Spatial distribution, total length frequencies and otolith morphometry as tools to analyse the effects of a flash flood on populations of roach (Rutilus rutilus)

Abstract

Juvenile roach were always more abundant in the less modified section (BPS) of the river than in the other sections (RES and TAIL). While the original primary river channel was directly impacted by the flash flood, no significant difference in otolith shape was observed before or after the flash flood. Our results suggest that this part of the reach provides refuge habitats used by fish during high flow events. K E Y W O R D SCyprinidae, flood event, Lower Rhône River, otolith morphometry | INTRODUCTIONThe channelisation and regulation of large rivers have severely impacted fluvial morphology and processes by changing natural hydrological and sedimentary regimes which contribute to the high ecological value of large floodplains (Bravard & Petts, 1996;Poff et al., 1997). The length and habitat heterogeneity of riverine ecotones have been reduced (Schiemer, Zalewski, & Thorpe, 1995;Tockner & Stanford, 2002) and the spatial and temporal patterns of hydrological connectivity have been highly altered (Pringle, 2003;Ward & Stanford, 1995). Populations of highly mobile organisms like fish, which use distinct habitats during their life cycle, have been seriously affected.Major changes in fish assemblages in large European rivers such as the Danube (Balon, Crawford, & Lelek, 1986; Holcik, 1988), the Rhine (Cazemier, 1988;Lelek, 1989) or the Rhône (Pattee, 1988;Persat, 1988) resulted from the 19th century river straightening, the channelisation and the construction of successive diversion dams (mainly during the 20th century) which have created new artificial environments. On the Rhône River, a typical hydropower scheme includes a reservoir (RES) created by the diversion dam built on the upper part of the river, a canal which redirects the main river flow to a power plant, and a bypassed old river that spans for several kilometres. Typically, the tailrace (TAIL) and the bypassed sections (BPS) converge in the downstream RES formed by next diversion dam (see Figure 1). Most of the time, the BPS receives a low minimum instream flow and overflows occur at the dam when river discharge exceeds the capacity of the hydropower plant. However, these released flows (discharge from the dam) are generally lower than the initial discharge prior to the

Otolith shape analysis and daily increment validation during ontogeny of larval and juvenile European chub Squalius cephalus

“…ImageJ software (NIH; http://www.imagej.nih.gov) was used for measurements of otolith width ( W O ), length ( L O ), area ( A O ) and perimeter ( P O ). To investigate how the otolith shape varied with age during ontogenesis, parameters from 200 pairs of lapilli were extracted using two methods (Morat et al ., ). The first method consisted of extracting morphological shape indices describing form factor ( I F ), roundness ( I R ) and aspect ratio ( I AR ; Tuset et al ., ; Agüera & Brophy, ), where I F = 4πA O (P O 2 ) −1 , I R = 4 A O (π W O 2 ) –1 and I AR = L O W O –1 .…”

“…Following Morat et al . (), the Fourier power spectrum was calculated for each otolith and the optimum number of harmonics required to define 99.99% of the contour accurately was determined (Crampton, ). This resulted in the selection of 17 harmonics and thus 64 Fourier coefficients, as the first harmonic (corresponding to the simple ellipse reconstruction) is not taken into account.…”

“…Following Morat et al . () who recommended using the otoliths of the same side (right or left) for all the analyses performed due to potential anatomical asymmetry, only right otoliths were used for further analyses.…”

“…The shapes of the otoliths were analysed as a two-dimensional projection with components called harmonics, each being characterised by four elliptic Fourier coefficients, mathematically normalised for shape and invariant in size, position and rotation of the otoliths. Following Morat et al (2018), the Fourier power spectrum was calculated for each otolith and the optimum number of harmonics required to define 99.99% of the contour accurately was determined (Crampton, 1995). This resulted in the selection of 17 harmonics and thus 64 Fourier coefficients, as the first harmonic (corresponding to the simple ellipse reconstruction) is not taken into account.…”

“…However, they are also influenced by environmental conditions and exhibit, therefore, inter and intra-specific differences (Lombarte & Lleonart, 1993;Panfili et al, 2002;Vignon & Morat, 2010). Otolith shape and structural properties are of great interest since they are related to habitat characteristics (e.g., water temperature, streamflow, salinity, food supply) or environmental stresses (Berghahn, 2001;Haworth & Bestgen, 2016), as well as major events in the fish's life history such as hatching, first feeding, metamorphosis from larva to juvenile, or specific life-history transitions during the 1st year (Stevenson & Campana, 1992;Fischer, 1999;Neuman et al, 2001;Morat et al, 2018). Fundamental morphological changes occur in the course of ontogenesis, but very few studies have assessed the extent to which otolith shape is dependent on ontogenetic stages (Vignon, 2012).…”