7843 - Laserfiche WebLink

Home Browse Search

18 BIOLOGICAL REpORT 29 sediment deposition on the redd, and with the right combination of depth and bed form to ensure move- ment of water through the redd (Hooper 1973). Locations for redd construction are apparently se- lected because they provide the best conditions for incubation and hatching success. Rates of intra- gravel flow, water exchange between stream and gravel, and dissolved oxygen concentrations are important determinants of hatching success in sal- monids. The exchange of water (measured as ap- parent or interstitial velocity) is directly and indi- rectly related to hydraulic conditions that enhance percolation through the redds (Coble 1961; Silver et al. 1963). Embryonic survival of steelhead was found to be significantly correlated with apparent velocity and intragravel dissolved oxygen concen- trations (Coble 1961). Gangmark and Bakkala (1958) and Wickett (1954) likewise related salmon egg survival to dissolved oxygen content and intra- gravel velocity. Coble (1961) learned that the ve- locity of subsurface flow was mostly a function of hydraulic head and permeability. Hydraulic head is a function of the current's depth and bed form; the head creates a differential water pressure across and through the spawning bed. Permeabil- ity is related primarily to bed particle size and the amount offine sediment occupying the interstitial spaces among the larger materials. Velocity and depth are important determinants of both bed par- ticle size and the embeddedness of fine materials, thus influencing permeability. Although the relations between microhabitat and spawning success are well documented in sal- monids, many species of minnows spawn in micro- habitats similar to those used by salmonids. These include chubs (Leonard et al. 1986; Lobb and Orth 1988), fallfish (Hubbs and Cooper 1936; Carbine 1939), and squawfish (Tyus 1990). Other species, such as stonerollers, daces, darters, and shiners, are known to spawn on the nests constructed by hornyhead and bigmouth chubs (Lachner 1952; Lobb and Orth 1988). This phenomenon led Lach- ner (1952) to suggest that the use of chub nests by other cyprinids for breeding purposes may be im- portant in the maintenance of a large forage base for piscivorous species. Spawning locations selected by centrarchids bear little resemblance to those chosen by sal- monids but are also selected to maximize reproduc- tive success. Whereas many species choose spawn- ing locations with appreciable water movement through or over the substrate material, centrar- chids characteristically select areas near some , form of instream cover where the velocity is zero or near zero (Newcomb 1992; Lukas 1993). Water movement over the nest greater than about 0.15 foot per second is often a significant cause of repro- ductive failure in smallmouth bass in lakes (Goff 1986) and in streams (Winemiller and Taylor 1982; Reynolds and O'Bara 1991). Lukas (1993) con- cluded that the primary cause of reproductive fail- ure for smallmouth bass in the North Anna River (Virginia) was high flow. Some nests were de- stroyed by siltation during flood events, but more typically, when the velocities over the nest site increased, the guardian male abandoned the nest, or the eggs and larvae were washed away. Similar spawning behavior has been observed in other sunfishes. Rock bass and redbreast sunfish use spawning habitats that are similar to those used by smallmouth bass (Monahan 1991; Lukas 1993). Reproductive failure in redbreast sunfish was also linked to high water velocities over nests (Lukas 1993) by mechanisms similar to those found for smallmouth bass. Energetics Riverine environments are distinguished from other types of aquatic habitat by the presence of a current. Velocity is arguably the most significant abiotic factor affecting the energetics of stream communities, whether at the level of algal commu- nities, aquatic invertebrates, or fish (Sprules 1947; Whitford and Schumacher 1964; Bovee 1975). Ifan organism is not morphologically adapted for living in currents (such as through streamlining, buoy- ancy control, attachment mechanisms, or other adaptation), it will adopt a behavior of seeking low velocity areas to reduce individual energy de- mands (Hubbs 1941). Many species of fish avoid velocity by occupying pools and locations in the water column near the streambed. Others make heavy use of instream cover or burrow into the substrate material to avoid energetic expenditure. McCrimmon (1954) observed that habitat require- ments offish change as they grow, with a general movement into deeper, faster water. For drift-feeding fish, a resting location of low velocity in proximity to an area of higher velocity is advantageous because proportionately more food will be delivered to the resting location (Fausch and White 1981). Kalleberg (1958) found that territories were smaller in rimes and rubble than in pools, leading to speculation that fish require less space in high velocity water because the amount of food passing a given point in the