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TOMÁS WALLER
The senior author with a Yellow Anaconda (Eunectes notaeus) just captured in La Estrella marshes.
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YELLOW ANACONDAS IN ARGENTINA IGUANA • VOLUME 14, NUMBER 3 • SEPTEMBER 2007 161
The Management of Yellow Anacondas
(Eunectes notaeus) in Argentina: From
Historical Misuse to Resource Appreciation
Patricio Alejandro Micucci and Tomás Waller
Fundación Biodiversidad, San Martín 945 piso 3 # 23, Buenos Aires, Argentina, C1003AAS
Abstract.—Herein we describe a program for the sustainable utilization of Yellow Anacondas (Eunectes notaeus) that was implemented
in 2002 in the Province of Formosa, Argentina. The management plan was conceived to manage an activity that had been misusing a
valuable wildlife resource with no regard for existing regulations. Delimited hunting areas were assigned to a restricted number of local
skin buyers (LSB). A LSB is authorized to acquire hides from enrolled hunters living or working in his assigned territory; overlapping
areas among buyers is discouraged and regulated. A minimum size limit of 230 cm was established for skins, while annual changes in
skinning patterns ensure that hunters or LBs do not stockpile hides from one year to another. Sustainability is regulated by examining
hunting effort in relation to catch-per-unit effort (CPUE) and monitoring traditional parameters like sex, origin, and size structure of
the skins harvested. About 15% of the program’s gross revenues return to cover program costs, whereas 13% goes to community mem-
bers. Quantitative harvest data from the first five years are presented and discussed.
Introduction provinces (Henderson et al. 1995, Dirksen 2002, Micucci et al.
M any developing nations are attempting to convert unman-
aged and often illegal wildlife exploitation to sustainable
utilization programs. Such projects seek to instill economic value
2006a). It is largely aquatic, a dietary generalist, and its range is
restricted mainly to wetlands and floodplains.
in components of natural ecosystems threatened primarily by
traditional land-use patterns. In many instance, a lack of scien-
tific data has been used to defend the status quo and to boycott
a sustainable use approach. However, recent history (Webb,
2002) suggests that management decisions rarely emerge from
pure research; instead, long-term research can be a beneficiary
of sustainable use plans.
Effective wildlife management results from a strong com-
mitment by governmental agencies, users, pro-active NGOs,
and other stakeholders. A well-planned management program
should provide for an optimum allocation of resources, mean-
ing that revenues have to be reasonably distributed among stake-
holders, balancing the different economic levels, investments,
risks taken, and responsibilities. Moreover, the main beneficiar-
ies should return part of the income to the community. If funds
are applied directly to the management plan, it will generate
income and promote conservation.
Harvesting wildlife has received increasing attention and
criticism in recent years. Biocentric views (Singer 1976, Callicot
1980) have been exacerbated in a media-dominated culture that
promotes antipathy regarding the killing of charismatic animals.
Although arguments against species exploitation are valid when
based on solid scientific or even philosophical criteria, much of
the criticism (e.g., Rivas, 2007) reflects emotional, political, or
ideological perspectives.
TOMÁS WALLER
The Yellow Anaconda (Eunectes notaeus Cope 1862) is the
largest snake in Argentina. It is distributed in the River Paraguay
drainage in Brazil, Bolivia, and Paraguay to northeastern
Argentina, where its range covers 120,000 km2 across six A Yellow Anaconda (Eunectes notaeus) from Formosa Province, Argentina.
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162 IGUANA • VOLUME 14, NUMBER 3 • SEPTEMBER 2007 MICUCCI AND WALLER
TOMÁS WALLER
The dorsolateral position of nostrils and eyes reflects the aquatic habits of Yellow Anacondas (Eunectes notaeus).
Anaconda skins, like those of other boas and pythons, are Sustainable Development Secretariat) asked us to design a man-
considered a valuable resource and are highly prized for the man- agement program for the species.
ufacture of exotic leather goods (Jenkins and Broad 1994). In
Argentina, trade in snake hides probably began earlier, but The Yellow Anaconda Management Program
peaked during the 1940s. An estimated 60,000 Boa Constrictor We conceived the Yellow Anaconda Management Program
(Boa constrictor) and Yellow Anaconda hides were exported from (YAMP), seeking to reconcile the traditional utilization of a
Argentina during each year of that decade (Gruss and Waller resource with its long-term conservation, and with the addi-
1988, Micucci et al. 2006a). From 1980 through 1999, about tional goals of promoting biological research on anacondas,
320,000 Yellow Anaconda skins were exported mainly from avoiding resource misuse and waste, and maximizing local
Argentina and Paraguay, primarily to the USA and Europe income favoring resource and habitat appreciation (Micucci et
(Micucci et al. 2006a). al. 2006a).
