Availability of Microhabitats and Their Use by Brown Trout (Salmo Trutta) and Grayling (Thymallus Thymallus) in the River Vojmån, Sweden

Abstract

Microhabitat preferences of brown trout and grayling were studied in the upper portion of the River Vojmån, northern Sweden in 1990–1993. Microhabitat preference was quantified for open water fish during the day and at dusk and for fish residing under stones during the day. In total, measurements were made for 665 trout and 230 grayling, ranging in size from 2.5 to 50 cm total length. Relationships were found between most microhabitat variables and fish length. Consequently, fish were divided into three size groups for each species. For diurnally active open water fish, small brown trout and grayling preferred slower moving water with finer substrates than large brown trout and grayling. In addition, small trout preferred shallower water than large trout, whereas grayling showed no size segregation with respect to depth. Interspecific microhabitat segregation for diurnally active open water fish was pronounced, with distance to instream cover, distance to shore and depth the major segregating factors. Brown trout that occurred under stones were generally ≤12 cm in length and preferred faster mean currents than similar sized trout in the open water. Trout had stronger preferences for bedrock and slightly faster mean current velocities at dusk than during the day. Grayling did not occur under stones and relatively few individuals were observed at dusk. These results indicate that microhabitat preferences vary with body size, species and time of day. Consequently, when developing water regulation strategies it is important to maintain a broad diversity of microhabitats at different flows, at least until we know more about the mechanisms responsible for this variation in microhabitat preference.

Daytime habitat selection for juvenile parr brown trout (Salmo trutta) in small lowland streams

“…Previous studies have illustrated the key importance of water depth in determining juvenile brown trout habitat use (Bohlin, 1977;Bagliniere and Champigneulle, 1982;Egglishaw and Shackley, 1982;Kennedy and Strange, 1982;Heggenes, 1988c, d), including Danish small lowland streams (Hermansen and Krog, 1984). All of the above studies and others have shown that there is a positive correlation between fish size and water depth, and that the larger the trout, the deeper water it prefers (Greenberg et al, 1996;Heggenes et al, 1999;Maki-Petays et al, 1997). This preference for deep water could be explained by the possibility that parr may primarily be feeding nocturnally during summer (Alvarez and Nicieza 2003;Orpwood et al, 2006;Conallin, 2009;Conallin et al, 2012), and seeking refuge during the day to avoid predation (Aarestrup et al, 2003;Gwiazda and Amirowicz, 2006).…”

River Hydrology, Flow Alteration, and Environmental Flow

“…The diversity of instream and floodplain habitat types has stimulated the evolution of species that use the habitat mosaic created by hydrologic variability. For many riverine species, completion of the life cycle requires an array of different habitat types, whose availability over time is regulated by the flow regime (Greenberg et al 1996).…”

Aquatic Habitat Modeling in Running Waters

“…This technique is most commonly used to survey juvenile salmonid populations but can also be used to assess other species groups. Snorkel survey programs have been designed and implemented so as to standardize procedures for underwater techniques to survey fish species in streams (Thurow 1994;Greenberg et al 1996;O'Neal 2007).…”

“…7.3). Fish were observed via snorkeling in the fully discharged sections (Thurow 1994;Greenberg et al 1996), and the abiotic characteristic (water depth, flow velocity, substrate, and cover) of used and available habitat depended on species and life stage were measured.…”