摘要:

We studied the existing distribution of native Lahontan cutthroat troutOncorhynchus clarkihenshawi and exotic brook troutSalvelinus fontinaliswith respect to geologic and geomorphic land-classes in the upper North Fork Humboldt River drainage, Nevada. We evaluated habitat conditions in study sites to determine which measured components of habitat structure provided the best discriminators among study stream reaches in the different land-classes and among trout-supporting and unpopulated study reaches. At a finer level of resolution, we used the habitat attributes with the most discriminatory power to plot the distributions of study areas by land-class and by presence or absence of trout along coordinate axes reflecting environmental gradients defined by these attributes. Elevation, substrate embeddedness, and streamflow were the variables with the most discriminatory power among land-classes defined by parent geologic material (geologic district), but gravel abundance in the substrate was more useful than streamflow in further discriminating among land-classes at the lower-level classification defined by geomorphic character (landtype association). Plots ofstudy areas along environmental gradients defined by these variables visibly separated study areas by land-class. Trout distributions at specific sites were clearly related to geologic district and, to a lesser extent, to landtype association. Trout were almost exclusively restricted to sites in the sedimentary mountains defining the western boundary of the drainage, and occurred elsewhere only in study areas that were upstream from the fine-textured valley floor. Of the variables measured, embeddedness appeared to be the most likely cause of the segregation of trout by geologic district. Although unmeasured variables (e.g., temperature, winter conditions, and turbidity) cannot be eliminated as potential limiting factors, peripheral evidence suggests that they alone probably are not determinants of trout distribution in the region. Trout were common in the sedimentary geologic district, but did not occur in all study sites. Important discriminating attributes in this region were stream width, abundance of large substrate (rubble and boulder), and streamflow; trout were principally associated with sites characterized by wider, well-watered stream reaches containing high percentages of large stream-bottom particles. Study sites meeting these criteria were concentrated in high mountain areas influenced by Pleistocene glaciation, but were also present in the fluvial canyons. All sites containing brook trout were in drainages that had been glaciated. These sites would normally be considered “better” trout habitat; native cutthroat trout occupied the more degraded sites.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1992)121<0405:TDAHIR>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The structure of fish assemblages in five reaches of a high desert stream in north-central Oregon was determined by snorkeling before and after a summer flash flood and two spring floods. One reach in each of two other streams that were unaffected by the first flood was used as a reference system. Stream reaches varied in habitat complexity as measured by hydraulic retention. Following the floods, hydraulically complex stream reaches lost proportionately fewer fish, had generally higher fish diversities, and had higher fish assemblage similarity than hydraulically simple stream reaches. Fish assemblages were resilient, and certain species such as speckled daceRhinichthys osculuswere exceptionally good at recolonizing disturbed habitats. Successful recruitment of different fish species depended, in part, on flood timing. Young of the year of species that spawn in early spring (e.g., rainbow troutOncorhynchus mykiss) were more negatively affected by early spring floods than summer floods. Species that spawn later in the season (e.g., cyprinids and catostomids) were more negatively affected by summer flooding. Higher fish diversities in hydraulically complex reaches (lower disturbance intensity) after floods support predictions of the intermediate-disturbance hypothesis and suggest that fish assemblage resistance may be related to overall habitat complexity in these small streams.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1992)121<0427:IOHCOR>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

We used artificial stream channels to conduct feeding trials with wild rainbow troutOncorhynchus mykissat three levels of suspended sediment. To examine the effects of turbidity on reactive distance and pursuit speed, we fed rainbow trout (87–185 mm standard length) pieces of mealwormsTenebriosp. as test prey. A video camera system was used to record the pursuit speed and reactive distance of fish during foraging bouts. Turbidity had a consistent and negative effect on reactive distance (analysis of variance,P< 0.05). On average, reactive distances in the 15- and 30-NTU (nephelometric turbidity units) treatments were only 80% and 45%, respectively, of those observed at ambient turbidities (4–6 NTUs). By contrast, turbidity did not significantly affect pursuit speed. Pursuit speed varied greatly among individuals but was similar for each fish across turbidity levels. These results indicate that sediment-producing activities, such as logging and road building, could reduce foraging success within trout populations.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1992)121<0437:TICIRD>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

