Demographic analysis of the night shark (Carcharhinus signatus, Poey, 1868) in the equatorial Southwestern Atlantic Ocean

A demographic analysis of the night shark (Carcharhinus signatus) was carried out to establish the conservation status of this species caught by longlines on oceanic banks off northeastern Brazil. The biological input parameters (age at first maturity, longevity, fecundity and natural mortality) used for the construction of life tables were taken randomly from their respective probability distributions, taking into account the uncertainty of the parameter estimates by employing Monte Carlo simulations. Nine scenarios were generated from natural (M), total (Z), initial (Z₀—corresponding to the first year of life of the cohort) and population equilibrium (Z′) mortality rates. Each scenario was executed 1000 times, varying the vital input rates for the estimation of the demographic parameters (net reproductive rate, R₀; mean generation length, G; and intrinsic rate of population increase, r). Age at first maturity for C. signatus is 10 years; 89.2% of the stock is made up of juveniles, with fishery recruitment beginning at 5 years of age. The scenarios reveal that catches prior to first sexual maturity result in a significant reduction in population (−8.1%/year) and that the population would only support current efforts if the individuals caught are over 10 years of age or if mortality due to fishing efforts corresponded to the equilibrium rate beginning with recruitment at 5 years of age. A low survival rate is estimated for the first year of life. In order for the population to remain in equilibrium with current mortality rates and recruitment age, survival should be around 0.9. The combination of a low initial survival rate, low fecundity, fishery efforts and the large number of juveniles caught indicates that the C. signatus population off northeastern Brazil is being overexploited.     

Bioeconomic assessment of size separators in Pacific saury fishery

In the middle of the 1990s, Pacific saury fishery vessels began to install “size separators” to selectively land large-size class fish with a higher price. Contrary to expectations, this resulted in removal of the separators in 2006 because fishers believed the separators had contributed to price collapses in the 2000s. The intent of this paper is to investigate the effects of separators on both the fishery economy and stock of Pacific saury by simulating population and economic models under a single framework. For this purpose, we developed (1) an age-structured population dynamics model with stochasticity, and (2) an economic model spanning both price and inventory dynamics with stochasticity, in which each set of model parameters were estimated on the basis of time series data. In a 10-year simulation, the harvest quota was set constant from 20,000 to 400,000 t at intervals of 20,000 t, and the effects of separators were incorporated by controlling the catchability of 0-year-old fish. We found that separators increase the expected yield and reduce the deficit risk for harvests of 140,000 t and smaller. However, separators have the opposite effects for harvests of 160,000 t and larger.     

西南春玉米MCO-3群体主要农艺性状遗传增益分析

以西南生态区9个骨干自交系为材料,建立西南春玉米基础群体MCO-0,用测交法和后代鉴定法对其进行改良,对其不同世代的群体产量及产量性状、穗部性状、株型性状增益分析。结果表明,以MCO-0为基础群体,经过两轮的改良,MCO-2群体主要目标性状单株产量、穗行数等均有所增益,穗长、轴粗等为负增益。MCO-2经过一轮改良后的MCO-3群体株高、穗位高等有所增益,穗长、穗粗等为负增益。以MCO-1相比,MCO-3主要目标性状单株产量、秃尖长、ASI均有所增益,其余性状有的轮次有所增益,有的轮次为负增益。     

陕西渭北旱塬区耕地时空格局变化分析

渭北旱塬区人地矛盾突出,准确认识该区耕地时空格局演变规律,有利于为耕地资源合理利用,粮食及生态安全保障提供决策依据.该研究基于1995—2020年耕地空间分布信息,采用重心模型、标准差椭圆、空间自相关和地学信息图谱等方法,从耕地总量变化特征、耕地空间变化特征和耕地LISA频率图谱特征3个方面开展,揭示陕西渭北旱塬区耕地...     

