Variations in food abundance for Japanese sardine larvae related to the Kuroshio meander

Long-term fluctuations of chlorophyll a concentration, and abundance of herbivorous or omnivorous small copepods during the spawning season of the Japanese sardine, Sardinops melanosticta , were examined in relation to the types of Kuroshio meander. The purpose was to clarify the influence of the meander on the production of food organisms for the sardine larvae and their survival in the Pacific coastal region of central Japan. During an A-type meander of the Kuroshio, when the offshore and inshore movements of the Kuroshio path were small except at the beginning of the meander, the surface chlorophyll a concentration in the coastal region was lower than that during a non-A-type meander with frequent and prompt fluctuations of the Kuroshio path. The abundance of small copepods was also low during the A-type meander except in the subsequent spring just after the beginning of an A-type meander, but often high during the non-A-type meander. Prompt fluctuations of the Kuroshio path during the non-A-type meander probably cause local upwellings which stimulate primary and secondary production near the Kuroshio, and may enhance the survival of the sardine larvae. On the contrary, the quasi-stationary state of an A-type meander may be unfavourable for the production of phytoplankton and nauplii of herbivorous or omnivorous small copepods, and therefore the survival of the sardine larvae becomes poor.     

Effects of physical barriers and eradication on recolonization of rodents in poultry farms

Abstract

Mus musculus, Rattus rattus and Rattus norvegicus are pests in poultry farms, causing economic losses and transmitting diseases. Control is commonly conducted through anticoagulant rodenticides, but this control is not effective through time. We aimed to assess the effect of rodent exclosure on long-term success of rodent control in poultry farms of the pampean region, Argentina, and to evaluate indirect estimators of rodent abundance. In both exclosure and non-exclosure sheds rodent abundance decreased significantly after eradication but mice populations showed a recovery, suggesting that the eradication was not complete. Rats did not recover, but the low abundance found at the beginning of the experiment does not allow an accurate conclusion.     

2005年夏季东太平洋中国多金属结核区小型底栖生物研究

“大洋一号”调查船于2005年7月在太平洋结核区中国合同区东、西小区调查中共进行了12个站位的小型底栖生物的取样.研究表明:调查区域小型底栖生物共有13个类群.东、西两小区小型底栖生物平均密度分别为(104.4±20.48)个/10 cm2,(40.26±25.84)个/10 cm2,线虫平均生物量分别为(5.25±0.99)(μg·干重)/10 cm2,(1.68±0.77)(μg·干重)/10 cm2,东小区小型底栖生物平均密度、线虫生物量明显高于西小区.线虫是绝对优势类群,分别占东、西小区小型底栖生物总密度的93.13％和91.36％,其它优势类群有桡足类,多毛类,介形类等.小型底栖生物密度随着沉积物深度的增加而减少,其数量的75％以上分布在0-2 cm层,东小区深层的小型底栖生物所占比例比西小区要大.与环境因子相关分析表明:调查区域的小型底栖生物密度,线虫密度,线虫生物量,桡足类密度,多毛类密度与经、纬度呈显著负相关,与脱镁叶绿素呈显著正相关,与沉积物微型生物生物量相关性不显著.小型底栖生物密度,线虫密度,线虫生物量,多毛类密度与叶绿素a呈显著正相关,桡足类与叶绿素a相关性不显著.脱镁叶绿素与沉积物微型生物生物量呈显著正相关.     

海岸带地理特征对沉水植被丰度的影响

对北美切斯比克海湾99个河口海岸带地理特征(流域土地利用类型、河口宽度、海岸线分形维度、流域面积与河口面积比、高分辨率平均波浪高度和沉积物等)对1984-2009年间沉水植被丰度的影响进行了研究.结果表明:相同盐度分区的不同土地利用类型下,以及相同土地利用类型的不同盐度分区下,沉水植被丰度存在着明显的差异;沉水植被丰度与海岸带地理特征各单因子之间呈微弱相关性(-0.157≤r≤0.442),其中,沉水植被丰度与河口宽度(r=0.442,P＜0.001)、分形维度(r=0.290,P=0.007)和平均波浪高度(r=0.306,P=0.002)相关关系相对较高,且呈极显著正相关(P＜0.01);分类回归树模型分析表明,影响沉水植被丰度的海岸带地理特征因子依次为流域与河口面比、河口分形维度、盐度和平均波浪高度,共可解释沉水植被丰度空间变异的60％以上.研究表明,海岸带地理特征直接或间接的影响着区域沉水植被丰度,二者之间存在一定的相关关系;不同特征因子对沉水植被丰度的影响程度不同,但整体呈现出多因素综合的复杂影响.研究结果对切斯比克海湾沉水植被的生态恢复具有一定的指导意义.     

Comparison of euphausiid population size estimates obtained using replicated acoustic surveys of coastal inlets and block average vs. geostatistical spatial interpolation methods

Because of their intense patchiness, euphausiid spatial distributions and stock sizes are often assessed using echosounder surveys. However, statistical error bars appropriate for individual survey results are not well known. We quantified these by examining the statistical repeatability of acoustic estimates of total euphausiid biomass within two enclosed fjords adjoining the Strait of Georgia, British Columbia. Within each inlet, paired and replicated `mirror image' zig-zag survey tracks provided sets of closely spaced backscatter profiles along the survey lines. Local stock density (biomass per unit area) was calculated by vertical integration across the euphausiid scattering layer. Total inlet population size was then estimated by horizontal interpolation and integration of the local measurements, both by block averaging and by geostatistical interpolation (kriging). By assuming no change in true population biomass over the short time interval separating replicate surveys, we could then estimate statistical precision by analysis-of-variance comparison among replicate survey grids. For the partial surveys (one or the other half of the mirror-image paired grid) multiplicative error bars were about a factor of 1.5 for Jervis Inlet and 1.7 for Saanich Inlet. Use of the full surveys (both parts of the mirror-image pair, roughly doubling the number of measurements in each estimate) reduced the error to about factor of 1.35 for Jervis but only to about 1.65 for Saanich. Statistical precision was similar for the block average vs. kriging interpolation and integration methods, however, kriging provided additional useful information about spatial pattern within the inlets.     

Weed or not a weed? Density,perceptions and management of Chromolaena odorata (Asteraceae) in West Africa: Voices from Ghana

The status (weed or beneficial shrub) of Chromolaena odorata in West Africa has been a major subject of debate since its introduction in the 1930s. Its negative impacts on agriculture and biodiversity are clear. However, indigenous people have harnessed several benefits of the plant, making management strategies less straightforward. Using indigenous voices in Ghana, the current perceptions of C. odorata in West Africa were assessed. Here, 90 respondents in three regions of Ghana were interviewed, using questionnaires, on aspects relating to the abundance, perceptions and management of C. odorata in their communities. Overall, results showed that the density of C. odorata had declined. The majority of the respondents considered C. odorata as a fallow shrub, a medicinal plant or both. However, impacts on crop production and injuries incurred during physical control were also highlighted. The local uses of the plant in Ghana included treating fevers and injuries, and as a fallow shrub for soil nutrient replenishment. Although most of the respondents classified C. odorata as a useful shrub in Ghana, they also highlighted the use of local farming tools such as cutlasses for the slash of the plant. The use of herbicides for the control of C. odorata was rare and not applied specifically for C. odorata. In conclusion, local awareness programmes on the deleterious impacts of C. odorata on ecosystem functioning and livelihoods are required for its effective management in West Africa.