bio_cons_sea_turtle_species.doc

advertisement
Diversity and status of sea turtle species in the
Gulf of Guinea islands
JAVIER CASTROVIEJO and JAVIER JUSTE B
Estación Biológica de Doflana. Avda. Ma Luisa s/n, 41013 Sevilla, Spain
JAIME PEREZ DEL VAL, RAMON CASTELO and RAMON GIL
Asociación Amigos del Cob de DaiTana, C/ Panama No. 6, 41012, Sevilla, Spain
Received 12 May 1994; accepted 14 August 1994
In West Africa, the Gulf of Guinea islands are important nesting places for four sea turtle species.
The Green turtle (Chelonia mydas), the Hawksbill (Eretmochelys imbricata), the Olive Ridley
(Lepidochelys olivacea) and the Leatherback (Dermochelys coriacea) turtles nest on Bioko’s
southern beaches. The Green, Hawksbill and Leatherback turtles breed on Principe and São
Tome. The Leatherback turtle nests, at least, on Annobén. The Leatherback turtle is reported on
the four islands for the first time, and the Olive Ridley turtle for Bioko. Bioko is probably the
most important island in terms of number of species and nesting individuals; the Green turtle
being the most abundant species. However, the nesting places are at present restricted to barely 20
km along the coastline. On Principe and São Tome, the most common species is the Hawksbill
turtle. Sea turtle nesting populations are being severely depleted on the four islands. The main
causes of overexploitation are the meat and egg trade on Bioko and the Hawksbill shell-craft
trade on São Tome and Principe.
Keywords: Gulf of Guinea, sea turtles, conservation, exploitation
Introduction
Information on the turtle populations in western Equatorial Africa and, in particular,
along the Gulf of Guinea is scarce (Brongersma, 1982; Maigret, 1983; Fretey and
Girardin, 1988; Butynski et at., 1989; Carr and Carr, 1991). For Bioko, some notes
appear in Crespo (1949), Guinea (1949) and Esteban (1950) who also published turtle
photographs from the southern beaches. More recently, Eisentraut (1964) gave precise
records of sea-turtles nesting on the island and reports on their exploitation on southern
Bioko have also appeared (Butynski and Koster, 1989). For the other Gulf of Guinea
islands, PrIncipe and São Tome, first references appear in 1883 but thereafter only anecdotal data are available. No sea turtles have been recorded for Annobón, the smallest
and most distant island in the Gulf.
Despite the current lack of information, there is no doubt that the Gulf of Guinea
Islands are some of the most significant sea turtle nesting areas in Africa. This richness
is at present threatened in all the islands, even before it has been properly assessed. The
aim of this paper is to present some facts on the status of the sea turtles as well as on
their economic importance for the local people. Data reported herein were collected
from 1985 to 1994 and arise mainly from direct observations of animals, tracks and
Diversity and status of sea turtles
other signs recorded during survey walks on nesting beaches on the four islands during
the nesting season. Numerous interviews with local fishermen, relevant authorities as
well as specialized sea turtle catchers have also proved to be very useful.
Description and distribution of nesting beaches
In all four Gulf of Guinea islands, nesting sea turtles typically chose unsheltered black
or white sand or shingle beaches. These beaches are often steep sloping even at low tide.
It is a common feature in the islands that some rivers do not reach the sea during the
dry season, the water being trapped by sand or shingle barriers to form a temporary
estuary which turtles have been seen using. Behind the shingle or sandy areas, there is
usually a belt of tropical vegetation, composed mainly of coconut trees (Cocus nucfera),
Terminalia catappa, Cammelina spp. (conf. C. erecta), Begonia spp., Polisota hirsuta and
the commoner Ippomea pes-caprae.
Bioko
Bioko is probably the most important island in terms of number of turtle species and
nesting individuals. Beaches used by sea turtles are at present restricted to the southern
part of the island, barely 20 km of coastline, between Punta Santiago and Punta
Oscura. According to local informants and our own observations the most important
beaches are:
(i) Sobo beach between the Sobo, Grande and Moaba rivers breeding ground for
the Leatherback turtle.
(ii) Mveló beach, to the west of the Potó river, after the Eolá river and a rocky area
breeding grounds for Leatherbacks and Olive Ridley turtles.
(iii) Ma and Eoca beaches, between the Potó and Sió rivers the best breeding
grounds for the Atlantic Hawksbill.
(iv) Moraca beach, from Punta Sagré to the river Ole or Tudela good breeding
ground for the Green turtle.
