Trans-oceanic characterization of zooplankton community size structure using an optical plankton counter

The Atlantic Meridional Transect (AMT), sampling between 50°N and 50°S, is a trans-oceanic research programme to characterize plankton community structure, productivity and bio-optical properties of the upper ocean in relation to ocean provinces and meso-scale features. As part of a suite of continuous measurements, an optical plankton counter (OPC) has been used on the AMT to characterize the surface distribution of zooplankton based on their abundance and community size structure. Results from the OPC were available in real time, and were subsequently validated against microscope counts of zooplankton sampled concurrently along the AMT. Zooplankton community size structure from two sections of the Transect are presented: from the northern edge of upwelling off West Africa to the UK shelf and between the Falkland Islands and Uruguay, where the Transect traversed a warm core ring. Results showing the zooplankton community size structure together with statistical analysis, using principal component analysis (PCA), are compared with the dynamic oceanographic characteristics along the Transect. The application of the OPC for such basin-scale studies provides a methodology for obtaining data on zooplankton abundance and community structure at the appropriate spatial scales for global-scale modelling of the marine ecosystem.     

Variation in reproductive potential and influence on Icelandic herring recruitment

Explaining recruitment variation in fish is essential for successful fishery management and is consequently under constant review, with an increasing focus on how maternal factors, relative to environmental influences, operate at the level of individual female spawners and extend from the spawning stock through to recruitment. We estimate total egg production (E) in Icelandic summer‐spawning herring (Clupea harengus) from 1963 through 1999 by using sequential population analyses (SPA) and their estimates of stock biomass and recruitment, various size and maturity metrics, and individual fecundity estimates that rely on total length and the condition of the spawners. Generalized linear models indicate that maternal effects are of significance in explaining SPA‐based recruitment‐at‐age‐3 (R). The best model explained 64% of the variation in R and incorporates E constrained to the repeat spawners (40%), the NAO winter index (18%) and ocean temperature (6%). The latter two represent the winter and spring periods subsequent to year‐class formation. Recruit spawner contributions to E were of no significance in explaining variation in R despite the fact that they could contribute as much as 55% of E when their contribution to E was consistently underestimated by a factor of ～ 2, based only on their contribution to spawning stock biomass. We conclude that the spawning potential of the repeat spawners should replace total spawning stock biomass for determining recruitment potential in stock assessment. In addition to the incorporation of oceanographic factors, this would provided a more cautious and risk‐adverse approach.     

Zingiber officinalis an herbal appetizer in the tiger shrimp Penaeus monodon (Fabricius) larviculture

Penaeus monodon postlarvae were fed with different percentages (0%, 25%, 50%, 75% and 100%) of the herbal appetizer Zingiber officinalis enriched Artemia. After 30 days of culture (i.e. PL‐1–30), a very positive result was found in Z. officinalis‐enriched Artemia‐fed postlarvae. The unenriched Artemia‐fed postlarvae consumed 91.0 mg/animal/30 days of feed, whereas the Z. officinalis‐enriched Artemia increased their consumption to 127.9 mg/animal/30 days. A similar pattern was noticed in feed absorbed (110.2 mg), dry weight growth (26.7 mg) and feed catabolized (83.2 mg) in Z. officinalis‐enriched Artemia because of enzymatic activities. The conversion efficiency of unenriched postlarva was 17.19%, whereas in 100%Z. officinalis‐enriched Artemia, the maximum conversion efficiency was 20.85%. The net production efficiency increased significantly (P < 0.05) to 22% from that of the unenriched Artemia‐fed postlarvae. The administration of Z. officinalis in all levels produced significantly (P < 0.05) higher weight gain and specific growth rate. The utilization efficiency of feed increased proportionately to the percentages of Z. officinalis. Digestive enzyme activity (amylase, protease and lipase) increased significantly (P < 0.05) in the 50%, 75% and 100% enrichment. Among the different percentages of enrichment, the 100%Z. officinalis‐enriched Artemia‐fed postlarvae performed better in the overall status.     

Pelagic ecology of a northern boundary current system: effects of upwelling on the production and distribution of sardine (Sardinops sagax), anchovy (Engraulis australis) and southern bluefin tuna (Thunnus maccoyii) in the Great Australian Bight

Shelf waters of southern Australia support the world's only northern boundary current ecosystem. Although there are some indications of intense nitrate enrichment in the eastern Great Australian Bight (GAB) arising from upwelling of the Flinders Current, the biological consequences of these processes are poorly understood. We show that productivity in the eastern GAB is low during winter, but that coastal upwelling at several locations during the austral summer–autumn results in localized increases in surface chlorophyll a concentrations and downstream enhancement of zooplankton biomass. Sardine (Sardinops sagax) and anchovy (Engraulis australis) eggs and larvae are abundant and widely distributed in shelf waters of the eastern and central GAB during summer–autumn, with high densities of sardine eggs and larvae occurring in areas with high zooplankton biomass. Egg densities and distributions support previous evidence suggesting that the spawning biomass of sardine in the waters off South Australia is an order of magnitude higher than elsewhere in southern Australia. Sardine comprised >50% of the identified prey species of juvenile southern bluefin tuna (SBT, Thunnus maccoyii) collected during this study. Other studies have shown that the lipid content of sardine from the GAB is relatively high during summer and autumn. We suggest that juvenile SBT migrate into the eastern and central GAB during each summer–autumn to access the high densities of lipid‐rich sardines that are available in the region during the upwelling period. Levels of primary, secondary and fish production in the eastern GAB during summer–autumn are higher than those recorded in other parts of Australia, and within the lower portion of ranges observed during upwelling events in the productive eastern boundary current systems off California, Peru and southern Africa.     

