BY
CHARLES M. FUGLER,
CONSULTANT TO UNDP-FAO PROJECT BGD/79/015,
FISHERIES RESOURCES SURVEY SYSTEM
APRIL 1985
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2. ENVIRONMENTAL CONSEQUENCES OF EXCESSIVE EXPLOITATION OF RANA TIGRINA
3. ENVIRONMENTAL CONSEQUENCES OF EXCESSIVE EXPLOITATION OF FRESHWATER CHELONIANS
4. BIOLOGICAL BASES FOR THE FORMULATION OF A MANAGEMENT PROGRAM OF RANA TIGRINA
5. BIOLOGICAL BASES FOR THE FORMULATION OF A MANAGEMENT PROGRAM OF FRESHWATER CHELONIANS
6. ECONOMIC IMPACT OF EXPLOITATION OF RANA TIGRINA IN BANGLADESH
7. ECONOMIC IMPACT OF EXPLOITATION OF FRESHWATER CHELONIANS IN BANGLADESH
8. PROPOSED MANAGEMENT PROGRAM OF RANA TIGRINA IN BANGLADESH
9. PROPOSED MANAGEMENT PROGRAM OF FRESHWATER CHELONIANS IN BANGLADESH
10. ENFORCEMENT OF PROPOSED MANAGEMENT PROGRAMS AND BANS
11. THE CONFINED PROPAGATION OF RANA TIGRINA IN BANGLADESH
LIST OF APPENDICES
Appendix I. Intensive Rearing Facility (fide Priddy and Culley, 1971)
Appendix II. Intensive Rearing Facility (fide Priddy and Culley, 1971)
Appendix III. High Density Rearing Tank for Larval Amphibians (fide Culley et al., 1977)
Appendix IV. Standard Diet for Larval Rana catesbiana (fide Marschall, 1978; Culley, et al., 1977)
Appendix VI. Preparation of Alginate-bound Diet (fide Marschall, 1978; Culley et al., 1977)
Appendix VII. Preparation of Gum and Agar Diet (fide Marschall, 1978; Culley et al., 1977)
Appendix VIII. Itinerary of Consultant
Appendix IX. Individuals Interviewed
THE MANAGEMENT OF THE EXPLOITED SPECIES OF AMPHIBIA AND REPTILIA IN BANGLADESH
The consultant will, with the advice of biologists of the People's Republic of Bangladesh and of interested governmental authorities, determine a program of management of the economically important species of amphibians and chelonians. The recommendations will be submitted to FAO for onward submission to the governmental officials concerned.
The program of management will include the following salient aspects:
The quantity which may be removed from specific populations at specific temporal periods.
The inclusive dates in which the wild populations may be exploited and the inclusive dates in which wild populations may not be exploited.
The assessment, where feasible, of the actual and potential consequences of excessive exploitation of the wild populations upon the ecosystem and agriculture.
The feasibility of re-introduction into suitable habitats in which the populations have been extirpated.
Numerous species of amphibians (Culley, in press; Fugler, 1983) and chelonians (Fugler, 1984) are utilized as a significant and available source of protein for the human populations of the tropical world as well as a culinary delicacy in the industrialized nations. The export of anurans and chelonians constitute a significant earned foreign exchange for Bangladesh, India, and Indonesia (Fugler, 1983, 1984).
Although many species of anurans are consumed locally throughout the world, only Rana catesbiana, Rana hexadactyla, and Rana tigrina are harvested for export. Rana tigrina is exported from Bangladesh, India, and Indonesia; Rana hexadactyla is exported only from India. China has recently banned the harvesting of Rana tigrina. Rana catesbiana, native to North America, has been introduced into South America, the islands of the Pacific, Europe, and Japan. The species is commercially exploited in the United States, Brazil, and Japan for its flesh and/or skin. The skin of Rana tigrina is fashioned into luxury items in Thailand.
As a result of the activities of concerned organizations, the import of frog legs into West Germany, Switzerland, and the United Kingdom have been drastically reduced.
Biologists, ecologists, and conservationists note with mounting concern the rapid decline of populations of Rana tigrina throughout its range, and especially in the Indian subcontinent. With the absolute ban invoked by China and the precipitous reduction of exports from India, Bangladesh is the principal exporter of frog legs to the international markets.
The unabated harvesting of Rana tigrina in Bangladesh and India, and of Rana hexadactyla in India, has seriously altered the ecosystems of the subcontinent. The wholesale exploitation of Rana tigrina and of Rana hexadactyla has resulted in increased destruction of agriculture by insects on which these species prey. Increases in insect-vectored diseases of cattle and of humans have been reported in India and in Bangladesh.
The indiscriminate broadcasting of insecticides in the Indian subcontinent has contributed further to the destruction of the environment and the interdependent fauna. The imported insecticides, of which DDT is a major component, is now a public health concern in both countries. India and Bangladesh spend more to import insecticides than earned in foreign exchange from the export of frog legs. The catastrophic effects of DDT on the ecosystem is well documented. It is absolutely prohibited as an insecticide in most industrialized nations.
The decimation of the populations of Rana tigrina in India and in Bangladesh, and Rana hexadactyla in India, aroused concern in both countries when financial data were presented. A collecting ban during the breeding season was invoked, but the enforcement is lax and universally contravened within India and Bangladesh.
In the absence of biological data pertaining to Rana tigrina and Rana hexadactyla, management programs could not be formulated. The accumulation of basic biological knowledge, based upon recent field studies in Bangladesh, permits the structuring of a management program which, if zealously enforced, will permit the populations to return to normal densities if the cumulative effects of DDT and of other insecticides are not irreversible and the environment not permanently disrupted.
It has often been stated that the alternative to the management of Rana tigrina and Rana hexadactyla is intensive cultivation. A thorough search of the extant literature produced no evidence whatsoever that either species has been successfully cultivated commercially. Intensive research has been conducted for decades on the commercial cultivation of the North American Bullfrog, Rana catesbiana. To date, the successful attempts to cultivate Rana catesbiana artificially are limited to the production of individuals to supply medical and institutional research in the United States. Cultivation techniques are constantly being refined through research. It is not certain, moreover, that the techniques for the intensive cultivation of Rana catesbiana are applicable to other species.
