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160 IGUANA  •  VOLUME 14, NUMBER 3  •  SEPTEMBER 2007 MICUCCI AND WALLER

The senior author with a Yellow Anaconda (Eunectes notaeus) just captured in La Estrella marshes.

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Introduction

Many developing nations are attempting to convert unman-
aged and often illegal wildlife exploitation to sustainable

utilization programs. Such projects seek to instill economic value
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.

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

provinces (Henderson et al. 1995, Dirksen 2002, Micucci et al.
2006a). It is largely aquatic, a dietary generalist, and its range is
restricted mainly to wetlands and floodplains.

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

IGUANA  •  VOLUME 14, NUMBER 3  •  SEPTEMBER 2007 161YELLOW ANACONDAS IN ARGENTINA

�
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.

A Yellow Anaconda (Eunectes notaeus) from Formosa Province, Argentina.

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Anaconda skins, like those of other boas and pythons, are
considered a valuable resource and are highly prized for the man-
ufacture of exotic leather goods (Jenkins and Broad 1994). In
Argentina, trade in snake hides probably began earlier, but
peaked during the 1940s. An estimated 60,000 Boa Constrictor
(Boa constrictor) and Yellow Anaconda hides were exported from
Argentina during each year of that decade (Gruss and Waller
1988, Micucci et al. 2006a). From 1980 through 1999, about
320,000 Yellow Anaconda skins were exported mainly from
Argentina and Paraguay, primarily to the USA and Europe
(Micucci et al. 2006a).

As with practically all squamates (Dodd 1993, Scott and
Seigel 1992), the exploitation of Yellow Anacondas was carried
out informally, without management guidelines or any regard to
the species’ biology (Waller et al. 2007). Our recent study shows
that Yellow Anaconda populations from Argentina exhibit favor-
able ecological attributes, with high scores in six broad scale cat-
egories that “enhance” (Shine et al. 1998) the species’ ability to
withstand decades of intense harvesting (Waller et al. 2007).

Hunting of Yellow Anacondas diminished abruptly when
trade was effectively banned in 1999; however, in several loca-
tions in Formosa, anacondas were opportunistically captured
and their hides smuggled to Paraguay for export. In 2001, we
carried out a study in the Province of Formosa, Argentina, for
the purpose of analyzing the feasibility of harvesting Yellow
Anaconda skins in a sustainable manner (Micucci et al. 2002).
Research focused on social and ecological aspects, and involved
experimentation with innovative management policies. In 2002,
as a direct result of that research, the CITES National Authority
(National Coordination for Biodiversity, Environment, and

Sustainable Development Secretariat) asked us to design a man-
agement program for the species.

The Yellow Anaconda Management Program
We conceived the Yellow Anaconda Management Program
(YAMP), seeking to reconcile the traditional utilization of a
resource with its long-term conservation, and with the addi-
tional goals of promoting biological research on anacondas,
avoiding resource misuse and waste, and maximizing local
income favoring resource and habitat appreciation (Micucci et
al. 2006a).

From a conceptual perspective, we followed the Adaptive
Management Approach (AMA; Holling 1978), which was
adopted due to the fact that we faced a system with high levels
of uncertainty, and because it provides the ideal conceptual
framework for exploited species for which research and popula-
tion monitoring by standard methods becomes unfeasible in
practical terms. The AMA works on a step-by-step basis, mon-
itoring the effects of actions taken through specific control vari-
ables and promoting changes, when appropriate, in a feedback
fashion to progressively reduce uncertainty.

Anaconda populations are actually managed on the basis of
“sustained yield” harvest theory (Caughley and Sinclair 1994,
Webb 2002). Specifically, we tested surplus-yield production
models (i.e., Schaefer 1954, Fox 1970), which have been used
mainly in fisheries, but also for terrestrial fauna.

From a methodological perspective, a harvest can be con-
trolled either by placing a quota or by controlling hunting effort
(setting a hunting season or limiting the number of people or
the amount of time they are harvesting a population; Caughley

162 IGUANA  •  VOLUME 14, NUMBER 3  •  SEPTEMBER 2007 MICUCCI AND WALLER

The dorsolateral position of nostrils and eyes reflects the aquatic habits of Yellow Anacondas (Eunectes notaeus).

