GIANT FRESHWATER CRAYFISH online learning package

Welcome to Module 4

GIANT FRESHWATER CRAYFISH

Welcome to the Giant Freshwater Crayfish module of Cradle Coast Natural Resource Management’s (NRM) online learning package. In this module, you will learn about the Giant Freshwater Crayfish (GFC)

Its habitat and ecology
Why the GFC is an important protected species
How and why the GFC is under threat
What you can do to help reduce the threats to GFC
What Cradle Coast NRM is doing to help protect the GFC

Female Giant Freshwater Crayfish (Astacopsis gouldi) / lutaralipina. Image credit: Rob McCormack

This module will take you about 1.5 hours to complete.

How to move through this online course

As you are guided through this module, you will learn about the Giant Freshwater Crayfish through reading text and watching short videos. At the end of this module there will be an electronic link to other modules about Coastal Saltmarshes, Little Penguins and Short-tailed Shearwaters.

What are Giant Freshwater Crayfish?

The Tasmanian Giant Freshwater Crayfish is the largest freshwater invertebrate in the world. Invertebrates are animals that don’t have backbone or bony skeleton, instead they rely on the hardness of their shell (exoskeleton) to support their body and protect their internal organs.

The scientific name for the Tasmanian Giant Freshwater Crayfish is Astacopsis gouldi, and it is categorised as a crustacean within the invertebrate group of species. Giant Freshwater Crayfish are slow growing and can live to up 60 years of age, which is old for a crayfish.

Tasmanian Giant Freshwater Crayfish are also known as lutaralipina, the name that Tasmanian Aboriginal people use and gave to this amazing creature. Some people also use the name Giant Freshwater Lobster.

Giant Freshwater Crayfish can vary in colour from dark brown to pale blue. This is what a blue one looks like:

Image credit: The Mercury

How Giant are they?

In the past, Giant Freshwater Crayfish have been reported to growing to over 80 centimetres in length and weighing 6 kilograms. Nowadays, the larger recorded specimens weigh between 2 and 3 kilograms.

There are two other related freshwater crayfish that are also native to Tasmania; Astacopsis franklinii and Astacopsis tricornis, but these two species do not grow as large as the Astacopsis gouldi.

In Tasmania, we also have burrowing crayfish, which are tiny in comparison to the Giant Freshwater Crayfish. These only reach a length of 10 centimetres. When Giant Freshwater Crayfish are small and growing, they can be eaten by platypus, fish, water-rats (rakali) and birds, but when they reach full maturity, they are too big to be preyed upon.

How do Giant Freshwater Crayfish live?

Giant Freshwater Crayfish can live in groups of up to 20 individuals in the same large pool, but they often claim a stretch of river for themselves. Males mature earlier than females, around 9 years of age when they reach around 76 mm in length and 300 g in weight. Males have larger pincers than females, are territorial and maintain a harem of several females.

What to see what they look like under water?

Take a look at a battle-injured male under water

When do they breed?

It is not until they reach around 14 years of ages that females are mature.

By this age, they are around 120mm long and weigh about 500g. Once mature, the females mate and spawn once every two years, after their summer moult (when they shed their exoskeleton and grow a new one).

Females produce a number of eggs that are proportional to their body, as they carry their eggs under their tails. The eggs stay under their mother’s tail all through the winter for around 9 months until they hatch.

Juvenile Giant Freshwater Crayfish are called hatchlings, and still need their mother, so stay attached to her swimming legs until autumn. Each female can produce between 220 and 1,300 eggs, so she spends most of her life with eggs or small hatchlings (up to 6mm in length) attached to her body.

This is what an adult female and juvenile Giant Freshwater Crayfish look like.

Image credit: Rob McCormack

How small is this young female?

(She measures only 28 mm)

Like her brothers and sisters, she will have to avoid being predated upon by aquatic predators such as birds and fish.

Young female Giant Freshwater Crayfish (Astacopsis gouldi).

Image credit: Rob McCormack

Fast fact: If she is fortunate enough to live to old age, a female Giant Freshwater Crayfish could have laid between 5,000 and 30,000 eggs in her lifetime!

What do Giant Freshwater Crayfish eat?

The diet of Giant Freshwater Crayfish varies depending on their age, but they predominantly eat decaying wood, leaves and the microbes that live on these. Giant Freshwater Crayfish can also eat small fish, insects, rotting animal flesh and other detritus (dead organic material including dead organisms and faecal material).

Giant Freshwater Crayfish are classified as benthic macro-invertebrates https://www.iihr.uiowa.edu/igs/publications/uploads/wfs-2010-07.pdf and have an important role in maintaining river ecosystems. When Giant Freshwater Crayfish eat, they mix sediments, influence energy flows and food webs, and therefore play a vital role in the decomposition of organic matter in https://academic.oup.com/bioscience/article/49/2/119/239602.

What goes on inside that hard shell?

Have you wondered what goes on inside the body of a Giant Freshwater Crayfish? Have a look at the graphic below and notice that their stomach is close to their head and their heart is located near their back.

Where do Giant Freshwater Crayfish occur in Tasmania?

You can see the distribution of the Giant Freshwater Crayfish today in the map below.

In the green areas, the species may occur

Image credit: Cradle Coast NRM.

Once the Giant Freshwater Crayfish was distributed from the Arthur River in the west, right across northern Tasmania, in rivers that flowed into Bass Strait (except for those in the Tamar catchment). Localised extinctions, or large declines in numbers, are thought to have occurred in the Welcome, Montagu, Rubicon, Don and Duck Rivers, as well as in most of the former north-eastern Tasmania species range.

The Giant Freshwater Crayfish has a reduced area of distribution due to:

Habitat destruction
Illegal fishing
Sedimentation and modification of waterways

Want to see a Giant Freshwater Crayfish in real life?

You can visit the Lobster Ponds at Flowerdale, where you can view them in captivity.

DISCOVER THE LOBSTER PONDS

VISIT THEIR FACEBOOK PAGE

Image credit: Discover Tasmania

What habitats do Giant Freshwater Crayfish live in?

Giant Freshwater Crayfish are shy and secretive. Their ideal habitat is an intact catchment where the streams can vary in size and type. These undisturbed, well vegetated streams allow water to flow and meander through snags, pools, riffles, and a variety of bank types including naturally undercut.

Here is an example of an ideal habitat for Giant Freshwater Crayfish.

Notice the mature vegetation cover, mossy rocks, large in-stream logs, permanent water flow and some undercut banks.

Image credit: Jen Evans

What Giant Freshwater Crayfish are looking for in an ideal habitat

Ideal habitats for Giant Freshwater Crayfish have:

Waterways, creeks and streams

with native vegetation
a dense canopy
shaded waterways

Good water quality

less than 20 degrees, and seldom exceeds 18 degrees
good flow to provide high oxygen content
low in chemicals such as pesticides and fertilisers
low in salts
be clear of sediment

Have rocks

to provide shelter and niches for juveniles
to trap leaves which are a food source
assist in oxygenating the water
help stabilise creek beds and minimise erosion

Have little mud

because it smothers rocks which should be a nursery for baby crayfish
it covers leaves which are the start of the detritus food chain
it smothers bugs which are an important food source
it can decrease oxygenation of the water and increase turbidity (‘mudiness’) of the water

Have trees

to provide shade to keep the water cool
to provide logs and branches for shelter
to provide leaves for food
to help stabilise the riverbanks and minimise erosion
to filter surface run-off to improve water quality

FOR ADULTS

deep pools
slow running water
decaying logs
overhanging banks

FOR JUVENILES

shallow water flowing over rocks (referred to as riffle zones)
faster-flowing streams
mossy boulders and cavities to hide under

What we don’t know about Giant Freshwater Crayfish

We are not sure of the exact population size of the Giant Freshwater Crayfish, as they are long-lived which makes it difficult to measure the populations over time. Also, comprehensive sampling of populations has not occurred, so we are not sure of population dynamics, how habitat affects population increases or how many juveniles survive.

What is their threatened status?

EX: Extinct, EW: Extinct in the wild, CR: Critically endangered, EN: Endangered, VU: Vulnerable, NT: Near threatened, LC: Least concerned.

Giant Freshwater Crayfish are a protected species, which means that it is illegal to catch them and eat them. They are listed as Vulnerable under the Environmental Protection and Biodiversity Conservation (EPBC) Act as well as on the Tasmanian Threatened Species Protection (Tas TSP) Act. Giant Freshwater Crayfish are listed as Vulnerable under the Act because it has been estimated that populations are declining, localised extinctions have occurred, high-quality habitat is declining, and their occurrence is limited.

William Buelow Gould 1832. Sketch of different Astacopsis species.

Who is helping to protect them?

Some people are fortunate enough have healthy creeks on their property, and report sightings of Giant Freshwater Crayfish with excitement. Although some see the Giant Freshwater Crayfish as iconic and very worthy of protection, others continue to fish them, which is illegal.

Fishing for Giant Freshwater Crayfish was banned in 1998, as it became evident that the fishing of large mature individuals was contributing to wide-scale population decline. The Tasmania Parks and Wildlife Service in conjunction with the Inland Fisheries Service conduct regular surveillance of Giant Freshwater Crayfish habitats and make successful convictions against those that attempt to fish them.

Click here to see recent convictions

A passionate Giant Freshwater Crayfish lover

Todd Walsh is recognised as a world expert on Giant Freshwater Crayfish. Todd has been tagging and researching the Giant Freshwater Crayfish population in Tasmania for decades and has tagged more than 2,000 Giant Freshwater Crayfish since 1998. Todd works hard to educate people about the importance of reducing the threats that Giant Freshwater Crayfish face, such as poor river health and illegal fishing. Meet Todd in the following video.

A Gentle Giant

What are the greatest threats that Giant Freshwater Crayfish face?

The greatest threats that Giant Freshwater Crayfish face are

illegal fishing

habitat loss

habitat disturbance

sedimentation of waterways

modifications to water flow

climate change

Illegal fishing

In the past people would fish the Giant Freshwater Crayfish and take large mature and sub-adults without knowing the consequences it was having on the population.

Because fishing for Giant Freshwater Crayfish was made illegal in 1998, we do not know the full impact it has had on the dynamics of the population.

Giant Freshwater Crayfish have a slow growth rate and we can see today that the reappearance of full-sized adults is very slow due to past fishing. Illegal fishing today still has the potential to significantly threaten crayfish populations.

Ignorance may have been bliss, but trophy images, like this one below, are a sad reflection of the lack of knowledge we had about Giant Freshwater Crayfish in the past.

Trophy Giant Freshwater Crayfish (Astacopsis gouldi) catch, Flowerdale River 1985. Image credit: unknown.

Habitat loss

With the expansion of forest operations comes new roads, which provide access to previously unexploited areas for illegal fishing of Giant Freshwater Crayfish. Waterways are continuing to be modified and habitats lost by ongoing suburban development, and expansion of agriculture and forestry.

Giant Freshwater Crayfish are slow-growing, have a low reproductive rate and are slow to colonise new areas. They can only survive in limited areas where good habitat is consistently available.

Expansion of forest operations into the headwaters puts pressure on water quality and habitat suitable to Giant Freshwater Crayfish. Image credit: CC BY-NC-SA.

Habitat disturbance

Giant Freshwater Crayfish need healthy waterways and good tree cover to survive. Unfortunately, their habitat can be lost or severely compromised by:

removal of riparian vegetation
bank erosion
removal of snags
channelisation
siltation
eutrophication (e.g. algal bloom)
toxic chemical and nutrient pollution
alterations to stream flow and water temperatures

Highly compromised waterway unlikely to provide Giant Freshwater Crayfish habitat. Image credit: DPIPWE.

Sedimentation of waterways

As habitat for Giant Freshwater Crayfish continues to be reduced, they rely more on small patches of healthy habitat in the upper catchments. When waterways are affected by sedimentation, the increase in siltation and turbidity of the water places increased stress on Giant Freshwater Crayfishes’ ability to transpire oxygen through their gills. Although adults may tolerate localised natural sedimentation, juveniles are more vulnerable, and the number of juveniles surviving to adulthood (known as recruitment) is reduced.

Eroded waterway with sedimentation. Image credit: NRM North.

Modification to water flow

Research has shown that higher abundances of Giant Freshwater Crayfish are found in permanent streams where water is plentiful. When forests surrounding the headwaters of a stream are clear-felled, the downstream sections of the waterway can suffer. When forests are removed, water flows become more random and often more turbid, base flows reduce, and high flows increase, creating flow flashiness. This affects the stability of the river banks, channel morphology and general flow of water, making it difficult for Giant Freshwater Crayfish to survive.

In agricultural areas of northwest Tasmania, native forest and pastures are being converted to cropping land, requiring new water sources for crops. This creates the need for additional water extraction from rivers, and reduces the sections and connectivity of healthy river habitats for Giant Freshwater Crayfish.

Clear-felling impacts waterways directly downstream. Image credit: Meaghen Brown.

Climate change

Climate change brings with it extreme weather events, alterations to stream flows and temperature, and can be devastating to catchment vegetation and Giant Freshwater Crayfish populations.

Sadly in 2016, during major floods, more than 100 Giant Freshwater Crayfish were washed up dead in Gunns Plains. See media reports here:

ABC News Report

What do healthy headwaters look like?

The upper catchments of the northern Tasmanian rivers are often well-forested and healthy. This area is known as the “headwater” of the river because it is close to the river’s source. Have a look at the image below of a healthy headwater where Giant Freshwater Crayfish are known to survive.

Donaldson River, takayna / Tarkine. Image credit: Jen Evans.

What can I do to help keep Giant Freshwater Crayfish healthy?

• do not fish for Giant Freshwater Crayfish and report any illegal fishing

• protect remnant bush in your community or on your land to help provide habitat for all our native animals, including the Giant Freshwater Crayfish

• support local efforts to conserve threatened species in your area by joining a local Landcare or a 'friends of' group

• participate in special community events, information nights, tree planting days and weed eradication programs

See what people are doing to help keep the Leven River healthy

Want to go ahead and join a group and make a difference?

You can join a local Landcare group - click below to find out how.

Landcare Tasmania

And you can make a difference by participating in projects supported by Cradle Coast NRM which we will advertise in our newsletter, on our website, or via our Facebook site.

Greening Australia also has opportunities - click below for more information.

Greening Australia

What if I own or manage land that is in the habitat range for Giant Freshwater Crayfish?

Here are some things that you can do to help them survive

Don’t clear or remove native vegetation along stream banks.
If you are removing willows from your waterways, gain expert advice and leave roots and stumps of willows intact to aid bank stability
Only use chemical sprays which are registered as suitable in watercourses.
Fence your stock out of your waterways, as they will muddy the water and degrade river beds and make it unviable for Giant Freshwater Crayfish to live in.
Plan your fencing so that you can completely exclude stock from waterways and install water troughs elsewhere, use hanging fences, electric and electronic fences, and drop fences.
Plant native vegetation (especially trees) along stream banks to create shade to keep the water cool to provide places for Giant Freshwater Crayfish to breed.
Don’t remove large logs and snags from your waterways, these are important for creating habitat. If a snag is completely blocking flow, seek advice on how to move it to the side. An angle of 20 to 40 degrees to the stream bank is usually appropriate. Contact Cradle Coast NRM or a river expert.
Don’t remove single rocks or large quantities of rock from the stream bed. This will alter crayfish habitat and cause sedimentation which can block the feather-like gills of the crayfish.
Be aware that it is illegal to modify rivers and streams. (Please refer to Working near Waterways Guide by clicking the button at end of this list).
Wherever possible, if you need to cross a waterway, install bridges instead of culverts.
Avoid using heavy machinery or placing structures in the stream bed.
Ensure year-round flow downstream from your dams.
In areas where water runs off the ground and forms into concentrated streams, create some buffers such as landscape depressions to break the flow.
Consider seeking help to sustainably manage and conserve your Giant Freshwater Crayfish habitat through the Private Land Conservation Program :

DPIPWE'S PRIVATE LAND CONSERVATION PROGRAM

NRM NORTH'S WATERWAYS GUIDE

Want to know how you can make your waterways Giant Freshwater Crayfish friendly?

Have a look at the image below to get some ideas of how to vegetate and protect your waterways to optimise habitat for Giant Freshwater Crayfish.

Illustration Paul Lennon in Lovett, S. & Price, P. (eds) (2007). 'Managing rivers and streams in Tasmania: A woolgrower’s guide'. Land & Water Australia.

Here is a good guide on what riparian widths are recommended for waterways

Want to know more about keeping your waterways healthy?

Here is some more information about managing stock near waterways

CLICK ME!

CLICK ME TOO!

What is Cradle Coast NRM doing to help keep Giant Freshwater Crayfish healthy?

Cradle Coast NRM and NRM North have been working on Giant Freshwater Crayfish protection, monitoring and knowledge extension over the past 10 years. Together with freshwater ecologists and experts, Todd Walsh and Dr. Alastair Richardson, the Friends of the Lobster Community Group and school-children in the region, we have been working to increase community knowledge and affinity for the Giant Freshwater Crayfish.

We are supporting local efforts to inform the public about the vulnerability of Giant Freshwater Crayfish at the Lobster Ponds in Flowerdale. Take a look at what is going on:

FRIENDS OF THE FRESHWATER LOBSTER

Cradle Coast NRM and NRM North are delivering Australian Government projects to help reverse the decline of the species.

Our key focus is to enhance and protect Giant Freshwater Crayfish habitat, to attempt to reverse population decline. Threats to Giant Freshwater Crayfish are serious and ongoing in our region, so we are focussing on the following:

increase community awareness of Giant Freshwater Crayfish
increase scientific understanding of the species
reduce threats caused by land management practices
reduce threats caused by poor water quality
enhance and protect good quality Giant Freshwater Crayfish habitat
reduce illegal fishing

CONGRATULATIONS! You have made it to the end of the Giant Freshwater Crayfish online learning module. We hope that we have provided you with interesting information about the Giant Freshwater Crayfish and that you have enjoyed your learning journey.

Before you go, let’s recap on the key learnings from this module. In this module, you have learnt about the Giant Freshwater Crayfish (GFC):

Its habitat and ecology
Why the GFC is an important protected species
How and why the GFC is under threat
What you can do to help reduce the threats to GFC
What Cradle Coast NRM is doing to help protect the GFC

You will have learnt about Giant Freshwater Crayfish:

How giant they are
How they live
When they breed
What Giant Freshwater Crayfish eat
Where Giant Freshwater Crayfish occur in Tasmania
What habitats Giant Freshwater Crayfish live in
What we don’t know about Giant Freshwater Crayfish
Their threatened status
The greatest threats that Giant Freshwater Crayfish face
What you can do to help keep Giant Freshwater Crayfish healthy

You will have learnt about the options for getting involved to make a difference:

Join a local Landcare group here

Participate in Greening Australia projects here

Get involved in one of Cradle Coast NRM’s projects

If you want to know more about the Giant Freshwater Crayfish and how you can get involved in protecting them, contact Cradle Coast NRM

Cradle Coast NRM

Are you interested in learning about other important species in the Cradle Coast region?

We have developed other online learning modules

COASTAL SALTMARSHES

LITTLE PENGUINS

SHORT-TAILED SHEARWATERS

Want to quickly recap?

Welcome to the Giant Freshwater Crayfish library where you will find resources to assist you in learning more about these important species.

Threatened species information for Giant Freshwater Crayfish

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TWO

THREE

FOUR

Riparian vegetation management

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TWO

THREE

FOUR

Video links

A GENTLE GIANT

GIANT FRESHWATER CRAYFISH online learning package

Welcome to Module 4