The freshwater chelonians involved in international trade are Trionyx gangeticus, Trionyx hurum, Lissemys punctata, and species of Kachuga. All of the aforenamed are listed in Appendix I (Endangered) of the Convention for International Trade in Endangered Species (CITES). Bangladesh, a signatory to the Convention, is in contravention to its agreement. Bangladeshi authorities continue to permit the illicit traffic of endangered species on a commercial level.
Recent field studies in Bangladesh indicate that the populations of these species are severely stressed through excessive harvesting. The effect of DDT and of insecticides on the Bangladeshi populations has not been established. Its effects are unquestionably cause for concern.
A management program to stabilize the populations of the freshwater chelonians can be formulated and effectively pursued with support of the proper governmental agencies. An intelligent management program, however, is contingent upon the acquisition of biological data currently unavailable.
In Bangladesh and in India, perhaps throughout much of its geographic range, the intensively harvested wild populations of Rana tigrina are in precipitous decline. The precarious state of the populations of Rana tigrina, indeed of many species of wildlife in Bangladesh, and the continued destruction of habitat, have been noted by Oliver (1979) and Fugler (1983). In certain districts of Bangladesh Rana tigrina has been exterminated through excessive harvesting.
National and international conservationists, biologists, and ecologists note with extreme concern the excessive depredation of Rana tigrina from Bangladesh. The total population of all species of amphibians in Bangladesh is estimated to be 500 million (Daily News, Dhaka, 9 February 1985) of which 500,000 kilograms of frog legs (Rana tigrina), approximately 12 million frogs, are exported annually (Bangladesh Observer, Dhaka, 30 January 1985).
In 1985, over 200 million frogs, all harvested from wild populations, are anticipated to enter the international trade from Asian countries (Bangladesh Observer, Dhaka, 30 January 1985). World Wildlife Fund-West Germany estimates that more than 150 million frogs are exported annually from India and Bangladesh to Europe, Australia, and the United States. Indonesia is also a major source of export (Bangladesh Observer, Dhaka, 30 January 1985).
National and international biologists, conservationists, and ecologists state that the continued uncontrolled exploitation of Rana tigrina will initiate an ecological catastrophe.
The population densities of noxious and agriculturally destructive insects have significantly increased with the decrease in the population densities of Rana tigrina. In the absence of biological controls, of which Rana tigrina is considered to be a principal predator, the import and utilization of insecticides to control insect populations are required.
DDT, one of the broad-spectrum insecticides imported into Bangladesh, is banned from most industrialized countries. The disastrous consequences of uncontrolled broadcasting of insecticides, particularly DDT, is abundantly documented. A serious threat to public health in Bangladesh now exists (Bangladesh Observer, Dhaka, 30 January 1985). The pesticides adversely affect the spawning areas of Rana tigrina and of other amphibians (Whiting, 1984), thereby reducing the populations. The effect on other important predators has led to significant increase in the rodent populations. India spends $1.5 million a year on rodent control. In Bangladesh rodents consume or spoil more than one million tons of grain, equivalent to the tonnage of imported food grains (Whiting, 1984).
According to Whiting (1984) the destruction to the ecology of India is widespread. DDT accumulation in the tissues of mice and rats affects the reproductive capacity of birds of prey. The White-Eyed Buzzard is rare in Konkan. The rodents, on which the raptors normally prey, infest rice fields and other crops.
Frogs also control the parasites of freshwater fishes, thereby maintaining healthy fish stocks. Insect-born diseases of cattle have increased. Malaria and encephalitis, mosquito-vectored diseases, are more frequently encountered (Whiting, 1984).
The destruction of Rana tigrina, from excessive harvesting and insecticides, and of other amphibians, from indiscriminate broadcasting of insecticides is merely one aspect of the ecosystemal disequilibrium generated by the “ripple effect.”
Rana tigrina is a predator upon agriculturally destructive insect pests (Ahsan, 1983). Field studies, in Bangladesh, conclude that a higher incidence of damage to rice fields occurs in those from which frogs are harvested (Daily News, Dhaka, 9 February 1985). In the monsoon season an adult Rana tigrina consumes daily its weight in insects.
The roles of the species of freshwater chelonians (Trionyx, Lissemys, Kachuga) in the ecosystem of Bangladesh is difficult to define. Biological data are not available, suggesting that field studies on the exploited species in question should be accorded immediate high priority (Fugler, 1984). The reproductive biology, food preferences and ecological parameters should be addressed.
In Bangladesh the annual breeding cycle begins at the advent of the monsoon, usually mid-April, and continues at least through mid-July, thereafter diminishing with the decrease in intensity and frequency of rainfall.
Rana tigrina oviposits in “new” monsoonal waters of high oxygen content and low temperatures rather than in “old,” stagnant, water. Males, emerging first from estival dormancy, establish breeding territories, after which females emerge.
The recorded fecundity of Rana tigrina, in Bangladesh, ranges from 3,601 to 13,560 ova. Pituitary-induced ovulation, under laboratory controlled conditions, produced 19,864 ova.
Field observations indicate that Rana tigrina develops rapidly, hatching occurring 23-hours post-fertilization. Complete metamorphosis is attained in approximately 33-days post-hatching. The initiation of the annual breeding cycle at the onset of the monsoon and rapid larval ontogeny may be adaptive strategies evolved to minimize desiccation, and to reduce larval and juvenile predation by competitive sympatric species.
In Bangladesh, the mean size-cohorts of harvested males are 101mm–110mm (24% of sample) and 91mm–100mm (23% of sample). Males greater than 150mm are rarely encountered in the samples.
The mean size-cohorts of harvested females are 111mm–120mm (24% of sample) and 121mm–130mm (21%). Less than 1% of harvested females exceed 150mm snout-vent length.
The mean size-cohort frequencies of harvested Rana tigrina in Bangladesh are significantly inferior to mean size-cohort frequencies of R. tigrina populations in India, suggesting that the Bangladeshi populations are severely stressed through excessive exploitation.
The mean size-cohort frequencies of males harvested in May, early June, late June and early July decline from 131mm–140mm to 111mm–120mm, and to 91mm–100mm.
Gravid females comprise 85% to 100% of all females harvested in May and June. Gravid females are encountered in the 71mm–80mm (minimal), 141mm–150mm (maximal), and all intermediate size-cohorts. The mean size-cohort frequencies of gravid females are 91mm–100mm, 111mm–120mm and 121mm–130mm (equal frequencies).
The reproductive potential (fecundity) of larger females, producing larger egg masses, and therefore more larvae, is negated by their prompt removal from the breeding population. Given the known high level of larval mortality and low hatching success, females of smaller size produce fewer ova, reducing drastically the recruitment potential.
In some, if not all, areas of Bangladesh which Rana tigrina inhabits, females attain annual reproductive readiness by mid-May, remaining sexually active at least through early July. The field data do not indicate if Rana tigrina oviposits one or multiple clutches throughout its geographic range or if the frequency of spawning varies regionally. Available data suggest that multiple oviposition may occur in the Districts of Mymensingh and Sylhet in which lengthy and unabated monsoons obtain.
It has not been ascertained at what age Rana tigrina attains sexual maturity. The data suggest that both sexes estivate at least once before entering the breeding population.
The sex-ratios of harvested individuals in the early weeks of the collecting season favor males in that they emerge first. Females comprise 16% to 60% of the harvested populations. Gravid females constitute a significant number of harvested individuals from May to mid-July, varying from 38% to 98% of all females collected.
Oliver (1979) cautioned that serious, deleterious effects upon the environment will exist if uncontrolled harvesting of Rana tigrina continues. In India, the adverse impact of uncontrolled harvesting of frogs, specifically Rana tigrina and R. hexadactyla, from rice fields and wetlands, where they protect crops by devouring damaging insects led to a collecting ban (1978) during the breeding season. There is ample evidence in Bangladesh that the current levels of exploitation of R. tigrina has caused ecological destruction of serious consequences.
Although Rana tigrina is omnivorous, insects comprise the greatest number of dietary items (Ahsan, 1983). Noxious and crop-devouring insects increased precipitously in districts in which R. tigrina is intensely exploited. Insect destruction extends beyond standing crops to encompass stored grain.
Khan (1973) determined that Rana tigrina, in India, is a primary predator upon insects, especially coleopterans and orthopterans known to be destructive to agriculture. Issac and Rege (1975) observed that the insectivorous habits of R. tigrina in India assist significantly in the eradication of agricultural and other pests. R. tigrina is a widely distributed and common species in fields under wet cultivation.
In Bangladesh, coleopterans also constitute the greatest volume of prey species of R. tigrina, followed in decreasing volume by orthopterans, anurans, hymenopterans, and orthopterans (Ahsan, 1983; Fugler, 1983). Coleopterans are also the most frequently encountered organism consumed by R. tigrina, followed in decreasing frequencies by hymenopterans, orthopterans, dipterans, lepidopterans, and hemipterans.
Fugler (1984) summarized the extant data pertaining to the temporal reproductive cycles, fecundity, ontogeny, size-cohorts of sexually mature females, geographic distribution, habitat, food preferences, species composition of harvested populations, and species exploited commercially.
The species of commercial importance in Bangladesh are Kachuga spp., Lissemys punctata, Trionyx gangeticus, and Trionyx hurum (Fugler, 1984).
Although data pertaining to the reproductive biology of freshwater chelonians in Bangladesh are minimal, basic studies on adjacent populations (India, Burma, Thailand) indicate reproductive trends.
The annual breeding season of most exploited species begins at the onset of the dry season, concluding at the advent of the wet season. Females oviposit on land near their aquatic habitat, excavating nests in vegetation. The semi-aquatic and terrestrial species construct nests at sites more distant from water. Oviposition is correlated with cessation of the monsoon, retreat of water, emergence and slight desiccation of soil, and abatement of high ambient temperatures.
The freshwater species are most intensively exploited in the dry season, although harvesting continues throughout the year.
The size, weight and age at which sexual maturity is attained in the exploited species are undocumented. The initiation of ovarian development in the annual reproductive cycle is unknown.
The published data suggest that the fecundity of exploited species is low (Fugler, 1984).
Trionyx gangeticus and T. hurum may produce less than 20 eggs per nest. Lissemys punctata deposits 10–12 eggs per clutch (in Burma). Kachuga tentoria deposits approximately 125 eggs per clutch; K. smithi, 5–8; and K. sylhetensis, not documented.
Low fecundity, failure of eggs to hatch, hatchling and juvenile mortality, and harvesting pressure suggest that these endangered species are not only stressed but in decline.
Although the food preferences of the exploited chelonians in Bangladesh are undocumented, stomach analyses of conspecific populations in adjacent areas have been published (Fugler, 1984).
Lissemys punctata and Trionyx hurum are either exclusively or primarily carnivorous. Kachuga tecta, K. tentoria, and Trionyx gangeticus are either exclusively or primarily herbivorous.
The ecological parameters of the exploited species, at least in Bangladesh, very widely. The semi-aquatic K. kachuga occurs in rivers; the semi-aquatic K. tecta and K. tentoria frequent flowing and stagnant waters, pools, and puddles. Lissemys punctata inhabits stagnant waters of village ponds and marshy areas. Trionyx gangeticus and T. hurum are restricted to major river systems, oxbow lakes, and larger bodies of water.
In the monsoonal months the primary harvested species are Trionyx gangeticus (75% of sample analyzed), T. hurum (24%), and Lissemys punctata (0.5%) (Fugler, 1984). In the winter months Lissemys punctata, Chitra indica and Kachuga spp. comprise a significant percentage of the harvested species.
The mean size-cohort of Trionyx gangeticus harvested in winter months is 380mm–399mm, and that of T. hurum, 280mm–299mm. Carapace-length, in the absence of other data, cannot be correlated with sexual maturity, age or ontogeny.
