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We conducted laboratory trials to test the vulnerability of young white sturgeon, Acipenser transmontanus, to predation when an alternative prey was available. In trials with two species of predators, we observed two feeding patterns. When equal numbers of white sturgeon and goldfish, Carassius auratus, were available, prickly sculpins, Cottus asper, ingested more white sturgeon. Conversely, northern pikeminnow, Ptychocheilus oregonensis, ate more juvenile coho salmon, Oncorhynchus kisutch, than white sturgeon in three out of four sets of trials, but ate more white sturgeon in one set of trials. White sturgeon size and the availability of cover did not affect the proportions of prey species ingested. Our results indicate that predation may be affecting survival of white sturgeon larvae and juveniles in the wild and could be one factor limiting recruitment of young-of-the-year white sturgeon in some locations. [ABSTRACT FROM AUTHOR]

We described skeletal deformities in Willamette River fishes from larval and juvenile specimens collected in 2002 and 2003. Deformities were found in most taxa examined but were more frequent in native broadcast spawners, especially minnows and suckers, than in native or exotic nest builders. Caudal deformities were uniformly distributed throughout the river, but precaudal deformities were more localized near the towns of Newberg and Salem (Wheatland Ferry). In northern pikeminnow,Ptychocheilus oregonensis, deformities were dependent on relative hatch date, with early season fish having about three times the deformity load as late season fish. In a subsample of northern pikeminnow and chiselmouth,Acrocheilus alutaceus, number of deformities was directly related to number of trematode metacercariae and precaudal deformities were twice as likely as caudal deformities to be associated with metacercariae. Based on a logistic regression, the probability of a precaudal deformity was dependent on number of metacercariae and geographic area with the area effect disappearing as the number of cysts increased. A separate analysis showed that some types of deformities were unlikely to be associated with metacercariae. However, even in cases where metacercariae were unlikely to be associated with deformities, metacercariae were usually present elsewhere in the fish and an indirect effect could not be dismissed. The taxonomic, spatial and temporal patterns of skeletal deformities in Willamette River fishes may be due to differences in intermediate host (snail or fish) resistance or susceptibility to parasites, to differences in life history ecology, or to anthropogenic effects that are manifest in increased precaudal deformities near Newberg and Wheatland Ferry or decreased rates elsewhere. [ABSTRACT FROM AUTHOR]

We investigated growth and mortality of age-0 northern squawfish during early rearing in shallow shoreline habitats. Larvae and juveniles (n = 22914) were collected by weekly seining at three sample sites in the upper John Day Reservoir, Columbia River, during June through early September 1994-1996. Using a length-based ageing method, it was estimated that the exponential growth rate (C) for a common growth stanza (10-28 mm standard length SL) was significantly higher in 1994 (G = 0.047) than in 1996 (G = 0.037). Growth rate in 1995 could not be estimated, but was probably intermediate between 1994 and 1996 based on mean standard lengths of fish collected at the end of each sampling season (46.3, 40.0, and 32.0 mm SL in 1994, 1995, and 1996, respectively). For many fish species, variations in early growth can influence survival through size-selective mortality processes. Consistent with this possibility, our estimates of instantaneous mortality rates (Z) demonstrated that larvae and juveniles had significantly higher mortality in 1996 than in 1994 (Z = 0.103 in 1994, versus Z = 0.138 in 1996). Enhanced growth and lower mortality in 1994 were associated with a number of interrelated environmental conditions - comparatively low flows and turbidities, abundant instream vegetative cover, and high near-shore water temperatures. [ABSTRACT FROM AUTHOR]

Diel and distributional abundance patterns of free embryos and larvae of fishes in the lower Columbia River Basin were investigated. Ichthyoplankton samples were collected in 1993 during day and night in the main-channel and a backwater of the lower Columbia River, and in a tributary, the Deschutes River. Fish embryos and larvae collected in the main-channel Columbia River were primarily (85.6%) of native taxa (peamouth Mylocheilus caurinus, northern squawfish Ptychocheilus oregonensis, suckers Catostomus spp., and sculpins Cottus spp.), with two introduced species (American shad Alosa sapidissima and common carp Cyprinus carpio) comprising a smaller percentage of the catch (13.3%). Similarly, in the Deschutes River native taxa [lampreys (Petromyzontidae), minnows (Cyprinidae), and suckers Catostomus spp.] dominated collections (99.5% of the catch). In contrast, 83.5% of embryos and larvae in the Columbia River backwater were of introduced taxa [American shad, common carp, and sunfishes (Centrarchidae)]. In all locations, all dominant taxa except sculpins were collected in significantly greater proportions at night. Taxon-specific differences in proportions of embryos and larvae collected at night can in some instances be related to life history styles. In the main-channel Columbia River, northern squawfish and peamouth were strongly nocturnal and high proportions still had yolksacs, suggesting that they had recently hatched and were drifting downriver to rearing areas. In contrast, sculpin abundances were similar during day and night, and sculpins mostly had depleted yolksacs, indicating sculpins were feeding and rearing in offshore limnetic habitats. Taxon-specific diel abundance patterns and their causes must be considered when designing effective sampling programs for fish embryos and larvae. [ABSTRACT FROM AUTHOR]