As with practically all squamates (Dodd 1993, Scott and From a conceptual perspective, we followed the Adaptive
Seigel 1992), the exploitation of Yellow Anacondas was carried Management Approach (AMA; Holling 1978), which was
out informally, without management guidelines or any regard to adopted due to the fact that we faced a system with high levels
the species’ biology (Waller et al. 2007). Our recent study shows of uncertainty, and because it provides the ideal conceptual
that Yellow Anaconda populations from Argentina exhibit favor- framework for exploited species for which research and popula-
able ecological attributes, with high scores in six broad scale cat- tion monitoring by standard methods becomes unfeasible in
egories that “enhance” (Shine et al. 1998) the species’ ability to practical terms. The AMA works on a step-by-step basis, mon-
withstand decades of intense harvesting (Waller et al. 2007). itoring the effects of actions taken through specific control vari-
Hunting of Yellow Anacondas diminished abruptly when ables and promoting changes, when appropriate, in a feedback
trade was effectively banned in 1999; however, in several loca- fashion to progressively reduce uncertainty.
tions in Formosa, anacondas were opportunistically captured Anaconda populations are actually managed on the basis of
and their hides smuggled to Paraguay for export. In 2001, we “sustained yield” harvest theory (Caughley and Sinclair 1994,
carried out a study in the Province of Formosa, Argentina, for Webb 2002). Specifically, we tested surplus-yield production
the purpose of analyzing the feasibility of harvesting Yellow models (i.e., Schaefer 1954, Fox 1970), which have been used
Anaconda skins in a sustainable manner (Micucci et al. 2002). mainly in fisheries, but also for terrestrial fauna.
Research focused on social and ecological aspects, and involved From a methodological perspective, a harvest can be con-
experimentation with innovative management policies. In 2002, trolled either by placing a quota or by controlling hunting effort
as a direct result of that research, the CITES National Authority (setting a hunting season or limiting the number of people or
(National Coordination for Biodiversity, Environment, and the amount of time they are harvesting a population; Caughley
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YELLOW ANACONDAS IN ARGENTINA IGUANA • VOLUME 14, NUMBER 3 • SEPTEMBER 2007 163
and Sinclair 1994). The YAMP follows the latter approach, vested. Controlling effort usually is a safer mean of regulating a
making no effort to control directly the number of animals har- harvest than imposing a quota. Harvesting a constant number
of animals each year is risky, particularly when the population is
affected by environmentally induced swings in abundance
(Caughley and Sinclair 1994) or when conducting a census of
populations is a major constraint, both situations we knew or
expected to occur in Yellow Anacondas inhabiting highly sea-
sonal savannas.
Fundación Biodiversidad (FB) was appointed by agreement
with the federal government to lead and execute the program.
Annual tasks and budgets are outlined in operative plans sub-
mitted annually for approval by the federal and provincial
wildlife authorities. Seven major reptile skin exporters finance
the program under a mechanism controlled by the central gov-
ernment. Federal regulations state that project benefactors will
distribute benefits (i.e., snake hides) among themselves in pro-
portion to the funds that each has contributed. Funds are
received from donors by an administrative NGO (Fundación
ArgenINTA), bonded by the federal authority, and then trans-
ferred to FB as needed. The Province of Formosa, in northeast-
ern Argentina, was selected for implementing the experimental
harvest program due to the abundance of anaconda habitat, a
long-standing hunting tradition, and a favorable governmental
predisposition. Formosa (Wildlife Agency, Ministry of
Production) has the responsibility for establishing and control-
ling procedures and guidelines for executing the program at the
Operative scheme of the Yellow Anaconda Management Program. local level.
TOMÁS WALLER
The floodplain of the Pilcomayo River in northeastern Argentina, locally known as “Bañado La Estrella,” covers approximately 3,000 km2 and
harbors a large population of Yellow Anacondas (Eunectes notaeus). This savanna exhibits drastic seasonal changes, from complete flooding in
autumn (shown) to almost complete drought in early summer. Yellow Anacondas take advantage of rodents and concentrations of birds during
both periods.
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164 IGUANA • VOLUME 14, NUMBER 3 • SEPTEMBER 2007 MICUCCI AND WALLER
from the Pilcomayo Riverbed; the original river inundated vast
dry woodlands during its progressive regression to the west.
Large grasslands, palm savannas, and standing dead Chaco for-
est patches, with tree stumps covered with climbing plants
(locally called “champales”) during the flood season, combine to
form a singular landscape matrix.
Formosan anaconda populations are comprised mainly of
adults. Females are larger than males, occasionally reaching a
maximum size of 335 cm SVL, whereas males rarely exceed 250
cm. Average animals are about 180 cm, and very large specimens
are uncommon (< 5%). Males exhibit larger cloacal spurs than
females, allowing the determination of sex even on skins.
