Seasonal home range estimates and habitat selection of saugeye in a small warmwater impoundment

Abstract Saugeye, a hatchery‐produced hybrid of walleye, Sander vitreus (Mitchill), × sauger, Sander canadense (Griffith & Smith), is commonly stocked by several state fishery management agencies in the United States. Saugeye is a top‐level predator that can restructure fish communities and provide supplemental angling opportunities. However, there are few published studies explaining distributions and habitat selection of saugeye. This study determined seasonal home range estimates and habitat selection of saugeye in a small warmwater impoundment using ultrasonic telemetry. Seasons for this study were defined as winter, spawn, spring, summer and autumn. Mean home range estimates were greatest during spawn when water temperature increased from 7.5 to 15 °C and lowest in winter when water temperature decreased below 7.5 °C. Saugeye selected open water and mid‐water ledge habitat during each season, but rock/gravel shoreline was increasingly selected during winter and spawn. These results corroborate previous studies that suggest saugeye exhibit seasonal variation in distribution and habitat use patterns. Managers should consider distribution and habitat selection trends of saugeye when assessing stocks or determining whether to introduce the species in a small warmwater impoundment.     

Environmental conditions, satellite imagery, and clupeoid recruitment in the northern Benguela upwelling system

The relationship between oceanographic conditions and clupeoid (pilchard, Sardinops sagax, and anchovy, Engraulis capensis ) recruitment in the northern Benguela upwelling system was investigated from 1981 to 1987 using a time-series of mean weekly SST images. Two approaches were taken. The first involved correlating recruitment success with the number of weekly coastal `SST events' above various cut-off temperatures during the main reproductive season. The second involved constructing a multiple regression model of recruitment success with two independent environmental variables: namely, the number of coastal `SST events' greater than 19°C, and an onshore retention index for the early life-history stages. The retention index was derived from a spatial time-series analysis of the SST images using principal components analysis. In general, pilchard recruitment showed a positive relationship with the `number of SST events' whilst anchovy recruitment had a negative relationship; 1987 was an outlier year, during which there were exceptionally high levels of both pilchard and anchovy recruitment. The multiple regression R ² values were high and significant for both species (pilchard R ² = 0.88, anchovy R ² = 0.96). The regression model also accounted for the 1987 outlier according to levels of onshore retention which, despite low inshore SSTs, were particularly high during the 1986/87 reproductive season. Although these results need to be validated with data from a longer time period, they show how satellite data might be used for predicting clupeoid recruitment success in the northern Benguela.     

烟田杂草防除试验研究

采用5种地膜和2种除草剂进行烟田除草试验。结果金都尔地膜、玉溪除草膜、绿色除草地膜和黑色除草地膜相对于普通白膜而言,对单子叶的防除效果分别为93．22％,95．27％,95．42％,99．83％,对双子叶的防除效果分别为43．12％,52.20％,73.85％,77．27％。敌草胺2次施药的防效明显优于1次施药。不同除草膜对地温的作用存在差异性。     

Antigenic stability of fimbriae of Bacteroides nodosus

Successful vaccination of sheep against footrot and attempts to eradicate the disease depend on there being a limit to the antigenic diversity of the causative bacterium, Bacteroides nodosus. Fimbrial antigenic variation was therefore investigated in vivo, both under conditions of chronic infection and under the pressure of a vaccine-induced immune response, to ascertain whether this represented an obstacle to such goals. Material was available from 5 experiments and although B. nodosus appeared to have undergone changes in its fimbrial antigens in one of these, the possibility that superinfection was responsible for the variation detected could not be ruled out because all sheep in this case were maintained at pasture. Overall, the results provided no evidence of fimbrial antigenic shift in B. nodosus in vivo and in conclusion, the survival of the organism in the sheep's foot, both in long-term natural infection and following vaccination, must therefore be related to factors other than the ability to undergo antigenic variation in order to evade the host's immune response.     

Reduced incidence of persistent chromosome aberrations in mice irradiated at low dose rates

A marked difference was observed between the effectiveness of high and low dose rates of ionizing radiation in producing persistent chromosome aberrations in the marrow cells of mice. Clones of cells with chromosome abnormalities were present in the marrow of all the mice previously exposed to single or fractionated doses of x-rays given at a rate of 30 rad/min. The frequency of chromosome aberrations in these mice varied from 14 to 72 percent of the cells exdmined. By contrast, none of the mice exposed to continuous gamma radiation at a low dose rate (1.45 rad/hour) showed definite clones of abnormal marrow cells, and the frequency of persistent chromosome aberrations varied from zero to 8 percent in this group.