Potential effects of global climate change on fisheries in the Trasimeno Lake (Italy), with special reference to the goldfish Carassius auratus invasion and the endemic southern pike Esox cisalpinus decline

Global climate changes have led to a gradual warming of the planet, resulting in decreased precipitation and rising temperatures in Mediterranean inland waters. In Trasimeno Lake, the largest shallow lake in Italy, some non‐native fish species have probably benefited from these changes as they are thermophilic and characterised by wider habitat preferences. Fish data collected by gillnets and fyke nets between 1956 and 2016, and by electrofishing in 1993 and 2014, were used to analyse changes over time in the fish community in relation to environmental conditions. An explosion in goldfish Carassius auratus (L.), following its introduction in 1988, coupled with water level fluctuations and reduced transparency, contributed to the reduction in commercial fish catch in the lake, and to the decline of the endemic southern pike Esox cisalpinus Bianco & Delmastro, already threatened by reduced spawning habitat and interspecific competition with other non‐native predatory fishes.     

Effective monitoring of freshwater fish

Freshwater ecosystems constitute only a small fraction of the planet's water resources, yet support much of its diversity, with freshwater fish accounting for more species than birds, mammals, amphibians or reptiles. Fresh waters are, however, particularly vulnerable to anthropogenic impacts, including habitat loss, climate and land use change, pollution and biological invasions. This environmental degradation, combined with unprecedented rates of biodiversity change, highlights the importance of robust and replicable programmes to monitor freshwater fish. Such monitoring programmes can have diverse aims, including confirming the presence of a single species (e.g., early detection of alien species), tracking changes in the abundance of threatened species, or documenting long‐term temporal changes in entire communities. Irrespective of their motivation, monitoring programmes are only fit for purpose if they have clearly articulated aims and collect data that can meet those aims. This review, therefore, highlights the importance of identifying the key aims in monitoring programmes and outlines the different methods of sampling freshwater fish that can be used to meet these aims. We emphasize that investigators must address issues around sampling design, statistical power, species’ detectability, taxonomy and ethics in their monitoring programmes. Additionally, programmes must ensure that high‐quality monitoring data are properly curated and deposited in repositories that will endure. Through fostering improved practice in freshwater fish monitoring, this review aims to help programmes improve understanding of the processes that shape the Earth's freshwater ecosystems and help protect these systems in face of rapid environmental change.     

Factors influencing the abundance of the common bully, Gobiomorphus cotidianus McDowall, in small, North Island, New Zealand, lakes

Adult common bullies, Gobiomorphus cotidianus McDowall, are small (total length =  30–120 mm), benthic fish commonly found in the littoral zones of New Zealand lakes where they are a major prey species for trout and eels. Differences in their relative abundance (CPUE) were determined between 21 shallow North Island lakes. Mean CPUE ranged from 2 to >  1000 fish net^{− 1} night^{− 1} and was inversely related to water transparency. The abundance of bullies was not reduced in lakes containing rainbow trout, Oncorhynchus mykiss (Walbaum), but was reduced in all lakes containing self-recruiting populations of eels, Anguilla spp. Mean densities of planktonic larval bullies in the limnetic zone were also inversely related to water transparency. Since low water transparency is related to increased trophic status for these lakes, the abundance of bullies is likely to be related to lake productivity, rather than turbidity.     

Factors influencing recruitment and growth of age‐0 yellow perch in eastern South Dakota glacial lakes

Variation in recruitment and growth of age‐0 yellow perch, Perca flavescens (Mitchill), was modelled across a range of nine eastern South Dakota glacial lakes to: (i) estimate factors influencing recruitment and growth dynamics during early ontogeny; and (ii) determine the relative importance of biotic versus abiotic processes in regulating recruitment and growth dynamics. Results provide a framework for future investigations and suggest that abiotic factors were more important in regulating recruitment of age‐0 yellow perch, whereas biotic factors were more important in regulating growth. Recruitment was positively related to springtime water levels and temperature and negatively related to spawning stock biomass and springtime wind conditions. By contrast, growth was negatively related to abundance of conspecifics and potential competitors (i.e. bluegill, Lepomis macrochirus Rafinesque) and positively related to abundance of potential predators [i.e. walleye, Sander vitreus (Mitchill) and northern pike, Esox lucius Linnaeus].     