(v) Small sandy beach between the Ole river to opposite the Eadyó rocks good
breeding ground for the Green turtle.
(vi) Bandera and Moalo beaches, between the Eadyó rocks and Punta Islote
reserves for the Green turtle.
Apart from these beaches, in the past sea turtles probably used other northern
beaches in Bioko and may still do so sporadically, as suggested by the sighting of a
couple mating and isolated individuals near Arenas Blancas beach (Luba) in December
1991.
—
—
—
—
—
—
—
PrIncipe
On Principe, unlike Bioko, sea turtles nest on suitable beaches all around the island’s
perimeter probably because of the lower human density. According to some fishermen
the most important beaches are:
(i) Praia Grande, after Ponta Café to the Bibi river breeding ground for three
species, and one of the main points for the Leatherback turtle.
(ii) Praia São Tome one of the most important nesting places on PrIncipe. We have
been told that a number of individuals of three species nest there every year.
(iii) Praia Formiga and Praia Rei breeding ground for the Atlantic Hawksbifl turtle.
—
—
—
(iv) Praia Mocotó and Praia Ribeira Izé, including the area between Ponta Marmita
and Ponta da Furna grounds for the Atlantic Hawksbill and the Green turtle.
Older fishermen claim that sea turtles have become even less common in the southern
part of the island. At present, they seem to be much more rare along the beaches close
to the city and along the Papagaio river mouth which crosses the city of São Antonio
during high tide, as they used to be in recent times.
—
Sdo Tome
It has been more difficult to obtain information on the beaches of this island. However,
it is quite certain that the most important nesting beaches are at present restricted to the
southern and western coasts. The following can be confirmed:
(i) Praia Micondó, Praia Pequeiro de Deus and Praia Inhame, near Porto Alegre
grounds for the Atlantic Hawksbill and Leatherback turtles.
(ii) Praia Café, Praia Pombo and Praia S. Antonio, all on the islet ‘das Rolas’
commonly used by Atlantic Hawksbill and, according to local people, also by Leatherback and Green turtles.
(iii) Praia Quija and Praia Palma, on the western coast probably the most important nesting beaches on São Tom” because of their wilderness; grounds for Atlantic
Hawksbill, Leatherback and Green turtles.
As on PrIncipe, there are suitable beaches for sea turtles all around the coast but these
are normally avoided because of human disturbance. One Leatherback was killed while
laying eggs on Praia Lembá (Northwest) in January 1993 and one Atlantic Hawksbill
was also killed when nesting on Praia Monte Forte (North) in December 1993.
—
—
Annobón
Turtle nesting on Annobón is limited because there are few suitable beaches. The most
important are the small bays between Punta Manjob and A Dyibó in the South
(Mabena).
Species accounts
Chelonia mydas
Green turtle (English), Tortuga verde (Spanish), Tartaruga branca (Portuguese). Local
names: Mulupapa (Bubi, Bioko), Ambo (Forro, São Tome).
This is certainly the most abundant species on Bioko. It is easily spotted and egglaying females were seen several times in 1986, 1987 and 1991. Similar reports were
made by Eisentraut (1964) and by Butyinski and Koster (1989). The nesting population,
probably around hundreds of individuals, may reach Bioko beaches from October to
February. Old inhabitants of Ureca, a small village on the southern coast, recall Green
turtles coming ashore near the village in considerable numbers even in daylight, as
reported by early naturalists (Crespo, 1949; Esteban, 1950). During the last 30 years, at
least, the species has made up the main yield for sea turtle catchers and numbers of
nesting individuals have decreased sharply.
This species is also common over the other islands and one specimen was seen in the
southern coast of PrIncipe in February 1994.
Eretmochelys imbricata
Hawksbill turtle (English), Tortuga carey (Spanish), Tartaruga vermelha (Portuguese).
Local names: Kuru (Bubi, Bioko), Sada (Forro, São Tome).
On Bioko, this species breeds on the same beaches as the Green turtle, occasionally
being captured when nesting. On both São Tome and PrIncipe, it is generally considered
the most common species. It has not been possible to confirm Hawksbills nesting on
Annobôn although young individuals are frequently captured offshore.
Lepydochelys olivacea
Olive Ridley turtle (English). Tortuga golfina (Spanish), Tartariiga bastarda (Portuguese). Local name: SanquIa (Bubi, Bioko).
An egg-laying female was photographed and identified (on the basis of its high round
carapace and considerable number of lateral scutes) as belonging to this species. This is
the first citation of this species breeding on Bioko beaches. Being rare, it is only occasionally caught but its presence was confirmed by local people who can easily identify it
and have a specific name for it in their local language.
