By A. Clare
Exotic leather comprises 1% of the leather industry; its unique pattern and structure distinguish it from leather produced from hides/skins of domestic species. Fish skins are an attractive material for leather making due to their unique grain structure. Stingrays are cartilaginous fish (Class: Chondrichthyes) often exploited for their meat in lower-income countries. Stingray skin is made up of placoid scales known as denticles, which increase in size towards the centre (figure 1), giving an attractive and unique appearance when used in leather products. Stingray and shark leather, known as ‘shagreen’, has very high tensile strength, making it a high-quality material for leather products.
Stingray Exploitation:
The Indo-pacific is a global centre for intense elasmobranch (i.e., sharks, rays and skates) fishing. Stingrays are widespread in the region, and the fishery sector plays an important role in the economy of adjacent low-income countries, which rely on the fishing sector for food security, protein, income and employment.
Stingrays are a major fishery export from India and Indonesia and, stingray meat is consumed throughout these regions. India is the second-largest producer of fish worldwide, producing approximately 6.9 million tonnes annually and being home to one of the world’s largest stingray fishing nations. The processing of stingray skins into shagreen became popular during the 18th century. During processing, the exterior wings are removed for consumption and the dorsal skin is removed for tanning (figure 2). This practice continues to occur today due to the development of policies; regarding the valorisation of fishing industry waste for the development of products with high economic value.
A By-product or Main Product?
The processing of stingray skins requires a different approach compared to conventional tanning. Historically, stingray skin was often considered worthless, however, technological advances have enabled the processing of this raw material into commercial leather products with high economic value. Stingray skins are sold at cheap prices but once tanned the total economic value increases by approximately 900%.
Although shagreen was initially derived from a fishing industry by-product, the opportunity for processing skins into unique materials with high value has been recognised by low-income countries. The high economic value of shagreen has led to many Indo-pacific whipray populations becoming exploited, which asks whether these species should receive more CITES protection.
Population dynamics and Conservation Status:
Exploited species are primarily from four genera: Maculabatis, Hemantura, Pateobatis and Urogymnus. Larger species provide more meat and larger skins and, therefore, these individuals are highly desirable by the fishing industry. The large size of the honeycomb whipray, Hemantura undulata, has resulted in this species being specifically targeted for its skin. Other highly desirable species include the whitespotted whipray, Maculabatis gerrardi, the round whipray, Maculabatis pastinacoides, the bleeker’s whipray, Pateobatis bleekeri, and the whitenose whipray, Pateobatis uarnacoides.
Despite their occurrence in near-shore environments, population dynamics and fishery impacts on whiprays have been poorly seldomly reported. Although there are no species-specific data available, overall stingray catches are declining; with Indonesia landings data demonstrating declines of 45-99% over the past three generation lengths (75 years).
The whitespotted whipray, round whipray, bleeker’s and whitenose whipray are highly desirable by Bangladesh, where their skins are transformed into leather. These species were declared vulnerable in 2016 but are now classified as endangered by the IUCN red list. The specific targeting of the honeycomb whipray has endangered the species and resulted in a continuous decline of mature individuals. Despite this decline in numbers and, although whiprays have high economic value, there are no conservation actions in place for any species from the four genera.
Fisheries selectively target larger, most profitable species. Large species have slow life-history traits, including slow growth rates, low fecundity and delayed age of maturity, which render them vulnerable to overexploitation. Stingrays show strong sexual dimorphism with larger females more likely to be targeted by fisheries. The removal of large, breeding individuals reduces the reproduction potential, resulting in rapid population declines.
The Indo-pacific region relies on stingrays for food security and income and; therefore, the loss of these organisms is likely to have significant social and economic impacts. Furthermore, reduction in abundance will cause ecological consequences, such as disruption of predator-prey interactions, which will likely cause cascading effects on food chains the fishing industry relies on.
Will a Ban on Stingray Fishing Increase Species Conservation?
The stingray fishing industry has for long played a vital part in the economy of countries surrounding the Indo-pacific region. In Indonesia alone, greater than 6 million people are directly or indirectly involved in the fishing sector. Placing a ban on stingray fishing will stop populations dependent on this industry from receiving a steady income flow.
In 1990, the exploitation of Olive ridley turtles for leather led to a rapid depletion in numbers. A subsequent ban on turtle fishing pushed populations that relied on this resource to switch to shark fishing. Sharks became exploited for their meat and leather, which has similar characteristics to ray shagreen. Substitution of turtle leather products by sharks was reflected by a sudden decline in shark populations. Banning stingray fishing is, therefore, likely to cause Indo-pacific populations to overexploit alternative natural resources.
Switching to ecotourism has recently been adopted by many areas to shift the economic value of vulnerable species to a more sustainable use. Many marine ecotourism industries now prevail and, although it is often viewed as a sustainable alternative to destructive activities, the lack of ecological data on this modern activity raises the concern of how sustainable these practices actually are. Ecotourism is likely to have severe ecological consequences, such as impacting energy budgets and reducing the ability to learn from conspecifics. These ecological changes are likely to lead to irreversible behavioural changes in future generations.
Placing a ban on stingray fishing is not likely to prevent exploitation from occurring. Small scale fisheries are economically important, comprising greater than 80% of the fishing sector in these regions. Small-scale sectors often receive less data collection and are more difficult to monitor by governments. The high occurrence of artisanal fishing in the Indo-pacific region suggests stingray skins are still likely to be exploited if a fishing ban is introduced.
Conclusion:
Valorisation of fishing industry waste to produce stingray leather with a high economic value was recognised during the 18th century by low-income countries in the Indo-pacific region. Although stingray leather was innovated to utilise a by-product, the high value of shagreen has resulted in many species becoming depleted.
Fish are a major source of accessible income in the Indo-pacific region; however, the demand for stingray skin cannot be met sustainably under current conservation efforts. All whipray species are in decline and, their slow life-history parameters render them vulnerable to overexploitation. Fishing bans are unlikely to provide environmental benefits, as products are likely to be substituted by alternative species with similar utility.
Authorities of low-income countries must focus on implementing fishing management plans to maintain economic security and prevent further exploitation. Management should involve; implementing marine protected areas, monitoring species, mandatory reporting of catch per unit effort and, limits on the size of species landed. Maintaining economic security requires the protection of vulnerable species to prevent overexploitation of these valuable natural resources.
Further management should also focus on conservation efforts through CITES certification. Fisheries should be active conservationists of protected species and, those who violate conservation orders should receive heavy penalties. Furthermore, custom authorities should implement stricter policing and monitoring of international shagreen trade.
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