Seasonal variation in the habitat available for 0+Rutilus rutilus (L.) in a regulated river

Abstract

1. Habitat availability for 0+ Rutilus rutilus (L.) was determined at four sites in the regulated River Great Ouse, Eastern England, using a modified version of the Instream Flow Incremental Methodology. Discharge–habitat relationships were then calculated using a modified version of the Physical Habitat Simulation (PHABSIM) computer package. A weighted usable area (WUA) time series was generated using the discharge–habitat models. 2. Habitat availability varied between sites and with discharge, although at three of the four sites some suitable habitat remained throughout the year. In general, more habitat was available for juvenile fishes than for young larval fishes and during the winter. 3. As discharge increased habitat availability decreased, primarily as a result of increased velocity and depth. This was exacerbated by the trapezoidal shape of the main channel. In a marina, which was thought to be acting as a flood refuge, WUA decreased as a result of increasing water depth. Only in a modified backwater did WUA increase with discharge. Owing to the morphology of the backwater, there was still a WUA minimum at intermediate discharges. 4. The output of the model indicates the variation in habitat available for small fish in both temporal and spatial dimensions, and reinforces the requirement for spatial heterogeneity in riverine habitats for the preservation of fish stocks. © 1997 John Wiley & Sons, Ltd.

Assessing variation in suitability curves and electivity profiles in temporal studies of fish habitat use

“…Thus, Heggenes and Saltveit (1990) attributed variation in habitat use of Atlantic salmon (Salmo salar) and brown trout (S. trutta) to different habitat availabilities and to varying discharge and temperature, respectively, and several authors have since reported between-site (e.g. Bozek and Rahel, 1992;Garner, 1997b) as well as diel differences in suitability curves (Harris et al, 1992;Roussel et al, 1999). Finally, the shortcomings of pooling may be exacerbated whenever changes in stream flows contribute to HSC variation (Shirvell, 1990;Heggenes et al, 1996).…”

Research on the Great Ouse: Overview and implications for management

“…Comparison of the habitat suitability curves with those based on expert opinion (Armitage and Ladle, 1991) revealed large differences, both in the shape of the curves and in the position of the optima. In general, Armitage and Ladle (1991) underestimated depth preferences and overestimated velocity suitability by comparison with the model of Garner and Mann (1996). At winter temperatures of 5±8 C, Garner and Mann (1996) estimated that optimum velocity would be`5 cm s À1 .…”

“…In general, Armitage and Ladle (1991) underestimated depth preferences and overestimated velocity suitability by comparison with the model of Garner and Mann (1996). At winter temperatures of 5±8 C, Garner and Mann (1996) estimated that optimum velocity would be`5 cm s À1 . Under moderate to high discharge conditions the extent of suitable habitat in the main channels and some side channels becomes considerably reduced (Pinder et al, 1991).…”

“…Larval and juvenile ®sh habitat Garner and Mann (1996) described a model of habitat suitability for 0 roach based on laboratory experiments and ®eld data from the Great Ouse. Young larval roach selected sites with shallower (median depth 1 m) and slower¯owing (`10 cm s À1 ) water in the presence of Nuphar lutea and algal cover, whereas juveniles were found in faster (optimum 10 cm s À1 ) and deeper (median 1.4 m) sites where Glyceria¯uitans and emergent plant cover were available.…”

“…Marinas and other boat-mooring facilities may also mitigate the impact of regulation by providing refuges during periods of high discharge (Copp, 1997). Garner and Mann (1996) observed an increase in the use of non-¯owing backwaters (marinas) in winter and Copp (1997) recorded higher densities of 0 ®sh in marinas than in regulated channels. However, because of the restricted width of the channels that connect marinas with the main river the numbers of ®sh that succeed in ®nding shelter during high discharge events is restricted (Copp, 1997).…”