In Principe, an ‘unusual’ sea turtle, whose description fits well with this species, was
captured ashore entangled in a piece of net in 1991.
Dermochelys coriacea
Leatherback turtle (English), Tortuga laud (Spanish), Tartaruga grande encourada
(Portuguese). Local names: Eguin (Bubi, Bioko), Tartaruga tractor o ambulancia (São
Tome).
Several specimens have been seen egg-laying on the beaches between Punta Dolores
and Punta Santiago in Bioko from 1986 to 1992. The Leatherback has been reported by
local people to nest persistently in São Tome and Principe beaches, but always in few
numbers. In 1994, four individuals were seen on Praia Queija (São Tome) and between
February and March this year at least one animal was killed in Praia Grande beach
(Principe) and another in the Lembá river mouth (São Tome). A track clearly belonging
to this species was seen on Mabena beach in the southern coast of Annobón on
December 1986. These are the first confirmed records of this species breeding on the
four islands of the Gulf of Guinea. It seems to prefer remote, large and open beaches.
It is interesting that the loggerhead turtle (Caretta caretta) has not been found in any
of the islands despite there being several citations from the Gulf of Guinea and along
the western African coast (Jverson and College, 1992).
Reproductive data
There are apparently no clear differences in the nesting requirements of any of the
species, since suitable beaches on every island are shared by more than one turtle
species. Nevertheless, it seems that Green turtles are proportionally (and in absolute
scores) more abundant on Bioko beaches while Hawksbills seem to prefer Principe and
São Tome for nesting. This difference may be due to the fact that the latter species
needs to penetrate well into the forest to egg-lay (Pritchard and Trebbon, 1984) which
may be easier to do in PrIncipe and São Tome.
Nesting takes place seasonally on all the islands from November until March, with a
peak in December—January in Bioko, and an apparent delay in PrIncipe and São Tome.
.
Table 1. Comparison of number of eggs laid by the two main species of turtles in the Guinea
islands
Species
Date
Green’ turtle
January 1963
March 1990
December 1991
November—March
Leatherback turtle
February 1991
November—March
No. eggs
Locality
Source
138
36
Bioko
Bioko
78/128/106
Bioko
Eisentraut (1963)
J.P. Gonzalez
(personal observation)
R. Gil
(personal observation)
Local people (Urecans)
Pritchard and Trebbon
(1984)
Pritchard and Trebbon
(1984)
100—200
mean 138
Bioko
Surinam
mean 147
Ile Europe
58
40—60
58—160
Bioko
Bioko
South Africa
J. Castroviejo
(personal observation)
Local people (Urecans)
Pritchard and Trebbon
(1984)
This period corresponds to the start of the dry season on Bioko (seca) and the short dry
season (gravanilla) on the other two islands. Nests are dug within circular areas (with a
diameter ranging from 4 to 5 m for the Leatherback and from 1 to 2 m for the Hawksbill turtle) and close to the forest fringe and the beach. These areas typically show the
sand-ground around them being intensely disturbed. Only scarce information about
clutch size is available, but our data for Bioko fits the ranges reported in the literature
(Table 1). Basic data on this matter is urgently needed for all the islands.
Human impact
Sea turtle eggs are consumed locally and man is undoubtedly the main predator on the
four Gulf of Guinea islands. Sea turtle nests are dug out, regardless of the species,
throughout the whole nesting season. Drills (Mandrillus leucophaeus) were seen eating
eggs on Bioko beaches and locals report crabs, rats and dogs eating both eggs and
hatchlings on all the islands. The impact of this is totally unknown.
Capture methods
There are no species-specific capture methods (Table 2) and beach-guarding is the most
widespread method in all the islands. Egg-laying females are turned upside-down and
eggs removed by people that stalk the beaches every night. The animals are kept tied in
the shade until there are enough to make their transport to local markets profitable.
Nets over 100 m long are strategically set up in the beachfront on Säo Tome and
PrIncipe during the nesting season. Fishermen also easily hook some individuals as they
rest off-shore or mate on the water surface.
Harpoons are used to catch small Atlantic Hawksbill while they feed near the
coast; these are mainly to be dried, polished and sold as souvenirs to foreigners.
Table 2. Main methods of capture of turtle species in the Guinea islands
Capture Method
Species
Time
Hunters
Island
Beaches guarding
Green turtle
Hawksbill turtle
Olive Ridley turtle
leatherback turtle (sporadically)
November—March
5—10 groups of ten men (agrupaciones)
in southern Bioko; at least ten families
in Principe and around other ten
families in São Tome
Bioko, Principe and São
Tome (Annobón?)