DOES CHANGING THE ORIENTATION OF A THORACIC RADIOGRAPH AID DIAGNOSIS OF RIB FRACTURES?

To test the hypothesis that changing the orientation of a thoracic radiograph aids diagnosis of rib fractures, a case–control study was carried out using 120 radiographs of small animal patients with recent thoracic trauma. Six independent observers representing three levels of experience viewed the radiographs in randomized order in conventional and unconventional orientations at 15‐s intervals in a PowerPoint^® presentation. Sensitivity for rib fractures was 53–69% and specificity was 74–97%, depending on the observer. Radiologists had higher specificity than less experienced observers (P=0.0001), but comparable sensitivity for rib fractures. Radiologists had significantly higher accuracy than residents (P=0.03), and residents had higher accuracy than interns (P=0.02). Accuracy of diagnosis was reduced significantly when based on lateral radiographs compared with dorsoventral (DV)/ventrodorsal (VD) views (P=0.02) mainly because of low sensitivity of lateral radiographs of dogs with rib fractures. Rotating radiographs 90° clockwise was associated with increased specificity of one intern (from 74 to 90%, P=0.03), but had no effect on accuracy of diagnosis by other observers (P>0.16). Turning DV/VD views upside down had no effect on accuracy of diagnosis of any observers (P>0.40). Changing the orientation of a thoracic radiograph may make it easier for some novices to examine the ribs; hence it could be considered a training aid rather than a technique that will benefit an experienced radiologist.     

The Fraser River plume: some preliminary observations on the distribution of juvenile salmon, herring, and their prey

Zooplankton and fish densities in the southern Strait of Georgia were observed to coincide with variations in surface salinities resulting from the outflow of the Fraser River. Vertical net hauls in the euphotic zone revealed that copepods, amphipods, and euphausiids were significantly more abundant per m³ in the brackish estuarine plume (surface salinities - 10–15 ppt) when compared to the area covered by the freshwater of the Fraser River plume (0–10 ppt) and the region of the Strait of Georgia (25–30 ppt) unaffected by the outflow of the Fraser River.
The estuarine and riverine plumes had significantly higher fish densities (adult and juvenile herring, and juvenile salmonids [excluding chinook]) than the Strait of Georgia region, with no significant differences in densities of juvenile chinook salmon observed between regions. The highest catches of juvenile salmonids were at the boundary between the estuarine plume and the Strait of Georgia. Zooplankton found in the stomach contents of both adult and juvenile herring suggested that the herring were filter-feeding on the zooplankton in the estuarine plume. Juvenile salmonids fed primarily on small unidentifiable juvenile fish. The existence of increased densities of prey items in the estuarine plume is proposed to be the primary mechanism resulting in increased residence time in this region by outmigrating juvenile salmonids. Utilization of aggregated zooplankton could lead to increased salmonid growth rates and therefore to enhanced survival of individuals utilizing the Fraser River plume environment.     

Nongovernmental Organizations and the Option Value of Donated Land

ABSTRACT Nongovernmental organizations frequently receive donations of land that have unknown characteristics. This paper presents an analytical model of the option to preserve such land. The nongovernmental organizations' option value arises from the option to preserve or sell the land to generate funds for other preservation projects. We show that die preservation option is equivalent to an option that allows the nongovernmental organization to choose between he maximum of the market value of the land and the preservation value of the land. From the resulting closed from solution of the option to preserve, we perform comparative statics showing how the relevant factors (preservation value of the land, the development value of the land, the length of the that the option is available, and the uncertainty surrounding the relative values of preservation and development) influence the value of the preservation option. In addition, to the basic model, we present three model modifications. The first examines the effects of costly preservation and costly nonpreservation. In the second extension, we examine the effects of freeriding modeled by a continuous variable. In the final modification, we relax the assumption of the fixed survey period and show the optimal development date.     

EVIDENCE OF RECOVERY FROM ACIDIFICATION IN MASSACHUSETTS STREAMS

A ten year survey of water quality in 330 Massachusetts streams was conducted to examine the rate and pattern of recovery from acidification. Meta-analysis was used to combine the results of the 330 non-parametric trend tests into an overall test for trend in a variety of water quality variables including pH, acid neutralizing capacity (ANC), and major inorganic ions. Analysis of trends in the raw data indicates both pH and ANC are increasing. After detrending for variations in stream runoff, we estimate the streams are recovering from acidification at a rate of +0.021 pH units/year and +2.4 μeq/L/year, for pH and ANC respectively. These trends appear to be related to declines in sulfate (–1.8 μeq/L/year), while base cation trends were mixed. Meta-analysis reveals the trends are not always homogeneous between seasons or between sites. While it is commonly assumed that the low ANC systems are most ‘sensitive’ to changes in acid or base inputs, we found the greatest rates of change in ANC were associated with the high ANC systems. The greatest increases in pH were seen in the low ANC streams as expected. The results also suggest streams respond quickly to changes in precipitation inputs and stream monitoring networks may be valuable as an early detection technique for changes in environmental quality.