle 9 1 0 0 9 abundance in areas where shrimp 9 1 9 fisheries are most active. (Modified 1 from Lewison et al. 2003.) Year Overexploitation 271

BOX 8.1 Adjustments of Quotas for the Marten (Martes americana) According to Previous Results John Reynolds, University of East Anglia

ommercial trapping of martens in each year, the population growth rate, lation growth rates can lead to effec- Ontario is regulated by trap-line and the population size. This example tive conservation management, even Cquotas, which are issued by the shows that good cooperation com- in the absence of detailed information. Ontario Ministry of Natural Resources. bined with an ability to predict popu- Fryxell et al. (2001) analyzed data from a district in the southern part of the province where trappers were com- pelled to report how many animals Abundance they caught each year. Trappers had Quota also been asked to submit carcasses Harvest voluntarily so that biologists could s 1250 n

e fpo determine the age structure of the ani- t r mals. Over the period of 1972–1991, a m

53% of the trapped animals were f 1000 o r

brought in for age determination. The e numbers and ages of animals caught b Figure A m Data from commer- were the only information available to u 500 cial trapping of marten, Martes local managers, who used this infor- N americana, in a district in south- mation to adjust quotas upward or ern Ontario, Canada. Estimated 250 downward each year. population sizes (open circles) How successful were the local man- 1970 1975 1980 1985 1990 were mirrored by quotas (gray Year circles) and number of martens agers in guessing the right quotas r e harvested (black circles). according to recent trapping results? b

To answer that question, Fryxell et al. m u

(2001) used an age-structured model n 30 to calculate population sizes and opti- a t mal quotas over the time period. They o 501 u

found that the marten population had q varied three-fold over the 20 years, n i fpo 0 and that although the local managers e g

did not have this clear information, n they set quotas that matched this vari- a –150 h

ation quite well (Figure A). The propor- C Figure B Changes made by tion of young animals in each year was –30 local managers to quotas were correlated with the quotas that the related to the proportion of 0.3 0.40.50.60.7 managers set the following year (Fig- young that were trapped in Prop ortion of young in p revious year the previous year. ure B). This proved to be a very sensi- ble strategy, because the proportion of young trapped was closely correlated with estimates of the annual rate of increase of the population (Figure C). Simulations by Fryxell et al. (2001) sug- 0.8 ) gested that the highest average yield r ( during this period would have been e s fpo obtained if 36% of the animals had a e 0.6 r been trapped each year. This was c Figure C The proportion of n remarkably similar to the average i young trapped was a good f value of 34% that had been set by the o 0.4 predictor of estimates of annu-

e al population growth rates, cal- local managers! t a culated as ln(Nt / Ns), where Nt

How did the local managers do so R Sinauer Associates, Inc. is the abundance at the start of well? Close cooperationGroom 3e between man- 0.2 the trapping season and Ns is agers and the trappersPrinciples was of Conservation essential, Biology the number of survivors from as were the strongGro0801ABox.eps links between the 0.3 0.4 0.5 0.6 0.7 the previous year’s trapping 100% of size proportion of young animals trapped Proportion of young animals in harvest season. 01.17.05 272 Chapter 8

One of the best-known rules of thumb has come to be variable, is rarely known for any given target species at known as the Robinson and Redford model, which was the sites being evaluated, and can easily be overestimated developed as a quick shortcut to assess whether ex- if the only available data come from populations in cap- ploitation of tropical mammals can be defined as sus- tivity or long-term studies in high-quality habitats. Nev- tainable (Robinson and Redford 1991). This model sim- ertheless, this model provides a preliminary measurement ply calculates the total annual sustainable production of hunting sustainability in poorly studied systems and (population increments through births and immigra- has the advantage of simplicity and side-stepping more tion), assuming that the maximum potential production data-hungry approaches that could not be applied to most

(Pmax) occurs at about 60% of carrying capacity (K). This game hunting scenarios in tropical forests. There have figure accounts for any density-dependent effects on been a number of applications (e.g., Fitzgibbon et al. 1995, population growth and is intermediate between the Muchaal and Ngandjui 1999) and criticisms and exten- (MSY) at 50% of K, as used in classic logistic models of sions of the Robinson and Redford model (e.g., Slade et al. population growth, and models where MSY is reached 1998, Peres 2000b, Milner-Gulland and Akcakaya 2001, at about 70% of K (McCullough 1982). The model is pos- Salas and Kim 2002), but it continues to be popular in sibly more realistic for tropical forest vertebrates and is tropical hunting studies. expressed as: Spatial and temporal comparisons P = (0.6D × λ ) – 0.6D [8.7] max max Most of the time, we have to settle for inferences about In this equation, D is an equilibrium population den- sustainability from simple evidence such as comparisons sity estimate near K (or in a nonhunted area similar in of densities of target species in locations that vary in the structure and composition to the hunted area); and λmax intensity of hunting, or interviews with hunters about is the maximum finite rate of increase for a given species changes in the abundance of their prey. Often these types from time t to time t + 1 (measured in years), which de- of evidence can be combined to yield powerful conclu- pends primarily on the number of breeding females and sions about whether extractive activities are sustainable, the annual number of offspring produced per female. In but without being able to make precise quantifications of addition, this method calculates maximum quotas for a benchmarks such as maximum sustainable yields. For species by assuming that the proportion of the maxi- example, a study of hunting of Madagascar radiated tor- mum production that can be taken is 60% for very short- toises, Geochelone radiata, used a combination of inter- lived species, 40% for short-lived species, and only 20% views with hunters, a comparison of changes in the for long-lived species. Estimates of maximum sustain- species’ range size over time, and comparisons of the able offtakes are then compared with hunting data (ob- tortoise’s abundance in sites that differed in hunting tained from interviews, counts of animal car- pressure (O’Brien et al. 2003). The tortoises are collected casses consumed at forest dwellings, and surveys of for food and the pet trade. This study estimated that wildlife meat sold in urban markets) to determine 45,000 tortoises are collected each year from southern whether the population production exceeds or is less Madagascar in the catchment of two cities. Hunters are than the demand within a given hunting catchment. traveling increasingly far to obtain their animals, and These data, however, cannot be easily translated into densities were highest in the most remote, unexploited actual cull rates because the collateral mortality induced sites. This activity is taking place in spite of the species by hunters may be considerable or even exceed the num- being protected by law. This information, combined with ber of kills that are actually retrieved and consumed. In documentation of range contraction, led the authors to the Brazilian Amazon, for example, the number of wool- conclude that the species is headed for extinction unless ly monkeys (Lagothrix lagotricha) that are lethally wound- corrective measures are taken. Hunting rates could be re- ed by shotgun pellets, but subsequently fail to be re- duced through education and awareness programs trieved by hunters, can be far greater than those that aimed at reducing demand, alternative income-generat- actually reach consumer households (Peres 1991). More- ing schemes, and enhanced legal enforcement. over, many studies are likely to overestimate production, and therefore sustainable hunting quotas, because reliable Sustainable Use Meets Biodiversity population density estimates are obtained from sites that are not comparable ecologically to the sites where hunting This chapter has repeatedly run into contrasts between is taking place. Moreover, density estimates are often ob- theory and practice, goals and implementation. A compar- tained from high-density sites, where field studies are ison between “north” and “south” illustrates the diversity most feasible, and then extrapolated to sites with much of issues surrounding exploitation. In most temperate lower densities (Peres 2000b). Finally, λmax can be highly countries hunting, fishing, and forestry management pro- Overexploitation 273

