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Sawfish. Ancient predators in need of modern conservation tools.

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Conservation geneticist Nicole Phillips and zoologist Barbara Wueringer reveal how vital northern Australia is to the future of sawfish. Sensitive detector and lethal weapon combined, there are few implements in nature as versatile as the snout of a sawfish. With it, they home in on weak electrical pulses and eddies created by fish and crustaceans, then stun or impale them. But this magnificent saw is also their Achilles heel as it makes them terribly prone to entanglement in fishing nets and is prized as a trophy. Sawfish are fast disappearing from most of the world.
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Conservation geneticist
Nicole Phillips and zoologist
Barbara Wueringer reveal how
vital northern Australia is to the
future of sawfish.
Sensitive detector and lethal weapon
combined, there are few implements
in nature as versatile as the snout
of a sawfish. With it, they home in on
weak electrical pulses and eddies created
by fish and crustaceans, then stun or
impale them. But this magnificent saw is
also their achilles heel as it makes them
terribly prone to entanglement in fishing
nets and is prized as a trophy. Sawfish are
fast disappearing from most of the world.
Few Australians ever see a wild sawfish
– for they are rare, well camouflaged and
often live in murky waters – but Australia
is critical to their future. Our northern
waters are the last stronghold for four of
the world’s five species. So, it is important
that Australians recognise them as part of
their iconic natural heritage to ensure that
resources are dedicated to safeguarding
their future. We have been studying their
population genetics (Nicole), sensory
adaptations and feeding behaviours
(Barbara) to better understand how to
achieve this.
GREEN PROBE – CONSERVATION WATCH
Sawfish
ANCIENT PREDATORS IN NEED OF MODERN CONSERVATION TOOLS
Green sawfish (Pristis zijsron) are listed globally
as critically endangered. According to the IUCN,
Australia has ‘some of the last remaining viable
populations … albeit at significantly reduced
levels’. They were once widespread in the Indo-
West Pacific region but have disappeared from
much of their range due to inshore gillnet and
trawl fishing. In Australia they used to occur as
far south as Sydney but are now extinct in NSW.
Juveniles use inshore waters and mangroves,
and adults use marine and estuarine waters.
Photo: Jeff Whitty
14 | Wildlife Australia | AUTUMN 2015
Ancient predators
Sawfish are a family (Pristidae) in the
class of fish with cartilage skeletons (the
Chondrichthyes) that includes sharks,
rays, skates and chimaeras. Although
their bodies and manner of swimming are
shark-like, sawfish belong to the shark’s
closest relatives, the rays. They emerged
around 60 million years ago.
Historically, many sawfish species
have been described, but recent genetic
analyses have reduced the number of
living species to just five. Northern
Australia is a sawfish hotspot, with
more species than any other region: the
largetooth, green and dwarf sawfishes
(genus Pristis) and the narrow sawfish
(genus Anoxypristis).
A versatile implement
The defining feature of sawfishes, their saw
(or rostrum), is an extension of the skull,
and can make up over a fifth of their body
length. The saw ‘teeth’ are actually modified
dermal denticles, the microscopic scale-like
structures on the skin of sharks and rays.
Unlike shark teeth, the sawfish saw teeth
are not replaced as they wear or break, but
grow continuously from their base, like the
incisors of rodents.
Swordfish and marlin can use their
rostrum to stun or kill prey, and the
snouts of animals like platypus and
northern hemisphere paddlefish can
detect the weak electric fields of hidden
prey, but the sawfish rostrum is unique
in combining these attributes. Captive
sawfish have been observed also using
their saw to fight over food and establish
social hierarchies.
The sawfish’s saw is covered in two
types of receptors: mechanoreceptors
that detect nearby water movements
and electroreceptors (known as the
ampullae of Lorenzini) that detect weak
electric fields. As all living beings are
surrounded by a weak electric field,
and any slight movement of animals in
water creates micro-currents, these two
senses enable sawfish to detect prey
in the dark and in highly turbid waters.
Largetooth sawfish, whose young live in
often-turbid rivers where visibility can
fall below 10 centimetres, have the most
electroreceptors, providing them with the
highest resolution.
Barbara’s studies on captive young
largetooth sawfish have challenged the
reputation of sawfish as sluggish bottom-
dwellers that search for food by raking
their saw through sediments. They are in
fact active and agile hunters. As well as
sometimes sitting and waiting for prey to
pass, they prowl on the bottom and in the
water column, holding their saw up at a
slight angle. When a fish is detected they
rapidly swipe the saw from side to side to
stun or impale it. They then pin it under
their saw, turn it around (to prevent scales
Our northern
waters are the last
stronghold for four
of the world’s five
sawfish species.
Largetooth sawfish (Pristis pristis) are listed globally as
critically endangered. According to the IUCN, the Australian
population ‘likely comprises a high proportion of the global
population’. They used to be widespread across the tropics
and subtropics but have been lost or much depleted in most
areas due to fishing and habitat loss and degradation. They
occur in Australia mainly from northeastern Queensland to
the Kimberley, with vagrants further south. They live in a
wide variety of habitats – floodplains, billabongs, creeks,
rivers, estuaries and marine waters. Photo: David Morgan
Dwarf sawfish (Pristis clavata) are listed globally as endangered. According to the IUCN, they are ‘possibly
now restricted to tropical waters of northern Australia’, from the Pilbara coast to the Gulf of Carpentaria.
They may have once occurred in the Indian Ocean region and Southeast Asia. Photo: David Morgan
Narrow sawfish (Anoxypristis cuspidata) are listed globally as endangered. According to the IUCN, northern Australia ‘contains the most
viable, ecologically functional populations that remain worldwide’. Although they still persist across most of their Indo-West Pacific range,
their populations have been much depleted by capture in gillnets and trawl nets. This sawfish was captured in Cleveland Bay for research
and returned to the water. Photo: Colin Simpfendorfer
wildlife-australia.org | Wildlife Australia | 15
and fins from getting caught in their
gullet) and swallow it. Sawfish can tackle
large prey – a 33 centimetre-long catfish
was found in the stomach of a 1.3 metre
largetooth sawfish.
Declines
Sawfish were once abundant in coastal
tropical and subtropical waters around
the world, but declines have been so
severe they are now considered the most
endangered of all the sharks and rays.
Their coastal habitats are among the
most densely populated with humans
and heavily exploited, an overlap creating
many problems for sawfish. All five species
appear on the IUCN (International Union
for Conservation of Nature) Red List,
three as critically endangered and two as
endangered. The largetooth sawfish was
recently listed by the IUCN as one of the
100 most endangered species on the planet.
In some regions, the only clues to
the former presence of sawfish are saws
displayed in restaurants and bars. The
best-documented decline was the loss of
largetooth sawfish from Lake Nicaragua in
Central America, where in the 1970s some
60,000 to 100,000 were fished in five years.
Not one was found during a 1992 survey.
Nicaragua’s 2006 ban on sawfish fishing
was likely decades too late.
Like many species susceptible to
over-exploitation, sawfish grow large,
live long, mature late, and produce few
offspring. Largetooth sawfish, the best-
studied species in Australia, can grow
to over 5 metres. They become sexually
mature when they are 2.5–3 metres long,
at roughly eight years of age. They may
breed annually, and give birth to up
to 12 pups after a gestation of about
five months. Other sawfish species are
probably similar, except for the narrow
sawfish, which reaches maturity after
three to six years.
Sawfish face their greatest threats
in Australia and elsewhere from
commercial and recreational fishing.
Their rostrum all too easily becomes
entangled in fishing nets and lines. It
is illegal to directly target sawfish in
Australian waters, but they are often
caught accidentally (as bycatch) by
commercial and recreational fishers.
Although Australian law requires that
they be quickly returned unharmed to
the water, recreational fishers sometimes
remove the saw as a trophy. Despite
reports of sawfish surviving the loss of
their saw, they are likely to be much
weaker and less able to reproduce or
defend themselves without it. Sawfish
fins are among the most valuable in the
illegal international fin trade, and have
been targeted in Australian waters by
foreign fishing vessels, but the extent of
this is unknown.
Northern Australian stronghold
Although Australian sawfish populations
have suffered substantial declines, leading
to the listing of the three Pristis species as
threatened under national laws, the losses
here have probably not been as severe
as elsewhere, probably because northern
Australian waters are still relatively pristine.
The Australian populations of largetooth,
dwarf, green and narrow sawfishes are
thought to be the last viable populations
of these species, and therefore central to
global conservation efforts.
We cannot assume that the future of
Australian sawfishes is secure. Essential
for conservation is a better understanding
of their biology, including whether the
regional populations of each species are
interconnected or isolated. Conserving
small, isolated populations can be
difficult because they are not replenished
by animals migrating from elsewhere.
The management of larger populations
also has its challenges for it requires
cooperative management across state or
international borders.
In some regions, the
only clues to the former
presence of sawfish
are saws displayed in
restaurants and bars.
