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At least 703 records · Page 39Linked to original sources

USGS1994

Importance of spatial pattern in estimating predation on juvenile salmonids in the Columbia River

The impact of piscivores in aquatic systems is often estimated by assuming that predation rate and predator density can be characterized as means throughout large, homogeneous areas. Predation losses of juvenile Pacific salmonids Oncorhynchus spp. migrating through Columbia River reservoirs were previously estimated with the assumption that each reservoir consisted of one or two homogeneous areas. Data from the John Day Reservoir and throughout the river system showed that predation rate and predator density vary greatly between near-dam and midreservoir areas, suggesting that reservoirs in the Columbia River should be divided into at least three or four areas for estimating salmonid losses. For example, the estimated number of salmonids annually eaten by northern squawfish Ptychocheilus oregonensis in John Day Reservoir decreased from 2.9 million when all samples in the reservoir were pooled into one area, to 1.4 million when samples were partitioned among four areas. Variance about the estimates also decreased steadily with finer partitioning. Mortality of juvenile salmon from predation was substantial with any type of partitioning; however, spatial variation in predation rates and other density-dependent processes may be especially important in river models of migrating juvenile salmon that repeatedly apply predation rates in a series of reservoirs or river reaches.

Transactions of the American Fisheries Society↗

USGS1995

Pattern of shoreline spawning by sockeye salmon in a glacially turbid lake: Evidence for subpopulation differentiation

Alaskan sockeye salmon Oncorhynchus nerka typically spawn in lake tributaries during summer (early run) and along clear‐water lake shorelines and outlet rivers during fall (late run). Production at the glacially turbid Tustumena Lake and its outlet, the Kasilof River (south‐central Alaska), was thought to be limited to a single run of sockeye salmon that spawned in the lakeˈs clear‐water tributaries. However. up to 40% of the returning sockeye salmon enumerated by sonar as they entered the lake could not be accounted for during lake tributary surveys, which suggested either substantial counting errors or that a large number of fish spawned in the lake itself. Lake shoreline spawning had not been documented in a glacially turbid system. We determined the distribution and pattern of sockeye salmon spawning in the Tustumena Lake system from 1989 to 1991 based on fish collected and radiotagged in the Kasilof River. Spawning areas and times were determined for 324 of 413 sockeye salmon tracked upstream into the lake after release. Of these, 224 fish spawned in tributaries by mid‐August and 100 spawned along shoreline areas of the lake during late August. In an additional effort, a distinct late run was discovered that spawned in the Kasilof River at the end of September. Between tributary and shoreline spawners, run and spawning time distributions were significantly different. The number of shoreline spawners was relatively stable and independent of annual escapement levels during the study, which suggests that the shoreline spawning component is distinct and not surplus production from an undifferentiated run. Since Tustumena Lake has been fully deglaciated for only about 2,000 years and is still significantly influenced by glacier meltwater, this diversification of spawning populations is probably a relatively recent and ongoing event.

Alaska↗

USGS1995

Age-at-maturity estimates for Atlantic coast female striped bass

This study was undertaken to estimate the percentage of mature female striped bass Morone saxatilis present in each age-class during annual coastal feeding migration. Migratory striped bass (N = 302) were sampled in coastal Rhode Island waters during spring (May-June) and fall (September-November) from 1985 to 1987. Stocks were identified by analysis of morphometric characters and isoelectric focusing of eye-lens proteins. Histological sections of ovarian tissue were used to categorize maturity state. Fish were considered mature if a class of oocytes measuring at least 150 μm and containing cytoplasmic inclusions was found in the ovarian sections. All females whose age at next potential spawning was 7 and older were mature. Our empirical observations indicated that 12% of fish in age-class 4, 34% of fish in age-class 5, and 77% of fish in age-class 6 were mature. The estimate of the proportion of mature fish in age-class 5 differs significantly from that of Merriman (1941), who also examined coastal migrants. No significant differences were found in maturity estimates of fish from stocks of different origin.

Transactions of the American Fisheries Society↗

USGS1995

Evidence for lack of homing by sea lampreys

Recently metamorphosed sea lampreys Petromyzon marinus were captured in the Devil River, a tributary to Lake Huron, during summer and autumn 1990. They were tagged with a coded wire tag and returned to the river to continue their migration to Lake Huron to begin the parasitic (juvenile) phase of their life. During the spawning run in spring 1992 when the tagged animals were expected to mature and return to spawn, sea lampreys were trapped in nine tributaries to Lake Huron, including the Devil River; 47,946 animals were examined for coded wire tags, and 41 tagged animals were recovered. None of the 45 mature sea lampreys captured in the Devil River in 1992 were tagged, a proportion (0%) significantly lower than the proportion of the recently metamorphosed sea lampreys tagged in 1990. The distribution of tag recoveries among streams lakewide, however, was proportional to catch. Tagged sea lampreys did not appear to home, but instead seemed to select spawning streams through innate attraction to other sensory cues.

Transactions of the American Fisheries Society↗

USGS1995

Some tests of the "migration hypothesis" for anadromous Dolly Varden (southern form)

Some aspects of a previously described migratory paradigm for the southern form of anadromous Dolly Varden Salvelinus malma were investigated with seven 3‐year mark–recapture experiments on fish that used lakes in eight watersheds as their winter residence. Weirs on Kodiak Island, around Prince William Sound, and near Juneau, Alaska, were used to capture Dolly Varden as they emigrated to the sea each spring. Dolly Varden (≥200 mm fork length) were individually marked during the first year of each experiment (1989 or 1990), and log‐linear models of their capture histories were used to estimate probabilities of capture during the second year (1990 or 1991). Our observations on timing of spring emigration and dispersal of Dolly Varden at sea confirm observations from earlier studies. Our results support the paradigm that Dolly Varden home to the same lacustrine watershed when overwintering in fresh water, as more than 98% of the recaptured fish did so. Our results contradicted the paradigm that Dolly Varden return to lakes each fall, for across study populations, 14–58% failed to return. The most probable explanation for this anomalous behavior is that some Dolly Varden spend the winter at sea. Differences in maturity, size, and growth of Dolly Varden and timing of their entrance into salt water during spring emigration were excluded as causes of this anomalous behavior.

Transactions of the American Fisheries Society↗

USGS1995

Index of predation on juvenile salmonids by northern squawfish in the lower and middle Columbia River and in the lower Snake River

We developed a predation index to describe the relative magnitude of predation on juvenile salmonids by northern squawfish Ptychocheilus oregonensis throughout the lower and middle Columbia River and lower Snake River. The predation index was the product of an abundance index and a consumption index. We evaluated various catch indices and found that catch per unit effort best reflected differences among northern squawfish abundances. Northern squawfish abundance was higher in the lower Columbia River than in the middle Columbia or lower Snake rivers and was highest in Bonneville Reservoir and the Columbia River downstream from Bonneville Dam. The consumption index was based on the concept of meal turnover time for a sample of northern squawfish. Variables needed to calculate the consumption index (CI) were water temperature ( T ), mean weight of the northern squawfish ( W ), mean number of salmonids in each gut ( S ), and mean weight of the gut contents (GW): CI = 0.0209· T 1.60 · W 0.27 ·( S ·GW −0.61 ). Generally, northern squawfish consumption of juvenile salmonids was highest in tailraces downstream from dams and higher in the Columbia River than in the Snake River. Predation on juvenile salmonids was much higher in the lower Columbia River than in the middle Columbia or lower Snake rivers and was usually higher in summer than in spring. Predation was highest in the Columbia River downstream from Bonneville Dam and in John Day Reservoir. The predation index identified areas where predator control efforts can be most effective. Angling for northern squawfish at dams should be concentrated in tailraces. Removal efforts concentrated in the lower Columbia River would have the greatest effect on predation.