tocols have been developed through a long history of trial the U.S. Endangered Species Act (e.g., smalltooth saw- and error based on biological principles. In most , Pristis pectinata, and white abalone). countries, exploitation regulations are typically nonexist- In many instances failure to protect species from over- ent or unenforceable. The concepts of game wardens, fish- exploitation has more to do with institutional short-com- eries officers, bag limits, no-take areas, and hunting licens- ings than lack of scientific knowledge. European and es are completely unfamiliar to the vast majority of tropical North American fisheries scientists know a tremendous subsistence hunters and fishers who often rely heavily on amount about the demography of the major commer- wild animals as a critical protein component of their diet. cially exploited fish species, yet this information has not In many tropical countries, wildlife is an “invisible” com- prevented some species from reaching historically low modity and local offtakes are often not restrained until the population levels in the past decade. Of course it would stock is depleted. This is reflected in the contrast between help to know even more about the animals that we are carefully regulated and unregulated systems where large trying to manage, such as impacts of low densities on re- numbers of hunters may operate. For example, Minnesota productive behavior, trophic interactions in relation to hunters sustainably kill over 700,000 wild white-tailed habitat alterations, and links between environmental deer every year, whereas Costa Rica can hardly sustain an variability and recruitment. But translating this informa- annual hunt of a few thousand individuals without push- tion into management action for the long-term benefit of ing the same cervid species, albeit in a very different food fishers and fishes would still run into the age-old prob- environment, to local extinction. lem of lack of political strength in the face of criticism But even well-meaning management prescriptions can from those affected negatively by restrictions. In many be completely misguided, bringing once highly abun- developing countries, such problems are compounded dant target species to the brink of extinction. The 97% de- by the dire lack of alternatives for food and employment. cline of saiga antelopes (from >1 million to <30,000) in the When combined with a lack of institutional structures to steppes of Russia and Kazakhstan over a 10-year period implement any policies that may be acceptable, it is easy has been partly attributed to conservationists actively to understand why exploitation often runs a course that promoting exports of saiga horn to the Chinese tradition- is slowed only by accessibility of the resource. al medicine market as a substitute for the horn of endan- As with most of the other conservation issues covered gered rhinos (Milner-Gulland et al. 2001). Saiga antelopes in this book, we feel that while the future holds some were finally placed on the Red List of enormous challenges, it is by no means entirely bleak. in October 2002 following this population crash. For example, the adoption of precautionary principles in Even within cultures, there may be a diversity of per- exploitation by many countries, combined with greater ceptions about the objectives of management. For exam- concern for impacts on ecosystems, is certainly a move ple, in countries that can afford to engage in fisheries in the right direction. We are also encouraged by the management, the standard goal has been to achieve max- large number of imaginative programs in many coun- imum sustainable yields of the target species. In the past tries that are aimed at giving local people incentive to 15 years, however, collapses of fish stocks and concerns make sustainable use of plant and animal populations about by-catches and damage to have led and their habitats; Elizabeth Bennett et al. discuss some to new objectives, such as obtaining sustainable yields of these programs in Case Study 8.2 and Michelle Pinard while minimizing impacts on ecosystems (Reynolds et al. et al. discuss them in Case Study 8.3 (see examples in 2002). Not everyone agrees with these objectives, espe- Chapter 16, also see Case Studies 6.1 and 6.2). Indeed, cially those who perceive that their traditional livelihoods there is a growing appreciation for the enormous eco- are at risk from reduced quotas. Furthermore, there is nomic and social value of ecosystem services from wild also debate within the scientific community about what nature that far exceed the economic benefits of conver- these objectives mean in practice, and how to implement sion to agriculture or other uses (Costanza et al. 1997; them. In some sectors, such as forestry, managers are Balmford et al. 2003). For example, a forest can provide used to dealing with highly polarized debates between far more than just timber, including flood defense, car- those who seek to preserve forests and those who seek to bon storage and sequestration, and of adja- log them. Today, fisheries managers are facing similar cent crops. Many researchers are now working to find scrutiny from many conservationists, who are asking novel ways of rewarding local people for exploiting re- new questions about impacts on habitats and ecosys- sources sustainably in return for benefits received by tems. Indeed, the past decade has seen the first listing by others. These are exciting times for integrating science the IUCN of commercially exploited fishes as threatened with the policy of exploitation, and it is imperative that with extinction (e.g., ), and the first cases of these efforts are successful if we are to meet the chal- exploited marine fishes and mollusks being listed under lenge of sustaining wild populations and their habitats. 274 Chapter 8

CASE STUDY 8.1 Overexploitation of Highly Rational Management and Restoration of Sharks

Julia Baum, Dalhousie University

“Sharks … may be considered as one of the richest ‘strikes’ in the only inexhaustible mine—the sea.” cm to the 12 m long whale , occupying habitats from Barrett, 1928, Scientific Monthly freshwater lakes to entire ocean basins, and occurring in and tropical waters from the surface to depths of a thousand meters. Our perception of sharks as ferocious predators belies Anthropogenic impacts on natural ecosystems have almost al- the fragility of their populations. Sharks tend to grow slowly, ways begun with the overexploitation of large vertebrates. mature at a late age, and give birth to few pups following a Consequent species collapses or extinctions had markedly long gestation period—characteristics more reminiscent of ma- transformed terrestrial, freshwater, and coastal ecosystems by rine mammals than fishes. These traits result in low intrinsic the early twentieth century, while oceanic species were still population growth rates, leaving sharks unable to withstand largely protected by their distant location and large geograph- heavy fishing pressure, and with little compensatory ability to ic ranges. , it seemed, were too vast and their creatures recover from over fishing. too plentiful and widespread to be unduly impacted by hu- Localized shark fisheries that developed in the few decades mans. But in the past few decades, humans have come to dom- following Barrett’s description were characterized by “boom inate these ecosystems as well. Today, industrialized fishing and bust” patterns. Fisheries for the soupfin shark in Califor- fleets are ubiquitous throughout the world’s oceans, reaching nia and Australia, dogfish in Scotland, and porbeagle shark in even the remotest locations and leaving few refuges for marine the Northwest Atlantic all collapsed in under a decade. species. As a result, overexploitation now threatens the future Despite this history of population collapses and sharks’ of many large oceanic vertebrates, including whales, tunas, known vulnerability, their exploitation has intensified globally. billfishes, and sea turtles. And sharks, rather than being one of Shark fisheries underwent a resurgence in the 1980s, driven both the richest “strikes” in the ocean are one of the most vulnera- by the decline of traditional food fish species and by increased ble (Figure A). demand for shark products. Shark meat is increasingly con- Sharks are among ’s oldest inhabitants, having evolved sumed in Western societies, and the high demand for shark-fin over 400 million years ago. Along with skates and rays, sharks soup in Asia has made shark fins one of the most highly valued comprise the subclass Elasmobranchii within the class Chon- marine products (Rose 1996). The practice of finning—removing drichthyes, distinguished from bony fishes by their cartilagi- the fins and returning the remaining carcass to the water—has nous skeletons. The world’s 350 shark species are a diverse now been made illegal in the Atlantic, but a worldwide ban is group, ranging in size from dwarf sharks that reach less than 20 needed. Besides these directed fisheries, many sharks are caught incidentally, in fisheries targeting other species. In particular, pelagic longline fisheries, which target swordfish and tunas throughout temperate and tropical oceans, are the world’s largest source of shark by-catch (Bonfil 1994). Quantifying the impact of current exploitation levels on shark species has proven difficult. Sharks have typically been a low research and management priority because of their histori- cally low economic value and because their catches are often in- cidental. As a result, basic population parameters such as age at maturity and longevity are unknown for many species, and shark catches have been poorly monitored. Fisheries observers usually monitor only a fraction of the overall fishing effort—per- haps 5% in domestic waters, and even less in international wa- ters—and until recently most fisheries recorded shark by-catch in a generic “shark” category rather than identifying individual Figure A Scalloped hammerhead sharks (Sphyrna lewini) swim- ming at Cocos Island, Costa Rica. (Photograph © Philip Colla species. Thus, many shark assessments are done on aggregated www.oceanlight.com.) species groups, obfuscating any variation in species’ responses fpo-hi-res-replace? Overexploitation 275

to exploitation. Compounding these problems are the wide 0 ranges of many sharks, which commonly cross international boundaries, and even entire oceans, imposing serious con- e straints on our ability to monitor their populations. c –20 n fpo New research provides strong evidence that coastal and a d n

oceanic shark populations have undergone rapid, large de- u b clines in the Northwest Atlantic (Baum et al. 2003). To demon- a –40 n i

strate this, researchers analyzed the largest dataset sampling e g n

the Northwest Atlantic pelagic ecosystem, that of the U.S. a h pelagic longline fishery. This type of gear consists of mainlines c –60 d e tens of miles long suspended horizontally in pelagic waters t a m (upper ) by floatlines and buoys, with baited i t

