Assessing the consequences of habitat fragmentation for two migratory salmonid fishes

Abstract

ABSTRACT1. Man-made barriers such as dams affect the movement of aquatic species, reducing gene flow and genetic variability. Such encroachments may also lead to selective changes in life history and behaviour. Hydropower construction worldwide has fragmented many previously continuous fish habitats, leading to loss of populations and production. It is therefore important to assess potential impacts on habitats before such developments begin.2. Here, the potential ecological and evolutionary consequences of planned hydropower development on two migratory salmonid fishes -brown trout (Salmo trutta) and European grayling (Thymallus thymallus) -were assessed, combining telemetry with population genetics. Almost 200 fish were radio-tagged and tracked weekly between March and November. Using microsatellite markers, the genetic population structure was assessed and the number of migrants among different river sections identified for both species.3. Overall, both species displayed extensive within-and between-river movement, with larger home ranges in grayling than in trout. Regular movements between distinct spawning, feeding and wintering areas were common. These vital habitats were often located within areas of planned hydropower development.4. Both species exhibited significant population genetic structuring within the study area, with waterfalls acting as impassable barriers to upstream gene flow for grayling. The structuring was more developed for trout than for grayling. However, downstream gene flow was common, resulting in a highly admixed trout population below a waterfall.5. The large-scale movement patterns and extensive connectivity of the system indicate that habitat fragmentation and changes in water flow will adversely affect both species, but most strongly the trout. The reduction in water flow over large and productive stretches of the river might select for less migratory genotypes in both species. The loss of particular genotypes may reduce the biocomplexity of the system and overall population resilience.

Habitat fragmentation has interactive effects on the population genetic diversity and individual behaviour of a freshwater salmonid fish

“…FIGURE 2 STRUCTURE results for inference of the number of genetic clusters in the study system based on the extended dataset, confirming that three barriers form four genetic clusters in the study system (Barson et al, 2009;Junge et al, 2014). We also tested for possible behavioural differences between individual fish of distinct genotypes spawning in the same river section (hypothesis 3).…”

“…Information on the genotyping of the 346 samples in Dataset 1 (Table 1) is available in earlier publications (Barson et al, 2009;Junge et al, 2011;Junge et al, 2014). Thirty-three samples in Dataset 1 were collected and genotyped simultaneously with the samples from Junge et al (2014) Before all analyses, data were checked for null alleles based on the methods of Chakraborty, Andrade, Daiger, and Budowle (1992) and Brookfield (1996).…”

“…or the distance from the confluence of Otta River and Gudbrandsdalslågen River (for Otta River). Details on the transmitter attachment and tracking are in the footnote of Table S1 and two previous publications (Junge et al, 2014;Van Leeuwen et al, 2016).…”

“…Among important impacts are habitat loss and reduced connectivity between the remaining habitats (Heggenes et al, 2006;Junge, Museth, Hindar, Kraabøl, & Vøllestad, 2014;Van Leeuwen, Museth, Sandlund, Qvenild, & Vøllestad, 2016). The strongest impact of habitat loss can be expected on fish that repeatedly rely on specific spawning locations as a result of philopatry.…”

“…To achieve our aims, we first reassessed the previously identified sub-populations in our study area (Barson et al, 2009;Junge et al, 2014) by expanding the dataset (from 346 to 527 samples) and improving the methodology. In these two previous studies, we assigned spawning locations to individuals based on their capture locations.…”