-Large numbers of spiny dogfishSqualus acanthiasmoved into the area near the mouth of the Big Qualicum River, British Columbia, at the time hatchery-reared smolts of Chinook salmonOncorhynchus tshawytschaand coho salmonO. kisutchwere leaving the river in 1988 and 1989. A small percentage of the spiny dogfish preyed on the smolts, but the resulting smolt mortality is believed to have been large because of the large numbers of spiny dogfish in this area. Spiny dogfish also fed on adult salmon in the fall. The long-term decline in survival of chinook salmon produced at the Big Qualicum Hatchery was similar to the pattern of survival of other hatchery-produced salmon. We propose that this long-term decline in survival results from predation.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1992)121<0444:SDPOCA>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

We examined genetic variation in mortality, mean time to death, and (for chinook salmon) weight for one population each of chinook salmonOncorhynchus tshawytscha, coho salmonO. kisutch, and chum salmonO. ketain British Columbia. In each of the three populations examined, 15 males were mated to 30 females in a nested breeding design. The progeny from each family were divided into groups, and each group was challenged with one of four pathogens:Vibrio anguillarumorV. ordalii, both of which cause vibriosis;Aeromonas salmonicida, which causes furunculosis; andRenibacterium salmoninarum, which causes bacterial kidney disease. When all three salmon species were considered as a group, heritabilities of mortality (sire component, binary character) were low – less than 0.15 for the Vibrio species andA. salmonicidachallenges, and less than 0.05 for theR. salmoninarumchallenge. Heritabilities of time to death were also low. Family mortality rates in theVibriospecies andA. salmonicidachallenges tended to be positively correlated, but not as a result of additive genetic variation. Similar results were obtained for family mean time to death. At the end of the experiments there was no consistent genetic correlation between family weight and observed mortality rates or time to death. Our results suggest that greater improvements in disease resistance for salmon in the aquaculture industry in British Columbia can be made by judicious selection for the strain or population for brood stock rather than by selective breeding for increased resistance.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1992)121<0456:GVIDRA>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Two phases ofgrowth can sometimes be distinguished in long-lived fish species. The first involves the growth of zooplankton-feeding juveniles and young adults. The second consists of accelerated growth of large, piscivorous adults. We present modified versions of the von Bertalanffy growth equation that account for this feature and fit them to length-at-age data on Nile perchLates niloticus(Centropomidae) from Lake Chad (north and south) in north-central Africa, and from Lake Nasser in Egypt. The growth parameters estimated for the new equations allow one to make preliminary estimates of the energy gains by Nile perch associated with transition from zooplanktivory to piscivory.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1992)121<0486:NFFTAO>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Because peak abundance of larval gizzard shadDorosoma cepedianumoccurs simultaneously with the midsummer decline of macrozooplankton in Ohio reservoirs, we hypothesized that zooplanktivory by larval gizzard shad caused this decline. To test this hypothesis, we compared larval food consumption with zooplankton productivity in two reservoirs. Larval gizzard shad began to influence zooplankton production in a reservoir with high zooplankton productivity (exceeding 125 mg·m−3·d−1) only after peak zooplankton biomass occurred, even at high larval densities (38 shad·m−3). However, consumption by early juvenile (25−30-mm) gizzard shad severely reduced zooplankton in this reservoir. Conversely, relatively low densities of larval gizzard shad (3–7 shad·m−3) had variable effects on zooplankton in a reservoir with low zooplankton productivity (at most 4 mg·m−3·d−1). Depending on larval gizzard shad density and zooplankton production, larval gizzard shad alone or in conjunction with early juveniles may control zooplankton assemblages, increasing competition for limited resources at a time when zooplankton are critical to sport-fish recruitment.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1992)121<0494:FCBLGS>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

