Enhancing amphibian mitigation outcomes

We’re very excited to be heading to the CIEEM Autumn Conference next week. The topic this year is mitigation, which got us thinking about all the ways in which DNA-based tools can help with maximising the chances of positive mitigation outcomes, particularly in regards to translocating amphibians.

When moving animals to a new pond, disease and predation are among the biggest risks. Amphibians are threatened by pathogens such as ranaviruses and chytrid fungus (Batrocochytrium dendrobatidis and B. salamandrivorans – commonly known as Bd & BSal), and they face predation by fish. None of these threats are easy to detect visually, but all can be assessed from a single eDNA sample.

Pathogens

qPCR assays for key wildlife diseases have been developed and validated. They have been used in the past to determine the infection status of animals from swab samples or tissue clippings. The trouble is that to establish that a pond is free from chytrid infection, it’s necessary to test between 30 and 60 different individuals – and that’s quite a formidable task even if you’re able to trap enough animals.

More recently, research has shown that filtering the water is an effective way to capture pathogens from the environment, providing a relatively quick and easy way to establish whether a waterbody is infected.

As well as testing the pond that you’re planning to move the animals into, you might also want to collect swab samples from the animals that you’re translocating to check that you’re not going to spread disease into an uninfected ecosystem.

Predators

Fish can be difficult to detect using conventional ecological survey approaches, but they are easily surveyed using eDNA metabarcoding. In fact, you can use the exact same sample as the one collected for pathogen analysis, so there’s no need for any extra fieldwork. The analysis can also return data on amphibians, so you can get an idea of the kind of competition your translocated animals are likely to face in their new home (read more about our aquatic vertebrate surveys).

Below is an example of a survey we carried out in exactly this context. The contractor had identified 6 candidate receptor ponds for GCN and wanted to check that they were (a) free from Chytrid and (b) free from potential predators. Strikingly, the only pond that contained three-spines sticklebacks was also the only pond to be totally free of amphibian traces. Based on this data, it’s easy to rule out Pond 6 as being a suitable receptor pond for GCN, and to move them instead to the other ponds where they stand a greater chance of survival.

When to Survey?

Fish can be surveyed all year round, but it’s best to wait until Spring if you want to screen for pathogens, as their density increases with amphibian activity. You should also bear in mind the turnaround time for the different analyses: while results for the pathogen tests can be returned very quickly, the fish survey takes a few weeks because the metabarcoding workflow is more complex.

Collecting samples in March or April would mean that you would receive all of your results within the GCN survey season, allowing you to make evidence-based decisions on the optimal mitigation strategy.

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