Hierarchical responses of soil organic and inorganic carbon dynamics to soil acidification in a dryland agroecosystem,China

Soil acidification is a major global issue of sustainable development for ecosystems. The increasing soil acidity induced by excessive nitrogen(N) fertilization in farmlands has profoundly impacted the soil carbon dynamics. However, the way in which changes in soil p H regulating the soil carbon dynamics in a deep soil profile is still not well elucidated. In this study, through a 12-year field N fertilization experiment with three N fertilizer treatments(0, 120, and 240 kg N/(hm~2·a)) in a dryland agroecosystem of China, we explored the soil p H changes over a soil profile up to a depth of 200 cm and determined the responses of soil organic carbon(SOC) and soil inorganic carbon(SIC) to the changed soil p H. Using a generalized additive model, we identified the soil depth intervals with the most powerful statistical relationships between changes in soil p H and soil carbon dynamics. Hierarchical responses of SOC and SIC dynamics to soil acidification were found. The results indicate that the changes in soil p H explained the SOC dynamics well by using a non-linear relationship at the soil depth of 0–80 cm(P=0.006), whereas the changes in soil p H were significantly linearly correlated with SIC dynamics at the 100–180 cm soil depth(P=0.015). After a long-term N fertilization in the experimental field, the soil p H value decreased in all three N fertilizer treatments. Furthermore, the declines in soil p H in the deep soil layer(100–200 cm) were significantly greater(P=0.035) than those in the upper soil layer(0–80 cm). These results indicate that soil acidification in the upper soil layer can transfer excess protons to the deep soil layer, and subsequently, the structural heterogeneous responses of SOC and SIC to soil acidification were identified because of different buffer capacities for the SOC and SIC. To better estimate the effects of soil acidification on soil carbon dynamics, we suggest that future investigations for soil acidification should be extended to a deeper soil depth, e.g., 200 cm.     

中国沿海刺网网具遗失率影响因子

为掌握影响我国沿海刺网渔船网具遗失率(R_G)的因子及其程度,对中国沿海渔民开展了问卷调查。利用调查数据,结合GAM模型分析了影响我国刺网渔船网具遗失率的因子及其程度。结果显示:(1)影响我国沿海刺网渔船网具遗失率的因子(解释偏差)分别为单航次天数(86.8%)、年作业天数(4.2%)、单航次渔具携带重量(2.8%)、作业水深(2.4%)、渔船吨位(0.9%)和年均渔具采购数量(0.1%);(2)GAM模型能用于研究渔船网具遗失率和影响因子之间的关系;(3)随着单航次天数和年作业天数的增加,R_G呈上升的趋势;(4)随着作业水深的增加、单航次渔具携带重量超过18 000 kg时,R_G呈下降趋势。建议采取以下措施以降低刺网渔船网具遗失率:(1)单航次天数不得超过30 d,减少年作业天数;(2)根据渔船的吨位,确保网具单航次携带重量在18 000 kg以上;(3)根据刺网渔具的高度规定作业水深和作业渔区;(4)渔船总吨位控制在200 t以内。     

南海中南部海域鸢乌贼CPUE影响因素的GAM分析

为更深入了解南海外海鸢乌贼的渔场渔期及单位捕捞努力量渔获量（CPUE）变化特征，研究基于广义加性模型（GAM），利用海上实测数据分析了多种因素对南海中南部海域鸢乌贼（） CPUE的影响。研究发现：（1）最佳GAM模型的影响因素包括经纬度、月相、海表温度SST、月份、作业时间与0~50 m温度梯度Δ50，以方差解释率降序排列，前三种因素依次为经纬度、月相、SST；（2）10°~12° N、112°~114° E附近海域鸢乌贼CPUE最高；（3）月黑夜与月光夜间的鸢乌贼CPUE存在显著性差异，月黑夜显著高于月光夜；（4）鸢乌贼渔场的最适SST范围为29.00~29.49℃，此范围内CPUE与渔获量均为最高；（5）不同月份间的鸢乌贼CPUE存在显著性差异，且8、9月的CPUE高于3、4月；（6）鸢乌贼CPUE随作业时间先变大后变小，最大值出现在凌晨1时；（7）Δ50在0.100~0.149℃/m时CPUE最高，0.000~0.049℃/m时渔获量最大。     

