During the 12 weeks of the experiment, the ethologists from Liege did not detect any habituation by the newts to the presence of a fish. In a previous study published in Ethology (3), where there was no direct contact between the two species (the fish was contained within an aquarium which, in turn, was placed inside a larger aquarium reserved for newts) the opposite effect was recorded. During the first few days, the newts of the ‘fish group’ took refuge much more often in the shelter than those in the control group, but this tendency disappeared after a while, therefore proving that the newts were able to recognize a potential danger.

Multiplying the shelters

The researchers would like to make the transition from the laboratory to the natural environment. They have an iron in the fire: to study how, in pools and ponds, the diversity of the habitat (and consequently, the abundance and structure of the shelters) can contribute to limiting the impact of the presence of fish on the sexual activity of amphibians. ”Indeed, it is probable that multiplying shelters has had a positive impact on the reproductive activity of newts in environments where fish have been introduced”, considers Mathieu Denoël. “In ponds, the main shelters for amphibians are offered by crevices or by vegetation. However, the latter is often consumed by fish.  As a consequence, it would seem necessary to equip a part of the endangered habitats in such a way that permanent shelters remain available, especially where it is impossible to remove the fish”

The risk for the survival of amphibian populations increases with the level of danger posed by fish that have been artificially introduced into the natural environment. While the goldfish may not be a direct predator for the adult newt, the trout certainly is. “On an ecological level, the trout is much more demanding so it cannot survive in agricultural pools. On the other hand, the problem can arise in alpine lakes, for example. Likewise, small carnivorous fish like pumkinseeds can also cause a lot of damage to amphibian populations”, explains doctor Denoël.

As we have seen, several factors are involved in the decline of newt populations. In an article which appeared in the journal PLoS ONE (4), researchers at the Laboratory of Fish and Amphibian Ethology have shown that the same environmental factors affected both rare (great crested newts) and common (smooth newts) species. The difference is that the decline of the latter is less obvious in the short-term.

It is a challenge to estimate the relative extent of each of the causal factors in the progressive decline in amphibian populations. Doctor Denoël’s team has carried out field studies in the Herve region and the Vesdre basin, where it examined environmental characteristics (including the presence of fish species) in several hundred ponds. Statistical models allowed the team to determine the individual variables that remain significant despite the presence of other variables. The answer is clear: all the variables taken into consideration (urbanization, pollution, abandonment of ponds and the presence of fish…) add up. It is the poor amphibians are the ones that are left to pay the price!

(3) Winandy, L, & Denoël, M. (2013). Cues from introduced fish alter shelter use and feeding behaviour in adult alpine newts. Ethology, 119(2), 121-129. 

(4) Denoël, M, Perez, A, Cornet, Y, & Ficetola, G. F. (2013). Similar local and landscape processes affect both a common and a rare newt species. PLoS ONE, 8(5), 62727.