Genetic diversity of freshwater pearl mussel (Hyriopsis cumingii) in populations from the five largest lakes in China revealed by inter-simple sequence repeat (ISSR)

Triangle sail mussel (Hyriopsis cumingii) is the most important mussel species commercially exploited for freshwater pearl culture in China. Its genetic diversity was studied among populations from the five largest freshwater lakes of China, Poyang Lake (PY), Dongting Lake (DT), Taihu Lake (TH), Hongze Lake (HZ), and Chaohu Lake (CH), by the polymorphism of the inter-simple sequence repeats (ISSRs). Polymerase chain reaction (PCR) detections showed that a total of 62 loci were amplified from eight primers; of those, 31.88%, 31.15%, 31.03%, 27.27% and 26.92%, respectively, were polymorphic in each of the five populations across all genotypes tested. The average heterozygosities were 0.4747, 0.3274, 0.2366, 0.2099 and 0.2018 in each of these populations from PY, TH, DT, CH and HZ, respectively. Phylogenic analyses showed that PY and TH populations clustered with CH and HZ and formed a group, while the DT population on its own formed a separated branch. The smallest distance (0.0404) was scored between PY and TH populations, indicative of their closest relationship; the biggest distance (0.2438) was found between PY and DT populations, suggesting their greatest divergence. The present study provided genetic basis for managing mussel stocks from these lakes separately to best preserve the genetic diversity of H. cumingii. On the other hand, since the population in PY displayed the highest genetic diversity, it may be used preferably in future selective breeding to improve pearl yield and quality.     

中国五大湖三角帆蚌群体遗传多样性的RAPD分析

用OPJ和OPM两组40条10碱基随机引物,对中国五大湖三角帆蚌地理群体及诸暨养殖蚌进行了随机扩增多态性DNA(RAPD)分析,其中12个引物的扩增结果具有丰富的群体多态性,多态率为55.6%～80%。群体内遗传相似度大小依次为:鄱阳湖(0.8889),太湖(0.8694),洞庭湖(0.8111),诸暨(0.7746),洪泽湖(0.7348),巢湖(0.7185)。依据群体间遗传距离指数及分子系统树,表明洞庭湖群体和洪泽湖群体亲缘关系最近,鄱阳湖群体则与巢湖群体的亲缘关系最近,并且诸暨人工养殖群体与鄱阳湖和巢湖的群体比较接近。     

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。     

浅水湖泊溶存甲烷浓度（dCH4）对气温升高及季节变化响应特征

揭示温度升高对浅水湖泊中溶存甲烷（CH4）浓度的影响,可为全球碳评估提供重要的理论支撑,为更好地应对气候变化对浅水湖泊碳排放的影响提供数据支持。采集梁子湖表层沉积物和湖水,并置于塑料水缸（沉积物厚度为10 cm,注入深度为1 m的湖水）,设置比周围环境温度升高3.5℃的升温组(W)和不进行温度设置的控制组(C),每组6个平行,2022年1月完成系统设置后放置两个月后开始采样,分别在春季（3、4月）和夏季（7、8月）进行,计算甲烷浓度,同时测量水温（T）、pH、电导率（EC）、溶解氧（DO）、总氮（TN）、总磷（TP）、正磷（PO43-）、氨态氮（NH4+）、硝态氮（NO3-）和亚硝氮（NO2-）、Chl-a、溶解性有机碳（DOC）等参数,并分析甲烷浓度和环境因子的相关关系。结果显示,W组的甲烷浓度与C组之间差异不显著,W组的甲烷浓度总体上低于C组;夏季甲烷的浓度显著高于春季,说明温度是影响甲烷排放的重要因素;Spearman相关性分析和逐步回归分析表明甲烷浓度主要与水温、营养盐含量（TP、PO43-、DOC）、pH、DO和电导率（EC）有关,其中,季节性温度变化是影响水体溶存甲烷浓度的最主要环境因子。