As the populations of edible frogs (Rana esculenta) in Europe declined through unabated exploitation, India began to fulfill the demands of the international markets. In 1959, India exported 93 tons, primarily Rana tigrina and Rana hexadactyla. In 1973, 2,698 tons were exported, and in 1978, 3,570 tons, equivalent to 10,700 tons of live frogs. These frogs would have consumed 10,000 tons of agriculturally destructive insects per day. In 1981, export decreased to 2,068 tons (approximately 130 million frogs) (Whiting, 1984).
With the decline of exports from India and China, Bangladesh entered the international market. China recently banned the sale of frogs after research revealed their importance in controlling injurious insect pests of rice.
In 1983, Bangladesh exported 1,300 tons of frog legs to the United States, 42% of the total tonnage exported; 39% of the exports were destined for the Netherlands, 7% to Belgium, 6% to West Germany, 3% to the United Kingdom, and 3% to France, Italy, Hong Kong, and Malaysia.
Earned foreign exchange increased from five million U.S. dollars in 1982 to over 7.5 million U.S. dollars in 1983. More than 30 companies engage in the export of frog legs. One of the largest earned 250,000 U.S. dollars in exporting 770,000 kilograms (1.7 million pounds) of frog legs in 1983 (Earthscan, 1984).
Bangladesh, in 1984, was the principal exporter of frog legs. According to Agscene (1984), Bangladesh exported 1,320,865 kgs. of frog legs. Calculations based on average weight and size conclude that eight million Rana tigrina were exported. Imports to the United Kingdom increased from 13,300 kg. to 109,600 kg. in 1983. An intensive campaign to ban the import of frog legs in the United Kingdom has been highly successful.
World Wildlife Fund reports that over 500,000 kg. (approximately 12 million Rana tigrina) are exported annually to West Germany. World Wildlife Fund-West Germany and World Wildlife Fund-Switzerland have mounted campaigns to exclude frog legs as permissible imports. Many restaurants and hotels have complied.
The reduction of the populations of Rana tigrina in Bangladesh and in India permitted the uncontrolled increase of noxious and of agriculturally destructive insects. The increase in insect populations, in the absence of Rana tigrina or its presence in greatly reduced densities, is associated with an increase in diseases of cattle and a higher frequency of insect-vectored human diseases. To control the insect populations, broad-spectrum insecticides are imported.
Dr. A. G. Joshi of the Bombay Natural History Society found that the spread of disease and destruction to crops was attributable to the great magnitude of frog harvesting. The 5.5 million U.K. pounds earned in foreign exchange from the export of frog legs is negated by the 13 million U.K. pounds spent to import insecticides (Whiting, 1984).
At present, Bangladesh earns approximately Taka 20 crore of foreign exchange from the export of frog legs (all Rana tigrina). However, Bangladesh spends approximately Taka 30 crore to import insecticides.
The cost-effectiveness is easily quantifiable in terms of export of frog legs and the import of insecticides to control the insect populations caused by the removal of Rana tigrina. The cost in terms of public health, diseases of domestic animals, rodent control, extermination of the natural order of predation, and the disruption of the ecosystem cannot be easily quantified.
All exploited species of chelonians are domestically consumed in Bangladesh. Live chelonians captured in the Districts of Mymensingh and Sylhet are transported to the markets of northern Bengal (Districts of Bogra, Dinajpur, Rangpur). The flesh of Hardella spp., Trionyx spp., Lissemys sp., and Chitra sp. is highly esteemed by ethnic minorities.
Although opportunistically exploited throughout the year, the greatest quantity of chelonians enter the economic network in the winter months. Depending upon weight and size, one chelonian commands Taka 25 to Taka 75.
The economics of the exported turtles encompasses the collector, the middleman, the supplier and the exporter. The price escalates as the chelonian progresses through the economic pyramid to the exporter and to the international markets in Thailand, Singapore, Hong Kong, and Japan (Fugler, 1984).
Within the present decade, based upon export data from Fiscal Year 1976 to FY 1981, the foreign exchange earned from chelonian export has increased 1,746%. In the two fiscal years for which detailed data are available, 1,578,870 pounds of live chelonians were exported (Fugler, 1984). The Forestry Department collects a royalty of Taka five per 40 kilograms of exported chelonians (Fugler, 1984).
Export data on juvenile (hatchling) chelonians (Kachuga spp.) involved in the pet trade are unavailable.
A definitive management program for the wild populations of Rana tigrina has neither been proposed nor implemented in countries in which the species is commercially exploited. Rather, a collecting ban during the breeding season has been invoked in India and in Bangladesh, but not enforced in either country.
It is imperative that a permanent collecting ban be enforced immediately, and that the ban be rigorously monitored to avert an ecocatastrophe. The wild populations of Rana tigrina cannot continue to sustain the present magnitude of exploitation. The adverse ecological effects may have attained the level of irreversibility through the “ripple effect.”
The yearly collecting ban during the breeding season (“closed season”) is inadequate and not biologically sound. Theoretically, the ban permits the sexually mature individuals to reproduce prior to their removal from the breeding populations, thereby allowing the recruitment of surviving post-metamorphic individuals into the populations to replace those harvested. The population densities, in theory, would remain stable in that the younger, and smaller, frogs would not be exploited through one growing and one breeding season.
Biological data confirm that the current ban on harvesting during the breeding season is untenable. Although the fecundity of R. tigrina in Bangladesh has been reported from a limited number of individuals, neither hatching success, nor larval, nor juvenile, survivorship are documented. It is doubtful that recruitment of young frogs into the wild populations maintains population stability given the immense number (more than 12 million) harvested annually. The utilization of diverse biological indices confirm that the wild populations are being rapidly decimated (Fugler, 1983).
Based upon ample biological data (1983) an absolute three-year collecting ban must be not only invoked but rigorously enforced by the responsible governmental agencies. In view of the drastic decline in population densities, experimental management programs for this natural resource should not be considered in the present time-frame.
