Key facts
- Gaelic name: Carrachan-sgèithe
- Length: up to 11cm (excluding tail)
- Distribution in UK: Two populations: New Forest (Hampshire) and the Solway Firth
- Status: Endangered within the UK and protected under Schedule 5 of the Wildlife and Countryside Act 1981
- Species on the Edge areas: Argyll and Inner Hebrides
Species information
How to identify
These prehistoric looking animals have a shield-shaped carapace making them look like a cross between a horseshoe crab and an extinct trilobite. In the wild our native tadpole shrimp can grow up to 11cm long (excluding their tail).
Lifecycle
The tadpole shrimp is the oldest known animal species in the world, with fossils dating it back 220 million years; this makes the species older than the Tyrannosaurus Rex! The reason it has survived so long can be attributed to the species’ very clever biology.
Tadpole shrimps live in seasonal pools which dry out in the summer. These pools may only last a few weeks before drying out, and then it may be years or even decades before the water returns. When the pools dry out all predators and competitors are killed off.
Tadpole shrimps, however, have adapted to these inhospitable conditions. They have very rapid development, maturing from an egg to adulthood in just two to three weeks. This means they are able to hatch from an egg and produce the beginnings of the next generation before their pool dries out, all in the space of a few weeks.
But what happens to these eggs when the pool dries out? When tadpole shrimp eggs are laid a proportion of the eggs hatch, and the rest go into diapause – this means the eggs dry out and their development is stopped. In diapause tadpole shrimp eggs are very durable and can survive up to an incredible 27 years. The eggs can also endure extreme temperatures, immersion in salt water, and can be eaten and excreted by an animal without harm! Once these eggs are rehydrated and the environmental conditions are right, the diapause will end and the eggs will hatch forming a new generation of shrimps.
Distribution
The tadpole shrimp can currently only be found in two locations in the UK: the New Forest in Hampshire and Caerlaverock on the Scottish Solway Coast. The species had formally been present on the Kirkcudbrightshire coast, however the population was lost in the 1960s, believed to be as a result of coastal erosion.
Habitat and feeding
Habitat: Adults can be found in seasonal brackish (slightly salty) or freshwater pools; these dry out in the summer months.
Feeding: Tadpole shrimps are omnivorous; they will eat small aquatic invertebrates, aquatic plants and sediment. In order to sustain their fast development they need to eat around 40% of their body mass each day.
Conservation status
Endangered within the UK – protected under Schedule 5 of the Wildlife and Countryside Act 1981
Threats
While tadpole shrimps have adapted to be a very hardy species, they have an extremely limited distribution, putting them intrinsically at risk of extinction. The introduction of predators, rising sea levels, water pollution and invasive aquatic plants add further pressure to the species.
What Species on the Edge is doing
To help secure a future for the tadpole shrimp in Scotland, Species on the Edge are working to introduce a second site for the species through a translocation prorgramme.
In 2023 to the summer of 2024, ecologist Larry Griffin reared tadpole shrimps hatched from sediment collected at Scotland’s last remaining site for the species at Caerlaverock. The sediment was heated to 60 degrees to kill off any pathogens present, then a small amount was re-wetted, resulting in tiny tadpole shrimps hatching from the eggs within 48 hours. 14 tadpole shrimp survived to adulthood and soon laid their own eggs in the tanks they were reared in. The sediment in these tanks, containing the eggs was removed and dried again.
In the summer of 2024, 10 kilograms of the dried sediment containing over 20,000 eggs was spread into the bare earth of at-the-time dry, but seasonally wet coastal pools at the RSPB’s Mersehead reserve on the Kirkcudbrightshire coast. Once the pools were re-wetted, adult tadpole shrimps were also introduced into two of the pools. We are now waiting to hear if the translocation has been successful (last updated – November 2024).
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