Effects of environmental variables on survey catch rates and distribution by size of shallow‐ and deep‐water Cape hakes,Merluccius capensis and Merluccius paradoxus off Namibia

In order to study the effects of temperature, oxygen, salinity and time of day on survey trawl catches, we modeled observed catches of juvenile, small, medium and large hakes per station as functions of zenith angle of the sun, geographical position, year, temperature, salinity, oxygen and depth. We used data from summer demersal surveys conducted during the period 2002–2015, together with a computation of the corresponding light level data from which the solar zenith angles were obtained, and fitted the generalized additive models to these data. Based on best model results, important covariates were oxygen, depth, geographical position and temperature. The best models explained 70%, 69%, 57% and 57% of the variability in catches of juvenile, small, medium and large Merluccius capensis, respectively, and 71%, 68%, 81% and 70% of juvenile, small, medium and large Merluccius paradoxus, respectively. The significant effects of temperature, oxygen, depth and geographical position on survey catches of hake of different size groups indicate that survey size structure may be affected by the behavior of both species towards environmental conditions. Greater care should therefore be taken when interpreting hake survey biomass estimates, based on swept area method, especially those that were collected during exceptional unfavourable environmental conditions. It would also be highly desirable if the oceanographic conditions are collected on each trawl station in order to improve understanding of the linkage between resources and environmental conditions.     

北太平洋柔鱼渔场资源与海洋环境关系的季节性变化

利用我国2002—2012年5—11月北太平洋鱿钓渔业的生产资料, 结合同期卫星遥感反演技术获取的海表温度(SST)、海水叶绿素(Chl-a)、海流等数据, 运用产量重心法和广义加性模型(GAM), 分析了北太平洋公海柔鱼渔场渔获量变化与海洋环境关系的季节性变化。研究结果显示北太平洋柔鱼5—6月渔场重心位于中、东部渔场, 在168°~171°E、38°~39°N的范围;7—11月集中在西部渔场, 重心位于150°~160°E、40°~44°N的范围, 渔场重心伴随着明显的季节性变化。通过GAM模型综合分析发现整个渔汛期的北太平洋柔鱼渔场最适SST范围为14~19 ℃;最适Chl-a范围为0.22~0.55 mg·m^-3;集中的经度范围为154°~157°E;集中出现的纬度范围为41°~44°N。柔鱼活动呈现每年北上索饵洄游和南下活动产卵洄游, 与环境因素的关系表现出不同的特征, 尤其是SST相关性最好, 从5月到9月SST与渔场重心的关系在北上时呈正相关, 从9月到11月南下时为负相关, 呈现明显的季节性变化。另外海流对渔场的影响甚为重要, 高产渔场一般位于黑潮、亲潮交汇区域的黑潮前锋、亲潮向背一侧附近, 随着暖、寒流的此消彼长而变化。     

Assessing swordfish distribution in the South Atlantic from spatial predictions

Generalized Regression Analysis and Spatial Prediction (GRASP) was used to map the spatial distribution of swordfish (Xiphias gladius) in the South Atlantic. Generalized additive models (GAMs) were used to relate catch to environmental predictor variables. Catch information from 38,000 Brazilian pelagic longline sets from 1980 to 2000 and size frequency data from 5000 longline sets from 1982 to 2000 were obtained from International Commission for the Conservation of Atlantic Tuna (ICCAT). Results highlight the importance of environmental variables for the fishery and for the spatial distribution of different size classes of swordfish (small, intermediate and large). The distribution of swordfish was closely associated with convergence zones (inter-tropical and sub-tropical), especially in the months of greatest convergence intensity. Spatial distribution patterns differed for the three studied size classes. The smallest size classes were found mainly in coastal zones and in areas with a shallow mixed layer (<20 m). In contrast intermediate-sized swordfish were mostly associated with the inter-tropical convergence and mixed layers of more than 20 m depth and large swordfish were often found in the vicinity of the sub-tropical convergence zone and in areas with mixed layers of less than 25 m and greater than 60 m.     