Factors which prompt the immediacy of an absolute three-year ban include (1) continued decrease in size-frequencies of harvested frogs; (2) high percentage of gravid females among harvested individuals; (3) extirpation of R. tigrina in certain favorable habitats; (4) constant increase in densities of noxious and agriculturally injurious insects; (5) increased use of insecticides, among them DDT; (6) rapid environmental degradation through excessive utilization of insecticides; (7) cost of imported insecticides exceeding foreign exchange earned from export of frog legs; (8) wholesale destruction of wildlife and ecosystem, and increasing frequencies of insect-vectored diseases of humans and domesticated animals, by insecticides; (9) increasing number of field collectors obtaining fewer frogs; (10) increasing quantity of frogs exported; and (11) continuing habitat destruction.
At the conclusion of the three-year absolute ban on harvesting, the population densities should be evaluated by qualified biologists. In the course of the total ban, Rana tigrina should be considered an endangered species. The populations must be monitored throughout the period to determine their status to ascertain the effects of insecticide residues.
If the population densities have stabilized at the conclusion of the three-year ban, alternative management strategies may be pursued. If the populations have not stabilized, the absolute collecting ban must be continued indefinitely. The criteria to assess population stability include: (1) equal population densities in suitable habits in all districts, (2) mean snout-vent length frequencies of both sexes greater than those in the baseline studies (Fugler, 1983), and (3) approximately equal sex-ratios. Population densities should be assessed at the beginning of the breeding season, in mid-season, and near the termination of the breeding season during each year of the three-year ban. The populations in the Districts of Mymensingh and Sylhet must be meticulously monitored.
If the status of the populations has returned to normal, in the opinion of competent biologists, limited and controlled harvesting may be permitted within the following restrictions (Alternative Management Strategy I).
A total collecting ban during the breeding season (May 15 to July 15) must be enforced for a five-year period. Harvesting may be permitted only from July 16 to September 16, and the number of frogs exported rigidly limited. The Government of India prohibits harvesting from mid-June in alternate years and controls the quantity exported.
The enforcement of the ban in the five-year period must center upon the collection centers in all districts specifically designated by authorized agencies. The collection centers are those sites to which the nightly catches are taken by the field collectors. The processing plants, the ultimate destination of live and processed frogs, must be monitored throughout the ban and periodically inspected during the year to discourage unauthorized processing.
Alternative Management Strategy II, similar to that currently enforced in India, may be invoked in lieu of the five-year ban during the breeding season. The strategy should be determined exclusively by biologists.
In Alternative Management Strategy II, Bangladesh is divided into two zones. The eastern zone, arbitrarily delineated, include the districts of Jamalpur, Tangail, Dhaka, Mymensingh, Sylhet, Comilla, Noakhali, and Chittagong. The western districts, similarly designated, include the districts of Dinajpur, Rangpur, Rajshahi, Bogra, Pabna, Kushtia, Jessore, Faridpur, Khulna and Patuakhali. Harvesting of Rana tigrina may be permitted in even-numbered years in the eastern zone (prohibited in the western zone), and permitted in odd-numbered years in the western zone (prohibited in the eastern zone) from mid-July to mid-September exclusively. The status of the populations must be constantly monitored throughout the five-year Alternative Management Strategy II. The allocation of districts to either the eastern or western zone may be revised to facilitate rapid transport to the processing plants.
Collection centers (vide Alternate Management Strategy I) must be established in each district to insure the provenance of the frogs and to control unauthorized harvesting.
Only live frogs may be accepted at the collection centers for shipment to the processing plants. Frogs harvested in the eastern districts may be processed at Chittagong, and those from the western districts at Khulna and Barisal. At the discretion of the authorities the harvested frogs may be distributed among the designated plants. If equal distribution of the harvest is preferred, a quota is to be determined for each processing plant.
Processing of frogs--the severing of the legs from the body--in villages and at collection centers must be absolutely prohibited. The procedure is unsanitary and inhumane (Fugler, 1983). The absence of quality control resulted in the loss of significant international markets (Fugler, 1983), especially to the United States.
The retention of frogs in holding pens adjacent to the processing plants must be terminated, and the holding pens dismantled. The holding pens contain frogs illegally collected during the breeding-season ban. Thousands of mature Rana tigrina are confined to pens in which the water is stagnant and foul, food non-existent, and mortality excessive (Fugler, 1983). The holding pens, euphemestically termed “breeding farms,” are a subterfuge to contravene the ban during the breeding season.
In summary, the following management strategies are proposed: (1) a total ban on the harvesting and export of Rana tigrina for three years during which the status of the populations is constantly monitored; (2) if the populations are deemed to be vigorous and stable at the conclusion of the total ban by competent biologists, a harvesting ban may be imposed during the breeding season (15 May–15 July) and controlled harvesting permitted from 16 July to 16 September (Alternative Management Strategy I) (the status of the populations must be constantly assessed); and (3) if the population densities are stabilized at the conclusion of the total ban, after assessment by competent biologists, harvesting may be permitted in the eastern and western zones in alternate years (Alternate Management Strategy II). An export quota must be determined and must not be exceeded.
The status of the populations must be constantly monitored during the initial three-year absolute ban and during the following five-year controlled harvesting. The responsibility for the protection, population assessment and harvesting should be the responsibility of the Forestry Department. The establishment of collection centers and the designation of processing plants as well as the monitoring thereof should be the responsibility of the aforementioned. Only live frogs should be accepted at the processing plants, and high standards of humane treatment and sanitation enforced. Rana tigrina should be re-introduced into those areas in which it has been exterminated and in which suitable habitat exists.
Although the status of the wild populations of freshwater chelonians in Bangladesh is virtually undocumented biologically, the species involved in commercial exploitation are under stress (Fugler, 1984). The exploited species, throughout their geographic range, have declined so precipitously in population densities that all are listed in Appendix I (Endangered) of CITES. International trade in endangered species is prohibited by CITES, of which Bangladesh is a signatory. Thus, the export of freshwater chelonians, permitted by the Government of Bangladesh, is in contravention of the CITES agreement.
That the populations of the freshwater chelonians are declining have been ascertained by the following biological criteria (Fugler, 1984): (1) most intensive harvesting occurs in winter months; (2) breeding and oviposition occur in winter months; (3) fecundity of the species is low; and (4) hatchling success is low and juvenile mortality is high under natural conditions.
Export data, of questionable reliability, indicate that the endangered species are exported primarily in the winter months and that the annual export weight increases yearly (Fugler, 1984).
In the absence of critical biological data pertaining to the exploited species, a management program is premature. Harvesting must be terminated (banned) immediately. The initiation of field studies to acculumate data on these endangered species is urgent. Detailed information on the following aspects of chelonian biology must be obtained: (1) geographic distribution and population densities of the endangered species throughout Bangladesh; (2) habitats and nesting sites; (3) fecundity, hatching success, hatchling mortality, and hatchling sex-ratios; (4) age and size at sexual maturity; (5) initiation and termination of annual reproductive cycle; (6) percentage of gravid females among sexually mature females in the exploited populations; and (7) food preferences of hatchlings, juveniles, and adults.
Although the collecting ban during the breeding season of Rana tigrina is unenforced by the responsible agencies (Fisheries) and the export of endangered chelonian species ignored by the Forestry Department, the responsibility for the proposed management programs of Rana tigrina and the enforcement of the absolute export ban of endangered chelonians should be allocated to the Forestry Department. The conservation of other endangered species of wildlife is currently within the domain of the Forestry Department.
The professionals of the Forestry Department possess greater awareness, in breadth and depth, of the biology of terrestrial species and their conservation. The Fisheries Department has proved uninterested, ineffectual, and inefficient in controlling the exploitation of Rana tigrina, destruction of habitat, and maintenance of quality control.
A thorough search of the retrievable literature reveals that the intensive and extensive culture of frogs, on a successful commercial level (for research and education), is restricted to the North American Bullfrog, Rana catesbiana. Although a vast body of biological information has been accumulated, Rana catesbiana has not been cultivated in sufficient quantities to supply the international markets with edible products.
The artificial culture of frogs is a relatively recent phenomenon, the technique originating in the United States as pond-culture (Priddy and Culley, 1971). Breeding stocks of North American Rana catesbiana were shipped to Japan where culture techniques of limited success were developed (Priddy and Culley, 1971).
In Japan the basic cultivation techniques involved confined metamorphosed juveniles to which fly larvae, silkworm pupae, crayfish, and table scraps were fed (Priddy and Culley, 1971). Increased consumption of bullfrogs, habitat destruction, excessive export, and contamination with DDT has drastically reduced the availability of bullfrogs.
In the United States frog culture is primarily limited to outdoor facilities, mainly ponds, in which success has been minimal (Priddy and Culley, 1971). The market for pond-reared frogs is restricted to breeding stock. The inability to control disease and predators, provide sufficient food, and prevent cannibalism, contribute to the failure of outdoor pond-rearing on a commercial scale. Further investigation in pond-rearing is obsolete in that ambient control is necessary in all phases of amphibian culture (Priddy and Culley, 1971).
Neither intensive nor extensive artificial culture of Rana tigrina should be undertaken on a commercial scale pending exhaustive experimental pilot studies. Fish culture techniques, extensive and intensive, are not applicable to amphibian culture. The experimental design for the artificial cultivation of Rana tigrina is modified from that for Rana catesbiana (Priddy and Culley, 1971). It must be noted that the culture techniques for Rana catesbiana may not be transferable to Rana tigrina or to other species. In the absence of successful culture techniques for Rana tigrina there is no alternative to the utilization of a proven rearing technique for another species.
The rearing facility is an enclosure measuring 30 feet wide, 160 feet long, and 10 feet high, constructed upon a six-inch concrete slab (Appendix I). The walls may be constructed of brick, concrete block, or other locally available material. The roof may also be fabricated of wood or of other local material (Appendix II). Two-inch Fiberglas insulation is applied to the interior surface of the walls and roof or ceiling. Windows, skylights, and other sources of natural illumination are not required. Adequate ventilation is obtainable through the opened doors at either extremity of the shelter.
Six fluorescent lights, affixed to the roof (ceiling), are spaced equidistantly throughout the shelter. Interior illumination is used sparingly to avoid precipitating stress on the nocturnally active amphibians. The absence of artificial and natural illumination have not proven detrimental to the cultivation of Rana catesbiana (Priddy and Culley, 1971).
A constant and plentiful source of water, preferably a bore, must be near the rearing facility. Water is transported to the facility by a two-inch P.V.C. conduit, and thence to the rearing tanks by one-inch rubber or plastic hoses (Appendices I, II).
The facility is heated by two 75,000 B.T.U. kerosene forced-air heaters (Appendix I). The interior temperature must be maintained at 70°F or above. Rana catesbiana (and Rana tigrina?) does not feed at temperatures below 70°F.
The rearing facility contains six 20-foot-diameter tanks constructed of concrete blocks (Appendices I, II). The walls of five circular tanks are 30 inches in height, and the sixth tank, 36 inches. The tanks are linearly aligned with an intervening space of 30 inches between the exterior facing of each tank (Appendix I).
Bore water, introduced into the tanks through rubber or plastic hoses, is removed through drains constructed of six-inch P.V.C. pipe level with the tank floor, and six inches from the interior wall (Appendix II). Additional sections of P.V.C. pipe may be inserted within the drain to maintain the water level at the desired depth. A metal collar with ¼-inch-mesh wire brazed upon it is inserted either into the drain level with the tank floor or inserted into the additional sections.
The interior walls and floors of the tanks are coated with two applications of “Davis Weld No. 303 Epoxy Paint” to waterproof the rearing containers.
The frogs are supplied crickets and worms in the morning. The tanks are maintained so that dry areas are present. In the evening, after cleansing the tanks, ½-inch depth of water is introduced, and thence small fishes. The water depth is sufficient for the fishes to survive but inadequate for swimming. Approximately 5,000 juvenile frogs will require two to five pounds daily of live fishes (225 fishes per pound).
The crickets are cultured in boxes thirty feet in length, six feet in width, and two feet in depth. Fifteen culture boxes within the facility provide adequate food, in conjunction with worms and minnows, for 5,000 to 6,000 frogs.
The earthworms are also cultured in boxes twelve feet in length, twelve feet in width, and two feet in depth, located in the facility.
The minnows and fishes may be obtained from adjacent culture ponds.
Significant mortality among intensively cultured frogs results from disease introduced into the tanks by poor standards of sanitation (Priddy and Culley, 1971).
The tanks and the frogs are sprayed daily with water after the morning feeding. The tanks are thoroughly cleansed and thoroughly rinsed. To avoid transferring contamination from tank to tank, separate cleansing instruments for each tank are used. In the evenings, prior to feeding, the tanks are again thoroughly scrubbed.
The tanks are disinfected weekly with “Mikroklene” (Economics Laboratory, Inc.) at a dilution of ¼-ounce per gallon of water. The solution is sprayed within the tanks and upon the frogs. If water hardness registers 36 ppm of calcium carbonate accumulation of disinfectant must be prohibited.
The frogs are examined thrice weekly for disease and injury. If diseased frogs are encountered, they are removed and destroyed. “Mikroklene” is then utilized daily at a dilution of 1/8-ounce per gallon.
The intensive cultivation of frogs characteristically commences with the collection of spawn although induced ovulation is now an experimental consideration.
The egg-masses are confined in nylon-screen baskets three feet in length by one foot in width by one foot in depth supported by two-inch supports. The baskets are placed in the rearing tanks. The water level is at least six inches in depth in the baskets. After hatching, a maximum of 200 larvae are allocated to each basket.
The water flow through the baskets must be constant without creating a current to eliminate the growth inhibitors liberated by densely aggregated larvae (Rose and Rose, 1965). Priddy and Culley (1971) recommend a total change of water within a 24-hour period.
Recent research suggests that the pH of the water is critical in larval development and perhaps in disease control in Rana catesbiana (Culley, et al., 1977). The pH of the water should vary within 6.5 and 6.9. Calcium and calcium carbonate must approximate 50 mg/l. In that the daily dietary requirements of calcium are unknown, a water source with calcium is preferred. Magnesium is also a critical element in early larval ontogeny. Water temperatures may vary between 20°C and 26°C.
A high density rearing system has been designed and tested by Culley et al. (1977). Each rearing unit of a longitudinal V-shaped 120-liter Fiberglas reservoir (Appendix III) is equipped with a full-length horizontal drain pipe for waste removal, and a vertical standpipe to maintain desired water level. Each tank will receive a rearing basket 64cm × 25cm × 20cm. The water depth in the rearing basket should be 15cm. The sides of the rearing basket are of nylon screen, and the bottom of 0.32cm mesh, allowing the feces to fall to the horizontal drain. Water is delivered to the basket by a tee-jet nozzle, producing a fan-shaped spray.
The high-density rearing containers may be placed in the rearing facility or in the laboratory. The controlled environment of the rearing facility and water quality must be rigidly maintained.
An experimental approach meriting detailed attention is that of induced ovulation and spermiogenesis, of which the literature is voluminous. However, no detailed experimental studies of large-scale induced ovulation and spermiogenesis in Rana tigrina and Rana hexadactyla have been reported. To date, all intensive cultivation of Rana catesbiana is initiated with egg masses collected in the wild during the breeding season. In order to rear throughout the year a constant source of ova must be available in large quantities. Successfully induced spermiogenesis is frequently reported in the literature. Successfully induced ovulation of large quantities of ova is infrequently reported, and multiple induced ovulation is even less frequent. Induced ovulation in 50% of wild stock and laboratory-reared Rana catesbiana is considered successful at present. Reproductive control of male Rana catesbiana has been reported (Culley, 1981).
Recent studies (Marschall, 1978; Culley, et al., 1977) determined that a mixture of animal and plant proteins, carbohydrates, vitamins, essential elements and antibiotics produce a suitable larval diet for high-density reared Rana catesbiana (Appendix IV, V). Protein levels in prepared larval food between 35% and 43% (dry weight) resulted in the largest larvae, more individuals attaining metamorphosis, and lowest food conversion values (Marschall, 1978; Culley, et al., 1977). Protein levels greater than 43% and less than 39% were not beneficial (Appendix V).
For the larvae reared in a high-density environment a proper and constantly available source of food must be available. Recent research (Marschall, 1978; Culley, et al., 1977) has determined that the ingredients must be bound with alginate, gum, or agar, and spread upon screens, and then introduced into the larval baskets. The ingredients, binders, and preparation for larval Rana catesbiana are detailed (Appendices VI, VII). The diet may be experimentally modified for larval Rana tigrina and Rana hexadactyla.
Ahsan, M.F. 1983. Study of food-items stomach analysis of the Indian Bullfrog, Rana tigrina Daudin, in Bangladesh. Fisheries Information Bulletin, Bangladesh Fisheries Resources Survey System, BGD/79/015, 1(4):52–66.
Culley, D. D., Jr. 1976. Culture and management of the laboratory frog. Lab Animals, 5(5):30–36.
Culley, D. D., Jr. 1981. Have we turned the corner on bullfrog culture? Aquaculture Magazine, 7(3):20–24.
Culley, D. D., Jr. In Press. Edible frogs. In Evolution of domesticated animals. Ed. Ian L. Mason. Longman Co., London and New York.
Culley, D. D., Jr., et al. 1977. A high density rearing system for larval anurans. Lab Animal, 6:34–41.
Culley, D. D., Jr., et al. 1978. Current status of amphibian culture with emphasis on nutrition, diseases and reproduction of the bullfrog, Rana catesbiana. In Proceedings of the Ninth Annual Meeting of the World Mariculture Society, World Mariculture Society, 653–669.
Fugler, C. M. 1983. The status of populations of Rana tigrina Daudin in Bangladesh. Fisheries Information Bulletin, Bangladesh Fisheries Resources Survey System, BGD/79/015, 1(4):1–51.
Fugler, C. M. 1984. The commercially exploited Chelonia of Bangladesh: Taxonomy, ecology, reproductive biology and ontogeny. Bangladesh Fisheries Information Bulletin, 1(4):1–42.
Huda, N. 1984. A frog in the throat of an economy. Earthscan.
