Local conservation: agile frog headstarting in 2009

Agile frogs (Rana dalmatina) are one of only three amphibian species native to Jersey, and Jersey is the only place in the British Isles where this frog species occurs. Unfortunately, its population on Jersey has been declining, and its range on the island decreasing, since the early 1900’s, largely due to pollution of breeding ponds and habitat loss. By the mid-1980’s there were only two populations remaining on the island (both in the south-western corner of the island), and one of these was lost in 1987 due to an agri-chemical spill. As part of efforts to conserve the species, individuals from the single remaining population have been translocated to this site in recent years, and breeding is again occurring at this site.

Durrell is heavily involved with conservation efforts for agile frogs on the island. One of the ways we participate is through a ‘head-starting’ programme – we rear egg clumps collected from the wild populations in a safe environment (tadpole mortality is usually very high in the wild, so we maximise the number of animals that make it through this vulnerable stage of their lives). After approximately four months, we release well-developed tadpoles and froglets back into the wild. Before being released, each individual is marked with Visible Implant Elastomer, so that we can evaluate the success of our head-starting programme.

In 2007, a grant from the States of Jersey Ecology Fund allowed us to establish a dedicated facility for head-starting tadpoles, and we’ve used this for the last two breeding seasons. The facility is a refrigerated shipping container set up as a biosecure unit; it allows us to provide a higher standard of care, and also to minimise as far as possible the chance of introducing diseases from the outside environment into the facility. This means that, if an amphibian disease (such as the amphibian chytrid fungus that is currently contributing to amphibian declines around the world) is introduced to the island, we can keep a ‘clean’ captive population for conservation purposes. Last year, we kept a number of tadpoles after they metamorphosed to make sure that we can successfully rear and keep frogs in the facility if necessary.

This year was a very good year for breeding in the wild – a total of 55 spawn clumps were laid, which is a big increase over the 29 clumps laid in 2008! In late February / early March, the States of Jersey Environment Department delivered 26 of these spawn clumps (including three from the site the species has been returned to) to Durrell for head-starting.

Almost 12,500 tadpoles hatched from these spawn clumps! In early May, we released 5,000 tadpoles; we had to release these ones as all the tadpoles were growing very quickly and we needed to reduce density so we could continue to provide good conditions for growth and development. All remaining tadpoles were released during June, just as they were approaching metamorphosis. The releases all went very well and a large number of the tadpoles have already metamorphosed and hopped away to start their life on land. Research is being carried out this year to determine the success of the head-starting programme.