摘要:

Historically, striped bassMorone saxatiliswere indigenous to many major drainages of the Gulf of Mexico (Gulf). It is believed that almost all natural populations were depleted by the 1950s and 1960s with the exception of fish in the Apalachicola–Chattahoochee–Flint (A–C–F) river system in northwestern Florida, Georgia, and Alabama. Striped bass of Atlantic ancestry were introduced into the A–C–F system during the 1960s and 1970s to enhance population size. We compared DNA fingerprints of striped bass collected from four Atlantic river systems with those offish from the A–C–F system to determine if genetic differences still exist. Moderate levels of polymorphism were observed with two probes, the bacteriophage M-13 genome and mouse sequences related to theDrosophilaPer gene. Striped bass DNA digested with single restriction enzymes and hybridized to these two probes generated single DNA fragments shared by 71 out of 75 A–C–F fish but not seen in any of 51 Atlantic fish. Heritability of DNA fingerprints was demonstrated from hatchery-raised fish of known parents. We believe that descendants of a genetically distinct ancestral Gulf population of striped bass still exist in the A–C–F and that efforts to maintain the genetic integrity of this population are warranted. Screening of potential A–C–F hatchery brood stock may be used to both maintain the genetic integrity of the Gulf strain and maximize its genetic diversity.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0273:UODFIT>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Allele-frequency differences at 11 polymorphic protein loci provided discrete genetic markers with which to estimate the extent of hybridization among native and introduced centrarchid basses in central Texas streams. Native Guadalupe bassMicropterus treculiand northern largemouth bassM. salmoides salmoidesnow coexist with introduced Florida largemouth bassM. s. floridanusand smallmouth bassM. dolomieuiin these streams. Interspecific hybridization was detected in three of four populations from the Blanco and San Marcos rivers, hybrids making up at least 31.8% of the individuals sampled. Complex hybridization patterns were evident, because F1, F2, and backcross hybrids were detected. At least one individual exhibited genetic markers of largemouth, smallmouth, and Guadalupe bass. Extensive multispecies hybridization threatens the survival of the endemic Guadalupe bass.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0283:MHANAI>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

We examined the diet of juvenile lake troutSalvelinus namaycush(<450 mm, total length) in Lake Ontario during four sampling periods (April–May, June, July–August, and October 1979–1987) in relation to changes in prey fish abundance in the depth zone where we caught the lake trout. Over all years combined, slimy sculpinsCottus cognatuscontributed the most (39–52%) by wet weight to the diet, followed by alewivesAlosa pseudoharengus(3–38%), rainbow smeltOsmerus mordax(17–43%), and johnny dartersEtheostoma nigrum(2–10%). Over 90% of alewives eaten during April–May and June were age 1, and 98% of those eaten during October were age 0 (few alewives were eaten in July–August). Mean lengths of rainbow smelt and slimy sculpins in stomachs increased with size of lake trout. Juvenile lake trout generally fed opportunistically—seasonal and annual changes in diet usually reflected seasonal and annual changes in abundance of prey fishes near bottom where we captured the lake trout. Furthermore, diet within a given season varied with depth of capture of lake trout, and changes with depth in proportions of prey species in lake trout stomachs mirrored changes in proportions of the prey species in trawl catches at the same depth. Alewives (ages 0 and 1) were the only prey fish eaten in substantial quantities by both juvenile lake trout and other salmonines, and thus are a potential focus of competition between these predators.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0290:DOJLTI>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Juvenile pink salmonOncorhynchus gorbuscha, chum salmonO. keta, and sockeye salmonO. nerkawere sampled in Hecate Strait, British Columbia, during July and August of 1986 and 1987. I described their seasonal and species-specific patterns of feeding, and I tested assumptions and predictions of models relating feeding success of juvenile salmon during their first summer at sea to survival and recruitment. The three species consumed a wide variety of taxa, but a few taxa made up most of the daily food intake. Diet composition was more similar among species within sampling periods than within species among sampling periods, although there were some apparent species-specific feeding preferences. Patterns of changing diet composition with increasing time and distance between samples were consistent with expected mesoscale patterns of plankton patchiness in coastal waters. Juvenile salmon fed selectively on larger-sized taxa in the plankton community, and larger salmon fed on larger prey. Contrary to the assumption of one model, however, young salmon did not switch to larger prey later in the summer. Weights of stomach contents and estimated daily rations were small enough to limit growth rates for all three species, especially sockeye salmon, and the hypothesis that limitation of growth during early ocean life affects survival and recruitment could not be rejected.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0303:DAFROJ>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

We examined the importance of zonation and species additions in explaining longitudinal changes in the fish assemblage of a Rocky Mountain stream that descends onto the Great Plains of Wyoming. Community changes along an elevational gradient from 2,234 to 1,230 m above mean sea level reflected a combination of zonation and downstream addition of species. Zonation was evident on a broad spatial scale as a result of stream temperatures. A coldwater trout (Salmonidae) assemblage dominated headwater reaches but was replaced by a warmwater minnow–sucker (Cyprinidae–Catostomidae) assemblage below 2,000 m. Within the warmwater zone, fish community change was due mainly to the addition of new species downstream. Headwater sites were dominated by members of the insectivore feeding guild, and other trophic guilds were added downstream. The major gradient of habitat change downstream consisted of a decrease in pool habitat and increases in stream width, depth, current velocity, turbidity, and proportion of the channel consisting of run habitat. Minor gradients of habitat change involved streambank condition and substrate particle size. Contrary to streams in forested regions, habitat diversity did not increase downstream, suggesting that increased living space and moderating environmental conditions contributed to the downstream increase in species richness. Local habitat modification due to cattle grazing or alterations in streamflow caused minor changes in fish assemblages but did not disrupt the dominant longitudinal patterns. Broad-scale zonation based on temperature regime and additive patterns within zones should typify other streams originating in montane regions

