Evaluating gillnetting protocols to characterize lacustrine fish communities

Allopatric and sympatric diversification within roach (Rutilus rutilus) of large pre‐alpine lakes

“…Within Lake Brienz, there are a total of four genetically differentiated whitefish species, segregated along the water depth and pelagic–benthic axes, which are distinct in their morphology, including the gill rakers (Doenz et al., ), thus suggesting adaptation to different trophic niches (Roesch, Lundsgaard‐Hansen, Vonlanthen, Taverna, & Seehausen, ). Given the abundances of perch and whitefish in Lake Brienz (Alexander et al., ; Doenz et al., ), the limited degree of diversification in roach could be a result of different factors: (a) Interspecific competition may have constrained roach from diversifying, (b) If the observed phenotypic differentiation (Figure ) is primarily due to phenotypic plasticity, the latter could have constrained diversification by shielding the genome from selection, thus decreasing the potential for genetic divergence (Ghalambor et al., ; Price et al., ), (c) The fundamental niche of roach may be narrower than that of whitefish, preventing roach to explore otherwise available niche space. For example, roach prefer warmer water and are therefore restricted to the shallow zones of lakes, whereas whitefish can tolerate colder water, allowing them to explore the deeper sections of lakes (Coutant, ; Kottelat & Freyhof, ), and (d) Recent genomic work suggests that adaptive diversification in stickleback and whitefish often occurs from standing genetic variation in genomic regions that show structural changes, including inversions (Jones et al., ; Marques et al., ) or chromosomal rearrangements (Dion‐Côté et al., ).…”

“…However, former biogeographic work found that R. rutilus from the Rhone drainage formed a genetic cluster with specimens from the Rhine drainage (Larmuseau, Freyhof, Volckaert, & Van Houdt, ), potentially reflecting human translocations and/or natural drainage crossings, which has been observed for other fish species between the Aare/Rhine drainage and Lake Geneva (Gouskov & Vorburger, ; Vonlanthen et al., ). All specimens were collected during Project Lac , a large fish diversity assessment of pre‐alpine lakes that aimed to probe all available littoral substrates and depth‐related habitats for each lake using a standardized gillnet approach (reviewed in Alexander et al., 2015a, 2015b). Briefly, for each lake the littoral habitats (<5 m deep) were classified based on substrate composition and particle size, macrophyte morphology and density, and proximity to an inwardly or outwardly flowing watercourse.…”

“…Briefly, for each lake the littoral habitats (<5 m deep) were classified based on substrate composition and particle size, macrophyte morphology and density, and proximity to an inwardly or outwardly flowing watercourse. Fishing was subsequently performed using a combination of two different gillnet protocols that combined different mesh sizes to reduce size‐selective catch biases (described in detail in Alexander et al., 2015a). Nets were set in a randomized way within the available area of both benthic and littoral habitats.…”

“…Nets were set in a randomized way within the available area of both benthic and littoral habitats. Netting effort reflected the relative abundance of each habitat with a minimum number of three nets per habitat (Alexander et al., 2015a, 2015b). Following capture, the total length of each specimen was measured and each sample was photographed on the left side for further morphological analyses.…”

Rapid buildup of sympatric species diversity in Alpine whitefish

“…This study includes genetic, ecological, and morphological data for 2,388 individual whitefish collected by habitat stratified random sampling in 2012 or 2014, and by species‐targeted fishing in the years 1950–1975 and 2000–2015 in Lakes Brienz and Thun (this study; Vonlanthen, ; Bittner, ; Vonlanthen et al., ; Supporting Information Table ). Stratified random fishing was conducted under a research program for the assessment of fish diversity in pre‐alpine lakes and involved quantitative and taxonomically unbiased sampling across the entire lake (Alexander et al., ; Vonlanthen & Périat, ; Vonlanthen et al., ). Contemporary species‐targeted fishing was conducted by commercial local fishermen during spawning seasons on spawning grounds known to local fishermen and targeted reproductively active fish of known whitefish species (Supporting Information Table ).…”