We analyzed the behavior of 3–4-d-old prolarval and 28–33-d-old metalarval American shadAlosa sapidissimain groups of 3–1,000 fish per 22-L glass tank, to determine whether (1) previously described juvenile behavior patterns first develop in larvae, (2) group size or density alters the behavior of larvae, and (3) schooling or other forms of cohesive behavior develop in larvae to promote social interactions. Twelve discrete behaviors or modal action patterns (MAPS) oflarvae were observed at all group sizes; halfthese patterns are unique to larval stages. Conversely, larvae do not develop five previously described juvenile MAPS. Stereotyped metalarval feeding sequences were absent or poorly developed in prolarvae. Group size was directly related to duration of free swimming in water column (metalarvae only) and to frequencies of “proximity to another fish” (all larvae), “contact another fish” (all larvae), and “escape or flee” (all larvae). Age or larval stage significantly affected all swimming-related activities and three feeding behaviors. Larvae foraged and fed independently of one another and used MAPs typical of other larval fishes (“fixate,” “sigmoid,” “lunge,” and “capture”). With one exception (a direct relationship between frequency of food capture and metalarval size), group size and individual size did not significantly affect larval feeding success. Neither schooling nor forms of behavior leading to coordinated group swimming were observed at either larval stage. Larval behavior differed from juvenile behavior in a way that suggests survival in riverine habitats is promoted by behavior that disperses larvae and enables them to function nonsocially.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1992)121<0508:LASEOA>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

We developed techniques for combining scanning electron microscopy with conventional measurements to estimate intestinal surface areas in blue tilapiaTilapia aureaand redbelly tilapiaTilapia zilli. These fish have natural diets that are similarly resistant to digestion. The former feeds on detritus and the latter on macrophytes. Intestinal lengths adjusted for total body length were not significantly different between the two species, but redbelly tilapia had a greater intestinal diameter. Intestinal walls of both species consisted of longitudinal folds winding through the length of the intestine. Mean fold width was greater in redbelly tilapia, but fold height did not differ between species. Scanning electron micrographs of cross sections of intestinal walls showed columnar epithelial cells topped by a brush border (i.e., microvilli) and a lamina propria underneath the epithelium in both species. Mean microvillus height was greater in blue tilapia. Microvillus diameter did not differ between species, but both diameter and height decreased distally. Dimensions of folds and microvilli obtained from micrographs were used to develop a technique for estimating surface area that involved expanding the surface area of a simple tube to the surface area of a tube with folds and microvilli. Microvilli accounted for more than 90% of the digestive surface area in both species. Digestive surface area of blue tilapia was 21% greater than that of redbelly tilapia (1,819 cm2versus 1,504 cm2for a fish of 145 mm total length). Blue tilapia's main adaptive features used to increase surface area of the intestine were greater fold development (i.e., convolutions) and taller microvilli. Perhaps these are adaptations to a detritivorous diet.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1992)121<0517:CAEOAI>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Since the early 1940s, several investigators have determined age-at-maturity schedules for female striped bassMorone saxatilisat various locations along the Atlantic coast of the USA. These researchers have used one of two sets of criteria to determine whether a female is sexually mature; however, recent work suggests that these methods may underestimate the number of females entering the spawning population at an early age (e.g., ages 3 and 4). The objectives of our study were (1) to compare three methods and criteria for establishing sexual maturity and (2) to use all three methods in establishing a maturity schedule for female striped bass. Also, we estimated potential fecundity of the fish as a function of size, weight, and age. Two hundred sixty-five female striped bass were collected from the Roanoke River–Albemarle Sound system of North Carolina during the prespawning and spawning seasons (March–May) of 1989 and 1990. Females ranged in size from 344 to 1,172 mm fork length and in age from 2 to 16 years. Age-3 females produced approximately 200,000 eggs. The relationship between fish age and the number of eggs produced was statistically linear; one age-16 female produced approximately 5,000,000 eggs. Maturity estimates based on three methods were not significantly different; they indicated that about 44% of age-3 females were sexually mature and that all females examined were mature by age 6. These data suggest that female Roanoke striped bass may mature at an earlier age than striped bass in other systems. The proportion of females reaching sexual maturity by age 3 appears to be increasing in the Roanoke–Albemarle system; however, viability and year-class contribution of eggs spawned by age-3 females are unknown. The cause of the apparent downward shift in the maturation schedule is undetermined; environmental stress, fishing pressure, and genetic changes are possible factors. Until the viability and recruitment potential of eggs spawned by age-3 females can be ascertained, we recommend that management agencies consider age-4 females to be the first age-class that contributes to formation of Roanoke–Albemarle year-classes.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1992)121<0524:MAFORR>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor