T. C. Bjornn

Trout and Salmon Movements in Two Idaho Streams as Related to Temperature, Food, Stream Flow, Cover, and Population Density

Abstract Many juvenile salmon and trout migrated from the Lemhi River drainage each fall-winter-spring period. Seaward migration of anadromous trout and salmon normally occurred in the spring but pre-smolt anadromous and non-anadromous fishes also left the stream usually beginning in the fall. I compared data on temperature, food abundance, stream flow, cover and population density with movements and conducted field and laboratory tests to determine reasons for the two types of movements. Smolts of the anadromous species migrated for an obvious reason but none of the factors I examined appeared to “stimulate or release” their seaward migration. Movement frequently coincided with changes in water temperature and stream flow, but I could not establish a consistent causal relationship and concluded that photoperiod and perhaps growth must initiate the physiological and behavioral changes associated with seaward migration. Non-anadromous and pre-smolt anadromous species emigrated from the streams for differen...

Effects of Chronic Turbidity on Density and Growth of Steelheads and Coho Salmon

Abstract Chronic turbidity in streams during emergence and rearing of young anadromous salmonids could affect the numbers and quality of fish produced. We conducted laboratory tests to determine the effect of chronic turbidity on feeding of 30–65 mm long steelheads Salmo gairdneri and coho salmon Oncorhynchus kisutch in straight and oval channels. Fish subjected to continuous clay turbidities grew less well than those living in clear water, and more of them emigrated from channels during the experiments. Received February 28, 1983 Accepted December 4, 1983

Abundance, Growth, and Interactions of Juvenile Steelhead Relative to Time of Emergence

Abstract Growth, interactions, and final densities of juvenile steelhead, Oncorhynchus mykiss (formerly Salmo gairdneri) emerging early versus later were compared in laboratory stream channels. When the two groups of juveniles were held together 1–2 months, early emerging fish generally outnumbered late fish about 2 to 1. On any given date and at the end of the experiment, early fish were significantly longer and heavier than late fish. At the end of the test, late fish were more abundant in channels they occupied alone than in channels shared with early fish. Densities were higher when early and late fish were stocked together than when either was stocked alone because fish of the two groups occupied different parts of the habitat. Aggressive interactions (charges, attacks, and nips) observed were mainly between early fish rather than between early and late fish.

Use of an extensive radio receiver network to document Pacific lamprey (Lampetra tridentata) entrance efficiency at fishways in the Lower Columbia River, USA

We used an extensive network of more than 170 radio receiving stations to document fine-scale passage efficiency of adult anadromous Pacific lamprey at Bonneville and The Dalles Dams in the lower Columbia River in the northwestern U.S.A. Each spring from 1997 to 2000, we released 197–299 lamprey with surgically implanted radio transmitters. Unique transmitter codes and the date and time of reception at each antenna site were downloaded electronically, and initial processing was conducted to eliminate false positive signals. The resulting large Oracle database was analyzed using an ArcView-based coding protocol. Underwater antennas positioned outside the fishway entrances detected lamprey approaches, and antennas positioned immediately inside the entrances indicated successful entries. Entrance efficiency (the number of lamprey that successfully entered a fishway divided by the number that approached that fishway) was compared for different types of entrances (main entrances versus orifice entrances) and entrance locations (powerhouse versus spillway). Lamprey used orifice-type entrances less frequently than main entrances, and passage success was generally low (< 50%) at all entrances to fishways at Bonneville Dam (the lowest dam in the system). Lamprey activity at the entrances was highest at night, and entrance success was significantly higher at The Dalles Dam (the next dam upstream from Bonneville Dam) than at Bonneville Dam. In 1999 and 2000, construction modifications were made to Bonneville Dam spillway entrances, and water velocity at these entrances was reduced at night. Modifications to increase lamprey attachment at the entrances improved lamprey entrance efficiency, but entrance efficiency during reduced velocity tests was not significantly higher than during control conditions.

Changes in Solar Input, Water Temperature, Periphyton Accumulation, and Allochthonous Input and Storage after Canopy Removal along Two Small Salmon Streams in Southeast Alaska

Abstract Changes in solar radiation, water temperature, periphyton accumulation, and allochthonous inputs and storage were measured after we removed patches of deciduous, second-growth riparian vegetation bordering two small streams in southeast Alaska that produce coho salmon Oncorhynchus kisutch. Solar radiation and leaf litter input were measured at the water surface at random locations dispersed through six alternating closed- and open-canopy stream sections. Water temperature, periphyton, and stored organic samples were collected near the downstream end of each section. Solar radiation intensity was measured with digital daylight integrators and pyronometers, periphyton biomass and chlorophyll a were measured on red clay tile substrates, allochthonous input was measured with leaf litter baskets, and benthic organic matter was measured with a Hess sampler. Average intensity of solar radiation that reached the water surface of open-canopy sections was significantly higher than in closed-canopy sections...

Summer Habitat Use by Young Salmonids and Their Responses to Cover and Predators in a Small Southeast Alaska Stream

Abstract We observed young coho salmon Oncorhynchus kisutch, steelhead O. mykiss, and Dolly Varden Salvelinus malma in a second-order stream on Prince of Wales Island, Alaska, to assess differences between species in habitat use and response to cover and predators. Habitat use by subyearlings of the three species differed primarily in depth of water and position in the water column. Coho salmon selected the relatively deep areas of the small stream; steelhead were more evenly spread across the bottom, regardless of depth; and Dolly Varden were close to the bottom in water less than 20 cm deep. All three species selected lower positions in the water column in pools without cover than in pools with riparian or instream cover. We detected no shift in habitat use in response to fish predators.

Effects of Canopy Removal on Invertebrates and Diet of Juvenile Coho Salmon in a Small Stream in Southeast Alaska

Abstract We assessed changes in availability and consumption of invertebrates by juvenile coho salmon Oncorhynchus kisutch in a small stream in southeast Alaska where patches of dense second-growth riparian vegetation bordering the stream had been removed. Benthic invertebrate populations were assessed during summer 1988 and 1989 with a Hess sampler. Aerial invertebrates were sampled during summer 1989 with wire-mesh sticky traps hung just above the water surface and with floating clear-plastic pan traps. Invertebrate drift was assessed during summer 1989 with nets placed at the downstream end of closed- and open-canopy stream sections. Diets of age-0 and age-1 coho salmon were sampled by flushing stomach contents of fish collected from closed- and open-canopy stream sections. Abundance and biomass of benthic invertebrates were larger in open- than in closed-canopy stream sections and were primarily dipterans, ephemeropterans, and plecopterans. More insects were caught on sticky traps in open than in clos...

Habitat Use by Steelhead and Coho Salmon and Their Responses to Predators and Cover in Laboratory Streams

Abstract Subyearling coho salmon Oncorhynchus kisutch and steelhead O. mykiss were placed together and separately in laboratory stream channels to assess their habitat use, interactions, and response to cover and predators. We studied the fish in six replicated riffle-pool-riffle units in the laboratory channels during 12 trials of 7 d each. In all test situations, we allowed the fish to emigrate from the test units. More fish remained in the units of the laboratory streams when both species were together than when either species was alone. The presence of larger fish (potential predators) caused both species to change habitats, regardless of cover available, and many left the test units or were eaten. Coho salmon used mainly the pools, whether stocked alone or together with steelhead; steelhead used both the riffles and pools when alone but shifted slightly toward increased use of the riffles when both species were present.

Response of Juvenile Salmonids to Riparian and Instream Cover Modifications in Small Streams Flowing through Second-Growth Forests of Southeast Alaska

Abstract We manipulated the canopy of second-growth red alder Alnus rubra and instream cover to assess the effects on abundance of juvenile salmonids in small streams of Prince of Wales Island, southeast Alaska, in 1988 and 1989. Sections of red alder canopy were removed to compare responses of salmonids to open- and closed-canopy sections. At the start of the study, all potential instream cover was removed from the study pools. Alder brush bundles were then placed in half the pools to test the response of juvenile salmonids to the addition of instream cover. Abundance of age-0 coho salmon Oncorhynchus kisutch decreased in both open- and closed-canopy sections during both summers, but abundance decreased at a higher rate in closed-canopy sections. More age-0 Dolly Varden Salvelinus malma were found in open-canopy sections than in closed-canopy during both summers. Numbers of age-1 and older coho salmon and Dolly Varden were relatively constant during both summers, and there was no significant difference i...

Migration and Survival of Redfish Lake, Idaho, Sockeye Salmon, Oncorhynchus nerka

Abstract Most adult sockeye salmon returning to Redfish Lake had spent two years in the ocean. Survival from smolt to returning adult at the lake ranged from 0.14 to 1.83%. The sex-ratio was nearly even. Survival of sockeye in the lake from potential egg deposition to smolt migration was usually less than 6%. In at least one year, smolts originating from kokanee and/or residual sockeye may have comprised a large proportion of the migration. There was little relationship between egg deposition and smolts produced. Sockeye salmon smolts migrated from Redfish Lake primarily from 1800 to 2400 hr. There was no consistent relationship between seasonal timing of the migration, lake ice cover, temperatures or flow of the outlet stream. The role of photoperiod in timing of the migration and the parr-smolt transformation is unclear. Growth of juvenile sockeye in the lake was inversely related to population density and age at migration was dependent upon first year growth in the lake. More than half the fish of a ye...