Common Yabby

## Background Information

### Alternate Name(s)

Yabby, Yabbie, Australian yabby, Blue yabby, Blue-claw yabby, Freshwater crayfish, Freshwater shellfish, Cherax crayfish, Marron, Redclaw, Gilgie, Gilgy, Lobby, Crawbob, Koonac

## Classification

### Subspecies

C. d. albidus

The common yabby ***(Cherax destructor)*** also known as the blue-claw yabby or freshwater crayfish, is a species of eastern Australian crustacean endemic to river systems and other wetlands. Yabbies have slender bodies with a mostly bluish or reddish grey carapace and triangular heads, with small eyes and long antennae, used for detection of their surroundings. The colours on their bodies transition to a deeper blue shade on the abdominal region, tail fin, uropods and telson. The abdomen is typically curled in life. This deeper blue also remains constant on the yabby's claws however, here it is much more prominent. In some specimens, the claws also have reddish-orange streaks on them, resulting in the common alternate name; redclaw, often used in Queensland. The yabby also possesses three walking legs, which are coloured similarly to the claws and abdomen. Like other crayfish species, the yabby also has a smaller pair of claws which it will use to lift chunks of food into its mouth while feeding. Depending on the water quality, yabbies will greatly vary in colour, from the described common blue, to black or dark brown in clear waters, to darker shades of green or light tan/brown in darker waters. Depending on the region, the species goes by a variety of names including but not limited to; koonac, gilgy/gilgie and marron, in Western Australia, redclaw, in Queensland and most commonly, the yabby, in Victoria and New South Wales. The name 'yabby' is a word stemming from the Aboriginal Australian language; Wemba-Wemba, spoken along the Murray river in northwest Victoria and southern-central New South Wales. When the species is addressed formally, it typically goes by the names; freshwater crayfish or freshwater shellfish. to Most commonly yabby reach only 10-20cm (4-8in) in length and weigh less than 70g (2.5oz), but may reach a larger size of 30cm (12in) occasionally.

## Diet

Yabbies are omnivorous scavengers, consuming a variety of food items. In the wild, yabbies commonly feed on dead organic material, such as detritus, but they may also feed on live algae. Yabbies also hunt and eat small invertebrates and fish. As a popular pet species, the yabby is often kept in captive environments, where it is often fed fruit and vegetable matter, such as potato peels, sliced carrots, peas and spinach, according to Better Pets and Gardens. The site also recommends that a pet yabby should also be fed occasional garden worms and fish carcasses as well as specially formularised yabby pellets.

## Conservation Status

Though the yabby is listed as vulnerable by the IUCN, the species' threats are not listed and the page requires an update. The notion that the yabby has no immediate threats may be accurate however, as the species is incredibly adaptive.

## Range and Population

The common yabby has the largest distribution of any Australian crayfish species and is endemic to eastern Australia, where it can be found in the states of Queensland, New South Wales, the Australian Capital Territory (A.C.T.) and Victoria. It occurs in various wetland environments like; rivers, billabongs, lakes ponds and various other water bodies. The yabby is extremely hardy and has even been found to be abundant in arid, drought-prone, regions and urbanised dams/barricades. Due to its adaptability however, the yabby has become an invasive species in some of the country's states. In Western Australia the species was introduced in the 1930s and has gone on to threaten the native hairy marron ***(Cherax tenuimanus)*** population (of which the species is often mistaken for). Concerns about the yabby possibly outcompeting the hairy marron have become common. The platypus ***(Ornithorhynchus anatinus)*** is one of the species' most prominent predators, controlling the yabby population in its range however, it and similar predators are not native to Western Australia, leading to the yabby populations thriving. In Tasmania the species was also introduced and it presently predates upon native crayfish, competes with them and even spreads harmful parasites. The yabby has also become an invasive species in countries it was introduced to in Europe and Asia. These countries include; England, the Netherlands, Germany, Switzerland, Italy (mainland), Austria and mainland China. The yabby's current population and population trend are unknown.

## Behaviour

As hardy and adaptive species, yabbies can often be found in dry environments and other areas where most aquatic species avoid. In order to survive in arid areas, yabbies will burrow underground, typically in river banks, in order to stay cool. Using this method, they can survive for an extended period of time. They have also been known to employ this burrowing strategy in dammed areas of rivers, often damaging river infrastructure like dams and levees. This behavioural adaptation gave the species its name; 'destructor'. Yabbies are prolific breeders, breeding in any waters above 15°C (59°F), typically in the summer months (December-February). Hundreds of eggs are laid by the female yabby, which then stick to her the underside of her abdomen and tail fin, with the assistance of tiny hairs. The eggs will hatch in a few months, depending on the water quality. Adults may practice filial cannibalism, where they eat their own young. For this reason, adult yabbies are typically kept separate from their young in captive environments. Yabbies are aggressive and handling of live individuals is not recommended, as they are prone to attacking with heir claws. They are also territorial and yabbies will fight one another if limited to small spaces.

### Relationship with Humans

Yabbies are commonly used as a food source by humans and the practice of fishing them, known as yabbying, is a hugely popular recreational activity. A common method of yabbying employs the use of a rod and string. A small piece of meat is attached to the string (typically a couple metres in length) and the rod is then stuck firmly in the river bank. Once a yabby grasps the meat and attempts to flee with it, the line will be pulled back to shore, while the yabby is most likely still hanging on. Once on land, the yabby and the bait are snatched up by the user's yabby net. It is said that riverine yabbies are typically less tasty and valuable as food when compared to wetland yabbies, as they consume less food sources that contain high-quality fatty acids. Bag limits apply to yabbies across Australia, with the exception of Western Australia, where overhunting of the species is encouraged, as they are a pest.

## In Captivity

The yabby can be found in zoos and aquariums internationally, such as the Toronto zoo, Canada. The yabby is however, much more prominent as an exotic pet. The yabby has actually been bred for this purpose and the species is part of a large aquaculture industry. The blue pearl yabby ***(Cherax albidus)*** is a direct product of this selective breeding and has become popular among pet owners for its vibrant blue appearance.

## Sources

* IUCN Red List of Threatened Species - https://www.iucnredlist.org/species/4622/11042150
* Research Gate - https://www.researchgate.net/figure/Map-of-Australia-showing-natural-distribution-of-yabbies-marron-and-redclaw\_fig1\_257938993
* Yabby | Sydney Fish Market - https://www.sydneyfishmarket.com.au/Home/Seafood/Species-Information/List/yabby
* Common Yabby | Wikipedia - https://en.wikipedia.org/wiki/Common\_yabby
* Yabbies - a Boon and a Blight | Department of Primary Industries and Regional Development - https://www.fish.wa.gov.au/Pages/news\_archive/Yabbies-a-boon-and-a-blight.aspx
* How to Care for Your Yabbies | Montone Aquarium - https://www.mentoneaquarium.com.au/post/how-to-best-care-for-your-yabbies
* It may nor be cute, but here's why the humble yabby deserves your love | CSIRO Scope - https://blog.csiro.au/important-yabbies/
* Crayfish | Australian Museum - https://australian.museum/learn/animals/crustaceans/crayfish/
* Yabbies | Better Pets and Gardens - https://www.betterpetsandgardens.com.au/fish/keeping-yabbies/
* Tasmania's Freshwater Burrowing Crayfish | Department of Natural Resources and Environment, Tasmania - https://nre.tas.gov.au/conservation/threatened-species-and-communities/lists-of-threatened-species/threatened-species-invertebrates/threatened-species-invertebrate-animals-e-z/freshwater-burrowing-crayfish
* Common Yabby (Cherax destructor) Ecological Profile - Section 62 - https://humanwildlifeecology.wordpress.com/2018/04/05/common-yabby-cherax-destructor-ecological-profile-section-62/