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0319:FAAHGI>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

I studied three sites in an undisturbed, third-order Blackwater stream in the central Savannah River drainage of South Carolina for 2 years before and 3 years after the accidental introduction of bluegillsLepomis macrochirus. Although large numbers invaded the stream, the species declined over the next 3 years and will likely disappear soon. The bluegills had no measurable effect on the numbers of species or individuals of the stream's indigenous fish fauna. Nearby in the same drainage, bluegills successfully colonized an impounded cooling reservoir and a downstream swamp, but they did not become established in the high-flow stream below the reservoir. Unsuccessful colonization of the two flowing-water systems indicates the importance of impoundments to successful colonization by many nonnative fishes. These data, together with examples from arid-zone streams of the American Southwest, illustrate that unimpeded flow in lotic habitats may protect against successful invasion by some introduced fishes, whereas stabilized flows may increase their likelihood of establishment.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0333:FIOASB>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Colorado squawfishPtychocheilus luciusspawned in widely separated areas throughout the 350-km section of the upper Colorado River upstream from Lake Powell, Utah, as evidenced by the movement of radio-tagged adults during the spawning season and the later capture of larvae. With one exception, tagged fish remained separated from each other during the spawning season. Distances moved by tagged fish were not related to fish size or location of initial capture along the river. Movements were generally shorter (mean, 23.2 km) than those reported for this species in the Green River basin, in part because of important habitat differences between the two rivers. Most tagged Colorado River fish were found near their initial point of capture after the spawning season.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0339:MOACSD>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Small, medium, and large (mean total lengths of 30, 36, and 44 mm, respectively) hatchery-reared age-0 Colorado squawfishPtychocheilus luciuswere held at winter temperatures (3–5°C) in aquaria for 210 d to assess the role of size, condition factor, and lipid content on overwinter survival. Fish of each size-class were either fed dry pellets or starved. Fish in all size-classes fed at winter temperatures. The fish grew little, and condition declined as length of exposure to winter conditions increased. Condition declined more rapidly in starved than in fed fish of all size-classes. Lipid content of fish was inversely related to winter duration for all size-classes and feeding regimes. Percent survival at the end of 210 d was significantly lower in starved small (3.3%) and medium (6.7%) fish than in fed small (95.1%) and medium (98.4%) fish. Large fish showed 100% survival regardless of feeding regime. In years of large, prolonged runoff that delays the seasonal warming of the upper Colorado River, late spawning by Colorado squawfish leaves age-0 fish with only 2 months to grow and accumulate fat reserves before the onset of winter. These small age-0 fish may be unable to accumulate adequate lipid reserves to survive until the following spring.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0346:ROSCAL>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

A Lagrangian time-series study of egg abundances of striped bassMorone saxatilisin the Pamunkey River in 1987 yielded mortality estimates of 10–91%/d. Mean daily mortality (68%/d) was incorporated into a model used to estimate annual egg production and female biomass from results of ichthyoplankton surveys conducted on Virginia spawning grounds in the Mattaponi River (1980), Pamunkey River (1980, 1983–1985, 1988–1989), Rappahannock River (1982–1983), and James River (1981, 1983). Annual egg production varied from 2.77 × 108eggs in the Mattaponi River in 1980 to 2.69 × 109eggs in the Pamunkey River in 1988. Results of contemporaneous surveys in 1983 indicated that egg production and biomass estimates were greatest on the Rappahannock and James rivers. Egg production estimates in Virginia are comparable to estimates for the upper Chesapeake Bay region and North Carolina. Our results indicate that an order-of-magnitude increase in female biomass was required to deposit the number of eggs observed during the 10-year period. The occurrence of peaks in juvenile abundance appears unrelated to stock size, because above-average recruitment was observed during years of high and low egg production. A substantial increase in spawning activity on Pamunkey River spawning grounds in 1987–1989 is attributed, in part, to the entry of 1982–1984 year-class females into the spawning population. We conclude that successful 1982–1984 year-classes and the implementation of more stringent fishing regulations have combined to increase present striped bass stocks in Virginia.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0354:SBEMPA>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Threadfin shadDorosoma petenenseare commonly introduced into reservoirs to supplement prey available to piscivorous fishes. To determine how early life stages of threadfin shad and their potential competitors and predators interact, we introduced this species into two Ohio lakes—Clark and Stonelick—and evaluated how its young of year influenced young-of-year bluegillsLepomis macrochirusand largemouth bassMicropterus salmoides. After adults were stocked in April, peak abundance of young-of-year threadfin shad occurred in August in both lakes. Bluegills generally spawned earlier than threadfin shad, which apparently reduced competition between young of these species. In Clark Lake, young-of-year threadfin shad did not reduce zooplankton populations, but in Stonelick Lake, peak abundance of young-of-year threadfin shad was followed by a precipitous decline in zooplankton. Data on cladoceran birth rates indicated this decline was due to increased predation by threadfin shad. Survival of bluegills to a size at which they move into the littoral zone also declined in Stonelick Lake, perhaps because of the virtual elimination of zooplankton. Limited survival of bluegills in turn contributed to reduced growth of young-of-year largemouth bass dependent on them as prey. Given that zooplankton declined in one but not the other lake, interactions among young-of-year fishes due to annually introduced threadfin shad will likely vary among systems and years. Nonetheless, introduced threadfin shad could, in some systems in some years, negatively affect growth and recruitment of the very species they were meant to enhance.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0368:STSCFY>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor