Margaret River Hairy Marron

## About

A hairy marron underwater.

The Margaret river hairy marron ***(Cherax tenuimanus)*** also known as just the hairy marron or 'hairies' colloquially, is a freshwater crustacean species native to southwest Western Australia. Hairy marrons have narrow bodies with slender abdomens and wide tail fins. Their heads are triangular and they possess four long antennae. The species is dark brown or black in colouration and its carapace, abdomen and tail fin are all covered with tiny brown bristles known formally as setae, giving it its name. Despite their vastly different appearances, the hairy marron is often mistaken for the invasive yabby ***(Cherax destructor)***. As with other crayfish species, the marron has five pairs of legs, with three walking legs and two sets of claws. One set of claws are large, used for defense, while the other pair is small and used to manipulate food and lift it into its mouth. Hairy marrons can grow to 30-40cm (12-15.7in), making them the third largest freshwater crayfish species in the world.

## Diet

The hairy marron is an omnivorous species that consumes both plant and animal matter. They most commonly feed on detritus and other forms of dead organic material as well as algae. They have also been known to hunt fish larvae and eggs and even smaller marrons. Marrons will also use rotten wood and detritus as shelter, doubling as a food source.

## Conservation Status

The hairy marron is threatened by its close relative, the smooth marron ***(Cherax cainii)***, which commonly out-competes the hairy marron in its own range. The smooth marron was first noticed in the Margaret river in the mid 1980s-late 90s and was likely introduced to the river through translocation in 1980. The smooth marron has replaced the hairy marron throughout the Margaret river of Western Australia, as a result of its adaptability. Due to the two species' close relation, they have been recorded to be able to hybridise with one another, which has resulted in the population of the upper Margaret river being comprised 10% of hybrids. Outside of competition with other freshwater crayfish, the hairy marron is threatened by habitat degradation and predation by fish. Illegal hunting of mature hairy marron for food is also still prevalent. As a way to preserve the species' wild population, the Western Australian Government has instilled captive breeding efforts however, success has varied due to a large population of hybrids within the stocks. To combat out-competition of the species The government had also begun selectively removing smooth marron from areas where hairy marron populations exist however, tis project only ran from 2013-2017, as it was found to not be benefitting the hairy marron as much as expected. As a last resort, the government has also banned the fishing of smooth marron in the upper Margaret river, in order to limit accidental (or purposeful) hairy marron casualties. Due to these threats, the hairy marron is listed as critically endangered by the IUCN, with a decreasing population.

## Range and Population

As the species' name suggests, the Margaret river hairy marron is native to the Margaret river of southwest Western Australia. After harsh competition with the smooth marron, the hairy marron has been limited completely to a select 3 locations in the upper Margaret river. The IUCN states that it has bee found at 11 sites in a habitat that stretches only around 50km (31mi) in length. As a species that feeds on rotten organic material, the hairy marron favours habitats with abundant underwater organic debris, such as detritus and wood. Hairy marrons are quite selective about their habitat requirements, enjoying clean, oxygen-rich waters of around 25°C (77°F). Through estimate it was concluded that from 2002-2004 there was a population of only around 10,000 hairy marrons however, it was discovered that there had been an almost 100% reduction of the species for the 13 years leading up to this point.

## Behaviour

The hairy marron is an enigmatic species and little is known about its behavioural characteristics however, the species' breeding habits are known relatively well. Hairy marrons will reach sexual maturity at 2-3 years of age, breeding in the months between July and October. A female hairy marron is able to lay anywhere from 200-800 eggs -depending on the size of the individual-, of which she will keep securely underneath her tailfin, via the use of her adept swimmerets. She will keep her eggs in this position for little under 6 months. The eggs are fertilised when a male hairy marron gives the female a sperm packet, of which she will use for fertilisation. Once the eggs have hatched, the new juveniles will feed upon their yolk sacs, until old enough to swim off of the swimmerets and eat other food. Independence is usually achieved in November or December after the eggs hatch at the breeding season's end. Some evidence has suggested that the smooth marron reproduces similarly however, earlier, allowing an advantage in size against the hairy marron.

### Relationship with Humans

Marrons as a whole have long been eaten by Australians. The Aboriginal people groups of southwest Western Australia have always eaten marron as a dish of cultural and traditional significance. They continue to fish and eat smooth marron today. The European settlers would also go on to hunt marron, treating it as a delicacy. In modern times, the hairy marron has become protected by the government of Western Australia, prohibiting the hunting of the species though, the smooth marron remains unprotected and is commonly hunted for recreation. Though the smooth marron remains a popular Australian dish, selling of wild-caught individuals, has been illegal since 1955. This law obviously also applies to the far more threatened hairy marron. Due to this law, marrons are regarded as a solely recreational fishery species. Smooth marrons have also seen a massive role in aquaculture, being reared in both private and commercial farms. A number of around 300 licensed 'marroners' as they're called, have been farming the species since 1972. Marron farming has even become popular in South Australia, particularly on Kangaroo Island, where smooth marrons are popular in many dishes. Western Australians of the southwest take great pride in both marron species, using them as a form of identity.

## In Captivity

The hairy marron has not been kept in public facilities however, it has been kept in captivity. As previously mentioned, the hairy marron was instilled in captive government facilities between 2013 and 2017. This is the only instance of the captive care of the hairy marron specifically.

## Sources

* IUCN Red List of Threatened Species - https://www.iucnredlist.org/species/4618/11033949
* Hairy Marron | Government of Western Australia, Department of Water and Environmental Regulation - https://rivers.dwer.wa.gov.au/species/cherax-tenuimanus/
* Australian endangered species: Hairy marron | The Conversation - https://theconversation.com/australian-endangered-species-hairy-marron-12075
* Cherax tenuimanus | Wikipedia - https://en.wikipedia.org/wiki/Cherax\_tenuimanus
* Marron | Government of Western Australia, Department of Fisheries - https://www.fish.wa.gov.au/Documents/recreational\_fishing/fact\_sheets/fact\_sheet\_marron.pdf
* Bush food: marron | The Guardian - https://www.theguardian.com/lifeandstyle/2014/feb/12/bush-food-marron