Oregon, Washington↗

USGS1995

Diet and feeding periodicity of ruffe in the St. Louis River estuary, Lake Superior

Ruffe Gymnocephalus cernuus , a percid native to Europe and Asia, is established in the Lake Superior drainage and could have negative impacts on native fish through competition for forage and predation on fish eggs. We investigated the diet of ruffes in the 4,654-ha St. Louis River estuary in May–October 1989–1990 and the feeding periodicity of ruffes in two adjacent habitats during five 24-h periods in summers 1990–1991. Ruffes were primarily benthophagous. Age-0 ruffes fed mostly on cladocerans and copepods in early summer and midge larvae (Chironomidae) in late summer and fall. Adult ruffes less than 12 cm fed mostly on midges and other macrobenthos but also consumed large numbers of microcrustaceans. Adult ruffes 12 cm and larger fed mostly on midges, burrowing mayflies Hexagenia spp., and caddisflies (Trichoptera). Ruffes consumed few fish eggs. Adult ruffes in deeper waters and all age-0 ruffes fed throughout the day as indicated by weight patterns of stomach contents. However, adult ruffes generally moved to shallower waters at night to feed most heavily. Results of this study indicate that ruffes will probably compete with other benthic-feeding fishes such as yellow perch Perca flavescens and trout-perch Percopsis omiscomaycus .

Transactions of the American Fisheries Society↗

USGS1995

Growth and survival of newly parasitic sea lampreys at representative winter temperatures

Larval sea lampreys Petromyzon marinus begin to metamorphose into their parasitic phase in July and migrate to the Great Lakes either in autumn, when they immediately feed on fish, or in spring after overwintering in the stream substrate. Survival and growth of newly parasitic autumn migrants (mean weight, 4.18 g) differed significantly between temperature treatments when sea lampreys were held over winter and allowed to feed on longnose suckers Catostomus catostomus at either the maximum available temperature (&tilde;4°C) or normal surface temperature (minimum <1°C) in the Great Lakes during winter. Survival from December 1990 to June 1991 was 60% for the animals held in the warmer water but only 30% for the animals held in the colder water until 23 April. The average increase in weight was 8.23 g for the 35 survivors in the warmer water but only 5.15 g for the 17 survivors in the colder water. Average increases in weight from December to May for sea lampreys at both temperatures were 3.8 to 6.6 times greater than increases reported previously. A newly metamorphosed sea lamprey that migrates to the Great Lakes in autumn could be 2.5 to 3 times larger in June than one that overwinters in the stream substrate, where it cannot feed, and migrates in spring. Hence, autumn migrants may have an advantage in growth and survival over spring migrants, particularly if food supply is adequate in the warmest stratum of the lake during winter.

Transactions of the American Fisheries Society↗

USGS1995

Evidence of impaired reproduction by Western mosquitofish inhabiting seleniferous agricultural drainwater

Western mosquitofish Gambusia affinis from the San Luis Drain (SLD), a major conveyance system for seleniferous agricultural subsurface (tile) drainage water in the San Joaquin Valley, California, experienced lower reproductive success than did mosquitofish from a nearby reference area (Pond 26 at the Volta Wildlife Area, VOLTA) that had no history of receiving tile drainage. At birth, mean survival of SLD fry was 70% in 1984 and 77% in 1985, whereas mean survival of VOLTA fry was greater than 99% in 1984 and 97% in 1985. Measurements of total length (TL) of offspring born to SLD females in 1985 showed that stillborn fry (mean TL, 7.5 mm) were significantly shorter than live fry (mean TL, 9.4 mm). In addition, most stillborn fry were at earlier stages of development (contained prominent yolk sacs or occasionally resembled eyed embryos) than most live fry (yolk sacs were fully resorbed). In comparison, stillborn and live fry born to VOLTA females did not differ significantly in TL (mean for stillborn fry, 7.1 mm; mean for live fry, 7.5 mm), and nearly all fry had resorbed their yolk sacs. Mosquitofish from the SLD contained over 100 μg/g (whole‐body concentration in dry weight) of selenium, whereas those from VOLTA averaged 1.5 μg/g. Although experiments are still needed to establish cause and effect, the high incidence of abnormal births of mosquitofish from the SLD is seemingly a response to selenium toxicity.