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IGUANA  •  VOLUME 14, NUMBER 3  •  SEPTEMBER 2007 163YELLOW ANACONDAS IN ARGENTINA

and Sinclair 1994). The YAMP follows the latter approach,
making no effort to control directly the number of animals har-

vested. Controlling effort usually is a safer mean of regulating a
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
local level.

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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Operative scheme of the Yellow Anaconda Management Program.

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164 IGUANA  •  VOLUME 14, NUMBER 3  •  SEPTEMBER 2007 MICUCCI AND WALLER

The Setting
The 72,066-km2 Province of Formosa lies entirely within the
Chaco region. For the purpose of our work, we divided the area
into two regions: (a) Eastern Formosa, a 35,000-km2 plain with
meandering rivers and creeks, palm savannas, mesic forest
patches, and swamps; and (b) La Estrella marsh, a 250-km long
seasonal floodplain covering nearly 3,000 km2 in the otherwise
dry west of the province. This very unstable wetland originates

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
of September to early November (local spring), and pregnant
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
correlated with female size, with an overall mean value of 24 off-
spring per clutch. Newborns are large (49 cm SVL), very aggres-
sive, and fast growers (Waller et al. 2007).

Anacondas are abundant everywhere in Formosa, with the
eastern provincial plains providing the most extensive habitat
(>6,000 km2 of scattered tropical wetlands) and harboring
potentially the largest populations. However, YAMP has
received particularly strong support from the local communities

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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Map of Formosa Province, Argentina, showing the areas with suitable
Yellow Anaconda (Eunectes notaeus) habitat.

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IGUANA  •  VOLUME 14, NUMBER 3  •  SEPTEMBER 2007 165YELLOW ANACONDAS IN ARGENTINA

living around La Estrella marsh, where a subsistence economy
of rural and indigenous people prevails. Eastern Formosa is more
socially complex, with a different land tenure scheme, more jobs,
and demanding a different approach. Because 90% of the har-
vest takes place at La Estrella marsh (Micucci et al. 2006a), most
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
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
YAMP guidelines, the exchange of goods for skins is forbidden,
unless it is at the specific request of an indigenous community.
To ensure compliance, at the end of each harvest season, we ran-

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-
lines. These activities are intended to regulate the hunting effort,
although the program places no limit on the number of hunters
(in practice they represent a finite number), actual numbers are
closely tied to the number of skin buyers for economic and cul-
tural reasons. During the last week of May, and immediately
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
cases, one on each side. This, in combination with leaving the
entire head attached to the skin or not, for instance, allows us to
select from a large array of different skinning specifications from
one year to the next in order to minimize the incidence of ille-
gal hunting and stockpiling.

Burn scars on the head of a Yellow Anaconda from La Estrella marshes.
The grasslands and dry wetlands are burned during the dry season to
facilitate removal of domestic pigs. Snakes are sometimes injured or
killed.

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Yellow Anacondas (Eunectes notaeus) are most vulnerable to
collection during the winter when they are cold and leave the water
to bask.

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Patricio Micucci (left) and collaborators from the Paraguayan CITES
office measuring Yellow Anaconda skins seized in Asunción, Paraguay
in 1996.

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Emergent logs and logs covered by climbing plants, locally known as
“champas,” are preferred basking sites of Eunectes notaeus in La Estrella
marshes in northeastern Argentina. Snakes seek these microhabitats
during the winter, when water temperatures drop to 15 °C or lower.
Both males and females need warmer temperatures to complete
gonadal cycles before the onset of the mating season in spring.

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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, r2 = 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
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-
ported live to the hunter’s home for data collection.

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
(purchasing agent), a provincial wildlife officer, and a program
team member for the purpose of buying skins. Anaconda hides
are checked for compliance to the year-specific skinning pattern
and minimum size guidelines. At this time, skins that conform
to program standards are individually tagged for control and
future tracking; non-compliant hides are seized and, according to
program provisions, destroyed. These visits occur at intervals of
about three weeks. These procedures and a gradual decrease in
flexibility criteria  have reduced the number of undersized skins
from 1,109 hides in 2002 to 142 hides in 2006.

During the sale, the LSB fills out an “effort form,” a legal
document that records the number of skins, the name of the
hunter, and the date and place of harvest. This document is
needed for the hides to be legally transported within Formosa.
The contents of the document are crosschecked against the
results from periodic hunter surveys. In case of irregularities, a
buyer could be penalized by the cancellation of his license.

Tagged hides obtained through the prescribed process are
transported periodically to a warehouse in the city of Formosa.
The representative of the exporters is the only person authorized
to transport anaconda hides. Once they arrive, skins are inven-
toried. At the end of the season, but before leaving the province,
hides are sexed (by spurs and bone remnants), measured, and
field tags are replaced by export tags that comply with federal
regulations. The export tag is required before a CITES export
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
YAMP supervise this procedure.

Once skins are tagged and all valuable data gathered, the
skins are released for distribution among the seven exporters. In
order to transport the hides to tanneries or export ports,
Formosan authorities must issue a Transport Guide to each
exporter. This document is enclosed with the shipment and is
required by CITES Management Authorities in order to issue
the pertinent CITES Export Permit.

Harvest Sustainability Monitoring
We monitor the impact of the harvest on anaconda populations
through traditional indicators (i.e., capture per unit effort vs.

effort, size and sex structure of the harvest). Hunting effort is
closely checked by means of the aforementioned effort forms,
on which basic data are recorded. The model assumes that each
batch of skins sold by a hunter to his local buyer (LSB) repre-
sents a short and measurable hunting period or event. In case of
suspicious data, we compare hunting effort information from
hunters among different years to detect possible changes in pat-
tern due to involuntary or intentional errors. For instance, since
the LSBs are the only middlemen approved to stockpile skins,
an excessive number of skins (above average values) sold by a
hunter is considered suspect and is investigated.

Most of our energy is invested in reducing data errors and
uncertainty. For example, since the beginning of the Program in
2002, we have been able to reduce uncertainty progressively
from about 15% to 5% with regard to the number of hunters
that are effectively collecting snakes in a given year. Since cur-
rent uncertainty values are stabilized and are acceptable, we can
check and recalculate weak hunting effort estimates from the
first year.

Hunting effort values depend not only on the number of
hunters, but also on the time invested in that activity. Because
we cannot closely monitor the time each of the 350 hunters
invests in collecting snakes, we record the gross time (or total
days) a LSB and its hunters are operative as a valid approxima-
tion of actual time invested. This is easily accomplished since
each hunting season is precisely framed by start and end dates:

166 IGUANA  •  VOLUME 14, NUMBER 3  •  SEPTEMBER 2007 MICUCCI AND WALLER

Table 1. Yellow Anaconda (Eunectes notaeus) harvest monitor-
ing indices for La Estrella marsh, Formosa.

Year Hunters Effort Capture CPUE2 Mean 
(dH-1) (u.)1 Autumn T

2002 305 24,779 3,973 0.14 18.0 °C

2003 303 37,000 3,327 0.08 20.7 °C

2004 313 22,407 4,275 0.15 16.6 °C

2005 301 22,187 3,834 0.12 20.0 °C

2006 213 16,051 2,346 0.11 18.7 °C

1 Skins >230 cm
2 See text for CPUE estimation

An excavation used by hunters in La Estrella marshes to keep the
snakes alive for biological studies.

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IGUANA  •  VOLUME 14, NUMBER 3  •  SEPTEMBER 2007 167YELLOW ANACONDAS IN ARGENTINA

(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-
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
main management unit for anacondas in Formosa, has a clear
landscape homogeneity delimited by definite natural boundaries
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
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
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
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

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)

A Yellow Anaconda skin nailed to the soil with Palm spines, which are
used for this purpose in eastern Formosa. In La Estrella marshes, spines
from a local bush (Prosopis ruscifolia) are used for the same purpose.

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The button marks used to identify skins prior to export (AR:
Argentina, YA: Yellow Anaconda, and the number).

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A hunter extracting Prosopis ruscifolia spines for use as “nails” to stretch skins.

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(May–June). The harvest takes place mostly during the cool win-
ter (June–August), when anacondas need to bask to raise their
body temperatures. In this sense, the relationship between CPUE
and temperature is an expression of vulnerability: When autumn
temperatures are high, fewer anacondas will bask and CPUE val-
ues in the subsequent season are expected to diminish. A predic-
tive model between CPUE and average autumn temperatures
was inferred by calculating the following linear regression: CPUE
= -0.015 � T ºCmeanM,J + 0.40 (R2: 0.78; Micucci et al. 2007)..

Appraisals of harvest intensity are derived from yield curves,
analyzing capture volumes in relation to applied effort. These
curves can be obtained from effort and CPUE data but, for this to
be accurate and have some predictive value, large temporal series
are needed in order to deduce the maximum sustainable yield. Our
data do not represent a large temporal series (only five years); thus
they do not yet exhibit the broad diversity of effort values needed
to present conclusive results for a particular surplus-yield model.

Total capture values are certainly useless to predict popula-
tion trends if they are not considered in relation to hunting
effort. While reductions in capture volumes should catch our
attention, data misinterpretation could lead to incorrect conclu-
sions. Because the rationale of sustained yield models implies
that a harvest represents a specific proportion of the total popu-
lation, a reduction of the crop would be expected, for instance,
in the case of a population decline caused by natural conditions
(i.e., drought, fires), but this does not mean over-harvesting in
that year (Caughley and Sinclair 1994). As temperatures play a
significant role in anaconda vulnerability, captures will vary from
year to year.

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 (R2:
0.97) (Micucci et al. 2007). 2006, for example, was a “bad” year
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
the number of hunters has not influenced CPUE values in a sig-
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
2003. In other words, if YAMP does not increase skin prices in
order to compensate for currency depreciation (as we are con-
stantly striving to do), the system tends to stabilize in such a way
that exporters’ actual profits are in consonance with actual struc-
ture. If exporters are reluctant to increase skin price as a means
of avoiding hunter desertion, evidence strongly suggests that, in
this effort-mediated system, a commercial collapse will precede
the biological collapse of the resource.

Although a substantial reduction in active hunters
inevitably leads to a drop in gross capture, the time variable is
also a significant component for estimating hunting effort. The
difference between hunters and effort is the sum of gross time
invested by each local buyer. This is evident from the capture
and CPUE values for 2003. The harvest season was extended for
two weeks due to exceptionally warm conditions, and, with the
same number of hunters compared to other seasons (2002 and
2005), both capture and CPUE diminished. In this way, we
deduced a preliminary maximum sustained yield (MSY) value
for La Estrella marsh of about 4,350 hides, with an ideal effort
of approximately 28,000 dH-1.

Monitoring sustainability must assess the evolution of the
sex ratio of the harvested population. Both sexes, due to low
temperatures, are equally vulnerable to capture (Waller et al.
2007). However, because females attain larger size than males,
the established size limit (> 200 cm SVL) was expected to result
in the harvest of more females than males, presumably in a
fairly constant and predictable proportion. Consequently, the
actual harvest sex ratio (ca. 75% females) reflects only the estab-
lished minimum size limit. The harvest sex ratio was relatively

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Drying Yellow Anaconda skins “nailed” to the dry Chaco soil using
spines of a local bush (Prosopis ruscifolia).

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The Yellow Anaconda Management Program observed yield curve.

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IGUANA  •  VOLUME 14, NUMBER 3  •  SEPTEMBER 2007 169YELLOW ANACONDAS IN ARGENTINA

similar season after season, with only a small increase in females
in later years. We consider this increase a mathematical artifact.
Eight percent of the skins in the first two years were classed as
“unknown” sex. Subsequently, sex determination became much
more accurate by also examining the attached limb bone rem-
nants rather than just the spurs, and the undetermined propor-
tion of skins diminished to 1.3%, although the proportion of
females increased, whereas the proportion of males remained
constant.

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-
plained because stretched skins would inevitably shrink
considerably when tanned.

In 2004, we established a single price and demanded that
all anaconda hides conform to a standard represented by the

Effects of skin minimum size limits on female anaconda harvest: (a)
Natural size distribution of anaconda populations in Formosa, females
in black (Waller et al. 2007); (b) Expected proportion of females in the
harvest at different size cut-off limits; (c) Proportion of potentially har-
vestable females in a natural population at different size cut-off limits.

Table 3. Main parameters for Yellow Anaconda (Eunectes
notaeus) skins harvested at La Estrella Marsh, Formosa.

Year 2002 2003 2004 2005 2006

Average skin 
length (cm)1 271 268 264 263 263

Number of 
skins < 230 cm 1,109 1,075 420 343 142

� coefficient2 -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).

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equation: skin width at midbody = 0.10 � skin length. In order
to correct hides for hunter-induced deformation and be able to
perform demographically sound interpretations of population
structure for any year, we developed the following formula to
convert rough skin length values to corrected skin length values:
Skin lengthc = (skin length + (skin width � 10))/2. This for-
mula assumes (due to the cross pattern of skin fibers) that, for
any increment in one dimension, a reduction in the other will
compensate. To control for skin deformation, we also devised a
stretching coefficient that permits us to determine the degree of
bias (%) of a harvested skin (uncorrected length) from its “real”
(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
on the stochastic nature of hunting.

