摘要:

The present distribution of salmonid fishes in Wyoming streams was found to be limited to regions where mean July air temperatures did not exceed 22°C. Much of the present salmonid habitat in streams is predicted to be lost if climatic warming occurs. For increases of 1, 2, 3, 4, or 5°C in mean July air temperature, the geographic area of Wyoming containing suitable salmonid habitat would be reduced by 16.2, 29.1, 38.5, 53.3, or 68.0%, respectively. This loss of geographic range would correspond to reductions of 7.5, 13.6, 21.0, 31.4, or 43.3% in the length of streams having suitable salmonid habitat. In the Rocky Mountain region, increases of 1, 2, 3, 4, or 5°C in mean July air temperature would reduce the geographic area containing suitable salmonid habitat by 16.8, 35.6, 49.8, 62.0, or 71.8%, respectively. As warming proceeds, salmonid populations would be forced into increasingly higher elevations and would become fragmented as suitable habitat for coldwater fish becomes separated from main river channels and restricted to headwater streams. A geographic information system (GIS) proved useful for combining the various databases necessary to assess the potential impact of global warming on salmonid populations.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0001:TLTSDI>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

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 perchPerca 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.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0014:SDEOCA>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Food webs in northern temperate lakes frequently exhibit tightly linked interactions between adjacent trophic levels that lead to top-down effects from piscivores to phytoplankton. To determine if these interactions occur in reservoirs dominated by an omnivorous planktivore, gizzard shadDorosoma cepedianum, we experimentally quantified crustacean zooplankton and phytoplankton responses to age-0 gizzard shad (23–90 mm total length) at four gizzard shad densities across three reservoirs, each with a different level of crustacean zooplankton productivity. Age-0 gizzard shad exerted strong top-down effects on crustacean zooplankton, eliminating it from most enclosures within 2 weeks. This decline in crustacean zooplankton did not lead to increases in phytoplankton unlessDaphniaspp. were initially abundant. As detritivores, gizzard shad can remain abundant when planktonic food resources are depleted. This trophic decoupling probably allows gizzard shad to structure reservoir food webs by overconsumption of crustacean zooplankton, which in turn may compromise recruitment of sport fishes with zooplanktivorous larvae. In our view, the potential for increasing crustacean zooplankton density by controlling gizzard shad with stocked predators will be limited to reservoirs where age-0 gizzard shad density can be reduced below 10 fish/m3and where daily zooplankton productivity exceeds 220 mg/m3.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0027:QLAGSZ>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The white abaloneHaliotis sorensenioccupied rocky reefs in high densities around the California Channel Islands at depths of 26–65 m in the early 1970s. By 1981, white abalone densities had declined two orders of magnitude, and the species had virtually disappeared by the early 1990s. From April 1992 through December 1993, we searched 30,600 m2of suitable habitat at 15 locations known previously to support the white abalone. We found three live individuals (mean density, 0.0002/m2; SE, 0.0005). All three were near the maximum size common for the white abalone. At average densities, an equivalent search in the 1970s would have revealed 6,120–30,600 adults. Fishery landings reflected this population collapse. Annual commercial landings averaged 41 metric tons in 1971–1976, peaked abruptly at 65 tons in 1972, then plummeted to 0.140 ton in 1981; landings averaged only 0.153 ton from 1991 through 1994. Recreational landings, never numerous, virtually ceased after 1983. During the 1992–1993 survey, we also found 119 empty white abalone shells, 42–195 mm long, at a mean density of 0.0085/m2(SE = 0.0065). The last major white abalone recruitment event at the California Channel Islands was apparently in the late 1960s. Survivors of legal harvest in the 1970s were so few and so sparsely distributed that no significant reproduction has occurred since then. The California white abalone population appears to have collapsed in the 1970s and is approaching extinction from natural causes some 20 years after intense exploitation ended.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0042:SATOWA>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

We used a survey of hypervariable, variable number of tandem repeat (VNTR) loci to detect nuclear genetic differentiation within and among populations of striped bassMorone saxatilisin the lower Chesapeake Bay. This species has been refractory to population genetic analysis because it is depauperate in genetic variability. Previously described morphological differences and possible physiographic barriers to gene flow suggest the potential for differentiation among lower bay populations. In this study, we found considerable interindividual variation but relatively small levels of interpopulation variation among samples from the lower western shore of the Chesapeake Bay. The results suggest that stochastic genetic differentiation among these populations is unlikely and that relatively strong selection for locally adapted genotypes would be required for interpopulation differentiation to occur.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0049:HDMRHG>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Allozyme expression of 14 loci was studied in diploid channel catfishIctalurus punctatus, blue catfishI. furcatus, and diploid and triploid hybrid catfish (channel catfish × blue catfish). This allowed appropriate interpretation of allozyme expression and estimates of gene–centromere distances in triploid hybrid catfish and contributed to genetic characterization of the commercially important ictalurid catfishes. Five polymorphic loci in the parental female channel catfish were used to confirm the retention of an extra diagnostic maternal allele in triploid offspring. Fidelity of gene dosage and allozyme expression of three parental alleles were found at 13 of 14 loci of triploid progeny; however, expression of phosphoglucomutase (PGM) in 174 and 197 triploid hybrids was similar to that of diploid hybrids. Electrophoretic variation for PGM was observed when different buffers were used, indicating nongenetic alteration of expression. Two polymorphic loci in triploid hybrid catfish provided new gene–centromere distances of 14 centimorgans (cM) for aspartate aminotransferase (mAAT*) and 45 cM for glucose-6-phosphate isomerase (GPI-A*). No differences were found in recombination rates of isocitrate dehydrogenase (IDHP*) and peptidase-5 (PEPS-1*) loci of triploid hybrids at different ages.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0056:IEAGCD>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Spawning of lake sturgeonAcipenser fulvescenswas documented from 1987 to 1992 below the Prickett hydroelectric facility on the Sturgeon River, a tributary to Portage Lake, Michigan. Lake sturgeons were captured at the spawning site with dip nets during periods of reduced flow. A change in the spawning characteristics of the population was noted that corresponded to a change in the operation of the hydroelectric facility. In 1987 and 1988 the facility operated in a peaking mode, which resulted in large daily fluctuations in river flows. The years 1989 and 1990 were years of transition, and in 1991 and 1992 the facility released near run-of-the-river (ROR) flows. Under near-ROR flows, which were more natural, adult lake sturgeons spent 4–6 weeks less at the spawning sites, 74% more fish were observed, weights were greater due to a 68% increase in number of females, and fish had increased reproductive readiness. The change in flow regime was the result of a Federal Energy Regulatory Commission relicensing action. The positive response observed in lake sturgeon spawning activity that resulted from the change of facility operation to near-ROR flows should be beneficial to the survival and perpetuation of this population. Similar results may be experienced in other lake sturgeon waters affected by manipulated flow regimes.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0066:ROSLST>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