s –8 0 hooks attached on branchlines at set intervals. Thus it resem- E bles a transect through the pelagic ecosystem. The fishery, which operates from Newfoundland into the Gulf of –100 and south to Brazil, and includes both coastal and distant off- HHD WSHTIG B SHMAK THR CSTOCS shore waters, covers the entire range of Northwest Atlantic Sp ecies coastal shark populations and a substantial proportion of oceanic shark populations. Because fishers were required to Figure B Total estimated change in relative abundance (± 95% con- fidence interval) for scalloped, great and smooth hammerhead record shark catches from each longline set and because their (HHD), great white (WSH), tiger (TIG), blue (BSH), shortfin and fishing effort was intense, researchers could estimate changes longfin mako (MAK), common and (THR) sharks be- in abundance even for rare shark species: Between 1986, when tween 1986 and 1999, and for bignose, blacktip, dusky, night, silky, and spinner (CST) and oceanic whitetip (OCS) sharks between 1992 fishers first started recording some sharks to species, and 2000, and 1999. the dataset comprises over 200,000 longline sets and 117 mil- lion hooks! Researchers used statistical models to standardize catch rates for variations in the gear, location, and timing of centuries, after anthropogenic influences began, the former sets. Estimated mean catch rates can then be compared across natural abundance of many large vertebrates in coastal ecosys- years as an index of a species’ relative abundance. tems was fantastically greater than today. Assessments based All shark populations examined in the study are estimated on recent data alone obscure the original abundance of species, to have declined by 40%–89% since the mid-1980s (Baum et al. such that we may become complacent about species that are 2003). Researchers estimate that since 1986 hammerhead sharks now rare. This lack of historical perspective on what is natural have declined by 89%, great white sharks by 79%, thresher is coined the “” (Pauly 1995). sharks by 80%, and tiger sharks by 65% (Figure B). The remain- Estimating the baseline abundance of pelagic sharks in the ing coastal sharks (CST), examined together because of the po- Northwest Atlantic is possible because of the short history of tential for misidentification in the logbooks of these similar disturbance in the open ocean compared to most other ecosys- looking congenerics, declined by 61% just since 1992. Blue and tems: We need only look back to the early development of in- mako sharks are estimated to have declined by 60% and 40% dustrial offshore fisheries in the late 1950s. In the Gulf of Mexi- respectively since 1986; oceanic whitetip sharks by 70% since co, research surveys were conducted in the mid-1950s using 1992 (see Figure B). These latter species range across the entire pelagic longlines, to determine the potential for a commercial Atlantic. Thus, while the data do not cover their entire popula- tuna fishery (Wathne 1959). These surveys provided some of tions, because other longline fisheries exert intense fishing pres- the first biological information available on pelagic sharks, and sure across the Atlantic, it is quite plausible that the pattern on the region’s offshore resources. Sharks were so abundant on found in the Northwest Atlantic is representative of the entire these surveys that they damaged a high proportion of tuna on region. Despite the enormity of documented declines, they are the longlines and were considered a serious problem. Re- likely underestimates because they do not accountSinauer forAssociates, changes Inc. searchers in the 1950s documented that between 2 and 25 Groom 3e that occurred during the first three decadesPrinciples of offshore of Conservation shark Biologyoceanic whitetip sharks were usually seen around their vessel exploitation in the Northwest Atlantic (i.e., fromGro08EssayB.eps 1957 to 1985). during gear retrieval (Wathne 1959). Oceanic whitetip and silky Halting shark population declines is necessary100% of ifsize we are to sharks were the second and fourth most commonly caught fish- 01.17.05 avoid species extinctions; reversing them is essential if we are es overall on the pelagic longline sets, comprising almost 15% to restore populations to their former levels. Restoration re- of the total catch, and 85% of all shark catches. Matching these quires that we understand the composition and abundance of data to comparable information from the current pelagic long- natural shark assemblages, that is, that we have some knowl- line fishery reveals a very different picture. By the late 1990s edge of what it is we want to restore. Jackson (2001) notes that these two species accounted for less than 0.5% of the total catch, because most ecological studies began years, and sometimes and only 16% of shark catches, suggesting that substantial 276 Chapter 8

changes have occurred in the Gulf of Mexico’s shark assem- monitoring constraints. Around the world, most sharks are blage in less than half a century. Recent research on caught in multispecies fisheries, be it pelagic longlines, bottom sharks have either not mentioned the oceanic whitetip shark or trawls targeting other fishes, or directed shark fisheries that catch have dismissed it as a rare exception in the Gulf of Mexico, with several species. This is problematic because the pursuit of pro- no recognition of its former prevalence in the ecosystem. In con- ductive target species will continue to drive the fishery, even after trast, a new analysis that incorporates these historic data esti- less-productive shark populations have collapsed. Finally, be- mates that oceanic whitetip sharks have declined by over 99% cause of the difficulty in adequately sampling the large geo- in 50 years, suggesting that this species is ecologically extinct in graphic ranges of shark populations, shark collapses and local the Gulf of Mexico (Baum and Myers 2004). extinctions may occur unnoticed. Local extinctions of two other Beyond the risk of species extirpations in the Northwest At- elasmobranch species, the common skate (Raja batis) and the lantic, estimated shark declines may indicate broad ecosystem barndoor skate (Dipturus laevis), for example, were only docu- changes. Consumers such as sharks usually exert important mented after the fact (Brander 1981; Casey and Myers 1998). controls on structure, diversity, and ecosystem func- Restoration of shark populations will require fundamental tioning. The generality of the loss of pelagic consumers in the changes to their management. If we are to avoid extinctions of Northwest Atlantic is particularly worrisome: Most pelagic shark populations, fisheries need to be managed for the viabil- shark populations appear to be remnants of their natural abun- ity of the most vulnerable, rather than the most productive, dance, and many other apex predators, including the sword- species. This means that substantial reductions in fishing pres- fish and marlin, are drastically reduced. Although the ecosys- sure in most fisheries that catch sharks are needed. Recovery tem impacts of overexploitation in the open ocean remain targets that incorporate a historical perspective are needed, largely unexplored, any changes are likely to be massive in and management must work toward these. Effective interna- scale given the vastness of these ecosystems, and are likely to tional management plans need to be implemented and en- be difficult to reverse given the life history of sharks. forced to account for sharks’ wide geographic ranges. Finally, The estimated loss of pelagic sharks in the Northwest Atlantic as individuals we need to make responsible choices about the may also reflect a common global pattern of decline in shark fish we consume by becoming informed about their status and species. Longlines and other pelagic fisheries are pervasive in all the effect of fisheries on incidentally caught species. oceans, catching many of the same shark species as in the North- Sharks have existed for over 400 million years, but have west Atlantic, turning the risk of extirpation in that region into been threatened with extinction in less than 50. We may now the risk of global extinction. Apart from the species discussed be a critical juncture—where the decisions made today will de- here, most other sharks face similar exploitation pressures and cide the ultimate fate of these species.

CASE STUDY 8.2 The Bushmeat Crisis Approaches for Conservation

Elizabeth L. Bennett, Society, Richard G. Ruggiero, U.S. Fish and Wildlife Service, Heather E. Eves, Natalie D. Bailey, and Andrew Tobiason, Bushmeat Crisis Task Force

In Africa, forest is often referred to as “the bush,” thus wildlife (Robinson and Bennett 2000). Recent estimates of hunting rates and the meat derived from it is referred to as “bushmeat.” in the Congo Basin show that a majority of species are hunted Bushmeat is eaten for subsistence, and is also traded in local unsustainably (Fa et al. 2002). The expansion of bushmeat and regional markets to supply protein to people in cities and hunting poses a risk not only to the viability of wildlife species, towns.The bushmeat trade in Africa is a multi-billion dollar a but also to the livelihoods of the people who share year industry involving millions of animals from cane to with them (Figure B; Milner-Gulland et al. 2003), as well as to elephants (Wilkie and Carpenter 1999; Fa et al. 2002), and mil- human, wildlife, and livestock health (Hardin and Auzel 2001; lions of hunters, traders, market sellers, and consumers (Figure Wolfe et al. 2004). A, Mendelson et al. 2003). Scientific studies show that the ma- Recommendations for promoting and regulating the bush- jority of this unregulated, commercial hunting for wild meat is meat trade as a means to support rural livelihoods (Brown unsustainable and threatens biodiversity conservation goals 2003) are generally not supported by current management ca- Overexploitation 277

Bushmeat ning, thereby facilitating increased access and unsustainable ex- ploitation of wildlife resources. Governments and other land managers often have low capacity for monitoring and enforce- ment, or have poorly designed or implemented wildlife policies. Commercial Wholesaler Farmer Rural and urban human populations frequently have inaccurate hunter hunter perceptions of the limitlessness of wildlife and a general lack of awareness of wildlife use impacts. The poor, in particular, lack protein and income alternatives to bushmeat. These driving Chopbars Market traders causes, compounded with the unsustainable commercial wildlife hunting levels impacting populations all across Africa have re- sulted in a crisis which threatens massive population declines; Customer fpo particularly vulnerable are the forest species which are an order of magnitude less productive than grassland species. Figure A The cycle of the bushmeat trade. Solutions to the bushmeat crisis must simultaneously ad- dress these causes while supporting both undisturbed core pacity, policy, ecological, or economic realities (Fa et al. 2003; areas and some regulated-use areas. Such plans may assure Wilkie et al. in press). While some suggest that a sustainable that wildlife and biodiversity are conserved for future genera- trade in wildlife for bushmeat can exist (Cowlishaw et al. tions and that the livelihoods of marginalized rural peoples are 2005), these claims are generally based on species with high re- supported (Milner-Gulland et al. 2003). Protected areas are an productive potential, such as rodents, in degraded habitats essential component to any landscape management plan. Bio- (Robinson and Bennett 2004). Such scenarios generally emerge diversity conservation goals and alternatives for income must after all the large-bodied mammals have already been hunted be coupled with appropriate wildlife regulations and enforce- out (Bennett et al. 2002). Long-distance commercial trade in ment to limit hunting to local areas and to nonendangered wildlife from tropical forests is almost inevitably unsustain- species with high reproductive rates (Eves and Ruggiero 2000). able, and under the very limited circumstances in which it Solutions include policy development, capacity building for might be biologically feasible, strong management capacity education and enforcement personnel, development of both must be in place. Such capacity is lacking across central Africa. protein and income-generating alternatives, incorporating Robinson and Bennett (2000) document numerous root caus- planning into economic development es of the bushmeat crisis that must be addressed in efforts to con- and extractive industry activities (especially logging, , serve wildlife. Expanding human populations increase demand and road-building), and collaborative information sharing and for bushmeat, while poverty and food insecurity create increased management for development of best practices, adaptive man- reliance on natural resources. Private companies in extractive in- agement, and long-term monitoring. Such solutions necessitate dustries usually do not engage in wildlife management plan- the commitment and collaboration of government, non- governmental (NGOs), the pri- vate sector, and communities to support essen- tial wildlife management planning activities that include governance, enforcement, and com- munity participation to support biodiversity protection (Ruggiero 1998). Progress in many of these areas is now being made. While the bushmeat issue was not well- known or understood before the late 1990s, it has since become a central issue for many con- servation projects and international efforts fpo (Bushmeat Crisis Task Force 2004). The Bush- meat Crisis Task Force (BCTF) was created in 1999 as the first coordinated effort by North American wildlife conservation groups and pro- fessionals from a range of disciplines to focus ef- forts on the growing unsustainable, illegal, and commercial trade in bushmeat in Africa and around the world. BCTF has prioritized four areas of engagement for this collaborative action: Figure B on the back of a logging truck in Gabon. (Photograph by R. Ruggiero.) information management; engaging with key 278 Chapter 8

decision-makers; formal education/training program develop- ples of the multi-stakeholder, multi-level effort that is essential ment; and public awareness. Professionals from conservation, to address the unsustainable bushmeat trade effectively, amidst government, industry and development fields work with the a landscape of human development activities. BCTF staff and steering committee to identify and analyze available information, develop consensus on solutions, produce Wildlife Management in Logging Concessions resources, and identify areas of collaboration potential. Major One example of such collaboration is the Project for Ecosystem BCTF initiatives include working with key decision makers Management of the Peripheral Zone of the Nouabalé-Ndoki (KDM) in Africa and the U.S. toward policy development and (PROGEPP), a wildlife management program mobilization of resources; the Bushmeat Education Resource based in the Kabo and Pokola logging concessions in the Guide (BERG), which supports public education by zoological northern Republic of Congo. This project, initiated in 1999, is a parks and other institutions; the Bushmeat Promise, a cam- joint effort of the Government of the Republic of Congo, the paign designed to engage the public toward action; and the Congolaise Industrielle des Bois (CIB) logging company, the Bushmeat Information Management and Analysis Project Wildlife Conservation Society (WCS), and the communities as- (IMAP), which provides geo-referenced BCTF project and pub- sociated with the concessions. Aside from the government, the lication databases online, assembles bushmeat-relevant datasets CIB logging company is the single largest employer in Congo from around the world, and gathers new data on relevant in- and their logging concessions have acted as a magnet for im- formation in the Congo Basin. For more information about the migration. The population of Pokola, the largest town near the bushmeat crisis and what is being done to address it, visit the concession, has more than doubled since 1999,from 7,200 to Bushmeat Crisis Task Force website: www.bushmeat.org. 16,000. Many would hunt bushmeat if not controlled and if Since the establishment of BCTF and other bushmeat efforts, other food options were unavailable. Instead, as a result of the public awareness in the U.S. and Europe has been raised con- project, wildlife populations are thriving, including , siderably. Only a handful of media articles were produced prior , elephants, and bongo, and people are maintain- to 2000, but more than 750 were produced in the five years that ing a healthy mixed, protein-rich diet. The key to this success followed (Bushmeat Crisis Task Force 2004). A number of is conducting a complex of activities that include wildlife man- awareness programs in urban and rural Africa communicate agement planning, training, monitoring, education, and en- the impacts of the bushmeat trade on wildlife and human com- forcement while simultaneously developing alternative munities that enable consumers to make better-informed deci- sources of income and protein-rich foods. sions (Obadia et al. 2002). Formal education and training tools Elkan and Elkan (2002) provide an overview of PROGEPP are also developed in Africa and the U.S. to further educate key including three key rules adopted with regard to hunting in decision makers, field personnel, and the public (Bushmeat Cri- the concession—no snare hunting, no hunting of legally pro- sis Task Force 2004; Bailey and Groff 2003). tected species, and no export of bushmeat outside the immedi- At the international policy level, the World Conservation ate community—a model established earlier with local com- Union (IUCN) adopted an official bushmeat resolution in 2000, munities associated with the adjacent Nouabalé-Ndoki the Convention on International Trade in Endangered Species National Park. The rules are made known to all workers and of Wild Fauna and Flora (CITES) created a bushmeat working their families, especially truck drivers who often serve as in- group in 2000, the Africa Law Enforcement and Governance termediaries for illegal trade, as well as communities not affil- (AFLEG) treaty signed in 2003 by both timber producer and iated with CIB, and are enforced by “eco-guards” at numerous consumer nations identified bushmeat as a priority concern, checkpoints. In addition, conservation and land-use zoning and the Convention on Biological Diversity (CBD) established was created according to traditional community zones and a working group to review the issues related to nontimber for- use. No-hunting areas, community hunting est products, including bushmeat. zones, and buffer zones around the Nouabalé-Ndoki National Further evidence of an increased focus on addressing the un- Park were adopted and established in the logging concessions. sustainable bushmeat trade is the Congo Basin Forest Partner- CIB, like any large company working in an area of limited ship (CBFP). Officially established at the World Summit on Sus- government capacity is in a position to dramatically influence tainable Development in September 2002, CBFP is an association how land and resources are being managed beyond their man- of 29 governments and international NGOs collaborating to pro- dated exploitation, and fulfills many public services for its em- mote biodiversity conservation and improved livelihoods. CBFP ployees and nearby communities. As a complement to the so- partner organizations and their projects employ aspects of the cial, health, and education programs CIB already provides, the bushmeat trade as indicators of the success of these landscape- wildlife management plan includes company provision of af- level management efforts. Three leading success indicators are fordable livestock and protein-rich food alternatives. directly related to bushmeat: wildlife management planning Since the project’s inception, snare rates are significantly re- and enforcement, protein and income-generating alternatives, duced, endangered species are found even in areas where reg- and training and awareness to enable behavior change. ulated hunting is taking place, and protein alternatives are While numerous projects focus on one or two focal aspects being incorporated into the culture of the logging concession of the bushmeat trade, there are a few that stand out as exam- (Elkan and Elkan 2002). In addition, national policies regard- Overexploitation 279

