摘要:

Top-down effects from piscivores to phytoplankton have been documented in north temperate lakes, thus permitting managers to regulate these food webs. From our review of the literature, reservoir trophic interactions appear less amenable to biomanipulation owing to the presence of a fast-growing, omnivorous planktivore, gizzard shadDorosoma cepedianum. If reservoir zooplankton can be enhanced by reducing gizzard shad through biomanipulation, this could increase survival of food-limited early life stages of sport fishes dependent on zooplankton and could improve water clarity by reducing phytoplankton. To quantify this potential, we evaluated responses of age-0 gizzard shad, crustacean zooplankton, and phytoplankton to the addition of hybrid striped bassMorone saxatilis×M. chrysops(22 kg/ha) to four of eight 0.4-ha ponds. Hybrid striped bass nearly eliminated age-0 gizzard shad from ponds within 10 d after being stocked, which permitted zooplankton density and size to increase but had no effect on phytoplankton. These pond results independently confirmed the relationships among zooplankton density, zooplankton production, and age-0 gizzard shad density that had been developed previously in 1-m3enclosures. Only reservoirs with fewer than 10 age-0 gizzard shad/m3and daily zooplankton production greater than 220 mg/m3may be amenable to biomanipulation; these conditions occurred in our ponds due to hybrid striped bass piscivory and high zooplankton productivity. About 5% of Ohio reservoirs possess these two characteristics, which makes the potential for improving sport fish recruitment by reducing age-0 gizzard shad abundance a limited option for reservoir managers.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0491:QRTHSB>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

KokaneesOncorhynchus nerka(lacustrine sockeye salmon) and Utah chubGila atrariafeed extensively on similar sizes and species of zooplankton in Flaming Gorge Reservoir. We measured the effects of Utah chub on the growth of kokanees in six 80-m3enclosures containing ambient zooplankton populations. Three kokanees and 0, 3, 6, 12, or 24 Utah chub were weighed and placed in each enclosure. After 21 d, fish were removed and kokanee growth was compared among treatments. Zooplankton biomass, chlorophyll-aconcentrations, and temperature profiles were monitored during each test. In May 1992, no competitive interactions were observed; in June 1992, however, zooplankton biomass and kokanee growth declined significantly as Utah chub densities increased. The best predictor of kokanee growth wasDaphnia pulexdensity, which explained 76% of the variance in kokanee growth. Differences in temperature and initial zooplankton biomass affected the strength of observed competition. Our results suggest that monitoring forage resources rather than nongame fish densities may provide a better framework for assessing competition among pelagic fish species.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0505:CBKAUC>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

As part of a study of trophic connectivity of boreal lakes and their riparian shorelines, juvenile lake troutSalvelinus namaycushwere collected from four small oligotrophic lakes on the Canadian Shield in northwestern Ontario and analyzed for nitrogen and carbon stable isotopes. Nitrogen isotope ratios indicated that these populations of juvenile lake trout were relatively omnivorous, exhibiting individual δ15N values (deviations of the15N/14N ratio from the isotopic standard) consistent with predation on opossum shrimpMysis relicta(41 % of samples), zooplankton (35% of samples), and littoral organisms (25% of samples). Carbon isotope ratios indicated that these juvenile lake trout obtained on average about half of their carbon from littoral sources outside the deepwater pelagic zone. These observations suggest that lake trout in small Canadian Shield lakes depend on some combination of terrestrial inputs and littoral foodwebs to satisfy their energy requirements.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0512:EPFJLT>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

We investigated the spawning biology of California golden troutOncorhynchus mykissaguabonita, an endemic subspecies of rainbow trout, in the Golden Trout Wilderness, California. We investigated the influence of stream temperature on the seasonal and daily timing of spawning, measured characteristics of completed redds, and quantified microhabitat use and preferences by spawning females. We also quantified size at sexual maturity, degree of sexual size dimorphism, and the operational sex ratio during the spawning season. Golden trout spawning began after peak stream discharge in mid-May, when maximum daily water temperatures consistently exceeded 15°C and continued for approximately 3 weeks. Stream temperatures also influenced the daily timing of spawning activity, with highest activity in the afternoon when stream temperatures approached the daily maximum. Among sexually mature fish (>95 mm), males were significantly larger than females, and ripe males were 3–9 times more abundant than ripe females. Females spawning early in the season were larger and constructed their redds in larger substrates than laterspawning females. Redds were characterized by very small substrates, and females showed distinct preferences for particular substrate sizes, water depths, and water velocities. Females selected spawning sites characterized by mean substrate sizes of 4–12 mm, water depths of 5–20 cm, and water velocities of 30–70 cm/s. Compared to spawning microhabitat preferences of other salmonids, female golden trout used smaller substrates, shallower water depths, and dug shallower nests. These differences may be the result of the unusually small size of golden trout in our study population, relative to salmonids used in previous studies of spawning microhabitat.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0519:SBCGTC>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

In all, 1,403 weakfishCynoscion regaliswere collected in 1991 and 1992 from commercial fisheries in the Chesapeake Bay region. Female gonads were examined macroscopically and histologically. Weakfish showed a strong diel periodicity in spawning activity, with almost all fish spawning at dusk. Although fish spawned from May through August, spawning activity varied within season and between years. Spawning activity decreased in late June and early July in both 1991 and 1992, but increased again in late July only in 1991. Spawning activity within and between years showed a temporal pattern similar to that of body condition, as measured by Fulton's condition factor. Batch fecundities ranged from 75,289 to 517,845 eggs/female and significantly increased with both total length and somatic weight. Spawning frequency was higher in 1991 (once every 2–3 d) than in 1992 (once every 12–13 d), leading to an average annual fecundity of 7.4 million eggs/female in 1991 and 1.8 million eggs/female in 1992.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0532:VSAAAF>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