Evaluating light trap efficiency by application of mesh to prevent inter- and intra-specific in situ predation on fish larvae and juveniles

Amongst passive collecting gear types, light traps have been used extensively to sample the larvae and juveniles of fish in both marine and freshwater environments, and especially so in structurally complex habitats. Although a number of modifications have been proposed to increase efficiency, no account has hitherto been made of the possible loss of trapped larvae and juveniles as a result of within-trap predation by piscivorous fish. To address this issue, we evaluated the efficiency of modified light traps by the addition of mesh (3 mm knot-to-knot wrapped around the entrance chambers), by combining results from a long-term monitoring study with those from a designed field experiment. Abundance of larvae and juveniles collected during the monitoring program was higher in the years following mesh application (hence, beyond monthly variation), and this was supported by the experiment. Based on the latter, light/mesh traps consistently caught only larvae/juveniles, hence excluding adults; whereas the opposite was true of the light/no-mesh trap combination. Also, mesh/no-light traps did not capture any fish, unlike no-mesh/no-light traps, which sampled only adults. Our findings suggest that in situ predation on larvae and juveniles within light traps should not be overlooked. The occurrence of piscivorous and cannibalistic behaviour in Hypseleotris spp. is also discussed.     

Environmental influences on the recruitment dynamics of juvenile European eels,Anguilla anguilla,in a small estuary of the Tyrrhenian Sea,Sardinia, Italy

1. The European eel, Anguilla anguilla, is a catadromous and migratory species of commercial importance. Its complex life cycle results in its exposure to many risk factors, which have resulted in stock declines across all life stages since the 1970s.
2. The temporal recruitment dynamics of juvenile eels (glass eels and elvers) were investigated in a small Mediterranean estuary (Sardinia, Italy). The composition of the population and the monthly and seasonal variations in the abundances of juvenile eels was assessed over 78 sampling events (from February 2017 to February 2018). Furthermore, the effects of abiotic variables on the abundances of glass eels and elvers were investigated using generalized additive models (GAMs).
3. Glass eels had the greatest abundance during the winter months, whereas elvers had the greatest abundance during spring. Modelling revealed that the abundance of glass eels was mostly explained by the combined effects of water temperature (12.3–14.5 °C), tidal coefficient (40–110 cm), moon phase, season, and river mouth condition, whereas the abundance of elvers was associated with water temperature (14–21 °C), dissolved oxygen content (>7 mg/L), and season. These results suggest that the annual recruitment of juvenile eels occurs throughout the year, with clear seasonal migration dynamics.
4. The use of multiple statistical approaches allowed us to identify the importance of several environmental variables in regulating the recruitment dynamics, providing useful information for conserving eel stocks through the restoration of the natural flow regime and the connectivity between freshwater habitats and the sea.

     

Standardizing catch and effort data: a review of recent approaches

The primary indices of abundance for many of the world's most valuable species (e.g. tunas) and vulnerable species (e.g. sharks) are based on catch and effort data collected from commercial and recreational fishers. These indices can, however, be misleading because changes over time in catch rates can occur because of factors other than changes in abundance. Catch-effort standardization is used to attempt to remove the impact of these factors. This paper reviews the current state of the art in the methods for standardizing catch and effort data. It outlines the major estimation approaches being applied, the methods for dealing with zero observations, how to identify and select appropriate explanatory variables, and how standardized catch rate data can be used when conducting stock assessments.