The common spadefoot toad in the river region

The common spadefoot toad has declined, because of the effects of water draw-down and acidification. In the areas alongside the large rivers it has declined less than elsewhere in the country, because the pools are regularly inundated with river water and therefore do not become too acid.

Trends

Since 1950 the population of the common spadefoot toad in the Netherlands has crashed (see figure). In the area alongside the large rivers, however, the decline has been less dramatic than elsewhere in the country: here, 45 to 50% of the population of this species is found. The common spadefoot toad is still found in 16 locations along the rivers: 14 of these are along the IJssel and Overijsselse Vecht (7 inside the dikes and 7 outside the dikes) and the other two are along the Waal and Regge (both inside the dikes). The species has recently disappeared from the Roer valley.

Causes

The main causes of the decline are acidification and the effects of water draw-down. Neither the spawn nor the tadpoles can tolerate acid water, and if a pool dries up they die. The small pools where the toad lives near the big rivers are occasionally inundated with base-rich river water, so their water never becomes too acid. Here too, however, the common spadefoot toad has declined. This is because confining the rivers inside the dikes results in fewer pools and other suitable bodies of water being created naturally. Furthermore, farmers have filled in some of the pools.

High levels of water in the rivers are actually a hazard for the common spadefoot toad, because then the toads cannot find any safe havens in the area within the dikes. Furthermore, the floods may wash away the spawn and tadpoles, or may wash fish that eat the spawn and tadpoles into the pools.

The common spadefoot toad is on the Red List of reptiles and amphibians.