California↗

USGS1995

Ebb and flow of encroachment by nonnative rainbow trout in a small stream in the southern Appalachian Mountains

Brook trout Salvelinus fontinalis is the native salmonid species of streams in the southern Appalachian Mountains. The present distribution of this species, once widespread from headwaters to lower reaches of large streams, is restricted to mostly headwater areas. Changes in the distribution of native brook trout in the presence ofˈ nonnative rainbow trout Oncorhynchus mykiss have been documented in Great Smoky Mountains National Park. When rainbow trout were first found in a tributary (Rock Creek) in the park in 1979, a study was begun to assess changes through time in distribution and abundance of rainbow trout in Rock Creek and to compare the brook trout and rainbow trout associations in Rock Creek with associations found in other park streams. Abundance of brook trout was low in the downstream sections of Rock Creek in 1979–1993. Brook trout abundance was highest in the steep‐gradient, pool‐dominated headwater section which was only 2 km from the confluence of Rock Creek and Cosby Creek. Rainbow trout were present in low densities in Rock Creek during the same period. Although rainbow trout were most abundant in the lower stream sections and never found in the headwater section, adult and age‐0 rainbow trout were found in the middle section in 1988. Rainbow trout were absent in the middle section in 1991, but one large adult rainbow trout was present in the section in 1992 and 1993. Floods, freshets, and periods of low stream discharge appeared to play an important role in the distribution and population structure of rainbow trout in Rock Creek. The lower portion of Rock Creek was poor trout habitat because the sections were dominated by cobble–rubble substrate and shallow riffle areas. Stream habitat appeared to be better suited for brook trout than for rainbow trout in the steep‐gradient upstream sections which were dominated by boulder‐cobble substrate and deep pools. The results of this study suggest that encroachment by rainbow trout can exhibit considerable ebb and flow in steep‐gradient tributaries in the park, and they suggest substantial evolutionary adaptation by brook trout to the hydrological conditions in the Rock Creek drainage.

North Carolina, Tennessee↗

USGS1995

A non-lethal measure of smolt status of juvenile steelhead based on body morphology

A nonlethal morphometric method to assess smolt status of juvenile steelhead Oncorhynchus mykiss was validated. Fish were collected from hatcheries before release and during their seaward migration in a large river system. Fifteen anatomical landmarks were digitized from photographs of each fish, resulting in 34 morphometric characters based on a truss network. Principal component and canonical discriminant function analyses were used to assess smolt status. A single canonical variate was significantly correlated with gill Na + ,K + ‐ATPase activity, a commonly used measure of smolt status. This nonlethal method may be a useful measure of smolt status when sacrificing fish is not desirable or possible; it requires little training to perform, but it does require a larger sample size than some other methods.

Transactions of the American Fisheries Society↗

USGS1995

Developmental instability in the Pacific Hake parasitized by the Myxosporean Kudoa spp.

A morphometric study of the otoliths of a population of Pacific hake Merluccius productus was conducted to detect developmental instability (DI) related to parasitism by Myxosporeans, Kudoa spp. We report a link between parasitism and DI, which we measured as fluctuating asymmetry by comparing the right–left differences in otolith shape, width, and weight in the same fish. Otolith shape provided the most sensitive measurement of DI asymmetry. Results suggest that Kudoa spp. could be a strong agent of selection in the Pacific hake.

Transactions of the American Fisheries Society↗

USGS1996

Size-dependent effects of continuous and intermittent feeding on starvation time and mass loss in starving yellow perch larvae and juveniles

Starvation rates of fish larvae living in patchy prey environments can have an important impact on cohort survival and recruitment. Despite this, little is known about how fluctuations in feeding experience influence starvation resistance and how this changes with ontogeny. Fish previously exposed to fluctuating food densities may not respond to long periods without food in the same way as fish previously exposed to a constant prey density. In a series of laboratory experiments with larvae and juveniles of yellow perch Perca flavescens , we tested the effects of continuous and intermittent feeding on times to starvation and on mass loss up to death from starvation for fish with initial total lengths of 10, 15, and 20 mm. Results indicated that proportional mass loss up to starvation was independent of fish mass, but that it did depend on feeding history. Fish that fed continuously before starvation all died after losing the same proportion of body mass (55%), but intermittent feeders died when they were slightly heavier (51–46% of body mass lost). Times to 50% mortality followed a different pattern; there was no significant difference in times to 50% mortality for fish that had fed continuously or intermittently for the same number of days before starvation. We conclude that short‐term fluctuations (≤4 d) in food availability do not appear to affect times to starvation but do influence mass loss during starvation in young yellow perch.

Transactions of the American Fisheries Society↗

USGS1996

Spawning of the shortnose sturgeon the Merrimack River, Massachusetts

We tracked 10 ultrasonically tagged shortnose sturgeons Acipenser brevirostrurn during spring in the Merrimack River to investigate spawning. Seven fish in 1989 and six fish in 1990 were tracked intensively to identify the timing and location of spawning and to characterize spawning habitat. In mid‐April 1989 and 1990, fish moved upstream to just below head of tide, concentrating in a 2‐km reach at river kilometers 30–32 (measured from the mouth) at Haverhill, Massachusetts. The estimated spawning time was a 5‐d period (26–30 April) in 1989 and an 8‐d period (22–29 April) in 1990. Spawning sites covered about 10.5 ha in 1989 and 13.5 ha in 1990. Fish spawned as river temperature increased from 9.6 to 14.0°C and river discharge decreased from 390 to 240 m 3 /s. Physical characteristics of spawning sites were boulder–rubble substrate, water depth of 1.8–5.5 m, and bottom water velocity of 0.3–0.7 m/s. We captured no ovulating females but verified successful spawning in 1990 by capturing two live embryos. Gill‐net captures and telemetry during spring showed that some males moved to the spawning area annually. The low abundance estimates of spawning fish (9 in 1989 and 16 in 1990) indicate that the shortnose sturgeon population in the Merrimack River is the smallest yet identified and is likely vulnerable to extirpation.

Massachusetts↗

USGS1996

Feeding response by northern squawfish to a hatchery release of juvenile salmonids in the Clearwater River, Idaho

We collected gut contents from northern squawfish Ptychocheilus oregonensis captured in the Clearwater River, Idaho, 0–6 km from its confluence with the Snake River, following the release of 1.1 million yearling chinook salmon Oncorhynchus tshawytscha from the Dworshak National Fish Hatchery. Before the hatchery release, northern squawfish gut contents (by weight) in the study area were 38% crayfish Pacifastacus spp., 26% insects, 19% nonsalmonid fish, and 16% wheat kernels Triticum spp. Juvenile salmonids constituted 54% of gut contents about 24 h after the hatchery release, 78% after 5 d, and 86% after 7 d. The mean number of salmonids per gut (1.2) after release was higher than typically seen in guts from northern squawfish collected in mid-reservoir areas away from hydroelectric dams on the Snake and Columbia rivers. Length-frequency distributions of juvenile salmonids eaten and those captured in a scoop trap 4 km upstream of the study area indicated that northern squawfish were selectively feeding on the smaller individuals. We attribute the high rates of predation in the study area to the artificially high density of juvenile salmonids resulting from the hatchery release and to the physical characteristics of the study area in which the river changed from free flowing to impounded. Our results suggest that northern squawfish can quickly exploit hatchery releases of juvenile salmonids away from release sites in the Columbia River basin.