ing the provision and training of eco-guards within all logging collected during one three-year period. This model is most ap- concessions in Congo have been adopted. plicable to subsistence and cash-crop farmers who have enough food but not enough income, live at a medium density, and pro- Conservation is Good Business duce conservation-friendly products (Lewis 2004). The information emerging from PROGEPP identifies wildlife Critical to the entire initiative is the linked focus on wildlife management planning and enforcement, partnership develop- protection. Experience across the entire tropical globe shows ment, and provision of protein and income-generating alterna- that providing protein and income alternatives alone do not re- tives as keys to bushmeat management success. Similarly, a proj- duce hunting. COMACO overcomes this by linking the coop- ect in Zambia involving an agricultural cooperative is showing erative with increased protection of wildlife; all cooperative signs of conservation success based on these same priority ac- members are also involved in wildlife enforcement, and their tions (Lewis 2004). The basic premise for this conservation pro- doing so is a prerequisite of their eligibility for the program. gram is that “food secure, farm-based communities with alter- Hence, they are both benefiting from improved livelihoods native sources of income to illegal use of wildlife can contribute while also protecting their local wildlife. positively to wildlife production” (Lewis 2004).. The Communi- While these examples are promising it is important to note ty Markets for Conservation and Rural Livelihoods (COMACO) that such systems are site specific, require trained and com- efforts developed by WCS in collaboration with the Zambia mitted experts in wildlife, community development, enforce- Wildlife Authority (ZAWA) and the Ministry of Tourism, Envi- ment, and education and demand long-term commitment of ronment and Natural Resources (MTENR) are designed to di- personnel, financial resources, monitoring, and evaluation. Ap- rectly address the causes that drive overexploitation of wildlife plication of similar programs without such resources and ca- for bushmeat in this region—food insecurity, need for income, pacity in place are unlikely to succeed. Caution should be used poor land-use practices, and access to markets. in responding to plans that support broad-scale policies of reg- The COMACO project is innovative among conservation ulated trade in bushmeat as they are unlikely to lead to achiev- programs as it actively engages individuals and communities ing either biodiversity conservation or development goals in in a business cooperative and has been very effective in coor- the long, or even in the short-term. Quite the opposite, they are dinating the support of the private sector. Producer depots more likely to result in further impoverishment of rural com- supply a central trading post and households and communi- munities and degradation of the natural resources upon which ties can belong to the cooperative as long as they make a com- they depend. What is required is a global commitment and re- mitment to improving land-use practices and supporting con- sponse that simultaneously and sufficiently supports nations servation. That is, families must agree to a specific land-use that have identified the bushmeat problem as a threat to their management plan and producer-group conservation by-laws natural and cultural heritage so that locally-designed efforts before being accepted in the program. such as those described have the opportunity to succeed. This The COMACO project in 2003–2004 had over 750 conserva- will include sufficient resources to enable training, enforce- tion farming groups supplying depots with rice, chickens, ment, development of protein and economic alternatives, land- groundnuts, and honey. The cooperative negotiates higher scape-level management that includes protected area as well prices for these products, and in turn farming groups turn in as multiple-use zones, and awareness programs for the public. hunting materials; over 30,000 snares and nearly 500 guns were

CASE STUDY 8.3 Managing Natural Tropical Forests for Timber Experiences, Challenges, and Opportunities

Michelle A. Pinard, University of Aberdeen, Manuel R. Guariguata, Environmental Affairs, Convention on Biological Diversity, Francis E. Putz, University of Florida, and Diego Pérez-Salicrup, Universidad Nacional Autónoma de México

Applied forest ecologists, or silviculturalists, find managing the overwhelming, natural forests in the moist tropics have many immense diversity of natural tropical forests for various goods of the attributes that one might consider conducive to manage- and services a challenge, not only because of the of ment. For example, they are productive in terms of the diversi- these forests but because the requirements for sustainability are ty of goods and services, and are known to be highly resilient; also diverse and complex. While the diversity may often seem many areas that currently support old-growth tropical forest 280 Chapter 8 fpo-hi res are the result of secondary forest suc- tion (nominally, the time it takes for a cession after agricultural fields were tree to grow to maturity). In theory, cut- abandoned hundreds of years ago (e.g., ting cycle lengths and harvesting inten- Darien, Panama; Bush and Colinvaux sities are determined on the basis of the 1994). Despite the opportunities repre- rate of commercial timber productivity. sented by these attributes, examples of Harvesting also can be done more good management are few. There is strategically, as a silvicultural treatment huge variation in forestry practices to promote the regeneration of ecologi- across the tropics, with some countries cally similar groups of trees. For exam- and forest owners moving toward ple, light-demanding tree species are fa- more sustainable practices, while oth- vored by intensive stand interventions, ers continue to convert or degrade for- whereas if less timber is harvested per est, often under the pretense of timber unit area, more -tolerant species management. benefit. Unfortunately, the temptation Our aim is to explore some of the of marketable standing timber often variation among forest management overwhelms efforts to secure sustained practices and to identify what seems to yields. As a result, timber-mining oper- be working to improve management. ations favor both slow-growing, shade- We also discuss what we see as the tolerant species, and fast-growing pio- main challenges and opportunities for neers, not the species with marketable sustainable management of natural timber. Moreover, given the general Figure A Selective logging typical involves cut- tropical forests. Although we focus on ting a few valuable species, and extracting them lack of reliable data on forest productiv- the ecological, economic, and social via skidders or draft animals. (Photograph by M. ity, managers establish cutting cycles by bases of sustainable forest manage- Pinard). making educated guesses at how fast ment for timber, our motivation is trees grow. principally forest conservation. It may The deleterious environmental im- seem strange to be trying to save tropical forests with chain- pacts of logging can be minimized if well trained and closely saws and bulldozers, but the majority of the tropical forests supervised crews fell and extract timber following a detailed that remain are only likely to be saved if they can be managed harvest plan. In forests from Borneo to Brazil, loggers partici- profitably for timber. In many cases, if people cannot make pating in research projects on “reduced-impact logging” have money from forests, then the forests will likely be destroyed in demonstrated that good logging practices are technically fea- favor of some more lucrative land use, such as agriculture. Background and Context for 60 Tropical Forest Management fpo Because of the high diversity of tropical trees and the con- 50 ) comitant low population densities of marketable species, log- s e g m a e ging in natural forests in the tropics is typically selective; a rel- t 40 s m a d

atively small number of trees above a threshold size (the d e t d s e minimum felling diameter) are felled and extracted. The logs n v

a 30 t r s a

are usually skidded out of the forest using bulldozers, rubber- l h a n u tired skidders, farm tractors, or draft animals (Figure A). u d

f 20 i s o

Where machines and draft animals are not available, large logs e % R ( are often sawn into thick boards that are manually carried out 10 of the forest. Logging impacts on the residual forest vary with harvest in- 0 tensity, level of pre-harvest planning and control, type and 0 20 40 60 80 100 120 140 160 terrain, and forest stature and structure, among other factors Harvest intensity (m3/ha–1) (Figure B). Due to the selective nature of harvesting, forests are Figure B Variability in harvest intensities (m3/ha–1) and incidental repeatedly logged after intervals of a few years to a few decades. damage to the residual stand (percentage of unharvested trees) across Where logging is scheduled so as to achieve a sustained yield of the tropics. Open symbols are areas in which harvesting was planned timber, this approach to forest management is referred to as a and controlled; closed symbols are areas in which harvesting was car- ried out in a conventional way (typical for the region, generally with polycyclic silvicultural system. Where properly designed, sev- little planning and control over operations). (Modified from Pinard et eral harvesting episodes (or cuts) are scheduled within a rota- al. 2005.) Overexploitation 281

