Jason L. White

Reduced streamflow lowers dry-season growth of rainbow trout in a small stream

Abstract A wide variety of resource management activities can affect surface discharge in small streams. Often, the effects of variation in streamflow on fish survival and growth can be difficult to estimate because of possible confounding with the effects of other variables, such as water temperature and fish density. We measured the effect of streamflow on survival and growth of rainbow trout Oncorhynchus mykiss in a small stream in northwestern California by manipulating the flow entering four of eight enclosed stream sections (9.0–15.3 m long) containing one pool and 2.5–4.0 m of upstream riffle habitat. In the four manipulated experimental units, we reduced inflow by 75–80% over a 6-week period in summer 2003. Flow diversion substantially decreased water velocity in riffle–pool transition areas but did not strongly affect habitat volume or water temperature. Fish in control units grew about 8.5 times as much as those in units with reduced streamflow; however, discharge manipulation did not affect sur...

AN EMERGENT MULTIPLE PREDATOR EFFECT MAY ENHANCE BIOTIC RESISTANCE IN A STREAM FISH ASSEMBLAGE

While two cyprinid fishes introduced from nearby drainages have become widespread and abundant in the Eel River of northwestern California, a third nonindigenous cyprinid has remained largely confined to ≤25 km of one major tributary (the Van Duzen River) for at least 15 years. The downstream limit of this species, speckled dace, does not appear to correspond with any thresholds or steep gradients in abiotic conditions, but it lies near the upstream limits of three other fishes: coastrange sculpin, prickly sculpin, and nonindigenous Sacramento pikeminnow. We conducted a laboratory stream experiment to explore the potential for emergent multiple predator effects to influence biotic resistance in this situation. Sculpins in combination with Sacramento pikeminnow caused greater mortality of speckled dace than predicted based on their separate effects. In contrast to speckled dace, 99% of sculpin survived trials with Sacramento pikeminnow, in part because sculpin usually occupied benthic cover units while Sacramento pikeminnow occupied the water column. A 10-fold difference in benthic cover availability did not detectably influence biotic interactions in the experiment. The distribution of speckled dace in the Eel River drainage may be limited by two predator taxa with very different patterns of habitat use and a shortage of alternative habitats.

Basin-scale patterns in the drift of embryonic and larval fishes and lamprey ammocoetes in two coastal rivers

We studied the distribution and abundance of drifting embryonic and larval fishes and lampreys in the Smith and Van Duzen rivers of northern California, U.S.A. We collected seven fish species in four families and at least one lamprey species in the drift. All taxa drifted almost exclusively at night. Sculpins, Cottus aleuticus and C. asper, outnumbered all other taxa, comprising 63% of the catch in the Van Duzen River and 90% of the catch in the Smith River. We estimated that sculpin drift reached 3×107 individuals h−1 during the relatively high flow period from late winter through early summer. Most sculpin in these two rivers appeared to drift to the estuaries; we estimated 2.5×109 sculpin embryos and larvae reached the Smith River estuary in 1995. In contrast to the sculpins, the patterns in the drift of other taxa suggest limited transport to the estuaries. Suckers, Catostomus occidentalis in the Van Duzen River, C. rimiculus in the Smith River, threespine stickleback, Gasterosteus aculeatus, and lamprey, Lampetra tridentata and possibly L. richardsoni, drifted at much lower rates and later in the year than sculpins. In the Van Duzen River, drift appeared to serve as a dispersal mechanism for only one of three introduced cyprinids. California roach, Lavinia symmetricus, drifted at low rates throughout the summer while we captured only seven Sacramento pikeminnow, Ptychocheilus grandis, and no speckled dace, Rhynichthys osculus. The information gathered on the drift of early life history phases is germane to both the conservation of native fishes and management of non-indigenous species in coastal rivers.

Habitat Relationships and Larval Drift of Native and Nonindigenous Fishes in Neighboring Tributaries of a Coastal California River

Abstract Motivated by a particular interest in the distribution of the nonindigenous, piscivorous Sacramento pikeminnow Ptychocheilus grandis, we examined fish-habitat relationships in small tributaries (draining 20-200 km2) in the Eel River drainage of northwestern California. We sampled juvenile and adult fish in 15 tributaries in both the summer and fall of 1995 and attempted to relate the densities of the most abundant species to physical variables. To determine which species used small tributaries for spawning, we also collected drifting larval fish during the spring of 1996 and 1997. Water temperature, as measured by maximum weekly average temperature, dominated the relationships between physical variables and the densities of age-0 Sacramento pikeminnow, age-0 steelhead Oncorhynchus mykiss, California roach Hesperoleucus symmetricus (also known as Lavinia symmetricus), and Sacramento sucker Catostomus occidentalis. Of these groups, only age-0 steelhead were most abundant in cool tributaries. In con...

Winter Feeding Success of Stream Trout under Different Streamflow and Turbidity Conditions

Abstract To investigate the relationship between turbidity and trout feeding success in natural systems, we sampled the stomach contents of resident rainbow trout Oncorhynchus mykiss and coastal cutthroat trout O. clarkii clarkii under different streamflow and turbidity conditions during winter in two northwestern California streams (total sample size = 161). Feeding success generally did not differ sharply for fish collected under low versus high streamflow and turbidity conditions. Bioenergetics modeling suggested that feeding success on average did not reach maintenance levels for seven of eight sets of samples, but extensive feeding on oligochaetes during one period of elevated streamflow resulted in positive energy balances. Occasional peaks in food intake could greatly influence the energy budgets and growth of trout in mild-winter systems. Under some natural conditions, trout appear able to achieve relatively high feeding success when turbidity limits visibility.

