Spawning and Early Life History of Largemouth Bass (Micropterus salmoides) in Wahweap Bay, Lake Powell

Spawning time and habitat of largemouth bass, survival of embryos, and growth and food habits of fingerlings were studied in 1968 and 1969 at Wahweap Bay, Lake Powell. Spawning began in mid- to late-April, when mean daily water temperature at nesting depths was 14.4-15.0 Centigrade (58-59 Fahreheit), and continued until mid-June. Most spawning took place on the northeast shore of the bay. Sandstone rubble was the most commonly used bottom type for nesting, either at the base of ledges or around large sandstone boulders. Mean nest depth increased from 1.63 meter to 4.54 meters (5.36 feet to 14.90 feet) in 1968 and from 1.51 meter to 2.93 meters (4.96 feet to 9.60 feet) in 1969, because bass sought the protection of ledges and boulders covered by continually rising water. Nearly all embryos required 4 days to hatch, and survival to hatching was 80.4 percent and 92.2 percent for 1968 and 1969, respectively. Growth of fingerlings was similar in both years and most rapid prior to August 1 in both years. Fingerlings from the 1969 year-class were longer than those from the 1968 year-class before August 21. Total length of bass on August 21 was 68.0 millimeters in both years but 86.5 millimeters and 80.2 millimeters on October 1 in 1968 and 1969, respectively. Growth may have been influenced by total temperature experience during the early part of the growing season but not during the latter part. Fingerlings ate mostly crustaceans, insects, and fish. Size of organisms eaten increased with increase in fingerling length, and fingerling bass fed selectively on larger Crustacea. Numbers of nests located and numbers of young-of-the-year taken in beach-seine catches indicated that the 1968 year-class was stronger than 1969. Estimated numbers of bass per 92.9 meters2 (1,000 feet2 ) seined varied from 0.82 to 3.39 in 1968 and from 0.23 to 2.65 in 1969. An index to year-class strength may be obtained from seine catches at any time of the summer after brood dispersal, but indices obtained in this study must be validated by determing the contribution of each year-class to the creel

Redbeds and thermoviscous magnetization theory

Thermal demagnetization characteristics of a Brunhes“age viscous overprint in Appalachian redbeds and a thermoviscous component acquired in the laboratory at moderate temperature agree well with relaxation time“blocking temperature relations for hematite proposed by Pullaiah et al. [1975]. Supporting evidence was obtained from redbeds associated with an igneous dike intrusion although the interpretation of these data are complicated by magnetochemical alterations. Paradoxically, experimental data for magnetite in some limestones were shown to agree more closely with an alternative theory of Walton [1980]. The hematite in redbeds is predominantly singledomain (SD) whereas magnetite in the limestones studied extends well into the multidomain (MD) range. Thus experiment and theory could be reconciled if it is assumed that Pullaiah et al. applies strictly to SD material whereas Walton's theory somehow describes thermoviscous effects dominated by larger MD grains

Paleomagnetism of the Upper Devonian Catskill Formation from the southern limb of the Pennsylvania Salient: Possible evidence of oroclinal rotation

Multiple components of magnetization were isolated in the natural remanent magnetization of samples of the Upper Devonian Catskill Formation red beds taken from the southern limb of the Pennsylvania Salient. The dominant, thermally distributed component (SF), previously thought to predate folding, is demonstrably synfolding in origin. The mean direction for SF based on data from the current study and a previous study is Declination/Inclination = 161.6°/7.9°, a95 = 3.9° (pole position 127.3°E, 43.1°N, A95 = 3.1°, N = 14 sites). Although the remagnetization is clearly synfolding in most areas, the relative ages of folding and remagnetization vary locally. A subordinate high unblocking temperature component (HT) has a mean tilt corrected direction of 160°/36°, a95 = 16° (pole position 123.5°E, 26.1°N, A95 = 15.4°, n = 7 samples). Comparison of HT with the prefolding magnetization isolated in the northern limb of the salient suggests that the paleolatitude of this part of North America was about 16°S and that part of the curvature of the salient was acquired during orogenesis

Regional trends in the timing of Alleghanian remagnetization in the Appalachians

Pole positions related to remagnetized components isolated in Appalachian limestone and redbed rock units range over about 60 m.y. of the Permian-Carboniferous apparent polar wander path for North America. Apparent ages of remagnetization are older in the southern Appalachians and younger to the north. If the remagnetizations are associated with fluids expelled during the Alleghany orogeny, then the apparent remagnetization age trend could describe the timing of thrust-sheet emplacement

Paleomagnetism of the Silurian-Devonian Andreas redbeds: Evidence for an Early Devonian supercontinent?

Two components of magnetization were isolated in the Silurian-Devonian Andreas redbeds of the central Appalachians of Pennsylvania (lat 40.75 degrees N, long 75.78 degrees W): a thermally distributed, synfolding B component, and a thermally discrete, pre-Alleghenian-age folding C component. The C component mean direction and associated pole position correspond to a Silurian-Devonian paleolatitude for the Andreas location of about 35 degrees S, which, in conjunction with Early Devonian results from Gondwana, is consistent with an Early Devonian supercontinent configuration

Synfolding and prefolding magnetizations in the Upper Devonian Catskill Formation of eastern Pennsylvania

