4.2 Identifying populations for monitoring
Recognizing genetic diversity occurring both within and between
populations is essential for conservation management of structured
populations (Caballero et al,. 2010). We used the structure
software to identify genetically distinct populations within systems of
interconnected lakes, and then we monitored these structures over time.
Our findings indicate that this approach was needed to identify and
monitor genetically distinct populations. If we had focused on lakes
only, the population diversity within them would have gone unnoticed.
To identify metapopulations we primarily used geographic location and
knowledge of waterways for potential migration. For instance,
metapopulations Skåarnja 1 and 2 were separated into two systems because
of waterfalls that most likely prevents migration between the two areas.
Our inferred metapopulation structure was supported by the phylogenetic
tree (Figure S2).
Life-history diversity of brown trout is complex, and the fish typically
spawn in streams and creeks and feed in lakes, but lake spawning is also
possible as well as river residency (e.g. Östergren et al., 2012;
Ferguson et al., 2019). Ideally, sampling would occur at spawning
grounds and during the reproductive period. In practice this is
difficult in these systems because they are located in remote areas that
are difficult to access, particularly in late fall/early winter when
spawning occurs and when weather conditions are typically harsh. We were
not able to sample all water bodies in any of the systems studied, and
thus cannot rule out that additional subpopulations exist that can
exchange migrants with the populations identified and monitored.