Catch rate and at‐vessel mortality of circle hooks versus J‐hooks in pelagic longline fisheries: A global meta‐analysis

We conducted a meta‐analysis of literature reporting on the use of circle hooks and J‐hooks in pelagic longline fisheries. Our study included more data than previous meta‐analyses of the effects of hook type, due to both a larger number of relevant studies available in recent years and a more general modelling approach. Data from 42 empirical studies were analysed using a random effects model to compare the effects of circle hooks and J‐hooks on catch rate (43 species) and at‐vessel mortality (31 species) of target and bycatch species. Catch rates with circle hooks were greater for 11 species, including four tuna species, six shark species and one Istiophorid billfish. Catch rates on circle hooks were lower for seven species, including two Istiophorid billfishes and two species of sea turtle. At‐vessel mortality was significantly lower with circle hooks in 12 species, including three tuna species, three Istiophorid billfishes, swordfish (Xiphias gladius) and three shark species. No species had significantly greater at‐vessel mortality when captured with a circle hook rather than a J‐hook. While our general approach increased model variability compared to more detailed studies, results were consistent with trends identified in previous studies that compared the catch rates and at‐vessel mortality (between hook types) for a number of species. Our results suggest that circle hooks can be a promising tool to reduce mortality of some bycatch species in pelagic longline fisheries, although the effects depend on the species and the metric (catch rate or at‐vessel mortality), emphasizing the need for fishery‐specific data in conservation and management decisions.     

Habitat partitioning among three predatory fish in a temperate reservoir

The diversity of predatory species plays a key role in ecosystem functioning but our understanding of the mechanisms underlying their coexistence is limited, particularly in freshwater ecosystems. Northern pike Esox lucius, European perch Perca fluviatilis and pikeperch Sander lucioperca are three widespread predatory species in European lakes, where they often coexist. As potential competitors, we hypothesised that partitioning habitat is a determinant of species coexistence. This was tested by quantifying the variability of their habitat use in tracking adult individuals in the Bariousses reservoir (France, 86.6 ha, mean depth 7.1 m). Specifically, we investigated their distribution along the littoral–pelagic and depth axes along the daily cycle and across seasons. From littoral to pelagic waters were first found pike, then perch and finally pikeperch. Pike was the closest to the surface while pikeperch was the deepest. This general pattern was, however, variable across seasons with the three species located in the upper layer in summer during reservoir stratification. Individuals were more evenly distributed along the littoral–pelagic axis and closer to the bottom when water was mixing (autumn, winter). In summer, perch used more intensively in the pelagic zone during the daytime. Other species did not show any diel change of habitats. Our results highlighted that species coexistence is associated with habitat partitioning among these three predators, with perch showing a more variable behaviour regarding habitat characteristics. Now more than ever, in the context of global change which modifies habitats, it is of crucial importance to understand the coexistence mechanisms of species that shape ecosystems.     

巢湖浮游甲壳动物功能群时空变化及其影响因子分析

为研究巢湖中浮游甲壳动物功能群的时空变化特征及其主要影响因子，在巢湖的主要河口区以及敞水区共设置了20个采样点，对浮游甲壳动物群落结构和水环境因子进行了调查和分析。结果表明：（1）巢湖河口区的8个采样点中共鉴定出枝角类10属21种，桡足类11属16种；敞水区12个点中鉴定出枝角类9属18种，桡足类12属13种；共22属39种。（2）巢湖河口区和敞水区浮游甲壳动物平均密度为530.8 ind·L^-1和506.3 ind·L^-1，平均生物量分别为14.7 ind·L^-1和21.5 ind·L^-1；浮游甲壳动物Shannon-Wiener多样性指数显示巢湖秋季河口区的污染程度高于敞水区。（3）巢湖浮游甲壳动物按照体型大小和食性可划分5个功能群，其中，河口区有SCF、LCF共2个优势功能群，敞水区有SCF、LCF、MCF共3个优势功能群，SCF在功能群中占绝对的优势地位。（4）水温是影响河口区和敞水区浮游甲壳动物功能群主要的环境理化因子；巢湖敞水区中浮游甲壳动物LCF功能群能显著影响SCF、MCC、LCC等功能群。巢湖河口区污染程度高于敞水区，巢湖的富营养化治理和藻类水华控制应侧重于河口区的外源污染治理；敞水区可以通过调整浮游甲壳动物功能群结构重建水生生态系统。