I used radio transmitters to determine the diel habitat use and movement patterns of California golden troutOncorhynchus mykiss aquabonitainside and outside cattle exclosures on the South Fork Kern River, Golden Trout Wilderness, California. Twenty-three golden trout were monitored from September 10 to 19, 1993, during 216 diel-tracking hours at four study sites in upper and lower Ramshaw Meadow. No differences in distances moved or home ranges were detected between golden trout inside and outside exclosures. Mean home ranges were 18.5–54.0 m inside the two exclosure sites and 36.0–68.7 m outside the two exclosures. Most golden trout were found within 5 m of their previously recorded location at both upper (93.5% of 521 observations) and lower (92% of 394 observations) Ramshaw Meadow sites. Movement of individual fish varied: five fish moved less than 5 m throughout the 10-d study period, whereas 12 fish moved 100–608 m. Golden trout were active both day and night, and I observed them feeding throughout the night, even when water temperatures were as low as 2°C. At all study sites inside and outside exclosures, golden trout used three macrohabitats (pools, runs, and riffles) but selected pools in higher proportions than the more available runs. Throughout the study, golden trout were associated with nine habitat features (undercut banks, willows, bare banks, collapsed banks, open channel, aquatic vegetation, sedge, boulders, or rootwads) but were most commonly found near sedge and undercut banks.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0078:DMAHUO>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Estimates of mean length at age and survival of rainbow smeltOsmerus mordaxcaptured at night during stepped-oblique midwater trawling in Lake Champlain in 1984–1985 were used to examine the condition of the population before a control program for sea lampreyPetromyzon marinusbegan. Stomach contents of lake troutSalvelinus namaycush, Atlantic salmon Salmo salar, and walleyeStizostedion vitreumwere analyzed to assess the role of rainbow smelt as prey. Estimates of mean length at age did not differ among six sampling sites, suggesting there is only one population of rainbow smelt in the study area. Mean length-at-age estimates in 1984–1985 were similar to those observed in 1976 but substantially smaller than those observed in 1929 and 1950. Survival estimates of rainbow smelt in Lake Champlain were similar to those for rainbow smelt in the Great Lakes prior to salmonid stocking programs. Rainbow smelt was the dominant prey species identified in the diets of lake trout, Atlantic salmon, and walleye in Lake Champlain. Atlantic salmon preyed more on smaller, immature rainbow smelt than did lake trout or walleyes. Slow growth and low mortality rates of rainbow smelt in Lake Champlain indicate that the population was not severely affected by predation.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0087:GASORS>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Studies of sunfishLepomisspp. have demonstrated that predation regulates size-specific habitat use and competitive interactions both within and among species. However, all of these studies were conducted in clear-water systems with dense littoral vegetation, resulting in well-defined littoral and open-water habitats. In contrast, little is known about predator–prey interactions among fishes that inhabit turbid lakes and reservoirs. In these systems, turbidity reduces detection (reaction) distance for both predator and prey, and can eliminate submerged vegetation that serves as a refuge. In laboratory experiments, we quantified reaction distance of juvenile bluegillsLepomis macrochirusto a predator, largemouth bassMicropterus salmoides, and determined shifts by bluegills between nearshore and offshore habitats across a turbidity gradient. Bluegill reaction distance declined as a negative power function of turbidity from less than 2 m in clear water to 23 cm at 10 nephelometric turbidity units (NTU) and 9 cm at 50 NTU. However, bluegill reaction distance was always greater than largemouth bass reaction distance. In tilted laboratory pools with a depth gradient of 0–50 cm and a largemouth bass predator, bluegills used deepwater habitat (>20 cm deep) less than 20% of the time in clear water and more than 80% of the time at all turbidities greater than 10 NTU. The presence of an obligate open-water prey for largemouth bass, gizzard shadDorosoma cepedianum, did not influence bluegill habitat use. The apparent reduction in open-water predation risk with a relatively minor increase in turbidity suggests that size-specific habitat use by bluegills in turbid systems may not be as simply defined as in clear-water lakes.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0097:DOPAHC>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor