An accidental island
On the remote Indonesian island of Buru, a population of largetooth sawfish (Pristis pristis) lives in complete isolation. Unlike most of their relatives who migrate between freshwater rivers and coastal marine habitats, these sawfish are confined to the island's freshwater lakes. This population, unknown to science until 1991, represents a unique evolutionary snapshot. Geological changes, likely a fall in sea level, are thought to have trapped a marine population inland, cutting them off from the ocean and forcing a permanent adaptation to freshwater life. This isolation has made them genetically distinct from their marine counterparts, a separate branch on the family tree.
The sawfish itself is an extraordinary animal. Despite its shark-like appearance, it is a type of ray. Its most famous feature, the long, flat rostrum lined with teeth, can be up to a third of its total body length. This "saw" is a weapon and a sophisticated sensory tool. It is covered with thousands of pores called ampullae of Lorenzini, which function as electroreceptors. These organs allow the sawfish to detect the faint electrical fields produced by prey like fish and invertebrates hiding in murky water or buried in sediment. Once located, the rostrum is used to stun or impale prey with powerful side-to-side swipes.
A precarious existence
All five species of sawfish globally are listed as critically endangered, making them one of the most threatened families of marine fish. The Buru Island population is exceptionally vulnerable due to its small size and isolation. Primary threats worldwide are fishing and habitat loss. The sawfish's rostrum, essential to its survival, makes it especially susceptible to entanglement in fishing nets like gill nets and trawls. In many parts of Indonesia, sawfish are a protected species, but accidental bycatch remains a serious problem.
The largetooth sawfish has a slow reproductive cycle, which hinders its ability to recover from population decline. They mature late, at around 8 to 10 years old, and females give birth to live young after a gestation of about five months. A litter contains up to 13 pups, each born measuring 70-90 cm. To protect the mother during birth, the pups' rostrums are covered in a soft sheath that dissolves shortly after they are born. Juvenile sawfish typically spend their first four to five years in freshwater nursery habitats before moving to more saline environments. For the Buru Island population, these freshwater lakes are their entire world, making the protection of this unique habitat absolutely essential for their survival.