Growth and maturity are quite rapid, with males capable of
breeding at 128 cm SVL and females at 147 cm, during the
third year of life, depending on food availability, genetics, and
individual life history traits. Courtship lasts from the beginning
Map of Formosa Province, Argentina, showing the areas with suitable of September to early November (local spring), and pregnant
Yellow Anaconda (Eunectes notaeus) habitat.
females are found during the summer months. Parturition in
Formosa occurs from late March to the end of April (local
autumn). Anacondas reproduce on average every two years,
depending on the female’s fat reserves. Fecundity is positively
The Setting correlated with female size, with an overall mean value of 24 off-
The 72,066-km2 Province of Formosa lies entirely within the spring per clutch. Newborns are large (49 cm SVL), very aggres-
Chaco region. For the purpose of our work, we divided the area sive, and fast growers (Waller et al. 2007).
into two regions: (a) Eastern Formosa, a 35,000-km2 plain with Anacondas are abundant everywhere in Formosa, with the
meandering rivers and creeks, palm savannas, mesic forest eastern provincial plains providing the most extensive habitat
patches, and swamps; and (b) La Estrella marsh, a 250-km long (>6,000 km2 of scattered tropical wetlands) and harboring
seasonal floodplain covering nearly 3,000 km2 in the otherwise potentially the largest populations. However, YAMP has
dry west of the province. This very unstable wetland originates received particularly strong support from the local communities
DANIEL GOMEZ
Yellow Anacondas (Eunectes notaeus) do not breed every year; however, clutch mass can equal half the weight of a female. Here, an individual from
San Juan Poriahu Ranch, Loreto, Corrientes, Argentina, is giving birth.
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YELLOW ANACONDAS IN ARGENTINA IGUANA • VOLUME 14, NUMBER 3 • SEPTEMBER 2007 165
domly survey hunters, collecting data on prices and payout
modalities. Each LSB serves a designated area, defined in the
local buyer’s license. If the buyer reaches beyond his area, this
could conflict with other LSBs, who will consequently report it
to relevant authorities. The infringer could suffer confiscation of
his goods, among other penalties. The rationale is to generate a
local socio-economic impact, equitably including as many fam-
ilies as possible.
During April and May, a series of trips are organized to reg-
ister and inform LSBs of any modifications to program guide-
TOMÁS WALLER
lines. These activities are intended to regulate the hunting effort,
although the program places no limit on the number of hunters
Burn scars on the head of a Yellow Anaconda from La Estrella marshes. (in practice they represent a finite number), actual numbers are
The grasslands and dry wetlands are burned during the dry season to closely tied to the number of skin buyers for economic and cul-
facilitate removal of domestic pigs. Snakes are sometimes injured or tural reasons. During the last week of May, and immediately
killed. before the beginning of the harvest (June), we notify the LSBs
of the skinning pattern to be used in the forthcoming season. In
some cases, hides must bear both spurs on one side, in other
living around La Estrella marsh, where a subsistence economy cases, one on each side. This, in combination with leaving the
of rural and indigenous people prevails. Eastern Formosa is more entire head attached to the skin or not, for instance, allows us to
socially complex, with a different land tenure scheme, more jobs, select from a large array of different skinning specifications from
and demanding a different approach. Because 90% of the har- one year to the next in order to minimize the incidence of ille-
vest takes place at La Estrella marsh (Micucci et al. 2006a), most gal hunting and stockpiling.
of the analysis and conclusions presented here pertain to that
region unless indicated otherwise.
Harvest Control Procedures
The harvest of Yellow Anacondas is strictly confined to three ele-
ments: hunters, local skin buyers, and exporters. Middlemen
(sub-local buyers and transporters) are not allowed. In the past,
middlemen increased the value of the skins to the detriment of
hunters. Anaconda collectors are rural and mostly indigenous
(pilagá, toba). They rely on livestock breeding, hunting, and
fishing. Some 250–450 families are involved in anaconda hunt-
ing, mostly (80%) from the area surrounding La Estrella marsh.
The local skin buyer (LSB) also serves as a food supplier or
EMILIO WHITE
market-man, and can manage the logistics of transporting and
stockpiling snake hides. Ten to 13 LSBs participate in a harvest,
with a mean number of 35 hunters per buyer. According to Emergent logs and logs covered by climbing plants, locally known as
“champas,” are preferred basking sites of Eunectes notaeus in La Estrella
YAMP guidelines, the exchange of goods for skins is forbidden, marshes in northeastern Argentina. Snakes seek these microhabitats
unless it is at the specific request of an indigenous community. during the winter, when water temperatures drop to 15 °C or lower.
To ensure compliance, at the end of each harvest season, we ran- Both males and females need warmer temperatures to complete
gonadal cycles before the onset of the mating season in spring.
TOMÁS WALLER
EMILIO WHITE
Patricio Micucci (left) and collaborators from the Paraguayan CITES Yellow Anacondas (Eunectes notaeus) are most vulnerable to
office measuring Yellow Anaconda skins seized in Asunción, Paraguay collection during the winter when they are cold and leave the water
in 1996. to bask.
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166 IGUANA • VOLUME 14, NUMBER 3 • SEPTEMBER 2007 MICUCCI AND WALLER
The minimum size of hides is 230 cm from the neck to the
anal scale, corresponding to a live specimen measuring approx-
imately 200 cm SVL (live SVL = 11.71 + 0.66 ⫻ skin length +
1.59 ⫻ skin width, r 2 = 0.93, P < 0.01; Micucci et al. 2003).
Because females mature at an average of 165 cm SVL (Waller et
al. 2007), this precautionary provision is intended to allow ana-
condas a reproductive opportunity before hunted.
The harvest takes place from June to August (local winter),
a period when Yellow Anacondas do not exhibit any reproduc-
tive behavior. The cool weather and the wide range of winter
TOMÁS WALLER
temperatures promote thermoregulatory behavior, allowing
hunters to find and capture snakes by hand. Snakes, depending
on program research requirements, are killed in place or trans- An excavation used by hunters in La Estrella marshes to keep the
ported live to the hunter’s home for data collection. snakes alive for biological studies.
Most of the conditions imposed on the hunters are enforced
when they bring their skins to the LSBs for sale. Skins that do
not comply with program standards are worthless. Furthermore,
LSBs are visited periodically by a representative of the exporters effort, size and sex structure of the harvest). Hunting effort is
(purchasing agent), a provincial wildlife officer, and a program closely checked by means of the aforementioned effort forms,
team member for the purpose of buying skins. Anaconda hides on which basic data are recorded. The model assumes that each
are checked for compliance to the year-specific skinning pattern batch of skins sold by a hunter to his local buyer (LSB) repre-
and minimum size guidelines. At this time, skins that conform sents a short and measurable hunting period or event. In case of
to program standards are individually tagged for control and suspicious data, we compare hunting effort information from
future tracking; non-compliant hides are seized and, according to hunters among different years to detect possible changes in pat-
program provisions, destroyed. These visits occur at intervals of tern due to involuntary or intentional errors. For instance, since
about three weeks. These procedures and a gradual decrease in the LSBs are the only middlemen approved to stockpile skins,
flexibility criteria have reduced the number of undersized skins an excessive number of skins (above average values) sold by a
from 1,109 hides in 2002 to 142 hides in 2006. hunter is considered suspect and is investigated.
During the sale, the LSB fills out an “effort form,” a legal Most of our energy is invested in reducing data errors and
document that records the number of skins, the name of the uncertainty. For example, since the beginning of the Program in
hunter, and the date and place of harvest. This document is 2002, we have been able to reduce uncertainty progressively
needed for the hides to be legally transported within Formosa. from about 15% to 5% with regard to the number of hunters
The contents of the document are crosschecked against the that are effectively collecting snakes in a given year. Since cur-
results from periodic hunter surveys. In case of irregularities, a rent uncertainty values are stabilized and are acceptable, we can
buyer could be penalized by the cancellation of his license. check and recalculate weak hunting effort estimates from the
Tagged hides obtained through the prescribed process are first year.
transported periodically to a warehouse in the city of Formosa. Hunting effort values depend not only on the number of
The representative of the exporters is the only person authorized hunters, but also on the time invested in that activity. Because
to transport anaconda hides. Once they arrive, skins are inven- we cannot closely monitor the time each of the 350 hunters
toried. At the end of the season, but before leaving the province, invests in collecting snakes, we record the gross time (or total
hides are sexed (by spurs and bone remnants), measured, and days) a LSB and its hunters are operative as a valid approxima-
field tags are replaced by export tags that comply with federal tion of actual time invested. This is easily accomplished since
regulations. The export tag is required before a CITES export each hunting season is precisely framed by start and end dates:
permit is issued and the skins can be transported out of the
province. Wildlife inspectors from Formosa, and eventually
from the central government, as well as a representative of Table 1. Yellow Anaconda (Eunectes notaeus) harvest monitor-
YAMP supervise this procedure. ing indices for La Estrella marsh, Formosa.
Once skins are tagged and all valuable data gathered, the
skins are released for distribution among the seven exporters. In Year Hunters Effort Capture CPUE2 Mean
(dH-1) (u.)1 Autumn T
order to transport the hides to tanneries or export ports,
Formosan authorities must issue a Transport Guide to each 2002 305 24,779 3,973 0.14 18.0 °C
exporter. This document is enclosed with the shipment and is 2003 303 37,000 3,327 0.08 20.7 °C
required by CITES Management Authorities in order to issue 2004 313 22,407 4,275 0.15 16.6 °C
the pertinent CITES Export Permit.
2005 301 22,187 3,834 0.12 20.0 °C
Harvest Sustainability Monitoring 2006 213 16,051 2,346 0.11 18.7 °C
We monitor the impact of the harvest on anaconda populations 1 Skins >230 cm
through traditional indicators (i.e., capture per unit effort vs. 2 See text for CPUE estimation
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YELLOW ANACONDAS IN ARGENTINA IGUANA • VOLUME 14, NUMBER 3 • SEPTEMBER 2007 167
(1) The day the skinning pattern is distributed to hunters (har-
vest opening day), and (2) The day the last skins are retired from
a local buyer’s facility (harvest closing day).
Capture per unit effort (CPUE = capture/hunters * total
days), the first of our indicators, is calculated at the end of the
harvest season. CPUE is an affordable and inexpensive estima-
tor of population trends and can be assessed at different spatial
scales from local to provincial. From a theoretical perspective,
rather than presenting estimates for a specific location or for the
entire province, calculating CPUE values for an ecologically uni-
TOMÁS WALLER
form and delimited area is desirable. From a management per-
spective, our resolution level should be the management unit
(Mendez et al. 2007). La Estrella marsh, aside from being our A Yellow Anaconda skin nailed to the soil with Palm spines, which are
main management unit for anacondas in Formosa, has a clear used for this purpose in eastern Formosa. In La Estrella marshes, spines
landscape homogeneity delimited by definite natural boundaries from a local bush (Prosopis ruscifolia) are used for the same purpose.
and exhibits no particular internal barriers to the dispersal of the
snakes.
Annual CPUE values for La Estrella marsh were calculated
from the slope of the “catch versus effort” regression line for each
year, using the catch and effort data from the different buying
centers (Micucci et al. 2007).
The effective hunting area (the cumulative territory of all
the hunters) encompasses 20,000–30,000 ha of wetlands,
depending on number of hunters. If we know the area for which
the CPUE value has been calculated, we can estimate other
TOMÁS WALLER
demographic parameters, such as anaconda population density
(Micucci et al. 2006b). To carry out this analysis, we made sev-
eral assumptions that render the estimate very preliminary and
without statistical significance, but nevertheless of great utility The button marks used to identify skins prior to export (AR:
Argentina, YA: Yellow Anaconda, and the number).
in providing an idea of abundance. For instance, we considered
that a hunter always follows the same trail, which we know is
not entirely true. However, we also assumed that collecting areas
do not overlap among hunters, and again this is not realistic,
although it compensates for errors caused by the previous
assumption. We assumed that all anacondas are removed in a
given year or season within a hunter’s territory, which could not
possibly be true, given the striking landscape complexity and
current rudimentary methods of hunting. Consequently, den-
sity values are presumed to be greatly underestimated. A calcu-
lated density value for Yellow Anacondas of approximately
TOMÁS WALLER
30–60/km2 of wetland is consistent with our subjective percep-
tions of abundance based on years of field observations.
CPUE values for the first five years of harvest show an oscil-
lating system tightly related to late autumn average temperatures A hunter extracting Prosopis ruscifolia spines for use as “nails” to stretch skins.
Table 2. Yellow Anaconda (Eunectes notaeus) density at La Estrella marsh compared to other large snakes for which data are available.
Snake Species S/km2 Locality and Source
Python regius 234 Southern Ghana, Africa (Gorzula et al. 1997)
Naja melanoleuca 212 Reserva Natural Abuko, Gambia, Africa (Starin and Burghardt 1992)
Dendroaspis viridis 120 Reserva Natural Abuko, Gambia, Africa (Starin and Burghardt 1992)
Python sebae 67 Reserva Natural Abuko, Gambia, Africa (Starin and Burghardt 1992)
Eunectes notaeus 30–60 This article
Bitis arietans 42 Reserva Natural Abuko, Gambia, Africa (Starin and Burghardt 1992)
Eunectes murinus 36 Hato El Catedral, Venezuela (Rivas 1999)
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168 IGUANA • VOLUME 14, NUMBER 3 • SEPTEMBER 2007 MICUCCI AND WALLER
TOMÁS WALLER
The Yellow Anaconda Management Program observed yield curve.
Actual harvest monitoring also takes into consideration the
significant correlation between number of hunters and gross
capture. More hunters usually implies more effort, more cap-
ture, and vice versa: Gross capture = 17 ⫻ hunters – 1.280 (R 2:
0.97) (Micucci et al. 2007). 2006, for example, was a “bad” year
TOMÁS WALLER
for captures because of the low number of hunters, which meant
that the effort for that year diminished in relation to previous
harvest seasons. In this sense, a gradual but permanent drop in
Drying Yellow Anaconda skins “nailed” to the dry Chaco soil using the number of hunters has not influenced CPUE values in a sig-
spines of a local bush (Prosopis ruscifolia). nificant manner (Table 1). This drop was in response to an
increased demand for labor and an indiscriminate distribution
of unemployment benefits to hunters and their families since
(May–June). The harvest takes place mostly during the cool win- 2003. In other words, if YAMP does not increase skin prices in
ter (June–August), when anacondas need to bask to raise their order to compensate for currency depreciation (as we are con-
body temperatures. In this sense, the relationship between CPUE stantly striving to do), the system tends to stabilize in such a way
and temperature is an expression of vulnerability: When autumn that exporters’ actual profits are in consonance with actual struc-
temperatures are high, fewer anacondas will bask and CPUE val- ture. If exporters are reluctant to increase skin price as a means
ues in the subsequent season are expected to diminish. A predic- of avoiding hunter desertion, evidence strongly suggests that, in
tive model between CPUE and average autumn temperatures this effort-mediated system, a commercial collapse will precede
was inferred by calculating the following linear regression: CPUE the biological collapse of the resource.
= -0.015 ⫻ T ºCmeanM,J + 0.40 (R 2: 0.78; Micucci et al. 2007).. Although a substantial reduction in active hunters
Appraisals of harvest intensity are derived from yield curves, inevitably leads to a drop in gross capture, the time variable is
analyzing capture volumes in relation to applied effort. These also a significant component for estimating hunting effort. The
curves can be obtained from effort and CPUE data but, for this to difference between hunters and effort is the sum of gross time
be accurate and have some predictive value, large temporal series invested by each local buyer. This is evident from the capture
are needed in order to deduce the maximum sustainable yield. Our and CPUE values for 2003. The harvest season was extended for
data do not represent a large temporal series (only five years); thus two weeks due to exceptionally warm conditions, and, with the
they do not yet exhibit the broad diversity of effort values needed same number of hunters compared to other seasons (2002 and
to present conclusive results for a particular surplus-yield model. 2005), both capture and CPUE diminished. In this way, we
Total capture values are certainly useless to predict popula- deduced a preliminary maximum sustained yield (MSY) value
tion trends if they are not considered in relation to hunting for La Estrella marsh of about 4,350 hides, with an ideal effort
effort. While reductions in capture volumes should catch our of approximately 28,000 dH-1.
attention, data misinterpretation could lead to incorrect conclu- Monitoring sustainability must assess the evolution of the
sions. Because the rationale of sustained yield models implies sex ratio of the harvested population. Both sexes, due to low
that a harvest represents a specific proportion of the total popu- temperatures, are equally vulnerable to capture (Waller et al.
lation, a reduction of the crop would be expected, for instance, 2007). However, because females attain larger size than males,
in the case of a population decline caused by natural conditions the established size limit (> 200 cm SVL) was expected to result
(i.e., drought, fires), but this does not mean over-harvesting in in the harvest of more females than males, presumably in a
that year (Caughley and Sinclair 1994). As temperatures play a fairly constant and predictable proportion. Consequently, the
significant role in anaconda vulnerability, captures will vary from actual harvest sex ratio (ca. 75% females) reflects only the estab-
year to year. lished minimum size limit. The harvest sex ratio was relatively
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YELLOW ANACONDAS IN ARGENTINA IGUANA • VOLUME 14, NUMBER 3 • SEPTEMBER 2007 169
similar season after season, with only a small increase in females Table 3. Main parameters for Yellow Anaconda (Eunectes
in later years. We consider this increase a mathematical artifact. notaeus) skins harvested at La Estrella Marsh, Formosa.
Eight percent of the skins in the first two years were classed as
Year 2002 2003 2004 2005 2006
“unknown” sex. Subsequently, sex determination became much
more accurate by also examining the attached limb bone rem- Average skin
nants rather than just the spurs, and the undetermined propor- length (cm)1 271 268 264 263 263
tion of skins diminished to 1.3%, although the proportion of Number of
females increased, whereas the proportion of males remained skins < 230 cm 1,109 1,075 420 343 142
constant. ⑀ coefficient 2 -4.0% -5.5% -0.4% +1.2% +0.4%
Females (%) 70.5 69.9 75.8 75.4 76.3
Males (%) 21.3 22.1 20.7 23.1 22.4
Unknown sex (%) 8.2% 8 % 3.5% 1.5% 1.3%
1 Average size of hides >230 cm after correcting for deformation (see text).
2 Skin deformation coefficient (see text for explanation).
Prior to the introduction of the sustainable use program,
anaconda exploitation was not permitted and illegal hunting
took place with total disregard of size. According to traders and
local dealers, Formosa’s annual production was approximately
20,000 skins with widths > 15 cm (Micucci et al. 2002, 2006a).
This hide width, according to our data, would correspond to a
skin length of 150 cm and a live anaconda of about 135 cm SVL
(Micucci et al. 2002). Many of the 500 or so seized Paraguayan
skins that we measured confirmed that the minimum size of
skins taken during illegal harvests were of that size. That trans-
lates to practically all (90%) anacondas of either sex older than
1.5 years of age (Waller et al. 2007) being vulnerable during that
market-driven hunting period. That current harvest policy has
been able to substantially reduce female hunting, both in terms
of juveniles and adults, is indisputable. Current production,
without mediation of quotas, represents a management-derived
reduction of harvest to a quarter of Formosa’s historical values
(5,000 vs. 20,000 skins), and a 40% reduction of female vulner-
ability to hunting. So, the Program has been very conservative
in establishing a minimum size limit despite the fact that, upon
initial consideration, it appears to promote the hunting of
females. What ultimately matters, however, is the overall num-
ber, not the proportion of females. If our harvest represents 5%
of the total population, a crop that is 75% female equates to an
overall female extraction of 3.75%, which is sustainable.
Hunters do not seek anacondas of specific sizes, but collect
serendipitously the snakes available in a given area (Waller et al.
2007). During the first years of the Program (2002–2003), dif-
ferent prices were paid for skins of three different size classes
(230–290 cm, 291–390 cm, > 391 cm), stemming from indus-
try traditions aimed at promoting the harvest of larger snakes.
We were aware that such guidelines were unlikely to produce the
desired results for traders. In fact, in 2002 and 2003, instead of
encouraging the harvest of large animals, this approach pro-
moted the hunting of undersized snakes and severe skin defor-
mation attributable to hunters stretching skins. Importers com-
Effects of skin minimum size limits on female anaconda harvest: (a) plained because stretched skins would inevitably shrink
Natural size distribution of anaconda populations in Formosa, females
in black (Waller et al. 2007); (b) Expected proportion of females in the considerably when tanned.
harvest at different size cut-off limits; (c) Proportion of potentially har- In 2004, we established a single price and demanded that
vestable females in a natural population at different size cut-off limits. all anaconda hides conform to a standard represented by the
Iguana 14.3 b&w text 7/28/07 9:57 PM Page 170
170 IGUANA • VOLUME 14, NUMBER 3 • SEPTEMBER 2007 MICUCCI AND WALLER
Size distributions of skins harvested from 2002–2006 (columns in
Size distribution of a shipment of Yellow Anaconda skins that were order). Only skins above 230 cm are included. Hide sizes are corrected
seized and measured in 1996 in Asunción, Paraguay (N = 539). for intentional stretching (see text).
Harvest Economics
The economic structure of YAMP includes government (federal
and provincial), exporters (7), hunters (about 350), local buyers
(10–13), and the NGO in charge of the technical program. The
government sector receives the smallest portion (4.2%) of par-
titioned benefits. In fact, the government delegates the admin-
istration of the program to an NGO in order to encourage
prompt and direct allocation of funds for research and monitor-
ing (14.8%). Hunters and local buyers collectively earn 13.3%,
but three-fourths of this amount goes into hunters’ pockets.
TOMÁS WALLER
Consequently, about one-third of the international value of a
skin remains in the region. Although actual earnings at the local
The cloacal region of a Yellow Anaconda skin with spurs (insert) that community level represent a three-fold increase over prices paid
allow sexing of the skin (in this case, a male). by illegal traders just a few years ago, we strongly encourage
higher prices to enhance the local allocation of benefits.
equation: skin width at midbody = 0.10 ⫻ skin length. In order Table 4. Yellow Anaconda Management Program benefit parti-
to correct hides for hunter-induced deformation and be able to tioning (based on a US $50 skin price).
perform demographically sound interpretations of population
structure for any year, we developed the following formula to Stakeholder US $ %
convert rough skin length values to corrected skin length values: Provincial and export taxes 2.1 4.2
Skin lengthc = (skin length + (skin width ⫻ 10))/2. This for- Program running costs (NGO) 7.4 14.8
mula assumes (due to the cross pattern of skin fibers) that, for
Hunters and local buyers 6.7 13.3
any increment in one dimension, a reduction in the other will
compensate. To control for skin deformation, we also devised a Stockpiling logistic expenses 3.1 6.2
stretching coefficient that permits us to determine the degree of Total expenses per skin 19.3 38.5
bias (%) of a harvested skin (uncorrected length) from its “real” Exporters income 30.7 61.5
(corrected length) shape. When we compared sizes of harvested
skins corrected for length, we found no significant difference in
population size structures for prior years that may have been
attributable to the stratified price scheme, confirming our views Conclusions
on the stochastic nature of hunting. The Yellow Anaconda Management Program has been in oper-
If a population is overexploited, we would expect to see a ation for five years. Aside from the beneficial local economic
reduction in the average size of skins harvested. Instead, we see impact, it has generated intense research on aspects of the
an oscillating pattern, partly attributable to changes in the skin- species’ biology (Waller et al. 2007) and population genetics
ning guidelines since 2004 and to a progressive reduction of (Mendez et al. 2007). The conservation biology of this species
small skins due to the imposition of intensive controls. Because had been completely ignored until the establishment of YAMP,
no significant consistent reduction in the average size of snakes and ongoing results are being incorporated into the model to
(i.e., skins) has been noted (Micucci et al. 2007), we suggest that reduce uncertainty levels.
current harvest guidelines are appropriate for continued sustain- No discernible negative, harvest-related population trend
able management of the anaconda populations. has been detected. CPUE values, as well as the descriptive sta-
Iguana 14.3 b&w text 7/28/07 9:57 PM Page 171
YELLOW ANACONDAS IN ARGENTINA IGUANA • VOLUME 14, NUMBER 3 • SEPTEMBER 2007 171
tistics for harvested skins, exhibit an oscillating but safe pattern Gruss, J.X. and T. Waller. 1988. Diagnóstico y recomendaciones sobre la
administración de recursos silvestres en Argentina: La década reciente.
of variation. CPUE values responded in direct relation to envi- TRAFFIC Sudamérica, WWF, Secretaría CITES, Buenos Aires,
ronmental factors that affect anaconda vulnerability (i.e., Argentina.
autumn temperatures). Observed differences in average skin size Henderson, R.W, T. Waller, P.A. Micucci, G. Puorto, and R.W. Burgeois. 1995.
or sex ratio during this period relate to changes in the skinning Ecological correlates and patterns in the distribution of Neotropical
boines (Serpentes: Boidae): A preliminary assessment. Herpetological
guidelines and sexing procedures since 2004, and to an improve- Natural History 3: 15–27.
ment in the control of undersized hides. Yield is determined by Holling, C.S. 1978. Adaptive Environmental Assessment and Management. J.
the number of active hunters, showing that controlling effort is Wiley & Sons, London.
a viable method of monitoring and limiting the harvest. Jenkins, M. and S. Broad. 1994. International trade in reptile skins. A review
The program impacts about 20–30 thousand ha of wet- and analysis of the main consumer markets, 1983–1991. A TRAFFIC
Network Report, TRAFFIC International, Cambridge, United
lands, representing 2–3% of suitable habitat available in Kingdom.
Formosa, which is relatively insignificant if we consider the Mendez, M., T. Waller, P.A. Micucci, E. Alvarenga, and J.C. Morales. 2007.
species’ total distribution. Assuming that current controls are Genetic population structure of the Yellow Anaconda (Eunectes notaeus)
maintained, the sustainable management of Formosa’s anaconda in northern Argentina: Management implications, pp. 405–415. In:
R.W. Henderson and R. Powell (eds.), Biology of the Boas and Pythons.
populations is possible. Eagle Mountain Publishing LC, Eagle Mountain, Utah.
The tools applied to control and monitor for harvest sus- Micucci, P.A., T. Waller, and E. Alvarenga. 2006a. Programa Curiyú. Para la
tainability have been effective, and could be replicated in other conservación y aprovechamiento sustentable de la Boa Curiyú (Eunectes
developing nations with marketable wildlife resources at a very notaeus) en la Argentina. Etapa experimental piloto 2002–2004,
Formosa, pp. 77–92. In: M.L. Bolkovic and D. Ramadori (eds.), Manejo
low cost. Considering the economic constraints that developing de Fauna Silvestre en la Argentina. Programas de Uso Sustentable. Dirección
countries face in implementing sound wildlife management de Fauna Silvestre, Secretaría de Ambiente y Desarrollo Sustentable,
practices, our experiences are encouraging. Buenos Aires, Argentina.
Wildlife management must consider sociology, economics, Micucci, P.A., T. Waller, and E. Buongermini P. 2002. Programa para la con-
servación y aprovechamiento sustentable de la Boa Curiyú (Eunectes
and a generous dose of psychology in addition to biology (Webb notaeus) en Argentina. Estudio de Prefactibilidad. ). Informe Técnico #
2002). In this broader context, whether the management pro- 1. Unpublished report, Fundación Biodiversidad Argentina, Buenos
cedures presented herein are optimal and the methods by which Aires.
Yellow Anacondas can be successfully managed for the long- Micucci, P.A., T. Waller, E. Alvarenga, and G.E. Lerea. 2006b. Programa para
la conservación y aprovechamiento sustentable de la Boa Curiyú (Eunectes
term benefit of local communities are appropriate questions that notaeus) en Argentina. Formosa. Informe Técnico # 4 (2005).
will require more than five seasons to be answered. Unpublished report, Fundación Biodiversidad Argentina, Buenos Aires.
Micucci, P.A., T. Waller, E. Alvarenga, and G.E. Lerea. 2007. Programa para la
Acknowledgements conservación y aprovechamiento sustentable de la Boa Curiyú (Eunectes
We express our deep thanks to Victoria Lichtschein (Biodiversity notaeus) en Argentina. Formosa. Informe Técnico Zafra 2006.
Unpublished report, Fundación Biodiversidad Argentina, Buenos Aires.
National Coordination Agency), Obdulio Menghi and
Micucci, P.A., T. Waller, E. White, and E. Alvarenga. 2003. Programa para la
Guillermo A. Puccio (Fundación Biodiversidad) for their con- conservación y aprovechamiento sustentable de la Boa Curiyú (Eunectes
stant support throughout the years; to Carlos A. Micucci for his notaeus) en Argentina. Etapa Experimental Piloto. Año I (2002).
help with data management; also to current and past Program Formosa. Informe Técnico # 2. Unpublished report, Fundación
Biodiversidad Argentina, Buenos Aires.
team members: Ernesto Alvarenga, Emilio Buongermini, Emilio
Rivas, J. 2007. Conservation of Green Anacondas: How Tylenol conservation
White, and Martín Mendez; and to Juan Carlos Orozco and macroeconomics threaten the survival of the world’s largest snake.
(Wildlife Agency Director) and Luis Basterra (Ministry of Iguana 14: 74–85.
Production) in Formosa for trusting in us. Schaefer, M.B. 1954. Some aspects of the dynamics of populations important
to the management of the commercial marine fisheries. Bulletin of the
Inter-American Tropical Tuna Commission 1(2): 27–56.
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