North American paddlefishPolyodon spathulahistorically occurred in the Mississippi, Saint Lawrence, and Alabama rivers, as well as several other Gulf of Mexico coastal drainages. Recent population declines in some locations and the local extirpations of others purportedly have been due to habitat loss, overharvest, and other biotic and abiotic changes to riverine ecosystems. Mitigation for these declines has emphasized hatchery production and supplemental stocking programs, which use a number of geographical sources for parental stock. To investigate phylogeographic relationships within and among several watersheds, we surveyed allozyme and mtDNA variation among 189 individuals collected from six regions of the Mississippi River drainage plus the Mobile Bay and Pearl River drainages. Paddlefish exhibited lower levels of allelic and haplotypic diversity than other freshwater species, a characteristic shared with other “primitive” fishes. Allozyme variation at 64 presumptive loci was segregated into two major groups: a Mobile Bay drainage group and a group from the Mississippi River and Pearl River drainages. More subtle population divergences were observed among major regional tributaries within the Mississippi River, although a clear and unambiguous level of geographical clustering was not delineated. Furthermore, several of the localities harbored “private,” but rare, polymorphisms. These results demonstrate that the populations are sufficiently divergent to warrant differential management considerations for any rehabilitation, restoration, or protection measures.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0546:GVOPAA>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The ruffeGymnocephalus cernuusis a European percid that was accidently introduced in Duluth Harbor, Lake Superior. This nonindigenous species is closely related to yellow perchPerca flavescens, and because the two species have similar diets and habitat requirements, they are potential competitors. Laboratory studies in aquaria and pools were conducted to determine whether ruffe can compete with yellow perch for food. Ruffe had capture rates similar to those of yellow perch when food was unlimited. Ruffe spent more time than yellow perch over a feeding container before leaving it and searching again, and they also required less time to ingest (or handle) prey. However, the presence of yellow perch shortened the time ruffe spent over foraging areas when food was more limited. In addition, yellow perch were more active than ruffe, as indicated by their more frequent visits to a feeding container. Hence, the outcome of exploitative competition was not conclusive; ruffe appear to have the advantage in some behaviors, yellow perch in others. Ruffe were much more aggressive than yellow perch, and interference competition may be important in the interactions between these species. Our results indicate that ruffe might compete with native yellow perch.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0562:CBNRAN>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Atlantic salmonSalmo salar, returning to freshwater to spawn, were angled and then terminally sampled to test the hypothesis that angling during warmer summer months (water temperatures of 20 ± 2°C) increases the magnitude of physiological disturbances in the white muscle. Angling immediately reduced white muscle ATP and phosphocreatine stores, but these high-energy phosphates were replenished within 2–4 h. Intramuscular glycogen stores were nearly depleted after angling, but unlike the response by salmon angled in the fall at 6°C, there was no glycogen resynthesis during the 4-h recovery period. Marked increases in white muscle lactate and the postexercise metabolic proton load (▵H+m) accompanied glycogen depletion. The time course of lactate elimination and ▵H+mcorrection, however, was much slower than previously observed in fall-angled salmon. Finally, considerable delayed postangling mortality (40%) was observed in a subgroup of Atlantic salmon that were angled at 22°C. We conclude that angling in warm summer water impairs restorative processes and increases the susceptibility of Atlantic salmon to delayed postangling mortality. We suggest that anglers can mitigate the magnitude of angling-induced physiological disturbances in Atlantic salmon during midsummer by minimizing playing time and postangling air exposure.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0572:PASOWA>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Gross external pathological abnormalities are frequently used as indicators of anthropogenic influence in estuarine and marine waters, but little baseline information is available to identify what constitutes normal prevalences (percentages of animals affected). To establish this baseline, trawl samples were collected from 120 randomly located estuarine sites in the Virginian biogeographic province (mid-Atlantic) in 1990 and from 220 randomly located sites in the Louisianian biogeographic province (Gulf Coast) in 1991 and 1992. Sediment contaminant concentrations were measured at each site. In all, 24,291 fish representing 143 species were examined for gross pathological abnormalities, and background prevalences were estimated to be 0.5% in midAtlantic and 0.7% in Gulf Coast estuaries. Fifteen types of gross abnormalities were noted. Skin lesions were the most prevalent abnormalities in both provinces, followed by ocular abnormalities (e.g., exophthalmia, keratitis) in the Virginian Province and branchial chamber abnormalities (e.g., parasites, gill arch deformities) in the Louisianian Province. The prevalence of gross abnormalities was about three times higher for demersal fish than for pelagic fish and was about eight times more prevalent at sites with high sediment contaminant concentrations. Among the major estuarine systems of the mid-Atlantic and Gulf of Mexico coastlines, pathological abnormalities were most prevalent in Galveston Bay and lowest in Long Island Sound and Mississippi Sound.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0581:POGPAI>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Estimates of gastric evacuation rates (GER) are needed to calculate consumption rates of fish from field-collected data on stomach contents. The results of 16 GER experiments designed to determine the effects of body size, prey type, and temperature on the GER in young-of-the-year (age-0) bluefishPomatomus saltatrixare presented. The linear, square-root, and exponential GER models similarly fit the data. Temperature had a highly significant effect on age-0 bluefish GER. However, there was no significant difference in GER between small (5.14 g wet weight) and large (35.99 g wet weight) age-0 bluefish. Among the three different prey types tested (age-0 striped bassMorone saxatilis, bay anchovyAnchoa mitchilli, and age-0 Atlantic menhadenBrevoortia tyrannus) there was no significant difference in GER. The exponential relation between bluefish GER and temperature can be used in estimating age-0 bluefish consumption rates in the field.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0591:GEROPY>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor