News - May 21, 2015

First bred freshwater crayfish released

Rob Ramaker

For the first time, bred European crayfish have been released into Dutch waters. On 11 May, Arnhem city councillor Ine van Burgsteden and forester Ben Oosting released 109 crayfish into an Arnhem pond.

Alterra ecologist Fabrice Ottburg has been working with heritage organization Gelderland Landscape & Castles on a rescue programme to save the animal for the Netherlands. Until recently there were European crayfish in only one Dutch river, and it seemed to be only a matter of time before the species would disappear from our country. This is in sharp contrast with the nineteen fifties, when the European crayfish was present in large numbers in Dutch streams, rivers and lakes. The canalization of streams, the introduction of the invasive American crayfish and the spread of crayfish plague proved disastrous.

Action was decided on in 2012. Ten specimens from the last population were caught (six females and four males) and allowed to breed in captivity. In order to increase the chances of a successful release into the wild, Ottburg aims to keep the crayfish in conditions that are as natural as possible. The eggs are not incubated artificially, the crayfish have to compete with each other and they live in as natural an environment as possible. They must be kept safe, though, so predators are kept away from them. Meanwhile, some of the causes of the decline of the European crayfish have been removed. Holland’s waters are cleaner and less canalized. The crayfish plague, to which only the American crayfish is immune, remains a serious problem. ‘We are working on a resistant line,’ says Ottburg. ‘But that is not something you can produce at the drop of a hat. It could take 20 years.’

But doing nothing was no longer an option: a habitat of two ponds is too vulnerable. As a safeguard against disasters, crayfish will be released at 10 isolated spots in the next few years. Ottburg would also like to introduce the European crayfish in two stream systems. They will need some attention after release. New specimens will be added all the time to ensure that not all the animals are the same age. It will also be important to monitor whether the released crayfish survive and reproduce.