Conservation implications of commercial hunting of black andspectacled caiman in the Mamiraua Sustainable Development

Reserve, Brazil

Ronis Da Silveira a, John B. Thorbjarnarsonb,*aProjeto Mamiraua, Cx. Postal 38, CEP 69470-000. Tefe, Amazonas, BrazilbWildlife Conservation Society, 2300 Southern Blvd, Bronx, NY 10460, USA

Received 1 May 1998; accepted 7 June 1998

Abstract

During the annual dry season, illegal hunting of black and spectacled caiman in the Mamiraua Sustainable Development Reservein western Brazilian Amazon is widespread. Hunting occurs throughout the reserve, but is particularly intense in the northernPanaua region, where it provides the primary source of income for local residents during the dry season. While hunting prior to1970 was principally to obtain caiman skins for sale, hunting today is entirely for the sale of caiman meat. People in the region do

not eat the meat themselves, but after salting sell it to buyers who mix it with fish and in turn sell it in Para state, Brazil, and inColombia. Preliminary information suggests that the annual harvest is approximately 115 metric tons of fresh caiman meat, whichwould represent a harvest of 5230 black caiman and 2865 spectacled caiman. Despite this illegal hunting, the population of black

caiman has one of the highest reported densities for Amazonia. The impact of hunting on wild populations may be reduced becausethe hunters take mostly adult and subadult males, from relatively accessible parts of the reserve. Hunting in the Mamiraua reserveillustrates that a sustained harvest of caiman populations may be possible under the right conditions.# 1999 Elsevier Science Ltd.All rights reserved.

Keywords: Caiman; Hunting; Amazon

1. Introduction

The black caiman (Melanosuchus niger) and spec-tacled caiman (Caiman crocodilus) are the two largestcrocodilians in the Amazon basin and both species havea long history of human exploitation. Commercialhunting of black caimans for their skins began in the1930s (Smith, 1980; Medem, 1983). Skins were exportedto tanners in Europe and the United States and subse-quently used to manufacture luxury items includingbelts, wallets, and shoes. Melanosuchus was the firstspecies hunted due to its larger size and the superiorquality of its skin. Hide hunting was particularly intensein the early 1950s (Fittkau, 1970), but was still in evi-dence in the late 1970s and early 1980s (Magnusson,1979; Rebelo and Magnusson, 1983). Medem (1971)and Smith (1980) report that between 1950 and 1965 atotal of 7.5 million caiman skins were exported from

Amazonas state alone. The great majority of these wereprobably Melanosuchus. Between 1960 and 1969, over1.5 million skins, largely from C. crocodilus, were legallyexported from the Brazilian Amazon (Smith, 1980). Bythe late 1970s and early 1980s, black caiman hadbecome rare and only approximately 10% of the con-fiscated caiman skins in Brazil were from Melanosuchus(Rebelo and Magnusson, 1983). Hunting of all wildlife,including caiman, was banned in 1967 (Federal Law5197). However, illegal caiman skin hunting continuedat least through the 1970s (Smith, 1980; Rebelo andMagnusson, 1983).In the 1970s, a major shift in caiman hunting occur-

red in the western Brazilian Amazon (Amazonas state).As markets for skins disappeared, hunters began sellingcaiman meat instead. By the early 1980s, a trade in sal-ted meat from the Amazonas to Para state in Brazil andto Colombia was reported by Best (1984), and this tradecontinues to flourish.Due largely to the severe depletion of black caiman

populations as a result of skin hunting, the species is

BIOLOGICAL

CONSERVATION

Biological Conservation 88 (1999) 103109

0006-3207/99/$see front matter # 1999 Elsevier Science Ltd. All rights reserved.PII: S0006-3207(98)00084-6

* Corresponding author. Tel.: +1-718-220-7158; fax: +1-718-364-

4275; e-mail: jcaiman@aol.com.

considered endangered (Groombridge and Wright,1982). Nevertheless, pristine populations remain in afew areas (e.g. Manu National Park, Peru; Herron,1991), and relatively dense populations are known fromBolivia (Pacheco, 1996), Ecuador (Jahoda, 1990),Guyana (Gorzula and Woolford, 1990), and Brazil (DaSilveira et al., 1997, and this study). While the potentialof M. niger to recovery from overexploitation is high(Rebelo and Magnusson, 1983), there has been con-siderable concern how continued hunting may aectpopulations of black caiman (Herron, 1991, Brazaitiset al., 1996).Here we report on illegal hunting of caiman in the

Mamiraua Reserve in the western Brazilian Amazon.The Mamiraua reserve consists of over 1.1 million ha ofseasonally flooded varzea habitat associated with theconfluence of the Amazon (Solimoes) and the Japurarivers (Fig. 1), approximately 500 km west of Manaus.The area was first protected as an Ecological Station bythe state of Amazonas in 1990. In July 1996, the areasstatus was changed to that of a Sustainable Develop-ment Reserve, the first ever in Brazil, for the purpose ofintegrating sustainable resource management with theconservation of biodiversity. Currently, the commercialhunting of caiman is a common dry-season activity forindividuals in a number of communities within thereserve, and one of the objectives of our study was todetermine the impact of hunting on caiman populationsas a first step towards evaluating the potential of con-trolled hunting as a management alternative. In thisstudy we estimate the size of the current caiman harvest,present data on the status of caiman populations, andcalculate the economic importance of the harvestingfor residents of the reserve. Finally, we discuss the

implications of this commercial harvest for the futureconservation and management of Amazonian caiman.

2. Methods

The Mamiraua Sustainable Development Reserve isdivided into two main sections, a 246,000 ha focal area,and a 878,000 ha subsidiary area (Fig. 1). In 1995, wecollected information on caiman hunting during visits to23 communities and seven isolated houses in the fol-lowing regions of the focal area: Mamiraua, Jaraua,Tijuaca, Barroso, Boa Uniao, Panaua, Horizonte, Lib-erdade. In the Panaua region of the subsidiary area wevisited four communities. At each community we ques-tioned residents about caiman hunting activities and,with the hunters permission, weighed the caiman meat.For freshly hunted caiman we recorded the snout-ventlength (SVL; to the posterior edge of the cloaca), totallength and sex (by cloacal probing). In some cases it wasnot possible to weigh the meat, and the quantity of freshmeat was estimated based on the relationship betweencaiman length and quantity of meat produced (weightfresh meat (WFM), in g) (M. niger: WFM=0.0077SVL3.11, r2=0.89,; C. crocodilus: WFM=0.0016SVL3.44, r2=0.93). The mass of dried meat was con-verted into an equivalent mass of fresh meat by multi-plying by 1.6.We evaluated the caiman populations in the reserve

by conducting nocturnal spotlight counts from a boat.In August 1995, 40 censuses were carried out in 37dierent bodies of water totaling 486 km. We locatedcaiman by their reflective eyeshine using a hand-heldspotlight, then approached to identify the species based

Fig. 1. Map of the Mamiraua Sustainable Development Reserve focal area at the confluence of the Solimoes (Amazon) and Japura rivers.

104 R. Da Silveira, J. B. Thorbjarnarson/Biological Conservation 88 (1999) 103109

on dierences in coloration and head morphology, andto estimate SVL. The size of caiman was estimatedvisually based on the observers experience (see Da Sil-veira et al., 1997). Hatchling caiman (

were in the 105125 cm SVL range, which in the greaterpopulation would correspond to subadult males andadult females. Nearly 80% of the M. niger were largerthan 100 cm SVL, the size at which females beginreaching sexual maturity (Brazaitis, 1973). Males prob-ably do not become mature until they are slightly larger.However, the sex-ratio of harvested M. niger was highlymale biased: 77 males and 22 females (3.5:1). The largestnumber of C. crocodilus taken was in the 125 cm SVLclass, which are large adult males, and the sex ratio waseven more male biased than in M. niger: 62 males to 5females (12.4:1). Using a value of 70 cm SVL for adultC. crocodilus, 97% of harvested Caiman were sexuallymature.

3.4. Status of the caiman population

In August 1995, 8541 caiman were counted duringsurveys of six sectors within the Mamiraua reserve.Although annual water levels are lower in Septemberand October, 1995 was an exceptionally dry year andthe river level was low at the time of the surveys.Of the caiman whose species could be determined

(N=2349), 53.7% were C. crocodilus, 46.0% were M.niger, and 0.3% were Paleosuchus palpebrosus. Densitiesof non-hatchling caiman ranged from 0.9/km to 115.0/km of shoreline. No significant dierence in caimandensity was found between the sectors (ANOVA,F5,33=1.50, p=0.22). Densities higher than 30 caimanper km were found only in the Mamiraua and theJaraua sectors of the reserve, where hunting pressure isthe lowest.

The size-class composition of caiman populations wasbased on estimated SVL of a sample of surveyed caiman(N=2337; Fig. 4). Of 1261 C. crocodilus, 24% were lar-ger than 70 cm SVL. ForM. niger, however, only 1% of1076 individuals were larger than 150 cm SVL.

4. Discussion

The commercial exploitation of crocodilians for theirskins has had devastating eects on a number of speciesworldwide (Groombridge and Wright, 1982). In theAmazon, the species that was most aected was theblack caiman (Plotkin et al., 1983). However, after a 15year hiatus in skin hunting, populations of black caimanare now recovering in many parts of their range (Ross,1998). In Mamiraua, this recovery has taken placedespite widespread commercial meat hunting. Some-what paradoxically, while skin hunting significantlyreduced caiman populations, meat hunting has not. Ourstudy in the Mamiraua Sustainable DevelopmentReserve has shed some light on the dynamics of meathunting caiman in the Amazon floodplain, and how itdiers from the previous system of skin hunting. Thesefactors include a complex interaction of factors includ-ing: the legality of the hunt, dierences in economicincentives of skin and meat hunting and the sizes ofanimals hunted, the ease of transport of the products(skins vs meat), caiman sexual size dimorphism, andpatterns of sex-specific habitat selection by the two spe-cies of caiman.Commercial skin hunting of caiman in the Mamiraua

region appears to have begun in the early 1940s. In

Fig. 4. Size-class distribution of M. niger (N=1076) and C. crocodilus

(N=1261) determined from nocturnal surveys in the Mamiraua

reserve.

Fig. 3. Size-class distribution of 217 M. niger and 131 C. crocodilus

harvested in the Mamiraua reserve. Size-classes in cm snout-vent

length (SVL). Arrows indicate minimum adult size of females, male

reproductive maturity is probably slightly greater.

106 R. Da Silveira, J. B. Thorbjarnarson/Biological Conservation 88 (1999) 103109

addition to the skins, which were traded overseas, thecaiman fat was used locally for a variety of purposes. InTefe, the oil was mixed with diesel fuel (70% caimanoil:30% diesel) for running generators that provided thecity with electricity (Pereira, 1944). According to inter-views with current residents of the reserve, the financialincentives were great and hunting during this periodextended into the most remote regions of the reserve.Families set up households along interior forest lakesand lived principally by hunting caiman for their skins,and to a lesser extent, fishing pirarucu. Commercial skinhunting continued, through cyclical periods of highsand lows, into the late 1960s. Hunting of caiman waslegal until 1967, when the Brazilian law No. 5.197/67banned all hunting of wildlife. Residents of Mamirauareport that during this period black caiman were extre-mely scarce; very few were seen in the lakes, and denselyvegetated back-swamp habitats may have been their laststrongholds. The outlawing of caiman hunting, plus thescarcity of black caiman brought an end to most com-mercial skin hunting. While some skins were traded intothe early 1980s (Rebelo and Magnusson, 1983), inter-national controls on the trade of crocodilian skinsapparently prevented the establishment of major skinmarkets in the Amazon.Commercial hunting for caiman meat began not long

after the end of skin hunting. Caiman populationsprobably began recovering to some degree in the early1970s. Local residents report that in 1970, traders star-ted buying caiman meat along with fish. From the verybeginning, the caiman meat trade appears to have hadtwo destinations (Best, 1984 and this study): upstream(Colombia/Peru) where it is sold as catfish, and down-stream (Para state, Brazil) where it is mostly sold ascaiman meat.The caiman meat trade follows the traditional enco-

menda system used by fish traders. Large trading com-panies are located in the major towns (for theMamiraua region these towns are Alvaraes and Tefe).In Alvaraes, there are currently three major traders.Each owns a number of boats that travel up and downthe Japura and Solimoes Rivers, stopping at small riv-erside communities to provide them with the necessarysupplies for hunting (gas, food, salt). Approximatelyone month later, the boat revisits the community andcollects the caiman meat. Hunters are paid primarily ingoods (food, coee, sugar, etc.) at very disadvantageousterms. The price of the initial supplies is also discountedfrom what is owed to the hunter. Because few huntershave the means to transport the meat and deal withother traders, they get paid very poorly. This is com-pounded by the fact the caiman meat is illegal, furtherlowering the prices paid by traders. Hunting begins inAugust, and while most of the hunting occurs duringthe low water period, some caiman meat is traded allyear long (the price goes up during the high water