Idaho↗

USGS1996

Comparison of three nonlinear models to describe long-term tag shedding by lake trout

We estimated long-term tag-shedding rates for lake trout Salvelinus namaycush using two existing models and a model we developed to account for the observed permanence of some tags. Because tag design changed over the course of the study, we examined tag-shedding rates for three types of numbered anchor tags (Floy tags FD-67, FD-67C, and FD-68BC) and an unprinted anchor tag (FD-67F). Lake trout from the Gull Island Shoal region, Lake Superior, were double-tagged, and subsequent recaptures were monitored in annual surveys conducted from 1974 to 1992. We modeled tag-shedding rates, using time at liberty and probabilities of tag shedding estimated from fish released in 1974 and 1978–1983 and later recaptured. Long-term shedding of numbered anchor tags in lake trout was best described by a nonlinear model with two parameters: an instantaneous tag-shedding rate and a constant representing the proportion of tags that were never shed. Although our estimates of annual shedding rates varied with tag type (0.300 for FD-67, 0.441 for FD-67C, and 0.656 for FD-68BC), differences were not significant. About 36% of tags remained permanently affixed to the fish. Of the numbered tags that were shed (about 64%), two mechanisms contributed to tag loss: disintegration and dislodgment. Tags from about 11% of recaptured fish had disintegrated, but most tags were dislodged. Unprinted tags were shed at a significant but low rate immediately after release, but the long-term, annual shedding rate of these tags was only 0.013. Compared with unprinted tags, numbered tags dislodged at higher annual rates; we hypothesized that this was due to the greater frictional drag associated with the larger cross-sectional area of numbered tags.

Transactions of the American Fisheries Society↗

USGS1996

First record predation on white sturgeon eggs by sympatric fishes

We report the occurrence of white sturgeon Acipenser transmontanus eggs in guts of four species of fish from the Columbia River. Three of the species—northern squawfish Ptychocheilus oregonensis , largescale sucker Catostomus macrocheilus , and prickly sentpin Cottus asper —are native to the river and one, common carp Cvprinus carpio , is exotic.

Oregon, Washington↗

USGS1996

Effects of implanted transmitters on adult bluegills at two temperatures

Laterally compressed panfishes are small and have limited intraperitoneal space; thus, they may suffer adversely from surgically implanted transmitters even if the transmitter meets the generally recommended ratio of transmitter weight to fish weight of 2%. We studied the effects of intraperitoneal transmitters (2.81 g) on survival, growth, healing, and health of bluegills Lepomis macrochirus (mean weight 133 g) held for 8 weeks at 6°C and 20°C. Radio‐tagged bluegills at 20°C had a mortality rate of 10% and tag loss rate of 15%. At 6°C, bluegills had no mortality or tag loss. Radio‐tagged and reference fish fed in both 20°C raceways; however, a few reference fish appeared dominant at feeding time. This dominance by a few reference fish was also indicated by a large weight gain for three reference fish in each 20°C raceway. At 6°C, neither reference fish nor radio‐tagged fish fed activity. Radio‐tagged fish held at 20°C exhibited pelvic fin erosion, erythema and necrosis at the antenna exit and at suture insertions, and lost or loose sutures, effects not observed in other test fishes. Examination of fish held at 20°C also showed enclosure of the transmitters in a fibrous capsule and adhesion of visceral organs. Epithelialization over the incision occurred in radio‐tagged bluegills at both temperatures, but there was little further healing at 6°C. At 20°C, tissue responses included chronic inflammation and dermal granulation. Radio‐tagged fish did not appear to be more susceptible than reference fish to bacterial infection. Mortality, adverse morphological effects, altered behavior, and limited healing in blue‐gills suggest that implanted transmitters impaired their health. Thus, movement and habitat use data collected by telemetry for this species and perhaps for other panfishes should be interpreted with caution.

Transactions of the American Fisheries Society↗