The Upper Devonian Catskill Formation was sampled for paleomagnetic study in east-central Pennsylvania (41°N, 76°W). In one area the dominant component of magnetization (SE) is revealed over a broad spectrum of demagnetization temperatures ranging to at least 660°C. A conventional fold test is positive at the 99% confidence level. However, statistical analysis of dispersion with incremental bedding tilt correction shows a significant peak in the precision parameter after about 3/4 unfolding. The magnetization is therefore secondary, with a mean direction of D = 166.6°, I = -1.8°. The corresponding pole position (48.1°N, 124.1°E, a95 = 4.0°) is indistinguishable from paleopoles from earlier studies of the Catskill, which therefore can also be regarded as representing Permo-Carboniferous remagnetizations. A second component of magnetization (SW, pole position 32.8°N, 90.0°E, a95 = 7.2°) with discrete unblocking temperature spectra and southwesterly declination was isolated in a few samples from the first area and in most samples from a second area. A prefolding origin of this magnetization is supported by a positive fold test on five samples from the first area. If this magnetization does represent a Devonian magnetization then the true paleolatitude for east-central Pennsylvania is 16° +/- 7.2°S, which is consistent with the paleolatitude observed in many of the Upper Devonian rock units in the Acadia region, although inconsistent with others. The question of the position of Acadia relative to North America in the Upper Devonian is therefore still open

Paleomagnetism of the Upper Ordovician Juniata Formation of the central Appalachians revisited again

Two components of magnetization were isolated in the Upper Ordovician Juniata Formation sampled in the area of the Pennsylvania salient. The thermally distributed, reversed polarity B component was most likely acquired during Alleghenian deformation, and although it is poorly grouped, it is similar to other Appalachian synfolding magnetizations. The pre-Alleghenian age C magnetization is entirely of normal polarity and shows a difference in declinations between the mean magnetizations isolated on the northern and southern limbs of the salient of 24° ± 23°. This anomaly is consistent with the sense and magnitude of declination anomalies observed in pre-Alleghenian magnetizations isolated in other throughgoing Appalachian red beds of Silurian, Devonian, and early Carboniferous age. The mean inclination of -44.7° suggests a paleolatitude of about 26°S for the central Appalachians in the Late Ordovician. This paleolatitude fits a trend of southward motion of North America from the Ordovician to the Early Devonian, followed by northward drift through the remainder of the Paleozoic

Paleomagnetism of Selected Devonian Age Plutons from Maine, Vermont and New York

In order to better define the Devonian paleolatitude and cratonic pole position of North America, eight Devonian plutons were studied: the Black Mountain Granite (and associated rocks) from southern Vermont, the Hartland, Lexington, Center Pond, Chain of Ponds, Pleasant Lake, and Horserace units from Maine, and the Peekskill Granite located in southeastern New York. Of the eight units, the best results come from the Peekskill Granite of New York (age ~360Ma) and the Pleasant Lake Granite of Maine (age ~400Ma) . The Peekskill yields a pole position of 117°E, 23°N, a 95 = 16° . This pole is identical to the pole from the earliest Carboniferous Deer Lake Formation from western Newfoundland, suggesting that the Peekskill Pluton has not suffered post emplacement rotation. However, the pole position is insufficiently precise to distinguish between rotation of one or both limbs of the Pennsylvania salient with respect to the craton in the Alleghanian orogeny or to evaluate the hypothesis that some portion of Newfoundland was offset from North America in the upper Devonian. Results from the Early Devonian Pleasant Lake Granite from Maine record a potentially Early Devonian magnetization with a pole position of 95°E, 2°N, a 95 = 17°. This magnetization suggests a paleolatitude of 42°S for the central Appalachians, consistent with results from the Early Devonian Andreas redbeds and so with the hypothesis that the Acadian orogeny resulted from collision of North and South America

Asymmetric Corporate Exposures to Foreign Exchange Rates

Research examining firms\u27 economic exposures to exchange rate movements has not differentiated periods of foreign currency appreciation and depreciation when estimating exposure coefficients. Recent theoretical developments regarding real options and pricing-to-market suggest corporate exposures may be asymmetric (i.e., the financial performance impact of a foreign currency appreciation may not be offset by the currency\u27s depreciation). Through an empirical examination of manufacturing firms\u27 economic exposures to exchange rate movements, this paper furnishes evidence on exposure asymmetries

Miocene stable isotopic stratigraphy and magnetostratigraphy of Buff Bay, Jamaica

Previously reported biostratigraphic relationships from middle-upper Miocene sections exposed near Buff Bay, Jamaica (18°N, tropical bioprovince), differ from the subtropical North Atlantic (Sites 563 and 558). Time scales for this interval rely on correlations established at these subtropical sites, and the differences with the tropical section have implications to global correlations. Planktonic foraminiferal Zones N13 and N15 are thick at Buff Bay but are virtually absent at Sites 563 and 558; nannofossil Zone NN9 is associated with Zone N15 and uppermost Zone N14 at Buff Bay but is associated with Zone N16 at the other sites. Magnetostratigraphic data presented here further complicate the interpretation: Zone NN9 is associated with a thick normal magnetozone at Sites 563 and 558; at Buff Bay, it is associated with a thick reversed magnetozone. Although a secondary magnetization at Buff Bay makes it difficult to identify confidently Miocene normal magnetozones, the thick reversed magnetozone most likely represents the paleomagnetic field and correlates with Chron C5r. The magnetobiostratigraphic relationships require either diachrony of taxa or two mutually exclusive hiatuses in Jamaica and the North Atlantic. We address this problem by analyzing benthic foraminiferal δ^18O and δ^13C from the Buff Bay section. These isotopic data allow us to evaluate three hypotheses that reconcile the magneto-, bio-, and isotopic stratigraphic data and conclude that the first and last occurrences of five taxa were diachronous by ~0.3-0.5 m.y. between tropical and subtropical locations. This requires revised age estimates for late middle to early late Miocene biostratigraphic datum levels. We suggest that the ranges of several taxa are useful for endemic tropical or subtropical zonations, but correlations between the low and midlatitudes were affected by an increase in latitudinal thermal gradients during the late middle Miocene. However, we admit that further studies are needed before this issue is resolved