Commercial and recreational fishing threaten sawfish in multiple ways. Their saw easily becomes entangled in nets and lines (as shown here for a green sawfish in
the Gulf of Carpentaria), and they are often unintentionally captured by fishers using prawn or fish trawls, gillnets or long lines (Australian law requires fishers to
quickly return them to the water unharmed). Sawfish are sometimes illegally targeted for their high value fins or for trophy saws, even though their international
trade is now illegal under the Convention for the International Trade in Endangered Species of Wild Flora and Fauna. Recreational fishers are known to sometimes
cut off the saw before returning them to the water, as is shown here for a green sawfish. Photos: Barbara Wueringer (right), David Morgan (left)
The magnificent snouts of sawfish serve many purposes: prey detection
and incapacitation, defence and probably fighting and establishing social
hierarchies. The saws can grow well over 1 metre long. Shown are the
two researchers, Nicole with the rostrum of a largetooth sawfish and
Barbara with a largetooth sawfish. Photos: James Tweedley (left), Ruth
Leeney (right)
16 | Wildlife Australia | AUTUMN 2015
Genetic revelations
It is a tough job to study rare animals
that live in murky waters in remote
regions and do not come to the surface
to breathe (like marine mammals).
Fortunately, modern genetic techniques
using small tissue samples (a biopsy
from a live animal or skin from a rostrum)
have made it much easier to study
the population biology of sawfishes.
Nicole has analysed patterns of mating
and dispersal in northern Australian
populations of largetooth, green and
dwarf sawfishes, using two types of
genetic markers to distinguish patterns for
males and females. This work has revealed
contrasting population structures in
species that use different habitats.
Largetooth sawfish live in freshwater
as juveniles and marine waters as adults,
a segregation unique among shark and
ray species living today. Their genes
show there is a flow of paternal genes
between regional populations but not
of maternal genes, which implies that
males and females have different patterns
of dispersal. It appears that female
largetooth sawfish give birth in the same
region, perhaps the same river mouth,
that they themselves were born in. Known
as philopatry, this strategy enhances the
chances of the young being born at the
entrance to a suitable river, from where
they travel upstream to spend the first
eight years of life. Female philopatry is
advantageous in northern Australia, where
high quality freshwater nursery habitats
are sparse. Male largetooth sawfish
differ from females in not being tied to
particular river mouths for breeding. A
male from the west coast, for example,
may mate with females from as far away
as the Gulf of Carpentaria.
This dual dispersal pattern – of females
with small reproductive ranges and wider-
ranging males – is common in the animal
kingdom but challenging for conservation.
Protecting females, pupping grounds, and
nursery areas need to be high priorities,
for if a population of largetooth sawfish
is lost from a river or group of rivers,
the species may not re-establish there
naturally, at least not for some time. This
is especially so for the west coast, where
the Fitzroy River has the only known
large population of largetooth sawfish. A
decline in one location could be to the
detriment of populations elsewhere that
are linked by male dispersal.
In contrast, there is little to no gene
flow between regional populations of
green or dwarf sawfishes. Like many
coastal rays, they live in marine and
estuarine waters their entire lives, and
use inshore and mangrove areas as
nurseries. Their genes reveal that the
dispersal and mating of both males and
females is highly restricted in northern
Australian, although we don’t know
where the boundaries between regional
populations lie. Because the risk of
localised extinctions for these species is
high, conserving both males and females,
as well as pupping grounds and nursery
areas, all need to be priorities.
These genetic insights are part of the
information being used by the Australian
government to develop recovery plans for
the largetooth, green and dwarf sawfishes.
Because the north is relatively undeveloped,
the prognosis for sawfishes in Australia could
be good, so long as they are kept safe from
fishing, and the habitats they use during key
life stages are protected. Proposed mines in
the Cape York and Fitzroy River regions could
harm sawfish populations.
There is still much more we need to
learn about these magnificent creatures.
Once they leave their nursery areas,
virtually nothing is known about their
adult lives, a large gap in the knowledge
needed to conserve them.
READING: For the latest on sawfish research and
conservation, go to sawfishconservationsociety.org
Phillips N. 2012.
Conservation genetics of Pristis
sawfishes in Australian waters
. Doctor of Philosophy
thesis. Murdoch University Phillips N, Chaplin J,
Morgan D, Peverell S. 2011. Population genetic structure
and genetic diversity of three critically endangered
Pristis
sawfishes in Australian waters.
Marine Biology
158: 903–15 Whitty J, Phillips N, Morgan D,
et al.
2014. Utility of rostra for the identification of Australian
sawfishes.
Aquatic Conservation: Marine and Freshwater
Ecosystems
24: 791–804 Wueringer B, Squire L,
Kajiura S, et al. 2012. The function of the sawfish’s saw.
Current Biology
22(5): R150–5 Wueringer B, Peverell S,
Seymour J,
et al.
2011. Sensory systems in sawfishes. 1.
The ampullae of Lorenzini.
Brain, Behavior and Evolution
78(2): 139–49 Wueringer B, Peverell S, Seymour J,
et
al.
2011. Sensory systems in sawfishes. 2. The lateral line.
Brain, Behavior and Evolution
78(2): 150–61.
DR NICOLE PHILLIPS is a conservation
geneticist who has been studying sawfish for
nearly 10 years. The genetic research described
here was conducted at Murdoch University.
She is currently working at the Cooperative
Institute for Marine and Atmospheric Studies,
University of Miami, on the population genetics
of bottlenose dolphins in the Gulf of Mexico.
DR BARBARA WUERINGER is a zoologist who
has been studying the behaviour of sawfishes for
over nine years. The research described here on
how sawfish capture their food was conducted at
the University of Queensland and the University
of Western Australia. Barbara is an Adjunct Senior
Research Fellow at James Cook University.
GREEN PROBE – CONSERVATION WATCH
Virtually nothing is
known about their adult
lives, a large gap in the
knowledge needed to
conserve them.
This green sawfish was caught off Picnic Point at Maroochydore, Queensland in about 1940. They are no longer found in those waters. Their current
distribution is thought to be from about Mackay (Queensland) across northern Australian waters to Shark Bay (Western Australia).
wildlife-australia.org | Wildlife Australia | 17
... The importance of habitat and life-history diversity for the resilience of a species as well as the importance of identifying and prioritizing life-history diversity within conservation plans is well understood (Beechie et al., 2006;Schindler et al., 2010;Schroeder et al., 2016). New tools which can increase the data richness of historical samples are needed, and attempts are currently underway to use archived rostral samples to understand historical genetic diversity and the population structure of sawfish worldwide (Phillips & Wueringer, 2015;Fearing et al., 2018). However, no tools currently exist which can elucidate life history in these archived rostral samples, or tie historical genetic information gleaned from them to the movement and behavioural aspects of sawfish ecology. ...
Article
• The ecology of endangered and rare species can be difficult to study owing to their low abundances and legal limits on scientist’s ability to catch, sample, and track them. This is particularly true of sawfish (family Pristidae), whose numbers have declined precipitously, placing all five species on the IUCN Red List of Threatened Species worldwide. Best known for their distinctive, toothed rostrum, the ecology, movement and life-history of sawfish are poorly understood. • Sawfish rostral teeth are modified placoid scales, which grow continuously throughout the life of the fish. This continuous growth, combined with their stable calcified makeup, makes sawfish rostral teeth a potential source of temporal records of chemical and isotopic changes through the life of the fish. • Rostral teeth are often preserved in museums and as curios, potentially providing a source of life-history data to inform conservation actions without the need for field study, or as an important compliment to it. This is the first study to recover temporally explicit chemical data from sawfish rostral teeth. • Using archived samples of largetooth sawfish (Pristis pristis) we show that multiple chemical tracers can be recovered from sawfish rostral teeth, and that these tracers can be used to understand movement across salinity gradients. We further show that sawfish rostral teeth contain repeated structures and indistinct banding which could potentially be used for ageing or growth analysis of fish.
Article
Full-text available
The distribution and density of the ampullary electroreceptors in the skin of elasmobranchs are influenced by the phylogeny and ecology of a species. Sensory maps were created for 4 species of pristid sawfish. Their ampullary pores were separated into pore fields based on their innervation and cluster formation. Ventrally, ampullary pores are located in 6 areas (5 in Pristis microdon), covering the rostrum and head to the gills. Dorsally, pores are located in 4 areas (3 in P. microdon), which cover the rostrum, head and may extend slightly onto the pectoral fins. In all species, the highest number of pores is found on the dorsal and ventral sides of the rostrum. The high densities of pores along the rostrum combined with the low densities around the mouth could indicate that sawfish use their rostrum to stun their prey before ingesting it, but this hypothesis remains to be tested. The directions of ampullary canals on the ventral side of the rostrum are species specific. P. microdon possesses the highest number of ampullary pores, which indicates that amongst the study species this species is an electroreception specialist. As such, juvenile P. microdon inhabit low-visibility freshwater habitats.