sible and that their application is financially viable (e.g., to promote sustainable forest management (Richards 1999). Holmes et al. 2002). Logging damage to the residual stand can Examples of how high opportunity costs interact with pol- be reduced by up to 50% when trees are felled in predeter- icy failures to promote deforestation in the tropics could be mined directions and logs are skidded out of the forest along cited from almost anywhere, but the liquidation of forests in pre-planned pathways (e.g., Pinard et al. 2000). Unfortunately, the 1980s in Costa Rica is especially illustrative. Costa Rican due to unsupportive forest policies, industry resistance to forest management is conducted on a strictly private basis. change, corruption, and the massive profits from exploitative There are no government concessions, nor does the govern- logging, reduced-impact logging methods are seldom fully ment directly manage production forests. Up until recently, the used (Putz et al. 2000). opportunity costs of managing forests for sustained timber The socioeconomic and political contexts in which forests production were apparently too high to make the option at- are exploitatively logged or managed for the sustained yield of tractive (Kishor and Constantino 1993). In addition, Costa timber vary tremendously across the tropics. Most tropical for- Rica’s relatively young, volcanically-derived can support est-rich countries are poor in terms of most economic meas- for many more years than those established in less fer- ures, many stagger under huge international debts to develop- tile locations such as in eastern Amazonia. Up until 1969, when ment banks, and some are poorly governed. The expertise the first modern was passed in Costa Rica, forests needed to manage forests is often scarce even in countries with were legally considered impediments to land conversion for governments committed to maintaining a permanent forest es- pasture, agriculture, and development activities. During the tate. Furthermore, corruption can seriously impede the best-in- 1970s and 1980s, forest conversion was fuelled by government tended efforts at management. Making more compli- subsidies for cattle production, coupled with excessive regula- cated is the fact that forests may be owned by individuals, tion of private landowners that caused them to lose interest in communities, corporations, or governments that grant conces- managing forests on a sustainable basis. As a result, annual de- sions to industrial corporations and, all too often, claims of forestation rates and consequent rates of forest fragmentation ownership overlap or are otherwise contested. Equally worri- were very high (Sanchez-Azofeifa et al. 2001). The driving some is the fact that although most of the large forest tracts that forces for forest conversion in Malaysia and Mexico were dif- remain in the tropics are currently in remote locations far from ferent from those in Costa Rica, but ended up with the same markets, accessibility is rapidly increasing as major road-build- massive scale of deforestation. ing efforts push back forest frontiers. It also should be noted Almost all Malaysian forests were claimed by the govern- that many forests planned for forest management are actually ment and let out to logging concessionaires, but after logging, inhabited by people who are not involved in management many were converted into oil palm plantations. Societal finan- planning and other decision-making processes. These social, cial benefits from logging, while a great deal less than they economic, and political challenges are coupled with the bio- might have been due to corruption and mismanagement, fu- physical challenges of managing little-known forests under elled national development. In Malaysia today, slash-and-burn what are often adverse environmental conditions. agriculture is rare and many people live in cities and work in high-tech industries but the biological costs of this develop- High Financial Opportunity Costs ment were immense. of Maintaining Forests In Mexico, the extensive deforestation that occurred in the Anyone promoting sustainable forest management must grap- 1960s and 1970s was an indirect result of the “green revolu- ple with the high financial opportunity costs of managing tion,” a global initiative to terminate hunger. The government forests relative to the profits from extracting all of the mar- implemented a “national deforestation plan” in which small- ketable trees and converting the forest to some more lucrative scale farmers were given the right to lands they converted to land use. By “opportunity costs,” economists refer to the cost agriculture. The objectives of the program were to produce associated with giving up or postponing an opportunity, such more agricultural goods and to relieve political pressure from as the chance to invest in alternative income-generating activi- landless farmers. Of course, the cost of such program was paid ties. This challenge is particularly powerful in many tropical by society at large, as the value of tropical forests was simply countries where , cattle ranching, and ignored (Dirzo and García 1991; Masera et al. 1997; Turner et predatory logging pay so much better than maintaining forest al. 2001). under sustainable management (e.g., Pearce et al. 1999; South- gate 1998). Due to the “time value of money” (future profits Pressures to Overexploit and future costs are “discounted” in terms of current value, see As countries rich in forests develop economically, the growth Chapter 5), even unsustainable and eventually very costly of capacity in wood-processing industries often exceeds the practices can be financially very attractive. Market failures, sustainable rate of supply of raw materials. Typically, where particularly the serious undervaluing of forest goods and serv- industries initially thrive on a large supply of timber from for- , and policy failures, such as the provision of subsidies for est conversion and first cuts in heavily stocked, old-growth unsustainable agricultural practices, further undermine efforts forests, with time, forests available for conversion decline and 282 Chapter 8

the industries need to rely on the more modest 70 harvests from the permanent forest estate (South- s e i 60

gate 1998). This type of “boom and bust” cycle c e has occurred in many different parts of the trop- p

s fpo

ics. For example, the government of Ghana is d 50 e t struggling to impose an annual allowable cut of i o 3 l only 1 million m , which is based on the best p 40 x available growth and yield data but is far below e f the industry’s capacity (Adam 2003). As in many o 30 r e

other places, Ghana’s timber-processing industry b has great political power and is applying pressure m 20 u on the government to increase the allowable an- N nual cut beyond the maximum sustainable yield 10 (Adam 2003). Any further increases in harvesting could only be achieved by reducing the lengths of 0 9 5 1 7 3 9 5 1 7 3 9 5 2 7 3 9 5 1 3 3 3 2 2 1 1 8 7 7 6 6 6 4 4 9 8 1 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 cutting cycles or by increasing the intensity of 9 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 each harvest by selecting more species or more 1 trees of the favored species by reducing mini- Year mum felling diameters. Available data on stand- Figure C The number of tree species exploited for timber in Ghana between 1911 ing volume, forest productivity, and ecological and 1989. Data compiled from annual reports of the Ghana Forestry Department. For those years without bars, no data were available. (Modified from Adam 2003.) impacts suggest that these options are not ecolog- ically viable in even the short term and are not economically viable in the long term. dophragma spp.). In contrast to conditions in the first half of the twentieth century, forest managers in the moist tropics now Insecurity of Land Tenure can market dozens of species (Figure C). In Amazônas, for ex- Among the problems plaguing tropical countries, property ample, in the early 1990s, 90% of the state’s timber production rights issues figure prominently. Because forest management was based on four species, Copaifera multijuga, Ceiba pentandra, is a long-term endeavor, insecurity of land tenure, or at least Nacleosis caloneura, and Virola surinamensis. With the exhaustion guaranteed access to the resources the forest provides, is a nec- of the economically accessible stocks of these species, increased essary prerequisite for making investments in sustainable demand for sawn timber, and improvement of law enforce- forestry. The failure of many tropical governments to assure ment, new industries have been established and the list of landowners and forest concession holders that they will con- species used by industry has expanded considerably (e.g., to tinue to control their property forever, or at least receive ap- 70 species in one 40,000-ha project; Freitas 2004). propriate compensation if it is taken away from them, is a Long lists of marketable timber-producing tree species pres- powerful justification for treating forests as if their natural re- ent managers with both opportunities and risks. Greater num- sources are not renewable. But while of tenure seems bers of commercial species increases a manager’s flexibility in like an important prerequisite for sustainable management, it selecting trees to be harvested, trees to be retained as seed is not in itself sufficient to assure that forests will be treated as sources, and future crop trees to be favored by judicious thin- if the future matters. Under some conditions, providing secure ning around their crowns. This flexibility is important given tenure can promote deforestation if forest owners use their the uncertainties in timber markets and the wide range of con- property as collateral for bank loans to buy cattle or chainsaws. ditions appropriate for the regeneration and growth of valu- able tree species. On the other hand, there is a risk of over-har- Marketing and Managing for More Species Groom vesting, particularly where there is little control of forest Although technical challenges for tropical silvicultureFigure Gro0803 (e.g.,bCaseStudy.eharvestingps operations or where harvesting decisions are based timber harvesting and stand tending) tend to be secondary to solely on minimum felling diameters without concern for the socioeconomic and political problems, applied forest ecologists regeneration requirements of the harvested species. still have important roles to play. These roles are expanding as conservation and environmental service provisions are includ- Variation among Forests ed more explicitly in management priorities. Furthermore, as Tropical forests are justly famous for their overall species diver- markets begin to accept formerly noncommercial timber sity, but ecologists have only recently recognized how much di- species, studies on the and physiological versity there is among forests in the tropics. Similarly, forest man- of these species become critical. agers are becoming increasingly aware that the silvicultural Tropical silviculture has its roots in the management of a treatments they apply must be appropriate for the particular few high value Asian and African species such as teak (Tectona characteristics of the species and forests they are managing. For grandis) and the African mahoganies (Khaya spp., Entan- example, retaining canopy cover by carefully harvesting spa- Overexploitation 283 fpo-hi res tially isolated trees is critical for managing forests for shade-tolerant trees that are abundant in the sub- canopy and understory. The same approach to har- vesting light-demanding species, in contrast, would not contribute to sustainability because these species only regenerate in large clearings. Foresters in the Dipterocarpaceae-dominated forests of southeast Asia as well as those working in the forests on the Guyana Shield of South America, where many of the commer- cial timber tree species are at least moderately shade- tolerant, are justifiably adamant about reducing the impacts of logging on the residual stand. Conversely, silvicultural intensification, including exposure of min- eral soil in large canopy openings, is being called for in seasonal forests on the rim of the Amazon where most of the commercially important timber tree species are light-demanding (Fredericksen and Putz 2003). While Figure D Oil palm plantations are becoming more common, replacing selective many forest management practices are widely applica- logging practices in much of Southeast Asia. (Photograph by M. Pinard). ble, such as the need to avoid sediment loading of streams with runoff from logging roads, no single sil- vicultural system is appropriate for all tropical forests. to the challenge of forest management. Natural forest man- Variation among forests also means that some forests may agers have to be comfortable working in remote areas and be easier to manage than others. For example, some of greatest need to be very sensitive to environmental issues where success in management of tropical forests has been in low di- slopes are steep and soils are easily damaged by heavy equip- versity forests with a high density of commercial timber trees. ment. Additionally, the costs of applying even the simplest of Mangrove and swamp forests are particularly notable, al- stand improvement treatments, such as cutting vines on fu- though low diversity forests can also be found in uplands. For ture crop trees, can become excessively expensive under these example, silviculture in oak-dominated montane forests in adverse conditions. Costa Rica has proven to be straightforward partially because Managers should also become aware that timber-producing the canopy trees produce very large crops of acorns that satiate forests are getting smaller. In the neotropics, while the annual their seed predators resulting in high seedling densities in the cutting area of a single logging company in the Bolivian Ama- understory (Saenz and Guariguata 2001; Guariguata and zon might average 2000 ha, the total area of production forest of Saenz 2002). The lowland forests of Peninsular Malaysia are individual concessionaires or forest owners in , Costa extremely diverse, but their management is also relatively easy Rica, and Honduras rarely exceed this same figure (Table A; one because the canopy is dominated by species of Dipterocarpaceae that TABLE A A Regional (Central versus South American) Contrast in the Estimated share silvicultural requirements. Un- Areas of Mixed-Species, Lowland Broad-Leaved Forest Currently Managed fortunately, the successful regenera- for Timber tion of an extensive area by good for- a b est management has been erased as Country Mean (range) N Observations most of these areas have been cut to Honduras 1342 (196–4149) 45 Includes community and privately-owned forest make way for oil palm plantations in the northern lowlands (Figure D). Nicaragua 2814 (5–42887) 39 Includes the entire country; management plans granted during 1999 only Working With Less Valuable Costa Rica 62 (2–481) 404 Privately-owned forests in the northern lowlands (excludes Carapa-Pentaclethra forests on and Fragmented Forests poorly-drained soils) After widespread deforestation for Perú 17460 (2697–49620) 31 State and privately owned forest, Amazonian cattle ranching, industrial farming lowlands and other agricultural uses, as well Bolivia 62420 (1171–365847) 95 Concessions and community forests, Amazonian lowlands as oil palm and wood fiber planta- tions, the land left for natural forest Source: Data from the following governmental institutions: Corporación Hondureña de Desarrollo Forestal management for timber is mostly re- (COHDEFOR) and Instituto Nacional Forestal (INAFOR). Data also from the non-governmental organization mote, steep, rocky, or swampy. The Fundación para el Desarrollo de la Cordillera Volcánica Central (FUNDECOR), and from the bilateral/multi- lateral research initiative BOLFOR and Center for International Forestry Research (CIFOR). conditions that render land unsuit- aThe mean (range) of the forest area is measured in hectares. able for more intensive uses also add b Number of sites. 284 Chapter 8

