Background

The use of indiscriminate fishing techniques, such as gillnets or purse-seine nets, are threatening manta and mobula ray populations all across the world. This situation is further exacerbated by target fisheries and retained bycatch driven by the escalating demand for their dried gill plates – the tough cartilaginous structures enabling them to filter plankton from the water column – in Chinese Medicine. Since these rays have extremely slow growth rates (manta rays can live to over 40 years), low fecundity, and late maturity, their populations have declined across their range and there is no doubt that commercial fisheries of these species will be unsustainable.   

Due to the difficulty in identifying these extremely similar looking rays, the inability to study them in confined waters, and since many of their aggregation sites are fairly remote, very little biological or ecological data is currently available for them. This has made protecting them quite challenging as policy management requires in-depth scientific evidence attesting to their threatened and declining status.

 

Primary Objectives

The primary objective is to conduct surveys at fish landing sites across Sri Lanka to obtain an overview of the scale and complexity of the mobulid fishery. This includes identifying the species being landed, collecting biological data such as dimensions, sex, maturity etc., and also establishing a genetic tissue data-bank to conduct studies on population genetics, stable isotope analyses, and toxicology studies.

In addition to surveying fisheries, this project is working to develop the first global identification guide book for all mobulid species. In partnership with Bangor University, a genetic kit is also being created. The combination of these two tools would enable the identification of tissue and gill samples, which is crucial in the monitoring and control of the international trade of mobulid rays in the enforcement of CITES, and also to advance research on these species through their positive identification.  

This ID guide and genetic kit project goes beyond the shores of Sri Lanka as it involves multiple global collaborators to acquire genetic material, and data on identification characteristics, all across the ranges of all species. These tools, upon completion, would be made accessible to scientists, field-researchers, policy advocates, and of course anybody enthusiastic to learn more about manta and mobula rays. 

Ultimately these resources will enable a larger number of individuals to effortlessly identify each mobulid ray down to species level, drastically increasing and improving data being collected for each species. This will in turn lead to improved conservation measures for manta and mobula rays.

Manta birostris gill plate

Mobula japanica killed for its gill plates

In this edition of Al Jazeera English 101 East, Chan Tau Chou explores the trail of manta gills from the seas to the shops and investigates how humans threaten the existence of one of the most graceful creatures in the ocean. How long can the manta population survive?

 

 

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