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Invasive crayfish alert! - cmsdata.iucn.org · Invasive crayfish alert! Procambarus clarkii...

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    Invasive crayfish alert!

    Procambarus clarkii (Louisiana crayfish)This freshwater crustacean, native to Southern USA, has become a big threat to African wetlands since its introduction several decades ago. Adults are dark red-brown in colour and may measure up to 15cm in length. It is considered to be one of the most adaptable freshwater crustaceans (Order Decapoda) and is able to grow quickly, even in only seasonally present water, being tolerant of dry conditions that last up four months.

    WHY SHOULD WE BE WORRIED?

    This alien freshwater crayfish has a destructive feeding behavior. It feeds on: submerged and emergent water plants, semiaquatic vegetation, snails and other molluscs, small fish, other crustaceans found in lakes, rivers and both natural and man-made wetlands (dams, reservoirs, farm ponds, swamps and floodplains) in shallow water and on the edges of deeper water bodies.

    Procambarus clarkii can destroy native wetland vegetation and the snail and crustacean fauna of freshwater ecosystems. It has been held responsible for the disappearance of water lilies and submerged vegetation as well as many species of snails in wetlands of Eastern and Southern Africa where it has become invasive.

    It is possibly a threat to the existence of smaller fish of biodiversity value.

    Its burrowing habits can damage dams and reservoirs.

    It may out-compete the native freshwater crabs and other aquatic species, and carry crayfish virus vibriosis and a number of worms parasitic on vertebrates.

    PATHWAYS OF SPREAD:

    In some cases P. clarkii was introduced to man-made wetlands to control bilharzia-spreading snails from where it spread to other wetlands.

    This species has been introduced to fish ponds in the adjacent catchments from where it has spread, initially upstream in rivers bit also across wetlands.

    As it can function as an air-breather, the adults can travel considerable distances across land (especially in damp grass) and so spread from one wetland to another and even from one river or lake catchment to another.

    Alien freshwater crayfish might enter the catchment of Lake Tanganyika from the Lake Victoria/Nile River catchment or from the Zambezi River catchment along the major inflowing rivers to the lake Rusizi River, Malagarasi River, Kalambo River, Lufubu River as well as smaller tributaries of the lake

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    Cherax quadricarinatus (Australian red-claw crayfish)

    The colour of C. quadricarinatus ranges from dark brown to blue-green and adult males have a distinct red patch or stripe on the outer margin of the chelae (claws) and may measure up to 20cm in length.

    WHAT IS MY ROLE IN PREVENTING SUCH

    INVASIONS?

    Do not introduce any species of freshwater crayfish into wetlands (for aquaculture or aquarium trade) as this aids their spread.

    Report any sightings of these crayfish to appropriate authorities (Lake Tanganyika Authority or Fisheries and Environment Agencies of the four riparian states).

    Freshwater crayfish have already been recorded in the neighbouring Zambezi basin, the Lake Victoria and Nile River basins. Mapping their spread is important in order to issue alerts of threats to freshwater systems not yet invaded and to prevent threats to the endemic and indigenous freshwater biodiversity of Lake Tanganyika and its catchment.

    IUCN Global Invasive Species InitiativeIUCN ESARO Regional Office, Nairobi, KenyaFor more information: contact: [email protected] or [email protected] or [email protected]

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    WHY SHOULD WE BE WORRIED? There are no native freshwater crayfish in mainland Africa and this

    species can out-compete and even eat native freshwater crabs; it is also capable of affecting the many endemic crustaceans, molluscs and small fish of Lake Tanganyika causing (in the extreme) significant changes in populations and even extinctions.

    These Crayfish are omnivorous and veracious feeders. In areas where this species has been introduced, it has been able to impact native fauna through direct competition and predation.

    The species may also modify the habitat thus making it unsuitable for native species.

    Freshwater crayfish may spread previously unknown parasites into native populations of crustaceans and other animals. They have been reported (in other places) to carry a number of pathogens, including viruses, bacteria, fungi, protozoan and metazoan parasites.

    CONTROL OPTIONS:

    Crayfish are extremely difficult to control and while predatory fish have been tried, none has been very successful. The use of reproductive hormones in small water bodies is being tested, but otherwise only drainage and physical removal have been effective. It is next to impossible to drain natural wetlands and certainly true of large lakes. Other management strategies include creating barriers to prevent its spread, prohibiting the transport of live crayfish, and improving public education about its risks to the environment. Freshwater crayfish should not be kept in aquaculture systems anywhere in the entire Lake Tanganyika catchment and especially not in the lake itself.

    mailto:info%40lta-alt.org%20?subject=mailto:geoffrey.howard%40iucn.org?subject=mailto:esther.abonyo%40iucn.org?subject=

  • Cherax quadricarinatus (Australian red-claw crayfish)

    The colour of C. quadricarinatus ranges from dark brown to blue-green and adult males have a distinct red patch or stripe on the outer margin of the chelae (claws) and may measure up to 20cm in length.

