Crayfish Reef at Vobster Quay! Created and Deployed by ARC Marine

In the UK there is only one species of native crayfish, Austropotamobius pallipes or more commonly known as the White Clawed Crayfish. This species is listed on the International Union for Conservation of Nature (IUCN) Red List as endangered as over the last 10 years it has had a reduction between 50%-80% across their range (IUCN, 2018). As a result of their dwindling numbers and in an effort to increase their abundance 17 ARK sites have been set up and Vobster Quay is one of them. The ARK sites are areas that act as safe havens and are free from invasive crayfish and the plague they carry.

From March to April 2017 ARC Marine successfully Crowdfunded £30,618 to create a freshwater reef composed of 250 marine friendly concrete Reef Cubes with tailored habitat inserts within Vobster Quay, an inland diving lake near Radstock, Somerset. During this time Bristol Zoo and Bristol University completed behavioural experiments to see which structure the crayfish preferred, a series of plastic pipes, engineered brick, and ARC Marine’s tailored habitat inserts. Preliminary results showed that the crayfish preferred ARC Marine’s tailored inserts to the other two options. During September, 2017 ARC Marine deployed all 250 of the Reef Cubes and placed them in several formations (Figure 1) in an area where divers are less active and there is a reduced chance of disturbance. Since then, while working in parallel with Bristol Zoo, ARC Marine have released 37 adult (21 male, 15 female) wild caught, PIT tagged crayfish onto the reef for them to settle before mating and going into hibernation for the winter months.

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Figure 1: One of the reef formations at Vobster Quay.

Prior to the installation of the reef a base line survey was completed for the area using a number of different techniques. Firstly, divers surveyed the area looking for a suitable site for the reef to be located. Following on from this, sediment and water samples were collected for DNA analysis. This gave us a comprehensive list of the species present in the area prior to the installation of the reef and to ensure that the area was clear of any invasive species of crayfish and the pathogens they can carry. This was essential as we have several invasive species in the UK with the American Signal Crayfish (Pacifastacus leniusculus) being the most prolific. This is because the Signal Crayfish is bigger, more aggressive and a carrier of the crayfish plague but is not affected by it. If the crayfish plague is introduced into an area it can wipe out susceptible species, including our native white clawed crayfish within a matter of weeks and it can persist in the sediments long after the populations have gone.

The reef has been monitored every two months over the winter months until the crayfish have come out of hibernation where the surveys were increased to monthly. On the first survey that was conducted after the water temperature had risen enough for the crayfish to come out of hibernation, the first crayfish was sighted utilising the reef, complete with the markings on the pincers used to identify their sex (Figure 2).

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Figure 2: A female crayfish inside one of the Reef Cubes at Vobster Quay.

ARC Marine plans to continue to develop the reef into the future by increasing the number of Reef Cubes and by releasing more crayfish into our safe haven dubbed Crayopolis. ARC Marine will continue to monitor the development of the reef by creating a citizen science programme so that the divers who frequent the area can be trained to survey the reef and to submit their data to us at ARC Marine.