Volume, volatility, and leverage: A dynamic analysis

This paper uses dynamic impulse response analysis to investigate the interrelationships among stock price volatility, trading volume, and the leverage effect. Dynamic impulse response analysis is a technique for analyzing the multi-step-ahead characteristics of a nonparametric estimate of the one-step conditional density of a strictly stationary process. The technique is the generalization to a nonlinear process of Sims-style impulse response analysis for linear models. In this paper, we refine the technique and apply it to a long panel of daily observations on the price and trading volume of four stocks actively traded on the NYSE: Boeing, Coca-Cola, IBM, and MMM.

Biodeposition and Biogeochemical Processes in Shallow, Mesohaline Sediments of Chesapeake Bay

Stocks of the eastern oyster, Crassostrea virginica, have been declining in Chesapeake Bay since the late 19th century, and current strategies involve restoring culture of Crassostrea virginica on-bottom and in devices suspended within the water column. Sub-tidal suspension culture of Crassostrea virginica in Chesapeake Bay occurs mostly in sheltered inlets and tidal creeks and, thereby, has the potential to influence shallow water biogeochemical processes. To assess the influence of Crassostrea virginica biodeposits and benthic microalgae on sediment nitrogen and phosphorus exchange, field studies with Crassostrea virginica held in aquaculture floats and laboratory experiments were conducted. Enhanced organic nitrogen deposition from Crassostrea virginica biodeposits led to gradual increases in surface sediment nitrogen and pore water ammonium concentrations; however, modifications to pore water concentrations were not always expressed at the sediment-water interface. Benthic microalgae often modulated the influence of biodeposits on sediment nitrogen exchange but, as observed in laboratory experiments, the supply of nitrogen from Crassostrea virginica biodeposits may exceed their biological demand. Organic carbon from biodeposits had varying influences on aerobic respiration but consistently stimulated anaerobic metabolism. Shifts in net phosphorus exchange were driven by this anaerobic remineralization and concentrations of iron and manganese oxy(hydr)oxides, with transitions in fluxes coinciding with changes in benthic photosynthesis and oxidation of surface sediments. Manganese and iron oxy(hydr)oxides from biodeposits supported incorporation of added phosphorus and prevented exchange at the sediment-water interface in the absence of iron-sulfide mineral formation. Differences in the response of shallow water sediments to Crassostrea virginica biodeposits were due to the quality and quantity of biodeposits supplied, as well as the spatial and temporal variability within these sediments. Initial conditions and corresponding reference sediments illustrated the potential for sediment biogeochemistry and nutrient exchange from tidal creek sediments to vary spatially and temporally on relatively small scales. Factors influencing variability within tidal creek sediments were related to shifts in riverine freshwater inputs, macroalgal blooms, nutrient concentrations in overlying waters, and bioirrigation from the clam, Macoma balthica.

Lack of cross-scale linkages reduces robustness of community-based fisheries management.

Community-based management and the establishment of marine reserves have been advocated worldwide as means to overcome overexploitation of fisheries. Yet, researchers and managers are divided regarding the effectiveness of these measures. The "tragedy of the commons" model is often accepted as a universal paradigm, which assumes that unless managed by the State or privatized, common-pool resources are inevitably overexploited due to conflicts between the self-interest of individuals and the goals of a group as a whole. Under this paradigm, the emergence and maintenance of effective community-based efforts that include cooperative risky decisions as the establishment of marine reserves could not occur. In this paper, we question these assumptions and show that outcomes of commons dilemmas can be complex and scale-dependent. We studied the evolution and effectiveness of a community-based management effort to establish, monitor, and enforce a marine reserve network in the Gulf of California, Mexico. Our findings build on social and ecological research before (1997-2001), during (2002) and after (2003-2004) the establishment of marine reserves, which included participant observation in >100 fishing trips and meetings, interviews, as well as fishery dependent and independent monitoring. We found that locally crafted and enforced harvesting rules led to a rapid increase in resource abundance. Nevertheless, news about this increase spread quickly at a regional scale, resulting in poaching from outsiders and a subsequent rapid cascading effect on fishing resources and locally-designed rule compliance. We show that cooperation for management of common-pool fisheries, in which marine reserves form a core component of the system, can emerge, evolve rapidly, and be effective at a local scale even in recently organized fisheries. Stakeholder participation in monitoring, where there is a rapid feedback of the systems response, can play a key role in reinforcing cooperation. However, without cross-scale linkages with higher levels of governance, increase of local fishery stocks may attract outsiders who, if not restricted, will overharvest and threaten local governance. Fishers and fishing communities require incentives to maintain their management efforts. Rewarding local effective management with formal cross-scale governance recognition and support can generate these incentives.

