Lead Isotope Variation with Growth Zoning in a Galena Crystal

A large crystal of lead sulfide from Picher, Oklahoma, has significant differences in isotopic composition of lead in successive growth zones. Lead isotope ratios in the parent ore-fluid evidently changed with time during crystal growth. The growth history of this crystal, interpreted quantitatively, points to a tentative hypothesis of genesis of Mississippi Valley deposits of lead and zinc.     

Reconstruction of Current Flow and Imaging of Current-Limiting Defects in Polycrystalline Superconducting Films

Magneto-optical imaging was used to visualize the inhomogeneous penetration of magnetic flux into polycrystalline TlBa2Ca2Cu3Ox films with high critical current densities, to reconstruct the local two-dimensional supercurrent flow patterns and to correlate inhomogeneities in this flow with the local crystallographic misorientation. The films have almost perfect c-axis alignment and considerable local a- and b-axis texture because the grains tend to form colonies with only slightly misaligned a and b axes. Current flows freely over these low-angle grain boundaries but is strongly reduced at intermittent colony boundaries of high misorientation. The local (<10-micrometer scale) critical current density Jc varies widely, being up to 10 times as great as the transport Jc (scale of approximately 1 millimeter), which itself varies by a factor of about 5 in different sections of the film. The combined experiments show that the magnitude of the transport Jc is largely determined by a few high-angle boundaries.     

Climate change and the cetacean community of north-west Scotland

1. Climate change is thought to affect the composition and structure of local ecological communities. We investigate whether ocean warming around north-west Scotland since 1981 has been associated with changes in the local cetacean community.2. Analysis of strandings from 1948 to 2003 found that no new species per decade were recorded in north-west Scotland between 1965 and 1981. This rose to 2.0 new species per decade from 1988 onwards. The new species recorded since 1988 are generally restricted to warmer waters, while those recorded prior to 1981 regularly occur in colder waters.3. In the period 1992 to 2003, the relative frequency of stranding of white-beaked dolphin, a colder water species, has declined while strandings of common dolphin, a warmer water species, have increased. Similarly, sightings surveys conducted in May-September 2002 and 2003 show that the relative occurrence and abundance of white-beaked dolphins have declined and common dolphins increased in comparison to previous studies.4. These observations are consistent with changes in the local cetacean community being driven by increases in local water temperature. If such temperature changes continue, some formerly abundant cold-water species, such as white-beaked dolphins, may be lost from this cetacean community. In a wider context, such changes may lead to populations of cetaceans moving out of areas specifically designated for their protection as they respond to changes in local oceanic conditions.     

An autumn profile of growth regulatory hormones in chinook salmon (Oncorhynchus tshawytscha)

We examined trends in the growth regulatory hormones growth hormone (GH) and insulin-like growth factor-I (IGF-I) from August to December in chinook salmon. Fish on 100% (ad libitum) and 64% rations of a low fat high protein diet, and a 64% ration of commercial feed (BioOregon-grower) were sampled twice a month. Fish were kept on simulated natural photoperiod at constant temperature. GH declined in late August and early September, consistent with photoperiodic regulation. No effects of ration or diet composition on GH were found. IGF-I increased to a peak on 4 October 1998 and declined thereafter. High dietary ration and the higher fat commercial diet increased IGF-I. Fish length and IGF-I level were positively correlated. This study shows that a peak in IGF-I may occur in the fall in chinook salmon. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of feed and feeding in the culture of salmonids on the marine aquatic environment: a synthesis for European aquaculture

While marine aquaculture has grown rapidly, so have concerns regarding the environmental impacts caused by the industry. In particular, increasing discharges of solid and dissolved fish excretions, nutrients and therapeutic chemicals have coincided with greater public awareness of the possibility of environmental damage. This has stimulated a number of criticisms, drawn from a wide spectrum of interests, ranging from the use of natural fish stocks to produce fish meal for aqua feeds to the effects of enhanced nutrient input on the coastal marine environment. The present study reviews available information on the environmental effects of feeding practices in salmonid aquaculture in Europe. Accumulation of waste food and fish faecal material results in changes in the sediment under fish cages, characterized by a low redox potential, high content of organic material and accumulation of nitrogenous and phosphorous compounds. Although significant environmental impacts have been reported in the literature at distances of up to 100 m from the cages, in general such impacts are reported to be localized to within 20–50 m around the cages. For farmed salmon and trout, mass balance models have been developed for nitrogen and phosphorus, indicating that 50% of the nitrogen and 28% of the phosphorus supplied with the food is wasted in dissolved form. The maximum nutrient release can be estimated from the hydrographic conditions in the immediate vicinity of the farm, such as water volume, tidal water exchange and currents. At present production levels, improvements in the feeding efficiency and feed quality of aquafeeds could reduce waste and consequent environmental impacts.     

Factors associated with distributions of six fishes of greatest conservation need in streams in midwestern USA

1. Many fish species of greatest conservation need (SGCN) in Iowa and Minnesota, USA, have been in decline for decades. A key reason for the decline is the alteration and degradation of naturally flowing streams owing to land use changes resulting from agricultural practices. Populations of several fishes have been adversely affected by widespread stream channelization that has resulted in more homogeneous stream habitats throughout Iowa and Minnesota.
2. The goal of this study was to determine the abiotic and fish assemblage characteristics associated with the presence of these rare fishes. Electrofishing and seining were used to sample fish assemblages and 43 abiotic characteristics were measured at 111 sites in the North Raccoon and Boone River basins in central Iowa and the Rock River and Beaver Creek basins in north-west Iowa and south-west Minnesota during 2016 and 2017.
3. Six SGCN, including the federally endangered Topeka shiner (Notropis topeka), were included in statistical modelling to determine habitat and fish assemblage characteristics associated with their presence.
4. Species-specific nonmetric multidimensional scaling ordinations indicated that abiotic characteristics and fish assemblages often differed between sites where SGCN were present and absent. Random forest and logistic regression models suggested that the presence of four of six SGCN were positively associated with species richness, whereas all other 10 important abiotic and fish assemblage variables were unique to only one or two of the six SGCN.
5. Topeka shiners were present at 36% of sites and were positively associated with orangespotted sunfish (Lepomis humilis) catch per unit effort while being negatively associated with canopy cover and fantail darter (Etheostoma flabellare) catch per unit effort.

     

Effects of feeding different concentration and forms of zinc on the performance and tissue mineral status of broiler chicks

1. Two studies were conducted to investigate the effect of feeding different concentration and forms of zinc (Zn) on the performance and tibia Zn status of broiler chicks.

2. In Experiment 1, chicks fed on the control or the diet supplemented with 12?mg of Zn as sulphate had lower feed intake, weight gain and tibia Zn content than other treatment groups. Chicks given 12 and 24?mg of organic Zn in starter and grower phases, respectively, had the same performance and tibia Zn content as those fed 40?mg of Zn as sulphate and the same performance but higher tibia Zn content than those given 12?mg of Zn as organic over the 42?d.

3. In Experiment 2, chicks given 24?mg organic Zn had greater weight gain than chicks fed on the other treatment diets in the starter period. Chicks fed on the control diet had lower tibia Zn content than chicks fed other treatment diets. Chicks given 80?mg Zn as sulphate had higher tibia Zn content than chicks fed the other treatment diets except those given 40?mg of Zn as sulphate.

4. The results from these trials indicate that feeding lower concentration of Zn as organic form may better promote the growth performance of broiler chicks.