Characterizing larval swordfish habitat in the western tropical North Atlantic

Swordfish Xiphias gladius (Linnaeus, 1758) are a circumglobal pelagic fish targeted by multiple lucrative fisheries. Determining the distribution of swordfish larvae is important for indicating reproductive activity and understanding the early life history of swordfish. We identify and characterize larval swordfish distributions during peak swordfish spawning throughout the Gulf of Mexico and western Caribbean Sea with generalized additive models (GAMs) using catches of swordfish larvae during ichthyoplankton surveys in April and May of 2010, 2011, and 2012. The best fit GAM, as determined by stepwise, backward Akaike Information Criterion selection, included both physiochemical (temperature at 5 m, sea surface height anomaly (SSHA), eddy kinetic energy (EKE)), temporal (lunar illumination, hour of sampling) and spatial (location) variables, while near surface chlorophyll a concentration residuals remained as a random effect. The highest probability of larval swordfish catch occurred at sub‐surface temperatures, SSHA, and EKE values indicative of boundary currents. Standard lengths of larvae were larger further downstream in the boundary currents, despite high variability in length with location due to multiple spawning locations of swordfish near these currents. Probability of larval swordfish catch also peaked during the crescent and gibbous moons, indicating a lunar periodicity to swordfish spawning. These results suggest that swordfish may spawn during select moon phases near boundary currents that transport their larvae to larval and juvenile habitat including the northern Gulf of Mexico and coastal waters of the southeast United States.     

Evaluating the utility of the Gulf Stream Index for predicting recruitment of Southern New England‐Mid Atlantic yellowtail flounder

The justification for incorporating environmental effects into fisheries stock assessment models has been investigated and debated for a long time. Recently, a state‐space age‐structured assessment model which includes the stochastic change in the environmental covariate over time and its effect on recruitment was developed for Southern New England‐Mid Atlantic yellowtail flounder (Limanda ferruginea). In this paper, we first investigated the correlations of environmental covariates with Southern New England‐Mid Atlantic yellowtail flounder recruitment deviations. The covariate that was most strongly correlated with the recruitment deviations was then incorporated into the state‐space model and alternative effects on the stock‐recruit relationship were estimated and compared. For the model that performed best as measured by Akaike information criterion, we also compared the estimates and predictions of various population attributes and biological reference points with those from an otherwise identical model without the environmental covariate in the stock‐recruit function. We found that the estimates of population parameters are similar for the two models but the predictions differed substantially. To evaluate which model provided more reliable predictions, we quantitatively compared the prediction skill of the two models by generating two series of retrospective predictions. Comparison of the retrospective prediction pattern suggested that from an average point of view, the environmentally explicit model can provide more accurate near‐term recruitment predictions especially the one year ahead recruitment prediction. However, the accuracy of the near‐term recruitment prediction from the environmentally explicit model was largely determined by the accuracy of the corresponding environment prediction the model provides.     

北部湾日本金线鱼摄食生态

根据2018年1—4月和8—12月在北部湾采集的248尾日本金线鱼(Nemipterus japonicus)样品,采用传统胃含物分析法和碳氮稳定同位素技术研究其摄食生态。结果显示,日本金线鱼为广食性底栖肉食性动物,摄食饵料生物包括8个类群,鱼类和虾类是优势饵料类群,相对重要指数占比为92.92%。日本金线鱼四季均大量摄食鱼类,另外,在春季兼食虾类,夏季兼食蟹类,秋季兼食虾类和多毛类,冬季兼食虾类和星虫类;随着体长增加,日本金线鱼由摄食虾类和鱼类为主逐渐转变为摄食鱼类为主,摄食转变体长节点为130 mm。摄食强度存在明显的季节变化,秋季最高,春季和夏季次之,冬季最低。日本金线鱼摄食饵料种类多样性较高,Shannon-Wiener多样性指数(H’)为1.77,Pielou均匀度指数(J’)为0.64,从春季到冬季,H’值和J’值随季节先升高后降低,秋季最高;H’和J’随体长呈增加趋势,体长≥160mm群体的摄食生态位宽度最大。在同位素分析方面,δ¹³C值范围为–18.25‰～–15.39‰,极差为2.86‰;δ¹⁵N值范围为13.01‰～17....     

基于LBB方法估算北部湾竹䇲鱼种群参数

为探究北部湾竹?鱼(Trachurus japonicus)不同组距的划分对其种群参数和资源评估的影响,利用2006—2018年北部湾竹?鱼叉长数据重构长度频率,通过逻辑斯蒂曲线拟合和长度贝叶斯生物量估算(length-based Bayesian biomass estimation method,LBB)方法,估算竹?鱼的初次性成熟叉长(L₅₀)、渐进叉长(L_∞)、相对自然死亡率(M/k)、相对捕捞死亡率(F/k)、相对总死亡率(Z/k)、最适开捕叉长(L_{c_opt})、开发率(E)和相对生物量(B/B₀)等种群参数。分析在不同组距情况下种群参数的差异。结果表明:初次性成熟叉长范围为157~162 mm;北部湾竹?鱼种群参数平均值分别为L_∞=248 mm、M/k=1.38、F/k=6.92、Z/k=8.28和L_{c_opt}=156 mm;北部湾竹?鱼相对生物量B/B₀低于0.5,E大于0.5;不同组距重构长度频率估算的种群参数结果有差异,且随组距的增大波动较为明显。研究表明,竹?鱼生物量相对低且处于过度开发状态,建议今后以样本数量、长度组成和生物特性共同确定某种鱼类长度分组组距。     

山水林田湖海多维测度环境影响与时空分异——以广西北部湾为例

[目的] 揭示山水林田湖海各要素之间的耦合协调效应关系及其驱动力因素，为更精准地开展陆海统筹生态修复工作提供科学依据。 [方法] 以广西北部湾为研究区，运用综合评价指数、耦合指数、协调指数、灰色关联指数(“4C指数”)，从山、水、林、田、湖、海6个子元素构建评价单元体系，揭示其各要素间的相互作用、综合发展水平、耦合协调情况，分析广西北部湾山水林田湖海生命共同体耦合协调分异特征及其驱动因素。 [结果] ①2005-2020年，广西北部湾山水林田湖海生命共同体综合评价指数上升了0.246 6，具体表现为：水系统＞林系统＞海系统＞湖系统＞田系统＞山系统。 ②2005-2020年广西北部湾耦合协调度上升了0.160 5，其类型表现为：初级协调-中级协调-良好协调的耦合协调演变过程。 ③灰色关联度高的是水系统和田系统及其子指标，灰色关联度分别为0.666 7，0.634 1。 [结论] 广西北部湾山水林田湖海生命共同体的主要驱动因子是水田系统和田系统。未来研究需以田、湖、水系统综合整治入手，发展海洋特色产业，注重海洋生态修复，减少山、田、湖系统对区域发展的制约，强化生态资源的保护，使其向可持续方向展开。