notable exception to this pattern is the forest community con- and more Americans move from the countryside to cities and cessions in Petén, Guatemala that reach thousands of hectares suburban areas where they have few opportunities to learn the [ha] [Ortiz and Ormeño. 2002]). Although generalizing how difference between sound and unsound forest management fragmentation affects the biological sustainability of timber practices, efforts to promote forest management as a conserva- management is currently difficult, penetration of light and tion strategy will become increasingly challenging. Counter- into fragmented forests from their edges results in increased balancing this trend, country of origin labeling, organic food flammability, a huge concern given the frequency of human in- certification, “fair-trade” programs, and marketing of “bird- duced ignitions of wildfires in many areas of the tropics (Lau- friendly, shade-grown” coffee, are all helping to make con- rance and Cochrane 2001). Also, vines and other forest weeds sumers in the U.S. aware of their potential power to increase proliferate on forest edges, and can greatly increase the mortali- social welfare and protect the environment. ty of edge-exposed trees (Laurance et al. 2001). Seed dispersal by vertebrates can also vary between fragmented and extensively Paying the true value for forested areas (Guariguata et al. 2002). One way to reduce the opportunity costs inherent in managing Biological considerations aside, a potential constraint on forests for timber is to capture the full economic value of trop- timber production in small fragments of forest relates to land- ical forests. Many of the values of forests are not included in scape-level planning of management operations. Forest frag- traditional market transactions for timber and even most non- mentation may limit the viability of selective logging schemes timber forest resources (e.g., rattan canes, Brazil nuts, and palm that might work well in extensive forests because of the low hearts). Although we recognize the roles of tropical forests as probability of securing an adequate volume of a given timber storehouses of fantastic biodiversity and for their effects on species. Even well intentioned policies can exacerbate this local and global , forest owners are generally not fi- problem. By law in Costa Rica, for example, harvesting quotas nancially compensated for these values. The costs or benefits for a given timber species should not exceed 60% of the total of forests that accrue to people other than the property owners number of harvestable individuals (Comisión Nacional de are known as externalities. Economists are working with ecol- Certificación Forestal 1999). Given that most Costa Rican ogists around the world to capture these externalities in eco- forests destined for timber production are only a few tens of ha nomic analyses by creating markets for sequestered , in extent, harvesting quotas guided by the “60%” rule may be transpired water, and protected biodiversity. In these efforts, financially unrealistic in many forest patches due to the small Costa Rica has been a world leader. absolute number of trees. An innovative for forest conservation, Payment for Environmental Services, was included in Costa Rica’s most How the Challenges of Tropical Forestry recent forestry law and implemented through a decentralized Can Be Confronted body (National Forestry Financing Fund [FONAFIFO]). These Many approaches may be helpful in reducing unsustainable payments represent an attempt to financially compensate small forestry practices. Among these, demand from consumers, ad- landholders for the services their forests provide including car- justed markets, policy changes, and technological advances all bon sequestration, watershed functions, maintenance of biolog- may play a part, often together. ical diversity, and protection of scenic beauty, going some way to reduce the opportunity costs of maintaining forest cover. Pressure from Socially and Environmentally Markets for sequestered carbon are developing all over the Concerned Consumers world, but use of carbon credits to promote forest conservation Frustrated by continued unsustainable forestry practices in the through improved management faces a number of serious tropics, environmentally concerned consumers of forest prod- challenges. Unfortunately, of deforested areas, af- ucts are using their market power to promote better manage- forestation of naturally nonforested areas (e.g., grasslands and ment. Initially, boycotts of tropical forest products were staged, savannas), and, to a lesser extent, strict have but they back-fired—driving down the market price of tropi- all received more support from international policymakers cal timber only served to increase the rate of logging as com- than reduced-impact logging and other changes in forest man- panies strove to maintain their profits. Much more successful agement that promote carbon sequestration (e.g., Putz and has been an international program of voluntary third-party Pinard 1993). Part of the problem is that many policymakers certification of good forest management practices coordinated cannot recognize the difference between well and poorly man- by the Forest Stewardship Council (FSC). aged forests, and doubt that anyone else can either. While every year the area of tropical forest certified as well managed according to FSC Principles (Table B) increases by Policy and legal reform about 1 million ha, global demand for certified forest products Policy and legal reform are often prerequisite to the removal of continues to exceed the supply. Unfortunately, consumer disincentives to sustainable forest management. For example, awareness of the beneficial influences of selecting certified for- ejidatarios (communal owners) or indigenous communities con- est products in the U.S. still lags far behind Europe. As more trol 80% of the forest resources of Mexico. Initially they were Overexploitation 285

