Introduced fish in Pyrenean high mountain lakes: impact on amphibians and other organisms, and conservation implications

Abstract

Introduced fish in Pyrenean high mountain lakes: impact on amphibians and other organisms, and conservation implicationsPyrenean high mountain lakes are naturally fishless due to hydrographic barriers that have prevented the natural colonisation of fish species from lower elevation streams. However, there have been numerous introductions of trout and minnows to such ecosystems, either in historical and recent periods. Trout and minnow introductions can cause large ecological problems and ecosystem changes in high mountain lakes, since both taxa occupy the top of a lake's food web. The study had two objectives. First, we wanted to investigate which particular anthropogenic and environmental factors best explained fish presence in the Pyrenean lakes. For that purpose we collected data on trout and minnow occurrence from 520 high mountain lakes > 0.5 ha in the southern Pyrenees. The second objective was to investigate the effect of introduced fish on several groups of organisms such as amphibians, conspicuous macroinvertebrates, planktonic crustaceans and littoral epilithic community. For that purpose we sampled 1736 lakes and ponds at different levels of intensity. The distribution of Salmo trutta in the lakes of the southern slopes of the Pyrenees was best explained by both anthropogenic factors and lake characteristics, while only anthropogenic factors linked to recreational fishing were associated with the distribution of the exotic trout Salvelinus fontinalis and Oncorhynchus mykiss. In the case of minnow occurrence, previous presence of trout in the lake was the most explanative variable, confirming its association with its use as live-bait in recreational fishing. Fish presence was linked with the disappearance of most amphibian species. Despite fish had a high local effect, at Pyrenean range scale, western-eastern patterns of some environmental variables were the main drivers of amphibian species distribution. Minnows also showed a sizeable impact on the pelagic habitat, reducing the occurrence of some crustacean zooplankton species that appeared to be unaffected by trout. In addition, we confirmed the presence of a littoral trophic cascade that defines most of the characteristics of the littoral epilithon of Pyrenean high mountain lakes and ponds through fish predation of tadpoles and hence, by a drastic reduction of grazing activity.

Scientists' warning of threats to mountains

“…For example, tourism drives fish stocking of naturally fishless lakes. In such naturally fishless mountain lakes fish introductions have an outsized impact and drive profound ecological change as a highly efficient aquatic predator is introduced in a naïve environment (Miró and Ventura, 2020). Stocking montane lakes with fish for subsistence purposes has been occurring since the Neolithic, through fish translocations from nearby lakes and rivers.…”

Food web differences between two neighboring tropical high mountain lakes and the influence of introducing a new top predator

“…With an extended littoral zone and introduced fish, the larger lake (El Sol) had a higher omnivorous fraction than the smaller fishless lake (La Luna) ( Table 3 ). Omnivore nodes were associated with the littoral zone; hence, rainbow trout may decrease food web stability, as observed in temperate lakes [ 67 ] and HMLs [ 68 ]. Nevertheless, macrophyte beds in the stocked lake El Sol represented an important basal resource and habitat that would increase the littoral sub-web complexity by allowing more trophic interactions [ 59 , 69 ].…”

“…rainbow trout may decrease food web stability, as observed in temperate lakes [67] and HMLs [68]. Nevertheless, macrophyte beds in the stocked lake El Sol represented an important basal resource and habitat that would increase the littoral sub-web complexity by allowing more trophic interactions [59,69].…”

Challenges for the Post-Market Environmental Monitoring in the European Union Imposed by Novel Applications of Genetically Modified and Genome-Edited Organisms

“…Effects on the quality of aquatic habitats may occur due to the churning up of sediment, damaging aquatic macrophytes, or water eutrophication. Such alterations in habitat quality can also affect higher trophic levels, such as amphibians and birds [ 141 , 142 , 143 ].…”