In Sri Lanka, fishermen report drastic decline of elusive radius
In the waters off Sri Lanka, the numbers of sawfish, a rare and globally endangered group of marine rays, have declined so much that the animal is now considered “functionally extinct”. The discovery, taken from a study by Rima Jabado, a member of Pew Marine, in the August 2021 issue of the journal Aquatic conservation: marine and freshwater ecosystems, urged lawmakers to explore measures to protect the sawfish remaining in the country.
Jabado and his colleagues at Blue Resources Trust, a Sri Lankan nongovernmental organization, interviewed more than 300 fishermen and fish traders to investigate the distribution, species diversity and health of Sri Lankan sawfish populations. Named for their saw-shaped muzzle, sawfish are a type of stingray whose skeleton is mostly made up of cartilage. And like many species of sharks and rays, these animals are targeted for their fins, which can fetch high prices in the marine life trade.
“Our aim was to gather information on the state of sawfish in Sri Lanka by interviewing fishermen from coastal communities, as they are very likely to have first-hand knowledge of these rare species,” said Jabado, who received a Pew Marine Fellowship in 2019 for his research on the operation of sea guitars and chocks. “Watching the decline of rare or elusive species can be difficult, in part because even when populations are healthy, they are rarely encountered in the wild. “
Once abundant in many parts of the world, the five living sawfish species are now listed as either Endangered or Critically Endangered by the International Union for the Conservation of Nature. These species, which are among the largest fish in the sea, mature slowly and have few descendants, making them particularly vulnerable to human exploitation. Once reduced, sawfish populations can take decades to rebuild.
Sawfish species have been recorded in Sri Lanka for over a century, but no studies to assess their status in the country have been carried out so far. Research in other Indian Ocean countries has revealed drastic population declines over the past decades, likely the result of targeted fishing, accidental entanglement in fishing gear – known as bycatch – and habitat loss due to dredging, pollution and coastal development.
Documenting decades of decline
To fill this knowledge gap, Jabado and his colleagues conducted interviews at 21 sites around the Sri Lankan coastline, asking fishermen for information on the frequency and seasonality of sawfish sightings, types of fishing gear. used and the value of sawfish meat or fins. Respondents were also asked about the local names of individual sawfish species and their perceptions of the animals’ cultural significance.
“We found strong evidence for the decline of sawfish populations in Sri Lanka, with knowledge of sawfish increasing with the age of study participants,” Jabado said.
No respondent aged 20 to 29 could identify sawfish from illustrations or reported seeing them in the wild. Conversely, all respondents aged 70 to 79 were able to identify and have seen the animals. The median year in which sawfish were last observed by respondents was 1992, indicating that population declines date back several decades.
The team also found that the language provided historical information about the distribution of sawfish species. Although researchers could not confirm the presence of a single species from photographs and dried specimens, study respondents from northern Sri Lanka provided local names for two different types of sawfish, a finding consistent with older checklists indicating two species of sawfish in the area.
The authors of the study attribute the decline of the sawfish in Sri Lanka to a combination of factors, primarily the fishery, which suddenly intensified in the 1950s in concert with a rapidly expanding fishery and peaked in the years 1980. Researchers also cite the expansion of the aquaculture industry, which can degrade or destroy mangrove forests and pollute lagoons and estuaries, all key habitats and nursery areas for sawfish. Aquaculture production in Sri Lanka developed in the 1970s and peaked in 1998, coinciding with the estimated period of sawfish decline.
Linking politics to science
In a good example of informative research on environmental management, Jabado and the Blue Resources Trust team presented the study evidence to decision makers at Sri Lanka’s Fisheries Ministry and worked with them to implement lists of local species of beveled fish and giant guitars under the Convention on International Trade in Endangered Species of Wild Fauna and Flora, including the development of non-detriment findings ( ACNP). NDFs assess whether international trade in a given species is likely to negatively affect its survival. In the case of the beveled fish and the giant sea guitar, a negative NDF would be tantamount to a ban on the export of meat or fins from Sri Lanka.
“Collaborative studies like this help highlight the realities of our shark and ray populations in Sri Lanka,” said Daniel Fernando, Founder of Blue Resources Trust. “And armed with this information, we can guide policymakers to implement management that will reduce pressures on threatened sharks and rays. ”
In collaboration with Blue Resources Trust, Jabado organized several workshops in Sri Lanka to train more than 60 fisheries managers in the identification of guitar rays and bison fins (the other two groups of species at the center of his project. Pew scholarship) and works with policymakers. recommend the ban on sawfish fishing in the country. Since there are so few sawfish left, the regulations are unlikely to have a significant impact on fishermen.
“I welcome the commitment of policymakers on this issue to give the remaining sawfish, sawfish and guitarfish a better chance of survival,” Jabado said. “The lessons we learn from protecting this group of species will also be useful in guiding the future scientific management of sharks and rays.”
Polita Glynn is Project Director and Nathan Fedrizzi is Senior Associate of the Pew Fellows Program in Marine Conservation.