Data from: Artificial barriers prevent genetic recovery of small isolated populations of a low-mobility freshwater fish

Habitat loss and fragmentation often result in small, isolated populations
vulnerable to environmental disturbance and loss of genetic diversity. Low
genetic diversity can increase extinction risk of small populations by
elevating inbreeding and inbreeding depression, and reducing adaptive
potential. Due to their linear nature and extensive use by humans,
freshwater ecosystems are especially vulnerable to habitat loss and
fragmentation. Although the effects of fragmentation on genetic structure
have been extensively studied in migratory fish, they are less understood
in low-mobility species. We estimated impacts of instream barriers on
genetic structure and diversity of the low-mobility river blackfish
(Gadopsis marmoratus) within five streams separated by weirs or dams
constructed 45–120 years ago. We found evidence of small-scale (<13
km) genetic structure within reaches unimpeded by barriers, as expected
for a fish with low mobility. Genetic diversity was lower above barriers
in small streams only, regardless of barrier age. In particular, one
isolated population showed evidence of a recent bottleneck and inbreeding.
Differentiation above and below the barrier was greatest (FST =0.13) in
this stream, but in other streams did not differ from background levels.
Spatially explicit simulations suggest that short-term barrier effects
would not be detected with our dataset unless effective population sizes
were very small (<100). Our study highlights that, in structured
populations, the ability to detect short-term genetic effects from
barriers is reduced and requires more genetic markers compared to
panmictic populations. We also demonstrate the importance of accounting
for natural population genetic structure in fragmentation studies.