Assessing the South African sardine resource: two stocks rather than one?

Sardine Sardinops sagax distributed off the west and south coasts of South Africa have traditionally been assumed to comprise a single well-mixed stock for assessment and management purposes. New research, however, lends weight to the possibility of two stocks in this region. A precautionary management approach thus needs to consider the impact of management decisions on the hypothesised two individual stocks as well as on the resource as a whole. As a first step in this process, Bayesian assessments of South African sardine are presented, which compare results for the traditional single-stock hypothesis with those that follow from a new two-mixing-stock hypothesis. Recruits from the west stock are assumed to move to and remain part of the south stock in annual pulses of varying size. This movement is estimated to be appreciable, and to take place from a substantially more productive west stock to the south stock. This immigration makes a greater contribution to the south-stock biomass than do years of above-average south-stock recruitment. Importantly, this two-mixing-stock hypothesis is shown to be consistent with the data available. Further alternative sardine stock-structure hypotheses suggested by the most recent data are discussed.     

Excess protactinium in phosphate nodules from a coastal upwelling zone

Measurements of²³¹Pa/²³⁵U and²³⁰Th/²³⁴U activity ratios have been made for a suite of Quaternary age phosphate nodules from the upwelling zone off Peru and Chile. Many of these samples contain more²³¹Pa than would be predicted based on closed-system²³⁰Th/²³⁴U ages unlike samples from non-upwelling environments which have been shown to have concordant²³¹Pa and²³⁰Th ages. Peru/Chile phosphate nodules apparently pick up²³¹Pa preferentially to²³⁰Th. This is most likely a result of prior fractionation of protactinium and thorium in the open ocean. Highly productive coastal upwelling zones may be added to the growing list of localities where fractionation between thorium and protactinium isotopes has been observed in marine sediments.     

Engineering properties and slope stability of lower coal measures rocks from monk wood cutting,Unstone-Dronfield by-pass,Derbyshire

This 30 m deep cutting has been the subject of a detailed geotechnical analysis, in view of mass-sliding wedge failures which had occurred in cuttings in similar geological situations in other parts of Britain.The sequence of rocks includes two coal seams, the upper being thin (0.3 m) and the lower thick (2 m), the latter with a recognisable seatearth (underclay). There is a thick sandstone at the top of the succession, with siltstone, mudstone and black mudstone also present.Both field and laboratory testing was carried out. The most probable failure mechanism within the more competent sandstone sequence to the south of the site would probably have been in the form of wedge failures on pre-existing discontinuities within the rock mass. It was necessary to evaluate the shear strength which could be mobilised along these planes and a field rock shear box was used. Drained-soil shear tests were also made on potential failure-surface materials, namely seatearth and clay shear zones. Weathered mudstone samples were tested to provide design parameters for the analysis of rotational slips. Additional laboratory testing carried out comprised bulk density, classification tests, slake durability and point-load indices. X-ray diffraction analyses were made on a range of materials such as seatearth, mudstone, shear zone and sandstone bedding-plane shear surface. This extensive test programme enabled parameters to be accurately determined for use in stability analyses. The latter show the critical effects of water conditions on the factor of safety.The performance of the cut has been monitored since early 1974 and no recordable movement has been noted.     

Laboratory actinide partitioning: Whitlockite/liquid and influence of actinide concentration levels

Fission and alpha track radiography techniques have been used to measure partition coefficients (D) at trace (ppm) concentration levels for the actinide elements Th, U, and Pu between synthetic whitlockite and coexisting “haplobasaltic” silicate liquid at 1 bar pressure and 1250°C at oxygen fugacities from 10^?8.5 and 10^?0.7 bars. Pu is much more readily incorporated into crystalline phases than is U or Th under reducing conditions (fO₂ = 10^?8.5), because Pu is primarily trivalent, whereas U and Th are tetravalent. Definitive valence state assignments cannot be made, but our best estimates of corrected partition coefficients for Pu⁺³, Pu⁺⁴, Th⁺⁴, U⁺⁴, and U⁺⁶ are, for whitlockite 3.6/<?0.6/1.2/0.5/?0.002. The effect of changing pressure and liquidus temperature is relatively small, which probably reflects a weak temperature dependence for D (whitlockite) but possibly could be due to cancellation of opposing temperature and pressure effects. Comparison of experiments at trace U levels with those containing percent concentrations of UO₂ indicate that Si is involved in the substitution of U in whitlockite with U + 2Si ? Ca + 2P being the most likely mechanism. D_u is lower. 0.3 vs 0.5. at percent levels compared to 20 ppm. This is best explained by the effect of U on melt structure or by a decrease in the fraction of tetravalent U at high U concentrations.     

Amino acid biogeochemistry and dating of offshore Peru/Chile phosphorites

Amino acid biogeochemical results for a suite of indurated sea-floor phosphate nodules from the Peru/Chile margin confirm the youthful nature of these deposits as previously indicated by uranium-series disequilibrium dating. Isoleucine epimerization is significant in the hydrolyzed acid soluble fraction of the nodules with a range in the D-alloisoleucine/L-isoleucine ratio from 0.06 to 0.32. Amino acid compositional patterns are uniform for all nodules and are similar to unlithified surface sediments from the region suggesting that the nodules and sediments constitute a single genetic series.     

Further studies of the nature,composition and ages of contemporary phosphorite from the Namibian Shelf

Major and minor element and radiochemical data are examined for a set of phosphorite concretions and other phosphatic material from the Namibian Shelf. The concretions were separated on a morphological basis from grab samples taken in a transect of shallowing depth over the diatomaceous ooze belt. Compositional data indicate that the samples are fairly pure carbonate-fluorapatite, and trend towards a maximum 32% P₂O₅ content. A range of compositional variability similar to other samples from the Namibian Shelf is observed.Radiochemical systematics confirm that pelletal phosphorite and glauconitized pelletal phosphorite from depths > 170 m are at radioactive equilibrium, and are therefore old and reworked. The concretions, collected from depths shallower than 78 m, are entirely Recent, with maximum ages in the range 500–3800 years. They may be much younger. Despite distinct textural and small compositional differences, similar ages are found for separates from the same grab. Samples of fish scales and an unidentified high-magnesian phosphate mineral are also shown to have incorporated uranium recently.     

Classification of marine bioregions on the east coast of South Africa

Marine bioregional planning requires a meaningful classification and spatial delineation of the ocean environment using biological and physical characteristics. The relative inaccessibility of much of the ocean and the paucity of directly measured data spanning entire planning regions mean that surrogate data, such as satellite imagery, are frequently used to develop spatial classifications. However, due to a lack of appropriate biological data, these classifications often rely on abiotic variables, which act as surrogates for biodiversity. The aim of this study was to produce a fine-scale bioregional classification, using multivariate clustering, for the inshore and offshore marine environment off the east coast of South Africa, adjacent to the province of KwaZulu-Natal and out to the boundary of the exclusive economic zone (EEZ), 200 nautical miles offshore. We used remotely sensed data of sea surface temperature, chlorophyll a and turbidity, together with interpolated bathymetry and continental-slope data, as well as additional inshore data on sediments, seabed oxygen and bottom temperature. A multivariate k-means analysis was used to produce a fine-scale marine bioregionalisation, with three bioregions subdivided into 12 biozones. The offshore classification was primarily a pelagic bioregionalisation, whereas the inshore classification (on the continental shelf) was a coupled benthopelagic bioregionalisation, owing to the availability of benthic data for this area. The resulting classification was used as a base layer for a systematic conservation plan developed for the province, and provided the methods for subsequent planning conducted for the entire South African EEZ. Validation of the classification is currently being conducted in marine research programmes that are sampling benthic biota and habitats in a sampling design stratified according to the biozones delineated in this study.     

Evaluation of the flushing rates of Apalachicola Bay, Florida via natural geochemical tracers

We used naturally occurring radium isotopes as tracers of water exchange in Apalachicola Bay, a shallow coastal-plain estuary in northwestern Florida. The bay receives fresh water and radium from the Apalachicola River, and mixes with Gulf of Mexico waters through four inlets. We deployed moored buoys with attached Mn-fibers at several stations throughout the estuary during two summer and two winter periods. After deployment for at least one tidal cycle we measured the ratio of the two short-lived radium isotopes ²²³Ra (half-life = 11 d) and ²²⁴Ra (3.6 d) to estimate “radium ages” of the water in the bay.During our four seasonal deployments the river discharge ranged from 338 to 1016 m³ s^− 1. According to our calculations the water turnover time in the bay during these samplings ranged from 6 to 12 days. Age contours in the bay showed that winds and tides as well as river discharge influence the water movement and the residence time of freshwater in the bay. We also calculated the mean age of river water in the bay which was between 5 to 9 days during the studied periods. We suggest that this approach can be used to quantify transport processes of dissolved substances in the bay. For example, soluble nutrient or pollutant transport rates from a point source could be examined. We conclude that the radium age technique is well suited for flushing rate calculations in river dominated shallow estuaries.     

Reduction in organic contaminant exposure and resultant hepatic hydropic vacuolation in winter flounder (Pseudopleuronectes americanus) following improved effluent quality and relocation of the Boston sewage outfall into Massachusetts Bay, USA: 1987-2003

Effluent upgrades for metropolitan Boston have included toxicant reduction, primary and secondary treatment and outfall extension. Between 1992 and 2003 winter flounder at five stations were surveyed annually for liver and muscle burden and chronic hepatic sub-lethal impacts of polynuclear and halogenated aromatic hydrocarbons, and metals. Trends in flounder availability and fin condition were also examined. In 1988 12% of the adult winter flounder in Boston Harbor exhibited hepatic neoplasms and up to 80% had hepatic hydropic vacuolation (HV). Tumor prevalence fell to 0-2% and HV to <50% by 1996. Since then tumors have been absent, while a steady prevalence of HV has persisted, consistent with lower hydrocarbon loading and tissue levels. Contaminants and HV also fell with distance from the Boston outfall. After the outfall extension was activated in 2000, there has been no significant change in flounder liver health at the new outfall site.