Fishing quota markets

In 1986, New Zealand responded to the open-access problem by establishing the world's largest individual transferable quota (ITQ) system. Using a 15-year panel dataset from New Zealand that covers 33 species and more than 150 markets for fishing quotas, we assess trends in market activity, price dispersion, and the fundamentals determining quota prices. We find that market activity is sufficiently high in the economically important markets and that price dispersion has decreased. We also find evidence of economically rational behavior through the relationship between quota lease and sale prices and fishing output and input prices, ecological variability, and market interest rates. Controlling for these factors, our results show a greater increase in quota prices for fish stocks that faced significant reductions, consistent with increased profitability due to rationalization. Overall, this suggests that these markets are operating reasonably well, implying that ITQs can be effective instruments for efficient fisheries management. © 2004 Elsevier Inc. All rights reserved.

Future requirements for and supply of ophthalmologists for an aging population in Singapore.

BACKGROUND: Singapore's population, as that of many other countries, is aging; this is likely to lead to an increase in eye diseases and the demand for eye care. Since ophthalmologist training is long and expensive, early planning is essential. This paper forecasts workforce and training requirements for Singapore up to the year 2040 under several plausible future scenarios. METHODS: The Singapore Eye Care Workforce Model was created as a continuous time compartment model with explicit workforce stocks using system dynamics. The model has three modules: prevalence of eye disease, demand, and workforce requirements. The model is used to simulate the prevalence of eye diseases, patient visits, and workforce requirements for the public sector under different scenarios in order to determine training requirements. RESULTS: Four scenarios were constructed. Under the baseline business-as-usual scenario, the required number of ophthalmologists is projected to increase by 117% from 2015 to 2040. Under the current policy scenario (assuming an increase of service uptake due to increased awareness, availability, and accessibility of eye care services), the increase will be 175%, while under the new model of care scenario (considering the additional effect of providing some services by non-ophthalmologists) the increase will only be 150%. The moderated workload scenario (assuming in addition a reduction of the clinical workload) projects an increase in the required number of ophthalmologists of 192% by 2040. Considering the uncertainties in the projected demand for eye care services, under the business-as-usual scenario, a residency intake of 8-22 residents per year is required, 17-21 under the current policy scenario, 14-18 under the new model of care scenario, and, under the moderated workload scenario, an intake of 18-23 residents per year is required. CONCLUSIONS: The results show that under all scenarios considered, Singapore's aging and growing population will result in an almost doubling of the number of Singaporeans with eye conditions, a significant increase in public sector eye care demand and, consequently, a greater requirement for ophthalmologists.

Secuestro de carbono y nitrógeno y emisiones de óxido nitroso del suelo bajo diferentes sistemas de labranza y secuencias de cultivo en la región semiárida pampeana argentina

El objetivo de esta tesis fue estudiar la influencia de diferentes secuencias de cultivos soja - maíz (sj - mz) y soja - soja (sj - sj), y sistemas de labranza, siembra directa con cultivo de cobertura (SDcc) y labranza reducida (LR); sobre los stocks de carbono orgánico total (COT) y nitrógeno total (Nt) y las emisiones de óxido nitroso (N2O) del suelo en condiciones de campo. El experimento está situado en Manfredi, Córdoba, Argentina. El clima de la región es semiárido y el suelo del experimento es un Haplustol éntico. Luego de 13 años se realizó un muestreo de suelo hasta 100 cm de profundidad y se analizó densidad aparente y composición química del suelo. Las emisiones de N2O se midieron durante un año a campo. Los stocks de COT y Nt comparado con LR y los tratamientos bajo sj-sj los menores stocks, tendencia que se mantuvo hasta los 100 cm. La siembra directa promueve la acumulación de COT y Nt y el efecto es mayor cuanto mayor es la inclusión de gramíneas en la secuencia. Respecto de las emisiones de N2O en general variaron considerablemente con el tiempo y las tasas más altas se asocian acon períodos de altos contenidos de agua y nitratos en el suelo. La aplicación de fertilizante nitrogenado en maíz aumentó las emisiones de N2O del suelo. Las emisiones anuales de N - N2O medidas fueron inferiores a las calculadas en base a Intergovernmental Panel on Climate Change (IPCC), esta metodología sobreestimó las emisioens de N2O, para las condiciones estudiadas.

Use of Continuous Plankton Recorder information in support of marine management: applications in fisheries, environmental protection, and in the study of ecosystem response to environmental change

The Continuous Plankton Recorder (CPR) survey was conceived from the outset as a programme of applied research designed to assist the fishing industry. Its survival and continuing vigour after 70 years is a testament to its utility, which has been achieved in spite of great changes in our understanding of the marine environment and in our concerns over how to manage it. The CPR has been superseded in several respects by other technologies, such as acoustics and remote sensing, but it continues to provide unrivalled seasonal and geographic information about a wide range of zooplankton and phytoplankton taxa. The value of this coverage increases with time and provides the basis for placing recent observations into the context of long-term, large-scale variability and thus suggesting what the causes are likely to be. Information from the CPR is used extensively in judging environmental impacts and producing quality status reports (QSR); it has shown the distributions of fish stocks, which had not previously been exploited; it has pointed to the extent of ungrazed phytoplankton production in the North Atlantic, which was a vital element in establishing the importance of carbon sequestration by phytoplankton. The CPR continues to be the principal source of large-scale, long-term information about the plankton ecosystem of the North Atlantic. It has recently provided extensive information about the biodiversity of the plankton and about the distribution of introduced species. It serves as a valuable example for the design of future monitoring of the marine environment and it has been essential to the design and implementation of most North Atlantic plankton research.

Climate change and marine plankton

Understanding how climate change will affect the planet is a key issue worldwide. Questions concerning the pace and impacts of climate change are thus central to many ecological and biogeochemical studies, and addressing the consequences of climate change is now high on the list of priorities for funding agencies. Here, we review the interactions between climate change and plankton communities, focusing on systematic changes in plankton community structure, abundance, distribution and phenology over recent decades. We examine the potential socioeconomic impacts of these plankton changes, such as the effects of bottom-up forcing on commercially exploited fish stocks (i.e. plankton as food for fish). We also consider the crucial roles that plankton might have in dictating the future pace of climate change via feedback mechanisms responding to elevated atmospheric CO sub(2) levels. An important message emerges from this review: ongoing plankton monitoring programmes worldwide will act as sentinels to identify future changes in marine ecosystems.

Impacts of fisheries on plankton community structure

There has been much debate on the extent to which resource availability (bottom-up) versus predation pressure from fish (top-down) modulates the dynamics of plankton in marine systems. Physico/chemical bottom-up forcing has been considered to be the main mechanism structuring marine ecosystems, although some field observations and empirical correlations support top-down modulation. Models have indicated possible feedback loops to the plankton and other studies have interpreted a grazing impact from long-term changes in fish stocks. In freshwater systems, evidence for top-down forcing by fish and trophic cascading is well documented. First, evidence for equivalent top-down effects in the marine environment is presented, with an overview of relevant publications. In the second part, time series, averaged for the North Sea (when possible from 1948 to 1997), of fish catch, recruitment, and spawning stock biomass are related to the abundance of species or larger groupings of zooplankton and phytoplankton from the Continuous Plankton Recorder survey and selected environmental parameters. Preliminary analysis suggests that there is strong interaction between different fish species and the plankton and that the fishery, through top-down control, may at times be an important contributor to changes in the North Sea ecosystem.

Long-term changes in the pelagos, benthos and fisheries of the North Sea

Pronounced changes have occurred in the fisheries, plankton and benthos of the North Sea over the last five decades. Attribution of the relative contribution of anthropogenic versus natural hydrometeorological modulation to these changes is still unclear. As a background a summary history of our understanding of the state of health of the North Sea is outlined. We then focus on two contrasting periods in the North Sea, one between 1978-82 (cold) and the other post 1987 (warm) when pronounced alterations in many ecosystem characteristics occurred. The scale of the changes in the second of these periods is sufficiently large and wide ranging for it to have been termed a regime shift. A combination of local, regional and far field hydrometeorological forcing, and in particular variability in oceanic inflow, is believed to be responsible for the observed changes. Finally attention is drawn to the poor status of North Sea fish stocks where 7 stocks are documented as being fished outside safe biological limits. This situation is primarily believed to be a consequence of overfishing, but may have been exacerbated by environmental change.

From plankton to top predators: bottom-up control of a marine food web across four trophic levels

1. Abundant mid-trophic pelagic fish often play a central role in marine ecosystems, both as links between zooplankton and top predators and as important fishery targets. In the North Sea, the lesser sandeel occupies this position, being the main prey of many bird, mammal and fish predators and the target of a major industrial fishery. However, since 2003, sandeel landings have decreased by > 50%, and many sandeel-dependent seabirds experienced breeding failures in 2004. 2. Despite the major economic implications, current understanding of the regulation of key constituents of this ecosystem is poor. Sandeel abundance may be regulated 'bottom-up' by food abundance, often thought to be under climatic control, or 'top-down' by natural or fishery predation. We tested predictions from these two hypotheses by combining unique long-term data sets (1973–2003) on seabird breeding productivity from the Isle of May, SE Scotland, and plankton and fish larvae from the Continuous Plankton Recorder survey. We also tested whether seabird breeding productivity was more tightly linked to sandeel biomass or quality (size) of individual fish. 3. The biomass of larval sandeels increased two- to threefold over the study period and was positively associated with proxies of the abundance of their plankton prey. Breeding productivity of four seabirds bringing multiple prey items to their offspring was positively related to sandeel larval biomass with a 1-year lag, indicating dependence on 1-year-old fish, but in one species bringing individual fish it was strongly associated with the size of adult sandeels. 4. These links are consistent with bottom-up ecosystem regulation and, with evidence from previous studies, indicate how climate-driven changes in plankton communities can affect top predators and potentially human fisheries through the dynamics of key mid-trophic fish. However, the failing recruitment to adult sandeel stocks and the exceptionally low seabird breeding productivity in 2004 were not associated with low sandeel larval biomass in 2003, so other mechanisms (e.g. predation, lack of suitable food after metamorphosis) must have been important in this case. Understanding ecosystem regulation is extremely important for predicting the fate of keystone species, such as sandeels, and their predators.

Continuous Plankton Records - Seasonal-Variations In The Distribution And Abundance Of Plankton In The North-Atlantic Ocean And The North-Sea

Charts are presented of the seasonal variations in the distribution of four phytoplankton and five zooplankton taxa in the North Atlantic and the North Sea. The main factors determining the seasonal variations appear to be the distribution of the main overwintering stocks, the current system and, in some instances, temperature control of the rate of population increase. Information is presented about the variation with latitude (over the range from 34° N to 65 ° N) of the seasonal regime of the plankton. On the assumption that there is a relationship between nutrient supply and vertical temperature stratification the main features of this variability can be interpreted. In the south (to about 43° N) nutrient limitation plus grazing appear to be dominant, resulting in a bimodal seasonal cycle of phytoplankton. North of about 60° N the system appears to be limited by the size of the phytoplankton stocks being grazed primarily by Calanus Finmarchicus and Euphausiacea. In an extensive zone, from about 44° N to 60° N, it would appear that the spring bloom of phytoplankton is under-exploited by grazing while in summer the zooplankton graze the daily production of the phytoplankton, the stocks of which are probably maintained by in situ nutrient regeneration. The implications, for at least this mid-latitude zone, that rates and fluxes of processes, as opposed to density dependent interactions between stocks, play a major role in the dynamics of the seasonal cycle is consistent with previously reported observations suggesting that physical environmental factors play a major role in determining year-to-year fluctuations in the abundance of the plankton.

Continuous Plankton Records - Persistence In Time-Series And The Population-Dynamics Of Pseudocalanus-Elongatus And Acartia-Clausi

Rates of population increase in early spring and the sizes of overwintering stocks were calculated for the planktonic copepods Pseudocalanus elongatus and Acartia clausi for a set of areas covering the open waters of the north-east Atlantic Ocean and the North Sea for the period 1948 to 1979. For both species, the rates of population increase were higher in the open ocean than in the North Sea and appear to be related to temperature. The overwintering stocks in the North Sea were larger than those in the open ocean and are probably related to phytoplanton concentration. P. elongatus shows higher overwintering stocks and lower rates of population increase than A. clausi, resulting in different levels of persistence in the stocks of the two species. It is suggested that this difference in persistence is responsible for differences between the two species with respect to geographical distribution in summer and different patterns of year-to-year fluctuations in abundance.

Continuous Plankton Records - Phytoplankton Zooplankton And Environment Northeast Atlantic And North-Sea 1958-1980

Year-to-year fluctuations in the abundance of phytoplankton in the North-East Atlantic and the North Sea for the period 1958 to 1980 are described. Based on similarities between their annual fluctuations in abundance, the taxa may be divided into two groups, one of 12 species of diatoms and 1 species of Ceratium, the other of 5 species of Ceratium. The annual fluctuations in abundance of the Ceratium group is negatively correlated with a component of sea surface temperature (representing changes in the open ocean) and with the frequency of cyclonic weather over the United Kingdom. The Diatom group shows very similar annual fluctuations to those of most of the zooplankton species. Both groups show a high ·proportion of long wavelength variability in the form of a more less linear downward trend in abundance over the whole period. There is evidence to suggest that the high proportion of long wavelength variability shown by the zooplankton is influenced by inherent persistence in stocks from year-to year. The phytoplankton show little or no persistence. The close relationship between zooplankton and phytoplankton may, therefore, involve feed-back through nutrient recycling so influencing the annual levels of abundance of phytoplankton.

Continuous Plankton Records - Persistence In Time-Series Of Annual Means Of Abundance Of Zooplankton

Time-series of annual means of abundance of zooplankton of the north-east Atlantic Ocean and the North Sea, for the period 1948 to 1977, show considerable associations between successive years. The seasonal dynamics of the stocks appear to be consistent with at least a proportion of this being due to inherent persistence from year-to-year. Experiments with a simple model suggest that the observed properties of the time-series cannot be reproduced as a response to simple random forcing. The extent of trends and long wavelength variations can be simulated by introducing fairly extensive persistence into the perturbations, but this underestimates the extent of shorter wavelength variability in the observed time-series. The effect of persistence is to increase the proportion of trend and long wavelength variability in time-series of annual means, but stocks can respond to short wavelength perturbations provided these have a clearly defined frequency.