    WHAT IS MY ROLE IN PREVENTING SUCH

    INVASIONS?

    Do not introduce any species of freshwater crayfish into wetlands (for aquaculture or aquarium trade) as this aids their spread.

    Report any sightings of these crayfish to appropriate authorities (Lake Tanganyika Authority or Fisheries and Environment Agencies of the four riparian states).

    Freshwater crayfish have already been recorded in the neighbouring Zambezi basin, the Lake Victoria and Nile River basins. Mapping their spread is important in order to issue alerts of threats to freshwater systems not yet invaded and to prevent threats to the endemic and indigenous freshwater biodiversity of Lake Tanganyika and its catchment.

    IUCN Global Invasive Species InitiativeIUCN ESARO Regional Office, Nairobi, KenyaFor more information: contact: [email protected] or [email protected] or [email protected]

    Phot

    o by

    : Har

    ris

    Phir

    i

    WHY SHOULD WE BE WORRIED? There are no native freshwater crayfish in mainland Africa and this

    species can out-compete and even eat native freshwater crabs; it is also capable of affecting the many endemic crustaceans, molluscs and small fish of Lake Tanganyika causing (in the extreme) significant changes in populations and even extinctions.

    These Crayfish are omnivorous and veracious feeders. In areas where this species has been introduced, it has been able to impact native fauna through direct competition and predation.

    The species may also modify the habitat thus making it unsuitable for native species.

    Freshwater crayfish may spread previously unknown parasites into native populations of crustaceans and other animals. They have been reported (in other places) to carry a number of pathogens, including viruses, bacteria, fungi, protozoan and metazoan parasites.

    CONTROL OPTIONS:

    Crayfish are extremely difficult to control and while predatory fish have been tried, none has been very successful. The use of reproductive hormones in small water bodies is being tested, but otherwise only drainage and physical removal have been effective. It is next to impossible to drain natural wetlands and certainly true of large lakes. Other management strategies include creating barriers to prevent its spread, prohibiting the transport of live crayfish, and improving public education about its risks to the environment. Freshwater crayfish should not be kept in aquaculture systems anywhere in the entire Lake Tanganyika catchment and especially not in the lake itself.

    Invasive crayfish alert!

    Procambarus clarkii (Louisiana crayfish)This freshwater crustacean, native to Southern USA, has become a big threat to African wetlands since its introduction several decades ago. Adults are dark red-brown in colour and may measure up to 15cm in length. It is considered to be one of the most adaptable freshwater crustaceans (Order Decapoda) and is able to grow quickly, even in only seasonally present water, being tolerant of dry conditions that last up four months.

    WHY SHOULD WE BE WORRIED?

    This alien freshwater crayfish has a destructive feeding behavior. It feeds on: submerged and emergent water plants, semiaquatic vegetation, snails and other molluscs, small fish, other crustaceans found in lakes, rivers and both natural and man-made wetlands (dams, reservoirs, farm ponds, swamps and floodplains) in shallow water and on the edges of deeper water bodies.

    Procambarus clarkii can destroy native wetland vegetation and the snail and crustacean fauna of freshwater ecosystems. It has been held responsible for the disappearance of water lilies and submerged vegetation as well as many species of snails in wetlands of Eastern and Southern Africa where it has become invasive.

    It is possibly a threat to the existence of smaller fish of biodiversity value.

    Its burrowing habits can damage dams and reservoirs.

    It may out-compete the native freshwater crabs and other aquatic species, and carry crayfish virus vibriosis and a number of worms parasitic on vertebrates.

    PATHWAYS OF SPREAD:

    In some cases P. clarkii was introduced to man-made wetlands to control bilharzia-spreading snails from where it spread to other wetlands.

    This species has been introduced to fish ponds in the adjacent catchments from where it has spread, initially upstream in rivers bit also across wetlands.

    As it can function as an air-breather, the adults can travel considerable distances across land (especially in damp grass) and so spread from one wetland to another and even from one river or lake catchment to another.

    Alien freshwater crayfish might enter the catchment of Lake Tanganyika from the Lake Victoria/Nile River catchment or from the Zambezi River catchment along the major inflowing rivers to the lake Rusizi River, Malagarasi River, Kalambo River, Lufubu River as well as smaller tributaries of the lake

    Phot

    o by

    : Geo

    ffrey

    How

    ard

    mailto:info%40lta-alt.org%20?subject=mailto:geoffrey.howard%40iucn.org?subject=mailto:esther.abonyo%40iucn.org?subject=

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