Nets
Green turtle
Hawksbill turtle
Leatherback turtle
November—March
The same families that guard the
beaches
Principe and São Tome
Hook
Hawksbill turtle
Green turtle
AU year
Undeterminated fishermen
Principe and São Tome
Harpoon
Hawksbill turtle
All year
Undeterminated fishermen
Bioko, Principe, São
Tome and Annobén
The Annobónese are the most skilled at this both in Bioko and Annobón, although this
activity is also common in São Tome and PrIncipe.
Economic importance
At present, there are no accurate records of the number of sea turtles killed each year in
the Gulf of Guinea islands but it seems that the largest number are taken on Bioko.
From our data, about 500 Green turtles are caught each year in Bioko, mainly by the
inhabitants of Ureca, although this figure can vary between years. The 2000—2500 specimens reported by Butysnki and Koster (1989) are likely to be an overestimate.
On average the Urecans sell turtles at 15 000 FCFA apiece; a total of around
7500000 FCFA (1 US$ 550 FCFA). As each of the 5—10 turtle-hunting groups pays
100000 FCFA in taxes to the Governor of Luba province, this figure becomes around
6500000 FCFA. A group consists of ten people and a total of 50—100 people may be
engaged in this activity. Each member can make about 65000—130000 FCFA per year,
excluding petrol costs and rental of the dugout canoe. Although low (particularly when
consumption costs are taken into account), profits made from this activity are the
Urecans’ sole source of income today. The situation has worsened since the most recent
decline in cocoa.
In Luba, turtles are slaughtered and carried to the capital’s main markets by intermediary dealers. The market price of turtle meat is about 1000—1500 FCFA a kilo.
Considering that each turtle weighs approximately 120 kg (Pritchard and Trebbon,
1984; Márquez, 1990) with 70 kg of meat on average, 500 samples would fetch between
35 and 52.5 million FCFA.
Incomes generated by the sea turtle trade are more difficult to calculate for PrIncipe
and São Tome since sea turtle extraction is not concentrated in one area as in Bioko.
Moreover, shell-handicraft is an important traditional activity in these islands and many
turtles are sold directly to craftsmen rather than being sent to the markets. A rough
estimate would give about 100 adult Hawksbills caught on each island per annum. For
an average of 40—60 kg of meat from each turtle, sold for a market price of 400 Dobras
per kilo (1 US$ = 600 Db), 200 turtles would fetch around 5 million Db. On the other
hand, Hawksbill shell is sold to craftsmen at a price which fluctuates between 15 000
and 20000 Db per kilo (depending on shell quality, and cheaper on PrIncipe). If 3 kg of
scutes can be obtained from each adult turtle carapace, a sum of 9—12000000 Db could
be obtained from this activity. This rough estimate clearly shows that in São Tome and
Principe, the shell trade produces higher profits to local fishermen than the sale of turtle
meat.
Shell handicraft products are sold in local markets but trade with Angola has been
reported (Stuart and Adams, 1990) and it is also likely with Europe.
In general, sea turtle commerce produces low returns for the local people in all the
islands. However, when put into the context of the countries’ weak economies and the
absence of alternative sources of income, the capture of sea turtles becomes an
portant complementary revenue and may thus even intensify in the short-term.
Conservation measures
All four turtle species are included in Appendix 1 of the Convention on International
Trade in Endangered Species (CITES); trade in their products and in live specimens is
prohibited. The IUCN Red Data Book (Groombridge, 1981) considers them as ‘en­
dangered’.
Turtle fishing is now illegal in Equatorial Guinea (Law 8/88, regulating the hunting of
wildlife in protected areas and decree 183/87 regulating fishing) but it is still not regulated in São Tome and PrIncipe. There is a general lack of knowledge of the impact of
adult female extraction on the dynamics of these populations, but if it persists at the
present scale it is likely to have serious, irreversible effects. It is essential, therefore, to
implement a series of urgent measures through research and conservation in the four
islands of the Gulf of Guinea by:
(i) Establishing a research programme to assess impQrtant demographic data for all
the breeding populations of sea turtles that would include:
(a) Size and characteristics of the breeding populations.
(b) Intra. and inter-seasonal nesting frequencies.
(c) Nesting success: no. of viable eggs, nest predation, etc.
(d) Dynamics of breeding beaches and factors involving nest-placing choice.