TABLE B Ten Principles of Forest Stewardship According to the Forest tively promote reforestation of lands Stewardship Council formerly cleared for agriculture Principle 1: Compliance with laws and FSC principles (Bocco et al. 2000). Forest management shall respect all applicable laws of the country in which they occur, Policy reforms are only effective in and international treaties and agreements to which the country is a signatory, and comply improving forest management prac- with all FSC principles and criteria. tices when supported by the appro- Principle 2: Tenure and use rights and responsibilities priate regulations and the institutions Long-term tenure and use rights to the land and forest resources shall be clearly defined, documented and legally established. needed to implement and enforce the Principle 3: Indigenous peoples’ rights new policies. In Bolivia, for example, The legal and customary rights of indigenous people to own, use and manage their lands, the passage of new forestry legislation territories, and resources shall be recognized and respected. in 1996 was followed by the creation Principle 4: Community relations and worker’s rights of a new institution that was assigned Forest management operations shall maintain or enhance the long-term social and eco- the task of assuring compliance with nomic well-being of forest workers and local communities. the legislation. In the first year of ac- Principle 5: Benefits from the forest tivity, the new national forestry au- Forest management operations shall encourage the efficient use of the forest’s multiple products and services to ensure economic viability and a wide range of environmental thority resolved millions of hectares and social benefits. of conflicting land claims, issued Principle 6: Environmental impact long-term cutting contracts, and in- Forest management shall conserve biological diversity and its associated values, water creased tax revenue to the Bolivian resources, soils, and unique and fragile ecosystems and , and, by so doing, government four-fold (Nittler and maintain the ecological functions and the integrity of the forest. Nash 1999). Principle 7: Management plan A management plan—appropriate to the scale and intensity of the operations—shall be Technological strategies written, implemented, and kept up to date. The long term objectives of management, and the means of achieving them, shall be clearly stated. Tropical silviculturalists have ap- Principle 8: Monitoring and assessment proached the problem of managing Monitoring shall be conducted—appropriate to the scale and intensity of forest manage- high diversity in tropical forests in ment —to assess the condition of the forest, yields of forest products, chain of custody, various ways. In the 1960s, uniform management activities and their social and environmental impacts. silvicultural systems (e.g., shelter- Principle 9: Maintenance of high conservation value forests wood systems or patch clearcuts) Management activities in high conservation value forests shall maintain or enhance the attributes which define such forests. Decisions regarding high conservation value forests were promoted as a means of domes- shall always be considered in the context of a precautionary approach. ticating the forest and increasing pro- Principle 10: Plantations ductivity by favoring a few light-de- Plantations shall be planned and managed in accordance with principles and criteria 1–9, manding species at the expense of and principle 10 and its criteria. While plantations can provide an array of social and eco- other more slow-growing, shade tol- nomic benefits, and can contribute to satisfying the world’s needs for forest products, they erant species. Polycyclic management should complement the management of, reduce pressures on, and promote the restoration and conservation of natural forests. systems (those more commonly used today) were considered less appro- Source: Modified from Forest Stewardship Council website, http://www.fscoax.org/. priate because of the high losses of volume caused by incidental damage associated with selective timber har- obliged by law to sell their forest products to companies and vesting, the risk of a shift in forest composition to more shade- thus had limited real control over the fates of their forests. This tolerant species, and the risk of over-harvesting if cutting cy- legal arrangement discouraged sustainable use and fuelled con- cles are too short (Dawkins and Philip 1998). flicts between the companies and the ejidatorios. The companies of tropical forests through intensive silvicul- were not interested in sustainable management because their tural interventions is generally not practiced today despite the concessions were short term and they had no prospects of be- fact that the silvicultural objectives of increasing stocking and coming forest owners. The ejidatarios, in turn, had little interest growth rates appear to have been met in many forests treated as in the forests because they had such little control over their use. early as the 1950s (e.g., Alder 1993; Manokaran 1998; Osafo 1968). This conflict was resolved in the 1980s when a new law allowed Two factors appear related to the lack of support for radical do- ejidatarios to manage their forests directly. Today, the best exam- mestication—one is the relatively high risk of forest clearing for ples of good forest management in Mexico come from ejidatar- agriculture during the first decades in the management cycle ios and indigenous communities that recognize the long-term when the forest holds little value, and the other is an assumed in- value of keeping their forests (Flachsenberg and Galletti 1998; compatibility between intensive silviculture and biodiversity Bray 2004). Moreover, some of the indigenous communities ac- conservation (Dawkins and Philip 1998; but see de Graaf 2000). 286 Chapter 8

Typical approaches to timber management in natural trop- Vermeulen 2002). Farm forestry will also continue to develop, ical forests currently are conservative, aimed at reducing the contributing to a shift in milling capacity to process smaller impacts of interventions (Fredericksen and Putz 2003). To a stems. As the big profit margins associated with exploiting old great extent, reduced-impact logging has become synonymous growth forest give way to the more modest profits associated with sustainable forest management, even though the former with sustainable harvests, smaller operators are likely to be at- is only one component of the latter. Where light-demanding tracted to the business. Provision of technical support to many species are being harvested yet failing to regenerate, more in- small operators may be more difficult than to fewer large op- tensive, locally imposed interventions are being promoted erators, but levels of motivation and innovation may also be (Dickinson and Whigham 1999; Fredericksen and Mostacedo higher. Where managers are committed to sustainable prac- 2000; Snook 1996). For example, thinning interventions that tices, more silviculture will be introduced into management. liberate individual crop trees and maintain overall diversity in Meanwhile, integration of inventory data, harvest planning, structure are sometimes recommended (see Wadsworth 1997 and monitoring operations into geographic information sys- for review). In forests in which the commercial timber is pro- tems (GIS) will facilitate the implementation of more intensive duced by both light-demanding and shade-tolerant species, a and directed operations. mixed system would seem most appropriate. For example, sin- The trends in policy towards broadening societal participa- gle-tree selection might be applied where there is advance re- tion in forestry are likely to continue with more efforts to de- generation of shade-tolerant species, while in other areas large volve forest management to rural communities. But early ex- gaps might be created near potential seed trees to promote re- perience gained across a broad range of socio-political and generation of light-demanding species (Pinard et al. 2000). economic conditions emphasizes the need for strategies that combine both short- and long-term objectives (du Toit et al. Looking Forward: 2004), institutional development, conflict resolution (Castro Where Will the Next Decades Lead? and Nielson 2001), and a recognition that in some cases, it will Whilst uncertainty in timber prices, politics, and priorities take a lot of time and effort for communities of subsistence make it difficult to predict where the next decades will lead farmers to become sustainable forest managers. tropical forestry, a few pathways seem more likely than others. As pressure to place remaining tracts of natural forest under Overall, while deforestation rates are likely to remain high, for- protection, the divide between those arguing for sustainable est management practices should continue to improve under use and those arguing for complete protection may grow wider the influence of the FSC’s timber certification processes (see (see Dickinson et al. 1996 and Pearce et al. 2003 for summaries Table B). These improvements will be a consequence of more and primary literature therein), one consequence being in- forest owners working towards certification, certified produc- creased competition for sources of funds for development. All ers improving their practices through the monitoring and feed- progress towards sustainable forest management depends on back programs built into the certification process, and in re- good governance. Where corruption and illegal logging contin- sponse to indirect influences of certification such as the ue, it will be difficult to improve forest management practices exchange of information and experience among forest owners, (Ravenal et al. 2004). managers, and regulators. The challenges facing tropical forest management are many. It is also clear that the focus of the timber industry will in- The field of natural forest management in the tropics needs en- creasingly move to marginal lands where opportunity costs are ergetic and dedicated people who are willing to put up with low and natural forest management is relatively attractive as a the rigors of tropical forestry work. Input from biologists is land use. With widespread devolution of control of forest needed to ensure that the development of good practices, and lands to indigenous groups and other rural communities, tim- the criteria and indicators used to assess and monitor these ber buyers will be motivated to develop socially acceptable ap- practices, are based on relevant biological and ecological infor- proaches to company–community partnerships (Mayers and mation (Putz and Viana 1996).

Summary taken, ranging from subsistence hunting and fish- ing, to recreational and economic pursuits carried 1. Overexploitation is ranked second only to habitat out by wealthy individuals and corporations. While loss as a cause of extinction risk in species whose most environmentalists are well aware that fisheries status has been assessed globally. It involves the un- and large-bodied birds and mammals are often sustainable use of wild animals, plants, and their overexploited, recent studies have shown that these products for purposes such as food, medicines, shel- changes can be far more dramatic than previously ter, and fiber. The motivations for such exploitation recognized. Fisheries can reduce the biomass of tar- are as varied as the plants and animals that are geted and nontargetted species by 80% or more in Overexploitation 287

10–20 years, and subsistence hunters in the Neotrop- ics can create a vacuum of large-bodied species Please refer to the website www.sinauer.com/groom for Suggested Readings, Web links, additional questions, within 10–20 miles of their villages. and supplementary resources. 2. The biological theory of sustainable exploitation is firmly rooted in the field of , which seeks to understand the responses of popula- tions to increased mortality of individuals through Questions for Further Discussion density-dependent compensation. This theory has 1. How can rich countries help encourage poor coun- produced a range of methods for estimating sus- tries to exploit their plants and animals sustainably? tainable limits of exploitation from simple rules of thumb based on life histories to highly sophisticated 2. Actions taken to protect vulnerable species may af- models that are appropriate for only a small fraction fect some people’s livelihoods. Because the decision of cases where the necessary input data are avail- to protect biodiversity is an expression of public able. This theory cannot be put into practice to make will, do you think that governments have an obliga- exploitation sustainable without a clear understand- tion to assist families and businesses whose liveli- ing of the motivations of people who use wild ani- hoods are harmed by a conservation plan? mals and plants, the alternatives available to them, 3. Many cases of overexploitation involve not only and the effects of management recommendations on people’s livelihoods, but their subsistence. How can their livelihoods. The “tragedy of the commons” we prioritize conservation versus human subsis- often looms large in overexploitation in both terres- tence? What mechanisms might we foster to reduce trial and aquatic ecosystems, exacerbated by “dis- this conflict? counting,” whereby we give wild populations a 4. In what ways can models help us exploit wild pop- higher value for what we can get from them today ulations more sustainably? What are some of the than in the future. Yet there is a growing realization limitations of the models typically used to estimate of the enormous economic and social benefits that safe harvest levels? we receive from ecosystem goods and services. With encouragement from processes such as the World 5. Why is overexploitation so large a problem in the Summit on Sustainable Development in 2002 and marine realm, and relatively less important in most the Millennium Ecosystem Assessment, many peo- terrestrial ? ple are now rising to the challenge of finding inno- vative ways helping people to reap the rewards of sustainable exploitation.