period). The meat is stored in warehouses in or near thetowns from where it is traded upriver or down.While commercial meat hunting has been taking place

for more than 20 years, the densities of M. niger inMamiraua are among the highest reported for thisspecies (Vanzolini and Gomes, 1979; Plotkin et al.,1983; Vasquez, 1991; Thorbjarnarson, 1992; Brazaitis etal., 1996; Da Silveira et al., 1997). In parts of the reserve(Mamiraua and Jaraua sectors) densities and the size-class distribution of black caiman are similar to thosereported by Herron (1994) for population that has neverbeen hunted. The coexistence of a meat hunting indus-try and a large caiman population is somewhat per-plexing. However, the dynamics of meat hunting arevery dierent that that of skin hunting. While skinswere a valuable commodity, meat has a relatively lowvalue. This is in part due to the abundance of fish, thelack of a tradition of eating caiman meat (except in Parastate), and the illegal nature of the trade.An analysis by Rebelo and Magnusson (1983) sug-

gested that due to the selectivity of skin hunters foranimals down to one meter long, few animals arerecruited into the adult population. In contrast, inMamiraua meat hunters take mostly Melanosuchus thatare 100150 cm SVL, corresponding roughly to a totallength of 200300 cm. In the overall population, thissize-class should be comprised principally of adultfemales and subadult and small adult males. However,the sex-ratio of the harvested animals was highly malebiased. The biological impact of the harvest on wildpopulations of caimans depends largely on the numberof animals taken, and the demographic characteristicsof the hunted population. Due to their presumed poly-gynous mating systems, a harvest that targets adultmale crocodilians will have less impact on the popula-tion than one that takes mostly adult females (Thorb-jarnarson, 1991). Under these conditions, a surplus malepopulation could be harvested with relatively littleimpact on the reproductive potential of the population.The strong male bias among hunted animals suggests

that there is some factor that skews the harvest sexratio. Based on our studies of the biology of black cai-man and discussions with hunters, we postulate it is dueto the preference of adult female M. niger for heavilyvegetated and dicult to reach interior lake systems inthe Mamiraua reserve, while hunters work mainly in themore accessible, open water systems, which are popu-lated principally by subadult and small adults males(R. Da Silveira and J. Thorbjarnarson, unpublisheddata). Breeding Caiman populations inhabit the easilyreached lakes and river overflow channels preferred byhunters, but the male sex bias of hunted animals waseven stronger. This is largely due to the fact that Caimanis a smaller species than Melanosuchus, and hunterstargeted only the largest caiman (>100 cm SVL),which are almost exclusively males. Hunters select

R. Da Silveira, J. B. Thorbjarnarson/Biological Conservation 88 (1999) 103109 107

larger Caiman because they provide more meat andhence are more profitable. These data suggest that thecurrent harvest of both species targets principally adultand subadult malesIn the past, skin hunting was a much more lucrative

activity than current meat hunting. The high prices paidfor skins translated into greater economic incentives forhunting. Local hunters report that when taking caimanfor their skins, they would enter even some of the mostinaccessible lakes and take caiman down to one meterlong. In contrast, because prices paid to hunters formeat are relatively low, and meat is more dicult totransport, it only pays to kill large caiman, and it is notworth the hunters time to make the arduous trips intothe small, forest interior lakes where most M. nigerbreed.The degree to which economic incentives drive the

dynamics of this system can be seen by comparing cai-man hunting with pirarucu harvesting. The pirarucu(Arapaima gigas) is a large, piscivorous fish that isfound in most of the same lakes as black caiman. Due tooverfishing, pirarucu are now scare in most parts of theAmazon floodplain. However, in Mamiraua, pirarucuare still common in many of the same interior forestlagoons used by female black caiman. Both caiman andpirarucu are hunted from a boat using a harpoon, andthe meat is sold salted. However, the price paid for sal-ted pirarucu is 2.53 times higher than that paid forcaiman meat. During the course of studies on the nest-ing biology of black caiman, we have entered many ofthe forest interior lakes, and found widespread evidenceof hunters taking pirarucu, but not caiman. Due to therelative scarcity of pirarucu, and the high prices paid fortheir meat, fishermen will enter these lakes to take pir-arucu, but not caiman.Because the trade is illegal, it is dicult to accurately

