Exploitation of frogs – a review with a focus on West Africa

2009·13.6 MB·English

by  Mohneke, M

Exploitation of frogs
SALAMANDRA 45 4 193-202 Rheinbach, 20 November 2009 ISSN 0036-3375
Exploitation of frogs – a review with a focus on West Africa
Meike Mohneke, Abiodun B. Onadeko & Mark-Oliver Rödel
Abstract. With a continuously growing global human population the exploitation of natural resources
is likewise increasing. Herein we provide an overview on exploitation and trade of amphibian species in
different regions of the world, with a main emphasis on West Africa. Whereas particular West African
tribes have always used frogs as food, medicine or for cultural reasons, the current increase in frog hunt-
ing seems to be new. Amphibian declines are likely and may result in measurable changes to aquatic and
riparian ecosystems.
Key words. Amphibia, Anura, Benin, Burkina Faso, freshwater ecosystem, Hoplobatrachus occipitalis, Ni-
geria, over-exploitation, West Africa.
Introduction species (mainly anurans), 54% of these be-
ing already listed as Vulnerable, Endangered
The human reliance upon natural resources or Critically Endangered when IUCN Red
is often seen as one of the strongest political List categories and criteria are applied. The
arguments to preserve the global biodiversity results of the IUCN Global Amphibian As-
(Convention on Biological Diversity – CBD sessment (now under the IUCN Red List of
2008 – www.biodiv.org, last accessed on 22 Threatened Species) support this statement
April 2008). However, an over-exploitation of by listing 220 species that are currently used
these resources is one of today’s major threats for food, already indicating that many more
to biodiversity, leading e.g. to habitat degra- species might be affected (Cox et al. 2008).
dation and conversion, erosion of genetic di- Amphibian species are harvested and used
versity, species decline and loss, destabiliza- worldwide mainly as a food source, i.e. frog
tion and destruction of ecosystems and hence legs are thought to be delicacies in many re-
is jeopardizing present and future livelihoods gions of the world. However, frogs are also
(Cowlishaw 2005, CBD 2008). collected for leather production and souve-
Amphibians are one of the most threat- nirs, for the pet trade and for cultural rea-
ened groups of animals, with at least one sons including traditional medicine (Oza
third of the ca. 6,000 known species being 990, Veith et al. 2000, Stuart et al. 2004,
threatened with extinction (Stuart et al. Young et al. 2004, Kusrini & Alford 2006,
2004, 2008). Reasons for this are numerous Gonwouo & Rödel 2008). Most attempts to
but besides habitat degradation and loss, dis- commercially breed frogs in larger quantities
ease and rapid enigmatic declines, over-ex- under artificial, farm-like conditions have
ploitation is mentioned as one of the main failed (Oza 990, Helfrich et al. 200) and
causes (Gibbons et al. 2000, Stuart et al. hence the majority of amphibians are still
2004, Halliday 2008). Whereas habitat de- taken directly from the wild (Helfrich et al.
struction, global change and most of all dis- 200, Kusrini & Alford 2006).
ease have gained much research interest, Where this exploitation exceeds sustain-
overexploitation of frogs is rarely mentioned ability amphibian species are doomed with
to be of any importance. However, a recent local declines or extinctions (Jensen & Camp
report by Niasse et al. (2004) states that uti- 2003). In addition to these direct impacts on
lization is the main threat for 28 amphibian particular species, other indirect effects like
© 2009 Deutsche Gesellschaft für Herpetologie und Terrarienkunde e.V. (DGHT)
http://www.salamandra-journal.com 193
Meike Mohneke et al.
the loss of ecosystem functions are likely con- [Bombina orientalis (Boulenger, 890), ap-
sequences (Duffy 2002, Wright 2006). For proximately  million] (Schlaepfer et al.
example, amphibians play an important role 2005). About 3,000 poison-dart frogs (Den-
in various terrestrial and aquatic ecosystems, drobatidae) were exported from Latin Amer-
both as predators and as prey (Toledo et al. ica between 987 and 993, the majority, near-
2007, Halliday 2008, Mohneke & Rödel ly 8,000 individuals, being imported into the
2009). A decline of particular amphibian US (Gorzula 996). A total of 22,000 frogs
species may thus result in an overabundance of different species (approximately 70% of
of prey species, i.e. various pest arthropods, them identified as Mantella spp.) were ex-
and/or leave predators with a limited food ported from Madagascar for the internation-
supply. From our long-term personal experi- al pet market between 2000 and 2006 (Car-
ence it seems that the use of particular frog penter et al. 2007).
species recently has dramatically increased in
West Africa. The consequences are unknown.
