Did you know that we have native Crayfish here in Ireland? They are under serious threat!

Ireland’s native crayfish species, the White-clawed Crayfish (Austropotamobius pallipes), are truly fascinating! They are similar looking to a lobster, although much smaller in size. Many people are unaware of their presence in Ireland, they are not seen very often due to their shy behaviour. Unfortunately, in recent years there has been a serious decline in Ireland’s crayfish population due to a plague. Read on to find out more about the White-clawed Crayfish and what you can do to help prevent the crayfish plague…

Crayfish in the River Blackwater, Cork (Credit: Pascal Sweeney)

Did you know…

The White-clawed Crayfish is a globally threatened species and Ireland is home to one of the largest populations! It is considered a keystone species due to its relatively large size and omnivorous diet; they graze on freshwater plants and feed on several freshwater invertebrates. They are also a food source for otters and eels! White-claw Crayfish can live to be 10 years old, they grow though moulting and can reach a length of between 10 and 12cm. Moulting can vary depending on their sex and age, with juveniles being able to moult numerous times in a season! Mature females will only moult once a year in late summer and mature males twice a year, once in early summer and again in late summer.

Habitat

White-clawed Crayfish can be found in calcareous streams, rivers, and canals with high oxygen levels, they are sometimes also found in lakes. Their shell is made up of calcium and so they need water systems with high calcium content (calcareous). They are nocturnal and need good hiding spaces during the day to avoid being eaten. They choose places which will not be washed away during flooding or high flows such as large rocks, cracks in underwater stonework, tree roots or sunken logs. Sometimes they are even found in burrows along the riverbank which they have dug out with their claws. To see some pictures of these lovely little creatures check out the link below! https://www.npws.ie/research-projects/animal-species/invertebrates/white-clawed-crayfish-austropotamobius-pallipes

White-clawed Crayfish (Austropotamobius pallipes) distribution – (Credit: Biodiversity Ireland)

Crayfish Plague

Crayfish plague (Aphanomyces astaci) is a fungus-like water mould which is highly infectious and kills any White-clawed Crayfish it encounters. It originated in North America and it is thought to have arrived in Europe through the illegal introduction of an American crayfish species or accidently on contaminated equipment. These species are carriers of the plague but are resistant to it. Although there have been recorded isolated incidence of this plague since the 1980’s in Ireland, it was not until the summer of 2017 which saw numerous areas seriously impacted by the plague.

What you can do to help prevent the spread of crayfish plague:

  • Familiarise yourself with the identification of the White-clawed Crayfish
  • Know the signs of an outbreak and report them to National Parks and Wildlife Services (NPWS). Signs can include unusual behaviour such as crayfish sightings in shallow margins in daylight.
  • Also report any sightings of dead crayfish.
  • If you participate in any water activities such as fishing, boating, kayaking, or canoeing then make sure you wash, disinfect, and dry all gear for 48 hours after use. Suitable disinfectants include Milton, Virkon Aquatic, and Proxitane
  • If drying equipment is not feasible then they should be power steamed washed above 64 degrees

We would like to thank Pascal Sweeney for allowing us to use his photographs for this article.

 

Written By Mary Moroney, Ecologist

References

https://www.offthescaleangling.ie/the-science-bit/crayfish-plague/

https://www.biodiversityireland.ie/wordpress/wp-content/uploads/Crayfish-Plague-FAQ.pdf

https://www.biodiversityireland.ie/crayfish-regulations/

https://species.biodiversityireland.ie/profile.php?taxonId=17487

https://www.irishtimes.com/news/environment/crayfish-plague-no-wonder-the-irish-species-is-white-clawed-1.3642260