(e) Contact and relationship between breeding populations on all the islands.
(ii) Protecting and monitoring nests to assure 100% of hatchlings reach the sea.
(iii) Establishing a compensation programme for local people involving the following:
(a) Payment of the equivalent, or higher, of the market price for each turtle
found and not killed.
(b) Exchange of food and other basic products (e.g. chicken eggs, soap, petrol,
lantern-batteries, rice, etc.) for the non-consumption of turtle eggs.
(c) Organization of communal shops in the important nesting areas with prices on
a par with the main city markets to compensate for income losses.
(d) Employment of local people for breeding turtles, nest monitoring and releasing hatchlings.
(iv) Initiating a programme for rearing wildlife (giant rat, blue duiker) or domestic
animals for sale in the market-place to provide protein. Training and transport to be
paid for by the project.
(v) Drawing up a study plan for ecotourism. This project should be combined with a
broader one for the conservation of the protected areas in which local people should
play an important role.
(vi) Publicising the projects throughout the islands.
Attitudes and perspectives of local people
These measures have already been discussed with the Urecans in Bioko in several
meetings over the last two years. They are aware of the extraordinary value of their
natural heritage in their traditional territory. They know that at the present rate of exploitation, the survival of turtles is threatened. The Urecans are prepared to conserve
these reptiles if alternative sources of income for their subsistence can be found. Proposals were met with a very favourable response.
Similar activities must be undertaken in the other islands. People contacted in PrIncipe
show the same awareness about the declining situation of sea turtles. At present, nothing
is being done to improve the situation in Bioko, while in São Tome and Principe only a
small monitoring project with an educational component is due to start shortly. Yet,
clearly, the situation is so precarious that to guarantee the survival of the sea turtles on
these islands a much more ambitious project with broader coverage is essential.
Acknowledgments
We thank all the fishermen and people that helped us to gather information on the sea
turtles from the Gulf of Guinea islands during all these years. We are especially
indebted to the Urecans (Bioko) for their kind hospitality during all our visits. C. Keller
and A. Andreu read the first draft and J.E. Fa helped in improving the manuscript.
References
Brongersma, L.D. (1982) Marine turtles of the Eastern Atlantic Ocean. In Biology and Conservation of Sea Turtles. (K. Björdal, ed.) pp. 407—16. Washington DC: Smithsonian Institution
Press.
Butynski, T.M. and Koster, S.H. (1989) Marine turtles on Bioko Island (Fernando Poo), Equatorial Guinea: A Call for Research and Conservatioh. Washington DC: WWF Unpublished
Report.
Carr, T. and Carr, N. (1991) Surveys of the sea turtles of Angola. Biol. Conserv. 58, 19—29.
Crespo, C. (1949) Notas para un Estudio Antropológico y Etnológico del Bubi de Fernando Poo.
Madrid: Instituto Estudios Africanos. (CSIC).
Eisentraut, M. (1964) Meeresschildkröten an der Küste von Fernando Poo. Natur und Museum
94, 471—5.
Esteban, J. (1950) Guinea Colonial. Esto es Espaila. Madrid: Argos SA.
Fretey, J. and Girardin, N. (1988) La nidification de la tortue luth, Dermochelys coariacea
(Vandeldi, 1761) (Chelonia, Dermochelyidae) sur les côtes du Gabon. J. Afr. Zoo!. 102, 125—
32.
Groombridge, B. (1982) The IUCN Amphibia Reptilia Red Data Book (Part 1). Gland, Switzerland: IUCN.
Guinea, B. (1949) En el Pals de los Bubis. Relato ilustrado de Mi Primer Viaje a Fernando Poo.
Madrid: Instituto Estudios Africanos (CSIC).
Iverson, J.B. and College, B. (1992) A Revised Checklist With Distribution Maps of the Turtles of
the World. Richmond, Indiana: Privately Printed.
Maigret, J. (1983) Repartition des tortues de mer sur les côtes ouest africaines Bull. Soc. Herp. Fr.
28, 22—34.
Márquez, M. (1990) Sea Turtles of the World. FAQ Fisheries Synopsis 125 (11). Rome: FAO.
Pritchard, P.C. and Trebbon, P. (1984) The Turtles of Venezuela. Athens, Ohio, Society for the
Study of Amphibians and Reptiles.
Stuart, S.N. and Adams, R.J. (1990) Biodiversity in Sub-Saharan Africa and Its Islands: Conservation, Management and Sustainable Use. Gland, Switzerland: IUCN.
—
Download