Habitat separation of prickly sculpin, Cottus asper, and coastrange sculpin, Cottus aleuticus, in the mainstem Smith River, northwestern California

Sympatric coastrange sculpin, Cottus aleuticus, and prickly sculpin, C. asper, occupied distinct habitats in the mainstem Smith River, northwestern California. For example, 90% of coastrange sculpin (n = 294) used habitat with water velocity > 5 cm s, whereas 89% of prickly sculpin (n = 981) used habitat with water velocity ≤ 5 cm s. Sixty-five percent of coastrange sculpin were found at depths 7 m. The strong spatial separation of coastrange and prickly sculpin in the mainstem Smith River contrasts with the overlap in their use of habitat in the nearby Eel River. Differences between the rivers in habitat availability, intensity of piscivory, and density of sculpins may contribute to this contrast.

The Effect of Deposited Fine Sediment on Summer Survival and Growth of Rainbow Trout in Riffles of a Small Stream

Abstract Elevated fine-sediment inputs to streams can alter a variety of conditions and processes, including the amount of fine sediment stored in riffles. We sought to measure the influence of deposited fine sediment on the survival and growth of juvenile rainbow trout Oncorhynchus mykiss (106–130 mm fork length) using a field experiment that included 18 enclosures in riffles of a small northwestern California stream. The experiment included six replicates of three levels of deposited fine sediment (low, background, and high) that embedded riffle cobbles at 0, 50, and 100%, respectively. Only 1 of 12 fish survived in high-sediment enclosures, while survival of fish in low- and background-sediment treatments equaled or exceeded 50%. Low- and background-sediment treatments could be distinguished from each other by a difference in fish growth: fish in the low-sediment treatment gained mass, on average, while all surviving fish in the background-sediment treatment lost mass. In addition to providing relative...

Use of Benthic Prey by Salmonids under Turbid Conditions in a Laboratory Stream

Abstract The negative effect of turbidity on the reactive distance of salmonids has been well established. However, determining the consequences of this relationship for overall feeding success remains problematic, as successful foraging by salmonids across a broad range in turbidity has been observed under a variety of conditions. Previous laboratory and field observations suggest that benthic feeding by salmonids in flowing water affects the turbidity dependence of foraging success. Two experiments were conducted in a laboratory stream to quantify benthic feeding success of salmonids across turbidity treatments ranging from 0 to 400 nephelometric turbidity units (NTU). In one experiment, cutthroat trout Oncorhynchus clarkii and coho salmon O. kisutch were offered the same nonliving prey in the drift and on the stream bottom; in the second experiment, cutthroat trout were offered only live oligochaetes moving along the stream bottom. In the first experiment, benthic feeding success of both cutthroat trou...

Response of Steelhead/Rainbow Trout (Oncorhynchus mykiss) Populations to Debris Flows

Abstract To better understand the effects of debris flows on salmonid populations, we studied juvenile steelhead/rainbow trout (Oncorhynchus mykiss) populations in six streams in the Klamath Mountains of northern California: three affected by debris flows on 01 January 1997 and three that experienced elevated streamflows but no debris flows. We surveyed habitat and fish in study reaches on all six streams in September for three years following the disturbance. Pool depths, substrate size and substrate embededdness varied among streams but with no clear patterns to distinguish debris-flow from no-debris-flow streams. However, the debris-flow streams had significantly less canopy cover and significantly more woody debris. Debris-flow streams did not differ from no-debris-flow streams in biomass and numeric densities of both young-of-year and age 1 and older (age 1 +) O. mykiss. In debris-flow streams in the first year following the debris flows (1997), we observed low numbers of age 1 + O. mykiss and variable year-class strength of young-of-year fish. In 1997, the young-of-year cohort in one debris-flow stream exhibited exceptional growth. In all three debris-flow streams, age 1 + biomass increased each year through 1999 when total O. mykiss biomass in the debris-flow streams exceeded that in the no-debris-flow streams. Surprisingly, we collected larval coastal giant salamander (Dicamptodon tenebrosus) in all streams in all years. We suspect the recovery of juvenile O. mykiss following the debris flows may have been hastened by increased productivity stimulated by clearing of dense, alder-dominated riparian corridors while salamanders likely recolonized from nearby unaffected tributaries.

Use of Cover for Concealment Behavior by Rainbow Trout: Influences of Cover Structure and Area

AbstractConcealment behavior by stream salmonids can benefit individuals and populations, but the availability of concealment habitat may be limited in many streams. Quantification of concealment habitat is likely to be a valuable process in the management of stream salmonids; it is a necessary step in the application of spatially explicit, individual-based models that incorporate concealment behavior. We conducted a series of laboratory experiments with Rainbow Trout Oncorhynchus mykiss to aid in the identification and quantification of concealment habitat. Overall, individual Rainbow Trout about 12 cm FL readily used low-ceiling spaces with one, two, or four openings for concealment. Structures analogous to weakly undercut banks were used less. Mean use of different cover types was less variable in an experiment in which groups of three fish were tested. Individuals in groups rarely shared cover spaces, even though in another experiment individual fish readily occupied spaces less than 25% of the area o...