estimate. Nevertheless, the amount of caiman meat soldin the region is sizable. Our estimate of 115 metric tonsin 1995 is based on a direct measurement of 13 tons inreserve communities. Aside from the caiman meatmeasured in this study, reports from other Mamirauaproject personnel indicated that in AprilMay 1995,commercial buyers in the town of Alvaraes had stored11.8 tons of caiman meat. The majority of this meatprobably came from the Mamiraua reserve. Based on anaverage price of US$ 0.8/kg dried meat, the sale of115,000 kg of fresh meat (equivalent to 72,000 kg driedmeat) would generate US$ 57,600 for local commu-nities. Studies of the socioeconomic activities of resi-dents of the reserve (Lima-Ayres, 1992) estimate thatthe average household sells 19 kg of fresh and 5 kg ofsalted caiman meat annually (equivalent to a total of 27kg fresh meat per household). This sale generates US$22 per year for the household. As 791 householdsextract resources from the reserve, a total of over 21,000kg of caiman meat is produced annually. However, this

is a minimum estimate as the study of Lima-Ayres(1992) was conducted in the southern section of thereserve, where relatively little caiman hunting occurs.The results of this study show that hunting is a muchmore important economic activity in the upstream sec-tions of the focal area, particularly in the Panauaregion. In this area during several months of the year,caiman hunting is virtually the only economic activityengaged in by most members of the community.Among the objectives of this ongoing study is the

evaluation of the potential for a legal harvest of caimanfor meat. Because it is illegal, hunters tend to get paidlow prices and most of the profit is made by the mid-dlemen dealers who market the meat. If properly man-aged, such a program could increase the economicbenefits for residents of the Mamiraua area, and leaveintact a large, healthy population of caimans. By asses-sing user fees, the government wildlife managementauthority could also benefit from a well-run, legal har-vest. Our study suggests that the current system has anumber of biological safeguards to reduce the potentialfor overexploitation, and could be used as the basis fora managed, sustainable harvest. While most sustainableuse harvest programs for crocodilians are currentlybased on hunting for the skin trade, hunting for meatcould have important advantages. Meat is a basichuman necessity and could be used to supply largenational markets. The prices paid for meat could also bemore readily controlled by factors endemic to thecountry where the harvesting takes place. One of thebiggest problems of skin harvest programs is the factthat the market is the international luxury skin tradewhere demand, and hence prices paid for skins, canfluctuate significantly. Harvests based on meat wouldexpect a more stable market and pricing of products.Prices paid for meat would also be lower than those forskins, which would reduce the profitability and thepotential for significant illegal trade, something that hasplagued the skin market. Also, under present regulationsof the Convention on International Trade in Endan-gered Species of Flora and Fauna (CITES), commercialtrade would only be possible for C. crocodilus, and notM. niger, which is classified in the restrictive Appendix Iof CITES.Nevertheless, the diculties associated with the

establishment of a legal caiman harvest program formeat must not be downplayed. The sustainability of thecaiman harvest in Mamiraua may be due to the fact thatlarge areas are inaccessible to hunters, providing asource-sink situation where the otake is relativelysmall relative to the total populations (Robinson andBennett, 1998). Because Mamiraua is almost unique inthe extent of its varzea habitat, this model of sustainablehunting may be a special case that is not applicable toother areas of the Amazon. Aside from biological con-siderations, as the consumption of caiman meat is only

108 R. Da Silveira, J. B. Thorbjarnarson/Biological Conservation 88 (1999) 103109

a tradition in areas around the mouth of the Amazon,any proposed program would have to evaluate themarketability of meat. Furthermore, the implementa-tion of adequate enforcement and monitoring infra-structure to guarantee the harvest guidelines areadhered to will be dicult in such a remote area, andwill require extensive planning and cooperation betweenthe Brazilian wildlife management authority (IBAMA),the Federal Police, the marketers of the meat, and localhunting communities.

Acknowledgements

Funding for this work was provided by the Depart-ment for International Development (formerly theOverseas Development Authority; Great Britain),World Wildlife Fund (England), the Conselho Nacionalde Pesquisas (CNPq) of Brazil, the European Union(DG XI) and the Wildlife Conservation Society. CNPqalso provided a fellowship for the senior author duringthis study. We thank Bill Magnusson for his insights oncaiman biology and hunting. J. C. Herron and F.Wayne King reviewed the paper and provided manyuseful comments. Dr. J. Marcio Ayres provided us withthe opportunity to work in Mamiraua, as well as con-siderable support during our studies.

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