In this paper we will summarize the most Europe
prominent examples of over-exploitation in
amphibians worldwide. We provide a first in- Frogs were already consumed during the Ro-
sight into the West African situation and we man Empire, and presumably much earlier.
highlight respective research needs. Since the 6th century frogs and their legs
in particular, have became a delicacy in Eu-
ropean gastronomy (Neveu 2004). The ma-
Unsustainable use of amphibians jority of them were harvested from nature.
In smaller quantities this was sustainable for
Although many amphibian species are adapt- centuries. However, after World War II the
ed to high mortality rates and hence to mod- demand seemed to increase tremendously.
erate exploitation alike, an intensive harvest The European green frog complex, Pelophy-
at least of particular species, may result in an lax spp. in particular, has served as the main
over-exploitation of local population or even resource for frog legs especially in France, fol-
whole species and thus in their decline. How- lowed by Belgium and the Netherlands (re-
ever, hard data on actual harvested frog num- sponsible for 80-90% of the European trade).
bers and respective consequences for popula- Due to the large numbers of harvested frogs
tions are still scarce or completely lacking. In in France (40-70 t per year; Neveu 2004), the
Table  we provide information on the main collecting, transport and sale of native frog
frog and salamander species harvested, in- populations was prohibited by French law
cluding their respective uses. In the following in 980. As a consequence France leads the
paragraphs we briefly summarize amphibian world today in the import rates of frog legs
exploitation in different regions of the world. (3000-4000 t per year) and living frogs (700-
We mainly focus on the use of frogs for con- 800 t per year) (Neveu 2004) from South-
sumption. Besides food trade, particular am- east Asia (see Veith et al. 2000). A more re-
phibians are also caught in large quantities cent example of autochthonous frog use in
for the pet trade (Schlaepfer et al. 2005). Europe is from Romania (Török 2003). As
The species in greatest demand are the Afri- fish stocks declined drastically in the Danube
can dwarf clawed frogs (Hymenochirus spp.; Delta the sustainable exploitation of frogs
2.4 million individuals officially imported was proposed. Between 960 and 970, an
into the US between 998 and 2002), fol- annual amount of 20 t of frogs was collect-
lowed by the Chinese fire-bellied newt [Cy- ed from Romanian waters, resulting in many
nops orientalis (David, 87), approximately depopulated biotopes which previously had
.6 million] and the Oriental fire-bellied toad been crowded with frogs.
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Exploitation of frogs
Asia mainly larger ranids. Recent investigations
have shown that in Indonesia large frogs have
Asian countries currently export the high- already completely disappeared from habi-
est numbers of frogs (see Warkentin et al. tats such as paddy fields and riversides close
2009). Until 985, 200 million frogs were ex- to human settlements, where they usually
ported each year from Asia to Europe, e.g. should be common (Veith et al. 2000). De-
West Germany imported 500 t (2 million pleted frog populations due to over-exploita-
frogs) from Bangladesh in 984 (Oza 990). tion seem to be a common Southeast Asian
For many years, India and Bangladesh were phenomenon. In China, 84 species are nega-
the main Asian exporters for frog legs. How- tively affected by utilization, because of ille-
ever, as a consequence of declining frog pop- gal collecting and a high domestic demand
ulations [mainly Hoplobatrachus tigerinus for these species. Especially, ranoid species,
(Daudin, 802) and Euphlyctis hexadacty- like Hoplobatrachus rugulosa (Wiegmann,
lus (Lesson, 834)], and a resulting increase 835), are harvested for utilization. Twelve
of insect pests, India banned exportation in out of 39 utilized species decline rapidly and
985 (Oza 990). Unfortunately there seems are threatened with extinction (Carpenter
to be no research to examine the potential re- et al. 2007). The collapse of populations of fa-
covery of these species since then. vorite frog leg species in Asia shows that even
With 4000 t of frogs harvested annually in common, fast-growing and fecund species
(Kusrini & Alford 2006), Indonesia is to- such levels of exploitation are not without
day’s world leading export country for frog limit (Lau et al. 2008).
legs, most of them (83.2%) still sold to Eu-
rope. Because of limited supplies, particular-
ly during the dry season, the export numbers North and South America
sometimes do not even meet the demand. Es-
tablished frog farms do not cultivate native Whereas frogs were probably used as food
species, but introduced species like the North by many Native American peoples for a long
American bullfrog, Lithobates catesbeianus time, it was the European immigrants who
(Shaw, 802) (Kusrini & Alford 2006). If introduced the commercial utilization of
these frogs make their way into the wild, this frogs in North America. Native frogs became
might pose a further threat to the native fau- important food sources and between the late
na. Bullfrog larvae are known to have strong 800s and early 900s, amphibians were ex-
negative effects on the growth and survival ploited for the American frog leg market.
rate of tadpoles of other species (Kupfer- During this period, hundreds of thousands
berg 997, Kiesecker et al. 200) and adults of Red-legged frogs (Rana aurora Baird &
regularly devour other amphibian species Girard, 852) and over 20 million Leopard
(Ficetola et al. 2007). Furthermore, L. cates- frogs [Lithobates pipiens Schreber, 872)
beianus is a successful carrier of chytridomy- and allied species] were collected annually
cosis (Daszak et al. 2004), an emerging in- from California wetlands and northwestern
fectious disease of amphibians caused by the Iowa (Gibbons et al. 2000). It has been esti-
amphibian chytrid fungus. mated that between 920 and 992 amphib-
Indonesian frogs are however, not only ian populations in an Iowa county declined
harvested for the overseas market, the local from at least 20 million to 50,000. At least
market seems to play an equal or even greater one-third of this decline could be attributed
role (Kusrini & Alford 2006). As the hu- to harvesting; two-thirds however were due
man population grows and resources such to wetland drainage (Lannoo et al. 994). As
as fish decline, people often switch to other local populations started to decline, frog legs
protein sources like particular frog species, have been imported from Asia, e.g. in 976
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Meike Mohneke et al.
Tab. 1. List of exploited amphibian species (excluding dendrobatid frogs), the scale of trade (R = regio-
nal, N = national, I = international) and the current conservation status based on the IUCN Red List of
Species Utilization Region Scale Time of exploitation IUCN Status Reference
Urodela
Ambystoma dumerilii Food, medicine Mexico I Present CR Carpenter et al. 2007
Ambystoma mexicanum Food, medicine, pet trade, research Mexico I Present CR Carpenter et al. 2007
Cynops orientalis Pet trade China I Present LC Schlaepfer et al. 2005
Anura
Astylosternus spp. Food Cameroon R Present LC-CR Gonwouo & Rödel 2008
Bombina orientalis Pet trade East Asia I Present LC Schlaepfer et al. 2005
Chaunus marinus Food, souvenir, pet trade, research America, Australia R, N, I Present LC Pough 200
Conraua crassipes Food Cameroon R Present LC Gonwouo & Rödel 2008
Conraua goliath Food Cameroon R Present EN Gonwouo & Rödel 2008
Conraua robusta Food Cameroon R Present VU Gonwouo & Rödel 2008
Euphlyctis hexadactylus Food India, Bangladesh I Past LC Oza 990, Veith et al. 2000
Fejervarya cancrivora Food Indonesia R, I Present LC Veith et al. 2000, Kusrini & Alford 2006,
Carpenter et al. 2007
Hoplobatrachus occipitalis food Africa R, N Present LC pers. obs.
Hoplobatrachus rugulosus Food South and Central China R, N, I Present LC Jensen & Camp 2003, Carpenter et al. 2007
Hoplobatrachus tigerinus Food Southern Asia, India I Present LC Pough 200, Oza 990, Carpenter et al. 2007
Hyla cinerea Pet trade United States I Present LC Schlaepfer et al. 2005
Hyla eximia Pet trade Mexico I Present LC Carpenter et al. 2007
Hymenochirus curtipes Pet trade DRCongo I Present LC Schlaepfer et al. 2005
Kassina decorata Food Cameroon R Present LC Gonwouo & Rödel 2008
Limnonectes macrodon Food Indonesia R, I Present VU Kusrini & Alford 2006, Carpenter et al. 2007
Lithobates catesbeianus Food North America Present LC Pough 200, Carpenter et al. 2007
Lithobates pipiens Food, research North America R, N, I Present LC Jensen & Camp 2003
Mantella spp. Pet trade Madagascar I Present LC-CR Carpenter et al. 2007
Pachymedusa dacnicolor Pet trade Mexico I Present LC Carpenter et al. 2007
Pelophylax lessonae Food Europe N, I Present LC Jensen & Camp 2003
Pelophylax nigromaculata Food Central and Northeast China R, N Present NT Carpenter et al. 2007
Pelophylax ridibundus Food, medicine, research Europe R, N, I Present LC Pough 200, Jensen & Camp 2003, Neveu 2004,
Carpenter et al. 2007
Pyxicephalus adspersus Food, pet trade Africa R, N Present LC pers. obs., Pough 200, Carpenter et al. 2007
Rana aurora Food North America R, N Past NT Jensen & Camp 2003
Rana chensinensis Food, medicine Central and Northeast China R, N, I Present LC Carpenter et al. 2007
Rana plancyi Food Central and Northeast China R, N Present LC Carpenter et al. 2007
Rana temporaria Food Europe N, I Past LC Neveu 2004
Rhinella arenarum Research Argentina N Present LC Young et al. 2004
Rhinella arunco Research Chile I Present LC Young et al. 2004
Telmatobius culeus Food (human & animals), medicine, leather Peru, Bolivia R, N Present CR Angulo 2008
Telmatobius marmoratus Food, medicine Peru R Present VU Angulo 2008
Trichobatrachus robustus Food, cultural purpose Cameroon R, I Present LC Gonwouo & Rödel 2008
Xenopus amieti Food Cameroon R Present NT Gonwouo & Rödel 2008
Xenopus laevis Research, food Africa R, I Present LC Weldon et al. 2007
196
Exploitation of frogs
Threatened Species (LC = Least Concern, VU = Vulnerable, NT = Near Threatened, EN = Endangered,
CR = Critically Endangered).
Species Utilization Region Scale Time of exploitation IUCN Status Reference
Urodela
Ambystoma dumerilii Food, medicine Mexico I Present CR Carpenter et al. 2007
Ambystoma mexicanum Food, medicine, pet trade, research Mexico I Present CR Carpenter et al. 2007
Cynops orientalis Pet trade China I Present LC Schlaepfer et al. 2005
Anura
Astylosternus spp. Food Cameroon R Present LC-CR Gonwouo & Rödel 2008
Bombina orientalis Pet trade East Asia I Present LC Schlaepfer et al. 2005
Chaunus marinus Food, souvenir, pet trade, research America, Australia R, N, I Present LC Pough 200
Conraua crassipes Food Cameroon R Present LC Gonwouo & Rödel 2008
Conraua goliath Food Cameroon R Present EN Gonwouo & Rödel 2008
Conraua robusta Food Cameroon R Present VU Gonwouo & Rödel 2008
Euphlyctis hexadactylus Food India, Bangladesh I Past LC Oza 990, Veith et al. 2000
Fejervarya cancrivora Food Indonesia R, I Present LC Veith et al. 2000, Kusrini & Alford 2006,
Carpenter et al. 2007
Hoplobatrachus occipitalis food Africa R, N Present LC pers. obs.
Hoplobatrachus rugulosus Food South and Central China R, N, I Present LC Jensen & Camp 2003, Carpenter et al. 2007
Hoplobatrachus tigerinus Food Southern Asia, India I Present LC Pough 200, Oza 990, Carpenter et al. 2007
Hyla cinerea Pet trade United States I Present LC Schlaepfer et al. 2005
Hyla eximia Pet trade Mexico I Present LC Carpenter et al. 2007
Hymenochirus curtipes Pet trade DRCongo I Present LC Schlaepfer et al. 2005
Kassina decorata Food Cameroon R Present LC Gonwouo & Rödel 2008
Limnonectes macrodon Food Indonesia R, I Present VU Kusrini & Alford 2006, Carpenter et al. 2007
Lithobates catesbeianus Food North America Present LC Pough 200, Carpenter et al. 2007
Lithobates pipiens Food, research North America R, N, I Present LC Jensen & Camp 2003
Mantella spp. Pet trade Madagascar I Present LC-CR Carpenter et al. 2007
Pachymedusa dacnicolor Pet trade Mexico I Present LC Carpenter et al. 2007
Pelophylax lessonae Food Europe N, I Present LC Jensen & Camp 2003
Pelophylax nigromaculata Food Central and Northeast China R, N Present NT Carpenter et al. 2007
Pelophylax ridibundus Food, medicine, research Europe R, N, I Present LC Pough 200, Jensen & Camp 2003, Neveu 2004,
Carpenter et al. 2007
Pyxicephalus adspersus Food, pet trade Africa R, N Present LC pers. obs., Pough 200, Carpenter et al. 2007
Rana aurora Food North America R, N Past NT Jensen & Camp 2003
Rana chensinensis Food, medicine Central and Northeast China R, N, I Present LC Carpenter et al. 2007
Rana plancyi Food Central and Northeast China R, N Present LC Carpenter et al. 2007
Rana temporaria Food Europe N, I Past LC Neveu 2004
Rhinella arenarum Research Argentina N Present LC Young et al. 2004
Rhinella arunco Research Chile I Present LC Young et al. 2004
Telmatobius culeus Food (human & animals), medicine, leather Peru, Bolivia R, N Present CR Angulo 2008
Telmatobius marmoratus Food, medicine Peru R Present VU Angulo 2008
Trichobatrachus robustus Food, cultural purpose Cameroon R, I Present LC Gonwouo & Rödel 2008
Xenopus amieti Food Cameroon R Present NT Gonwouo & Rödel 2008
Xenopus laevis Research, food Africa R, I Present LC Weldon et al. 2007
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Meike Mohneke et al.
2500 t of frog legs were imported to the US, Xenopus laevis in South Africa are restricted
predominantly from Japan and India. to certain areas and during specific time peri-
It seems that some South American indig- ods to prevent over-exploitation. However, it
enous people were always familiar with the has been hypothesized that X. laevis is a suc-
use of frogs. Frogs of the genus Telmatobius cessful carrier of chytridiomycosis and that
have traditionally been consumed or used the international trade in this species might
for medicinal and ritual purposes by locals in have introduced this fungal disease to other
the Andes of Peru and Bolivia. Their medici- regions of the world (IUCN 2008). In general
nal use locally varies, comprising treatment the African frog trade and especially the ac-
of asthma, epilepsy, headaches, and stress tual dimension of frog harvest and consump-
(Angulo 2008). Today, the overall numbers tion have not yet been a topic of scientific in-
of consumed Telmatobius is on the increase vestigation.
and populations of different species [e.g. T. In some regions amphibians (mainly
arequipensis Vellard, 955, T. culeus (Gar- toads) are used for medical treatments by vil-
man, 876), T. gigas Vellard, 969, T. jelskii lagers (e.g. south-eastern Guinea and Benin).
(Peters, 873)] are declining dramatical- Children’s cough, appendicitis or skin injuries
ly (IUCN 2008). In Peru, dealers were sell- are among the diseases treated with toads.
ing about 80 frogs daily at one market in However, in Africa most amphibians are col-
Cusco (Angulo 2008). Each week between lected for food. The consumption of larger
200 and 2400 frogs are requested per dealer. frog species like Pyxicephalus adspersus Ts-
Thus, besides agricultural practices and wa- chudi, 838, P. edulis Peters, 854, Hoplobat-
ter pollution, commercial utilization is one rachus occipitalis (Günther, 858), Tricho-
of the main threats to many members of this batrachus robustus Boulenger, 900, Con-
severely threatened genus (De la Riva & raua spp. or Ptychadena spp. is known from
Lavilla 2008). a wide range of African countries e.g. Benin,
Several American frogs have also been Burkina Faso, Cameroon, Côte d’Ivoire, Gha-
collected for research and teaching purposes, na, Guinea, Namibia, Nigeria, South Africa
especially leopard frogs during the 960s and and Togo (Okeyo 2004, Gonwouo & Rödel
970s in the US. In South America thousands 2008, authors’ unpubl. data). A variety of dif-
of Rhinella arunco (Molina, 782) in Chile ferent ethnic groups from West Africa, e.g.
and R. arenarum (Hensel, 867) in Argen- the Gourmanché and Mossi in Burkina Faso
tina were collected for science and education (Fig. ), the Yacouba in Côte d’Ivoire, the Ba-
(Young et al. 2004). Today, more than 000 kossi in Cameroon, and the Yoruba in Niger-
t of amphibians and reptiles still cross the US ia, traditionally use frogs as food or for medi-
border each year, 96% of them for commer- cal and cultural reasons. African amphibians
cial purposes (Schlaepfer et al. 2005). The are mainly harvested and consumed in and
consequences for the respective source popu- around the villages and often there is little se-
lations and ecosystems are unknown. lection for particular species other than size,
i.e. larger species are preferred. Even toads
[Fig. 2, Amietophrynus maculatus (Hallo-
Africa well, 854), A. regularis (Reuss, 833)] and
tadpoles (Fig. 3) are harvested, prepared and
For research and medical purposes the Af- sold in local markets.
rican clawed frog [Xenopus laevis (Daudin, On the Obudu plateau, Nigeria, we ob-
802)] has been used since the 930s. In South served a very intense collection of frogs and
Africa each year over 0,000 of these frogs their tadpoles from small rivers (Fig. 3). This
are collected from the wild and exported to traditional use of frogs seems to have become
over 30 different countries since 998 (Wel- unsustainable in recent years. Women har-
don et al. 2007). The four major suppliers for vesting these species now have to walk much
198
Exploitation of frogs
Fig. 1. Gourmantché woman offering Hoploba- Fig. 3. Astylosternus tadpoles and small catfish,
trachus occipitalis as travel snack along a main smoked for sale on the Obudu Plateau, Nigeria.
road in southern Burkina Faso (Photo: A. Thi-
ombiano).
Fig. 2. Mossi woman preparing toads (Amieto- Fig. 4. Adult Hoplobatrachus occipitalis dried, smo-
phrynus maculatus and A. regularis) for sale in ked and packed for sale on a Nigerian market close
southern Burkina Faso. The toads are beheaded, to the Benin border. One sack contains about a
skinned, disembowelled, washed and cut into pi- thousand dried adult frogs, all caught along River
eces before being dried. These toads are the harvest Niger in northern Benin.
of one day.
longer distances than previously to arrive at into Nigeria. We are currently investigating
rivers that still provide enough amphibians the amount of harvested frogs and the trade
to make the harvest feasible (authors’ unpubl. routes this commercial use follows. Especial-
data). A similar situation has been recently ly Hoplobatrachus occipitalis is harvested and
reported from nearby Cameroon (Gonwouo traded in huge quantities (Fig. 4). One frog
& Rödel 2008). Harvesting the larval stage collector was observed harvesting between
in addition to adults may lead to a much fast- 50 and 200 adult H. occipitalis per day. On
er breakdown of populations than collecting average collectors needed 7 to 0 days to fill
adults only, as this could result in an even up one large sack of dried frogs (app. 000
more substantial loss of juvenile recruitment. individuals, Fig. 4). One sack sold to Nige-
Besides a mainly local or national trade rian traders generates an income between 5
market, we also detected larger cross-border € and 45 € depending on the season (2.50-
trade of amphibians from northern Benin 4.50 € per day). Selling fish only yields a daily
199
Meike Mohneke et al.
income of .50-3.00 € and hence many fish- diseases. One of the few studies estimating
ermen change to hunting frogs. During one the effects of frog species removal from the
season a collector catches a minimum of 0.9 t wild was done in India (Abdulali 985). An
of H. occipitalis from a maximum area of only adult Hoplobatrachus tigerinus devours ap-
20 square meters (m²) along the river banks proximately 0% of its own weight in insects
of the Niger River, where the frogs accumu- every day. During legal exports of Indian frog
late during the dry season. With the begin- legs, 9000 t of Hoplobatrachus tigerinus were
ning of the rains H. occipitalis usually migrate harvested annually. Hence, 900 t of insects,
far into the savanna (Spieler & Linsenmair including mosquitoes and agricultural pests,
998). Thus the removal of frogs affects not survived daily and instead had to be control-
only the area along the rivers, but huge parts led by other means, such as insecticides (Ab-
of the hinterland. dulali 985). The commercial frog exploi-
In Burkina Faso we detected commer- tation and resulting decline thus resulted in
cial frog trade in some regions (Ganzourgou an increased use of agrochemical products
province), whereas in other regions (Gourma in rice paddies, leading to increased envi-
province) frogs are harvested for local con- ronmental pollution and higher financial in-
sumption. In the province of Ganzourgou 0 vestment to achieve harvests comparable to
frog collectors caught approximately 2.2 t of the previous ones. Thus in summary the frog
H. occipitalis during one dry season, the ac- leg trade resulted in minor economic gains
tual number of active frog collectors, how- in the form of foreign exchange, but simul-
ever, being much higher in this area. Gan- taneously has led to major ecological and
zourgou province comprises 85 villages and economic losses (Oza 990). Unfortunately,
36,969 households (INSD 2006). Assuming similar studies are lacking for most parts of
there would be only one frog collector in the world, including Africa.
every village, the actual amount of collected In West Africa, the arid and semi-arid re-
frogs would exceed 40 t. Judging from inter- gions in the Sahel and Sudanian zones are al-
views with villagers and colleagues (i.e. Prof. ready affected by climate change (De Wit &
Dr. A. Thiombiano, Université de Ouaga- Stankiewicz 2006). Alterations in rainfall
dougou and member of the royal family of patterns, increasing droughts, and decreas-
the Gourmanché, pers. comm. 20 May 2008) ing availability of open waters will strike local
it seems that in the province of Gourma, the human populations as well as wildlife. Unre-
hot phase of frog harvest is already over, due liable and shrinking crops, however, do lead
to declining populations of H. occipitalis and towards increasing dependence upon and
other frog species. Comparable West Afri- use of natural resources. Under this scenar-
can ecosystems are still rich in amphibians io, it is unlikely that the demand for amphib-
and all frogs from these regions so far tested ians will diminish in the near future. In case
for chytridiomycosis have been found to be of a potential overexploitation of particular
chytrid negative (50 samples of 20 aquatic frog species, the effects on the respective eco-
and semi-aquatic species; C. Weldon & M.- system may be inevitable (Lau et al. 2008).
O. Rödel, unpubl. data). The frog declines in In a second paper we will summarize which
south-eastern Burkina Faso hence seem to be effects potentially may result from declin-
at least mainly driven by human collectors. ing frog populations (Mohneke & Rödel
2009).

Economic consequences of
over-exploited frog populations
Acknowledgements
Frogs play a vital role in eradicating insect We especially thank Adjima Thiombiano and
pests. These pests destroy crops and carry Brice Sinsin, as well as all respective authorities in
200
Exploitation of frogs
Burkina Faso, Benin and Nigeria for their support Stuart, S. N., M. Hoffmann, J. S. Chanson,
and the necessary permits to undertake research. N. A. Cox, R. J. Berridge, P. Ramani & B. E.
Bilassé Zongo, Ahandi Thiombiano, Gere- Young (eds.): Threatened Amphibians of the
mi Kaboré, Norbert Assongba and Monique World, Barcelona, Spain, Lynx Editions.
Sabo Gado were of invaluable help during field
De Wit, M. & J. Stankiewicz (2006): Changes in
work and interviews in villages. Timo Moritz di-
surface water supply across Africa with predict-
rected our attention to the cross-border frog trade
ed climate change. – Science, 3: 97-92.
from northern Benin into Nigeria. This study is
Duffy, J. E. (2002): Biodiversity and ecosystem
part of the BIOLOG-program of the German Mi-
function: the consumer connection. – Oikos,
nistry of Education and Science (BMB+F; Project
99: 20-29.
BIOTA-West III, amphibian projects, 0LC067J).
This support is gratefully acknowledged. Ficetola, F. G., C. Coic, M. Detaint, M. Berro-
neau, O. Lorvelec & C. Miaud (2007): Pat-
tern of distribution of the American bullfrog
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Manuscript received: 8 January 2009
Authors’ addresses: Meike Mohneke, Mark-Oliver Rödel, Museum für Naturkunde, Leibniz Insti-
tute for Research on Evolution and Biodiversity at the Humboldt University Berlin, Invalidenstraße 43,
10115 Berlin, Germany, E-Mail: [email protected], [email protected]; Abiodun
B. Onadeko, Department of Zoology, Faculty of Sciences, University of Lagos, Akoka, Yaba, Lagos,
Nigeria, E-Mail: [email protected].
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