Issac, S., and M. S. Rege. 1975. Food of Rana tigrina. Journal Bombay Natural History Society, 72(1):143.
Khan, M. S. 1973. Food of the Tiger Frog, Rana tigrina Daudin. Biologia (Lahore), 19(1–2):93–107.
Marschall, D. G. 1978. Development of testing procedures, feed formulation, and protein requirements for Rana catesbiana larvae. Unpublished thesis. Louisiana State University, ii-ix, 1–56.
Oliver, R. C. D. 1979. Wildlife conservation and management in Bangladesh. UNDP-FAO Project BGD/72/005. Field Document No. 10. FAO, Rome.
Priddy, J. M., and D. D. Culley, Jr. 1971. The frog culture industry, past and present. Southeastern Association Game and Fish Commissioners. Proceedings, 25:597–602.
Rose, S. M., and F. C. Rose. 1965. The control of growth and reproduction in freshwater organisms by specific products. Mitt. Internat. Verein. Limnol., 13:21–35.
Whiting, D. 1984. Frog legs - a study in cruelty and short-sighted stupidity. Agscene, 75:2–4.
The consultant wishes to thank heartily the generous assistance of Dr. Harold C. Loesch, Project Manager, BGD/79/015, Fisheries Resources Survey System, Dhaka, Bangladesh, and his Executive Assistant, Mr. Md. Zaman. The supportive staff of UNDP-FAO Project BGD/79/015 enthusiastically extended the expertise to encompass the particular concern of the consultant, especially in the cartographic, transportation, and secretarial units.
The consultant wishes to express his gratitude to the faculty of the Department of Zoology, Dhaka University, and to the faculty of the Department of Fisheries, Bangladesh Agricultural University, Mymensingh, for the numerous courtesies extended during the three consultancies in Bangladesh.
Ms. Polly Harris, Department of Biological Sciences, The University of North Carolina at Wilmington, most kindly supervised the report through numerous drafts to the final copy. Mr. Erwin Rowe of Wilmington, North Carolina, most generously executed the designs of the appendices, and Ms. Elizabeth S. Clemmons, Department of Earth Sciences, The University of North Carolina at Wilmington, transferred the designs to the final copy.
Lastly, but most importantly, the consultant wishes to express his sincere gratitude to the untold number of urban and rural Bangladeshi who made his tenure in Bangladesh so pleasurable.
| Ingredient | Protein Concentration % of Ingredient in Diet | |
|---|---|---|
| 39% Protein | 43% Protein | |
| Shrimp meal | 13.0 | 14.0 |
| Fish meal | 8.5 | 11.0 |
| Soy protein | 6.0 | 8.0 |
| Yeast protein | 5.0 | 5.0 |
| Meat protein | 7.0 | 8.0 |
| Rice bran | 41.0 | 33.5 |
| Fish protein concentrate | 7.0 | 8.0 |
| Fish solubles | 5.0 | 5.0 |
dry ingredients (shrimp meal, fish meal, soy protein, yeast protein, fish protein concentrate, rice bran, vitamin premix-milled (1mm) and well mixed
liquid ingredients (fish solubles, fish oil, linolenic acid)
binder (2% of solids)
antibiotics (sulfamerazine, oxytetracycline)
water (diet should be 50% water)
CaCl2 (15%–20% aqueous solution)
aluminum window-screen (cut to desired size)
Heat water to boiling.
Add binders slowly, stirring or mixing well until smooth gum is formed.
Add liquid ingredients while mixing; blend 2–3 minutes.
Add antibiotics; mix well.
Add dry mix, about ¼ at a time, stirring first, then kneading until pasty dough is formed.
With spatula or putty knife spread food on both sides of pieces of screen. Food should be 1/16-inch thick on each side. Too much moisture will soften food and prevent it from sticking to screen. A damp sponge is helpful.
Place screen in shallow CaCl2 bath for one minute. Replace CaCl2 bath after 6 screens.
Keep screens moist thereafter. Stack screens between damp paper towels and refrigerate in plastic bags.
If dough is too thick, add water for easier spreading. One kg. of prepared food requires 15–18 pieces of 10cm × 20cm screen, and 2 liters of CaCl2 solution. Food remains on screen up to 60 hours at 25°C or less. Surface of prepared screen should be rubbery but no so thin as to peel off. Local water can affect binding quality. If food is too tightly bound, the larvae cannot rasp it off. Binder should be reduced or added if needed but not by more than ±0.5%.
dry ingredients (shrimp meal, fish meal, soy protein, yeast protein, fish protein concentrate, rice bran, vitamin premix-milled (1mm) and well mixed
liquid ingredients (fish solubles, fish oil, linolenic acid)
binder (xanthan or other gum, or agar, 2% of solids)
Antibiotics (sulfamerazine, oxytetracycline)
water (diet should be 75% water)
ethanol (enough to suspend binder, for gum only)
petri dishes
(1) Heat water to boiling.
For gums
(2a) Add dry ingredients to water slowly, mixing constantly.
(3a) Add binder to heated ethanol.
(4a) Add suspended binder to water/feed mixture, mixing constantly.
For agar
(2b) Add binder to hot water, stirring until viscous, 2–3 minutes.
(3b) Add dry ingredients to binder solution, stirring to mix well.
(5) Pour into petri dishes.
NOTES: Petri dishes must be ready before mixing of foods. Dishes may be refrigerated for 3 weeks or frozen, if desired. Local water may affect binding quality. If food is bound too tightly, larvae are unable to rasp it off. Binder should be reduced or added if needed, but not by more than ±0.5%.
| 22 December 1984 | Depart Wilmington, North Carolina, U.S.A. |
| 23 December 1984 | Arrive London |
| 24 December 1984 | Depart London |
| 25 December 1984 | Arrive Dhaka |
| 26 December 1984 | |
| 12 January 1985 | Dhaka |
| 13 January 1985 | Bangladesh Agricultural University, Mymensingh |
| 19 January 1985 | Depart Dhaka |
| 20 January 1985 | Arrive Rome |
| 28 January 1985 | Depart Rome, arrive Wilmington, North Carolina |
