Can We Predict the Future: Juvenile Finfish and Their Seagrass Nurseries in the Chesapeake Bay

The importance of estuarine seagrass beds as nurseries for juvenile fish has become a universal paradigm, especially for estuaries that are as important as the Chesapeake Bay. Yet, scientific tests of this hypothesis were equivocal depending on species, location, and metrics. Moreover, seagrasses themselves are under threat and one-third of seagrasses have disappeared worldwide with 65 of their losses occurring in estuaries. Although there have been extensive studies of seagrasses in the Chesapeake Bay, surprisingly few studies have quantified the relationship between seagrass as nurseries for finfish in the Bay. Of the few studies that have directly evaluated the use of seagrass nurseries, most have concentrated on single species or were of short duration. Few landscape-level or long-term studies have examined this relationship in the Bay or explored the potential effect of climate change. This review paper summarizes the seagrass habitat value as nurseries and presents recent juvenile fish studies that address the dearth of research at the long term and landscape level with an emphasis on the Chesapeake Bay. An important conclusion upon the review of these studies is that predicting the effects of climate change on fishery production remains uncertain

Framework and Initial Analyses of Fertilizer Profitability in Maize and Cotton in Zambia

Inorganic fertilizers will play a role in government programs, but whether or not a single policy is valuable for all farmers depends upon the net gain for the farmers. The research here seeks to demonstrate how to answer the question “Is fertilizer profitable in Zambia for maize and cotton in the smallholder sector?” This study identifies the key components determining profitability and then sets up a framework to evaluate the probability of farmers to obtain profitable results with fertilizer use on maize and cotton. Several cases are selected and the results are evaluated. Private profitability for the farmer at market prices is discussed, leaving social profitability to other researchers. A simple method for farmers and extensionists to use to assess a fertilizer investment is given, to assist in more site specific analysis, given prices and environment.food security, food policy, Zambia, maize, cotton, fertilizer, Agribusiness, Q18,

Chemistry of Surface Waters: Distinguishing Fine-Scale Differences in Sea Grass Habitats of Chesapeake Bay

We tested the hypothesis that the physical and chemical processes acting in sea grass habitats of the lower Chesapeake Bay are spatially structured and that dissolved elemental chemistry of sea grass-habitat surface waters have their own unique identity. We sampled surface waters from July to September 2001 in five sea grass habitats of the lower bay: Potomac, Rappahannock, York, Island (Tangier-Bloodsworth), and Eastern Shore. Dissolved Mg, Mn, Sr, and Ba concentrations were measured by sector field inductively coupled plasma-mass spectrometry. As expected, Mg, Sr, and Ba exhibited conservative behavior, but Mn exhibited nonconservative behavior along the salinity gradient. Spatial differences in the chemistry of surface waters over sea grass habitats were fully resolvable independently of time. Moreover, classification accuracy of water samples was low in Rappahannock, moderate in Potomac and Eastern Shore, and high in the York and Island habitats. The chemistry of York was distinct because of the effects of physical mixing, whereas Island chemistry was unique, potentially because of the influence of Coriolis acceleration and river discharges from the Susquehanna River. The results of this study show that sites so close to one another in physical space maintain distinct chemical differences

Age, Growth, and Mortality of Black Drum, Pogonias cromis, in the Chesapeake Bay Region

We used otolith ageing to describe the population dynamics of black drum, Pogonias cromis, collected over a three-year period from the Chesapeake Bay region\u27s commercial and recreational fisheries. Black drum average age, total length, and weight were 26 years, 109.5 cm, and 22.1 kg respectively. The oldest fish was 59 years and fish older than 50 years were present in the catch from 1990 to 1992. Growth in length slowed by age 20, whereas growth in weight did not slow until age 45. A von Bertalanffy growth function was fitted to our data (L(infinity) = 117.3 cm, K=0.105, t(0)=-2.3 yr) and was similar to that for northeast Florida, but dissimilar to that for the Gulf of Mexico. Fish grow slower but reach larger sizes in the Atlantic than in the Gulf. Estimates of instantaneous total mortality, Z, from maximum age and catch-curve analyses were low, 0.08-0.13, indicating that fishing mortality is also low in the Chesapeake Bay region. Studies to date lend support to the hypothesis that black drum from the east coast of the United States are from a common stock. The fishery of the Chesapeake Bay region is made up of old, large migrants from that larger population and should be managed accordingly

Grade Span Configuration and Academic Performance for Students in Poverty: A Texas Multiyear Analysis

Grade-span configuration refers to the range of grades within a school (Coladarci & Hancock, 2002). The debate over the benefits of one grade span configuration over the other has ensued for decades (Howley, 2002). Specific questions in this debate are (a) Which grade span configuration is most cost effective?; (b) Which grade span configuration yields the best academic achievement?; and (c) Which grade span configuration best meets the social and emotional needs of middle level children? (Howley, 2002)

Radiocarbon From Nuclear Testing Applied to Age Validation of Black Drum, Pogonias cromis

Radiocarbon ((14)C) in the world\u27s oceans increased sharply between 1950 and 1970 as a result of the atmospheric testing of nuclear weapons. Through comparison with the (14)C time series reconstructed from atmospheric measurements and marine carbonates, Kalish, in 1993, used the (14)C concentration measured in fish otolith cores as a means of confirming the annulus-based age estimates for some South Pacific fish species. Here we report the pre-and postbomb (14)C chronology of North Atlantic adult black drum (Pogonias cronis), assumed to be between 15 and 42 yr of age on the basis of otolith annulus counts. According to accelerator mass spectrometry (AMS) assays, (14)C in otolith cores in creased sharply between 1958 and 1964, with a timing and magnitude which was very similar to that of the atmospheric bomb (14)C signal. The correspondence between the two (14)C chronologies indicates that the annulus-based age assignments were accurate on average to within 1-3 yr. Differences between the black drum Delta(14)C chronology and that of other marine carbonates in the North Atlantic are explained by the estuarine habitat of young-of-the-year black drum and by the fact that estuarine Delta(14)C values more closely reflect atmospheric values than surface ocean values. At present, there is no other age-validation technique that can confirm the absolute age of long-lived fish species with comparable levels of accuracy

Substituting Otoliths for Chemical Analyses: Does Sagitta = Lapillus?

Chemical analysis of fish otoliths has become an important technique in fisheries science with widespread applications. Most research up to this point has focused predominantly on sagittal otoliths, but the underlying assumptions may also apply to lapilli. The goal of this study was to determine whether lapilli and sagittae have the same otolith chemistry and whether one can be substituted for the other for solution-based chemical analysis in wild-captured fish. We compared the stable isotope chemistry (δ13C and δ18O) of paired sagittae and lapilli of juvenile spotted seatrout Cynoscion nebulosus collected from Chesapeake Bay seagrass beds in 2002. Stable isotopic signatures were significantly different in both carbon and oxygen for paired sagittae and lapilli. Both δ13C and δ18O values were higher in the sagitta relative to the lapillus. As a correlate to isotopic analysis, shape measurements were taken on paired sagittae and lapilli for growth comparison. While the 2 otoliths are a similar size at formation, the sagitta grows faster, quickly outgrowing the lapillus during the juvenile stage. We expected that after detrending isotope data to account for fish length, the relation with otolith growth would become clear. Surprisingly, this was not true for either δ13C or δ18O. Carbon isotopic differences appear to be strongly influenced by metabolism, and the relationship of δ18O with otolith growth is obscured by a variable environment. Our results clearly show that sagittae is not equal to lapilli for solution-based whole otolith analysis. Moreover, while the sagitta reflects the juvenile stage environment with greater fidelity, the lapillus reflects the larval stage more strongly

Effect of Laser Ablation Depth in Otolith Life History Scans

Life history scans of fish otoliths are bringing new insight into the structure, connectivity, and movement of fish populations. Data obtained from such scans, however, possess in-herent limitations that have not yet been fully addressed or understood. For example, several investigators have noted delays in otolith elemental uptake that do not appear to reflect habitat exposure. We hypothesized that the 3-dimensional structure of otoliths may produce sampling artifacts in the results obtained from laser ablation scans. To test this hypothesis, we sampled sagittal otoliths from juvenile Atlantic croaker Micropogonias undulatus with laser ablation inductively coupled plasma mass spectrometry to obtain elemental molar ratios of a common environmental marker (barium). We ablated 2 trenches of different depths on each otolith and performed spectral analyses on the data to investigate the effects of ablation depth, including differences in the periodicities and temporal variability between trenches. The mean barium concentration between the 2 trenches was significantly different (t = 114.25, p \u3c 0.0001). From shallow to deep trenches, variance decreased; the standard error about the means was reduced from 0.609 to 0.086. Peaks in spectral density, which estimate the ingress timing for this species, were shifted in absolute value an average of 32 d. Our results highlight the necessity of considering depth of laser ablation when conducting life history scans

Reproduction of Black Drum, Pogonias cromis, from the Chesapeake Bay Region

Ovaries of black drum, Pogonias cromis, collected from the Chesapeake Bay region in 1992, were used to describe reproductive strategy and fecundity. Histological examination showed that black drum spawn in the Chesapeake Bay region from April through early June. Distributions of oocyte diameter showed distinct oocyte-developmental groups indicating that Chesapeake Bay black drum are group-synchronous batch spawners. Female black drum are extremely fecund ranging from 414,000 to 3,736,000 hydrated oocytes (mean = 1,389,000) per batch with a spawning periodicity of 3.8 days. Estimates of spawning strategy, spawning periodicity, and batch fecundity for black drum from the Chesapeake Bay region were similar to reported estimates from the Gulf of Mexico