Biology and Ecology of a Sawfish

Taxonomy Phylum: Chordata Class: Chondrichthyans (sharks, rays and chimeras) Subclass: Elasmobranchii Superorder: Batoidea (rays) Order: Pristiformes Family: Pristidae

Biology Life history strategy K-selected life history strategy Long-lived 25-30 years Large size Up to 7m Late sexual maturity Approx. 10 years old Low fecundity 8-24 pups

Distribution and Habitat Global distribution in tropical and sub-tropical regions Distribution is currently fragmented with most populations thought to be depleted Occur in marine, freshwater and coastal habitats Tolerance to freshwater dependent on species Preference for shallow, inshore coastal and freshwater habitats but can occur to at least 80 m depth

Description Closely related to rays with modified bodies similar to sharks Also similar to and often confused with sawsharks Distinguished by presence of gills on the underside of head

Behaviour Sawfish are nocturnal Sawfish are top order predators Sleep in the day Hunt at night Sawfish are top order predators Actively seek out prey items such as Fish Crustaceans Squid Use rostrum for feeding by Stunning slow moving schooling fish with slashing motion Locating and dislodging prey buried in sand or mud Locate buried prey by using sensors on rostrum Will also eat dead prey and strike at lures

Anatomy Rostrum can also be used to; Rostrum rake through sediment to find prey Stun prey with slashing motion Protect from predators Also used to distinguish species Number of teeth Shape of rostrum Rostrum Most distinguishing feature Long flat and saw-like Made of cartilage Contains pairs of teeth on sides Modified scales Used to detect and catch prey using motion and electro- sensors Allow detection from long distance and under sediment

Anatomy Eyes Spiracle On top of head so can see when partially buried Eyesight good but often not useful due to murky habitat Make up for this with sensitive sense organs in rostrum Spiracle Located behind the eye Used to take in water when lying on the bottom

Anatomy Dorsal Dorsal means back or upper surface 2 dorsal fins Used for stabilisation Pelvic Pair of pelvic fins located on side behind the pectoral fins Used for stabilisation while swimming Caudal Also known as the tail fin Shape differs between species Used to generate power and speed in swimming Fins The sawfish has 4 different types of fins all with different uses Pectoral Pair of pectoral fins located behind the head Used to lift fish when swimming Helps with steering Consists of cartilage spread out in fan shape Does not reach edge of fin Makes fin pliable increasing manoeuvrability

Anatomy Pelvic Dorsal Caudal Pair of pelvic fins located on side behind the pectoral fins Used for stabilisation while swimming Caudal Also known as the tail fin Shape differs between species Used to generate power and speed in swimming Dorsal Dorsal means back or upper surface 2 dorsal fins Used for stabilisation

Anatomy Internal Anatomy Underside of Sawfish Sawfish don’t contain swim bladder for buoyancy Instead have an oil filled liver like sharks and rays Underside of Sawfish Like rays the flat ventral or underside of sawfish contain Nostrils (nares) Mouth Gill slits Jaw contains thousands of dome shaped teeth Used to crush small fish and crustaceans e.g. Crabs and shrimp

Reproductive Biology Reproduce through internal fertilisation Male contain claspers Modification of pelvic fin Used to insert sperm into female Ovoviviparous Eggs are fertilised and grow within mother Hatch within womb and mother gives birth to fully developed pups

Reproductive Biology Average of 8 pups are born at around 65-90cm Gestation period (fertilisation to birth time) is approx. 5 months Number and size of pups increase with maturity of birthing mother Pups born with a toothed rostrum which is covered by a enclosed membrane designed to protect mother from teeth Growth rate Rapid in first year of life Slows considerably as maturity reached

Threats to sawfish

Saw fish are threatened throughout the world All Australian species are on the IUCN Redlist of threatened species as critically endangered Because they prefer an inshore benthic habitat for breeding ,the juveniles are vulnerable to human interference They are also known to actively seek out dead baits or strike at lures making them vulnerable to recreational fishing

Major threats include Hunting Habitat modification and pollution Entanglement in fishing nets

Hunting Sawfish are hunted for their Rostrums Fins Flesh Other body parts These are sold for food and use in traditional Asian medicines Rostrums are sold as valuable souvenirs, trophies or curios Sawfish may also be collected as live specimens for aquariums

Habitat modification and pollution Building of weirs and barrages can restrict movement of sawfish in rivers Other problems include increased pollution from: Land clearing - increased sediment runoff Use of fertilisers - increased nutrient runoff Use of pesticides - reduced health and death of organisms Urban and industrial development Loss of soft bottom feeding and breeding habitats also poses a threat

Entanglement in fishing nets Sawfish are vulnerable to entanglement as the rostrum is easily entangled in nets and fishing line The sawfish thrashes around to get free causing further tangling When unable to swim the sawfish is unable to move water over gills and may drown Entanglement may occur in Trawling nets Shark nets Recreational fishing line