Common Sawfish

Very little is known of this rare sawfish, but features of its biology can be deduced from studies of other sawfish species. All sawfishes are ovoviviparous (2), a method of reproduction whereby the young develop inside a weakly-formed egg shell within the adult female, receiving nourishment from their yolk sac. During development, the sawfish's rostrum is soft and flexible and the teeth are enclosed in a sheath, possibly to protect the female sawfish whilst giving birth. Shortly after birth, the teeth become exposed (5). Sawfish generally feed on small schooling fish, but are also reported to feed on crustaceans and other bottom-dwelling animals. They attack fish by slashing their 'saw' sideways through schools, impaling fish on their teeth. The speared fish are scraped off the teeth by rubbing them on the bottom and then ingested whole (5). Sawfish spend much of their time lying on the sea bottom which, as their gills are located on the underside, means that water does not flow over the gills. Like other rays, sawfish overcome this problem by drawing in oxygen-rich water through large holes located behind the eyes, called spiracles, when breathing (8).

The common sawfish is listed on Appendix I of the Convention on International Trade in Endangered Species (CITES), meaning that international trade in this species is prohibited except in exceptional circumstances (4). Besides this listing, there are currently no conservation measures in place for this species, and it is believed that without urgent intervention, there is a high probability that this sawfish will become extinct (2).

The common sawfish has an ironic name as it is actually a rare species, facing a very real possibility of extinction (1) (2). The most distinctive feature of the common sawfish is its long, flattened, tapered snout (2) (5), which may measure up to a fifth of the total length (3). Along the edge of this blade are a series of 16 to 20 evenly-spaced, long, thin teeth, creating the appearance of a 'saw' (2) (5) (6). The skin of the common sawfish is greyish-ochre on the back and sides, and creamy-white on the undersides (7). Sawfish are classed in the same group as sharks, skates and rays (the elasmobranchs), and despite their appearance, are actually more closely related to rays than sharks, having their gills located on the underside of the body and not on the sides (8).

The common sawfish inhabits coastal areas, estuaries, lagoons, and also enters freshwater habitats; and thus populations have been recorded in a vast array of habitats, from the ocean, to 750 kilometres up the Amazon River, and in Lake Nicaragua (9). It is a benthic fish, meaning that it lives near the bottom, generally over soft substrates (3).

Occurs in the tropical eastern Pacific, from the Gulf of California to Ecuador; the western Atlantic, from Florida to Brazil; and the eastern Atlantic, from Portugal to Angola. The common sawfish used to also occur in the Mediterranean (1) (2) (3).

Classified as Critically Endangered (CR) on the IUCN Red List (1), and listed on Appendix I of CITES (4).

Once common in the Mediterranean and the Eastern Atlantic, the common sawfish has now been extirpated from the Mediterranean and European waters, and populations in Africa are believed to be severely depleted (2). Similarly, in Lake Nicaragua where this species used to be abundant, the common sawfish barely continues to exist (3). These distressing declines have been largely due to over-fishing and the degradation of important estuarine and freshwater habitats (5). The common sawfish is hunted for its unique and peculiar blade-like snout, fins and meat. They are also captured for public aquaria, where they are highly prized as exhibits (5). Incidental capture in fisheries also poses a significant threat, as its toothed saw makes this fish especially prone to getting entangled in fishing nets (2) (5). Characteristics of the sawfish's life history, such as slow growth rate, poor rate of reproduction, and high age of maturity, makes the common sawfish extremely vulnerable to over-exploitation, and unable to easily recover from low numbers (5).