Performance and effects of small ruminal boluses for the electronic identification of fattening lambs

Two types of electronic boluses were evaluated in two experiments using intensively reared lambs. In Experiment 1, 148 lambs were assigned to three treatments defined by bolus type and lamb's age: mini (M, 5.2 g) applied as early as possible; small (S, 20.0 g) applied after weaning; and control (C), without bolus. Application of the M and S boluses required lambs older than 8 and 46 days, respectively. No differences in total mortality (6.8%), milk and concentrate intakes, and final live weight (LW) were observed between bolus types at the end of fattening (11 weeks). Total retention rates of boluses were 59.0% and 100% for the M and S boluses, respectively. Abattoir retrieval was 100%. Conventional ear tag loss rate in the same period was 2.1%. In Experiment 2, we used 94 lambs in three treatments, 2 of them applied with M boluses at: M1, 1 week before weaning; M2, 1 week after weaning; and C, without bolus. Bolus retention rate (43.5%) of M boluses was not affected by weaning. Ear tag loss rate was 3.2%. In conclusion, application age of M boluses was earlier than 8 days of age but their retention rates need to be improved. The S boluses are feasible to use as a permanent identification system in lambs older than 7 weeks. For earlier tagging, boluses as small as M but with greater weight and specific gravity should be developed.     

ESTIMATING DENSITY AND POPULATION SIZE OF TIBETAN SNOWCOCK IN TIBET

PREFACETibetansnowcock(Tetragallustibetanus)isakindofplateaubird,whichlivesinhighestlandamongseveralpheas-antsintheworld.ThesnowcockismainlydistributinginTibetanditshabitatstretchesfromeastinQinlingMountainstowestinPamirPlateau.Tibetisavastexpanseofplateauterritorywithe1evationofmorethan4,OOom.TherearemanysnowmountainsinTibet,especial1yinwesternparts.Theriversand1akesspreadovera1lplaces.BecauseofhightopographyfeaturesandtheHimalayasmountainsys-temacrossfromeasttowest,thechimateisveryco…     

天然次生林群落中刺五加种群生态学的研究（V）──刺五加种群增长的Leslie矩阵模型

本文介绍了Ｌｅｓｌｉｅ矩阵的构造过程，对处于不同群落中的刺五加种群建立了Ｌｅｓｌｉｅ增长模型，由此预测出刺五加种群在近期将呈现出不断增长的趋势．     

用填充法巧解物理问题

以实例介绍了用填充法求解非安全对称性物理量的解题思路及解题技巧。     

The Michigan equine monitoring system. I. Design, implementation and population estimates

The Michigan equine monitoring system (MEMS) was designed and implemented in the State of Michigan, starting in 1991. The program was designed systematically to track the State's equine population, its health, and its economic implications to the equine industry. The MEMS was designed as a two-phase program. Phase I (the population and economic survey; the subject of this paper) was designed to provide new and statistically valid information describing the size, composition, location and economic characteristics of the Michigan equine industry. A standardized questionnaire was used to collect data via mail, telephone and personal interviews.

Of the 3000 randomly selected list-frame samples, 2800 (93%) participated. However, 650 of these had no equids. There were 129932 equids reported compared with 160000 in 1984. The American Quarter Horse, Standardbred and Arabian breeds were the most numerous. Detailed results, including the size of equine operations/herds, uses, geographical distribution and the financial structure of the industry, are presented. A detailed account of the strategies used in designing and implementing the system is provided.     

Effect of Population Levels of Soybean on Physiological Growth Parameters of Sorghum CO 24 in Sole and Intercropped Stand

A field experiment was conducted during kharif, 1985 and summer, 1986 in sandy clay loam soil under irrigated condition at Tamil Nadu Agricultural University, Coimbature, with a view (i) to assess the suitable method of planting of sorghum CO 24 when intercropped with soybean, (ii) to evaluate the suitable planting ratio of sorghum - soybean intercropping system, (iii) to find out the compatible population level of soybean when intercropped with sorghum CO 24.
Direct sown sorghum at 4: 2 and 2: 2 recorded grater leaf area (LA) compared to transplanted sorghum in both kharif and summer. Sorghum transplanted with 14 days old seedlings recorded higher Crop Growth Rate (CGR) compared to 21 days old seedlings. Increased Net Assimilation Rate (NAR) were recorded in sorghum transplanted with 14 days old seedlings as compared to direct sown and 21 days old transplanted crop. Transplanted sorghum recorded higher Relative Growth Rate (RGR) as compared to direct sown sorghum. Summer sorghum recorded higher Relative Growth Rate (RGR) as compared to kharif season.