If a population is overexploited, we would expect to see a
reduction in the average size of skins harvested. Instead, we see
an oscillating pattern, partly attributable to changes in the skin-
ning guidelines since 2004 and to a progressive reduction of
small skins due to the imposition of intensive controls. Because
no significant consistent reduction in the average size of snakes
(i.e., skins) has been noted (Micucci et al. 2007), we suggest that
current harvest guidelines are appropriate for continued sustain-
able management of the anaconda populations.

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.
Consequently, about one-third of the international value of a
skin remains in the region. Although actual earnings at the local
community level represent a three-fold increase over prices paid
by illegal traders just a few years ago, we strongly encourage
higher prices to enhance the local allocation of benefits.

Conclusions
The Yellow Anaconda Management Program has been in oper-
ation for five years. Aside from the beneficial local economic
impact, it has generated intense research on aspects of the
species’ biology (Waller et al. 2007) and population genetics
(Mendez et al. 2007). The conservation biology of this species
had been completely ignored until the establishment of YAMP,
and ongoing results are being incorporated into the model to
reduce uncertainty levels.

No discernible negative, harvest-related population trend
has been detected. CPUE values, as well as the descriptive sta-

170 IGUANA  •  VOLUME 14, NUMBER 3  •  SEPTEMBER 2007 MICUCCI AND WALLER

Size distribution of a shipment of Yellow Anaconda skins that were
seized and measured in 1996 in Asunción, Paraguay (N = 539).

Table 4. Yellow Anaconda Management Program benefit parti-
tioning (based on a US $50 skin price).

Stakeholder US $ %

Provincial and export taxes 2.1 4.2

Program running costs (NGO) 7.4 14.8

Hunters and local buyers 6.7 13.3

Stockpiling logistic expenses 3.1 6.2

Total expenses per skin 19.3 38.5

Exporters income 30.7 61.5

Size distributions of skins harvested from 2002–2006 (columns in
order). Only skins above 230 cm are included. Hide sizes are corrected
for intentional stretching (see text).

The cloacal region of a Yellow Anaconda skin with spurs (insert) that
allow sexing of the skin (in this case, a male).

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IGUANA  •  VOLUME 14, NUMBER 3  •  SEPTEMBER 2007 171YELLOW ANACONDAS IN ARGENTINA

tistics for harvested skins, exhibit an oscillating but safe pattern
of variation. CPUE values responded in direct relation to envi-
ronmental factors that affect anaconda vulnerability (i.e.,
autumn temperatures). Observed differences in average skin size
or sex ratio during this period relate to changes in the skinning
guidelines and sexing procedures since 2004, and to an improve-
ment in the control of undersized hides. Yield is determined by
the number of active hunters, showing that controlling effort is
a viable method of monitoring and limiting the harvest.

The program impacts about 20–30 thousand ha of wet-
lands, representing 2–3% of suitable habitat available in
Formosa, which is relatively insignificant if we consider the
species’ total distribution. Assuming that current controls are
maintained, the sustainable management of Formosa’s anaconda
populations is possible.

The tools applied to control and monitor for harvest sus-
tainability have been effective, and could be replicated in other
developing nations with marketable wildlife resources at a very
low cost. Considering the economic constraints that developing
countries face in implementing sound wildlife management
practices, our experiences are encouraging.

Wildlife management must consider sociology, economics,
and a generous dose of psychology in addition to biology (Webb
2002). In this broader context, whether the management pro-
cedures presented herein are optimal and the methods by which
Yellow Anacondas can be successfully managed for the long-
term benefit of local communities are appropriate questions that
will require more than five seasons to be answered.

Acknowledgements
We express our deep thanks to Victoria Lichtschein (Biodiversity
National Coordination Agency), Obdulio Menghi and
Guillermo A. Puccio (Fundación Biodiversidad) for their con-
stant support throughout the years;  to Carlos A. Micucci for his
help with data management; also to current and past Program
team members: Ernesto Alvarenga, Emilio Buongermini, Emilio
White, and Martín Mendez; and to Juan Carlos Orozco
(Wildlife Agency Director) and Luis Basterra (Ministry of
Production) in Formosa for trusting in us.

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