A large data set on stomach content (over 27,000 individual fish) – collected in the Barents Sea in 2015 – was used to examine ontogenetic and interspecific changes in diet with size for 35 fish species. The analysis combined the use of hierarchical clustering and random forest. Two different diet metrics were used (% weight of prey types per weight of stomach content or per weight of fish, the latter reflecting also feeding intensity), and data were analysed based on average diet of predator groups (species and size groups) across the entire sample series (from the whole Barents Sea in different seasons), or for data broken down by geographical areas and seasons. Similar trophic groups (clusters) were identified for the various data sets suggesting that the results on trophic structure were robust. The trophic groups including size information were broadly similar to groups found earlier with data averaged at species level. Hierarchical clustering produces a hierarchy of trophic groups (or trophic guilds) at various levels of diet dissimilarity. With 12 clusters identified, one cluster had fish as dominant prey, and 5–6 others had either plankton or benthos as dominant prey. The clusters tended to be distinct and homogenous with one dominant prey category in average diet (often > 60 %). This was especially the case for the plankton clusters, with copepods, euphausiids, hyperiid amphipods, or gelatinous zooplankton as dominant prey in each of 4 trophic groups. The benthos clusters tended to be less dissimilar with more overlap in diet composition, with predominance of either hard-shelled forms (echinoderms and molluscs) or softer prey (polychaetes and crustaceans) for groups of clusters. There were clear patterns of ontogenetic shifts in fish diet. Fish that clustered as piscivores at larger size tended to grow from being planktivores when smaller. Smaller species of planktivores or benthivores shifted position among trophic groups but remained within the categories of planktivores or benthivores, respectively. Taxonomy (species) tended to be more important than size for explaining the diet composition of the different clusters of fish predators.

中文翻译：

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巴伦支海鱼类的饮食和营养结构：物种内（个体发育）和物种间大小的影响


2015 年在巴伦支海收集的关于胃内容物的大型数据集（超过 27,000 条鱼）被用来检查 35 种鱼类的个体发育和饮食变化。该分析结合了层次聚类和随机森林的使用。使用两种不同的饮食指标（猎物类型重量占胃内容物重量或鱼重量的百分比，后者也反映摄食强度），并根据整个捕食者群体（物种和体型组）的平均饮食对数据进行分析。整个样本系列（来自不同季节的整个巴伦支海），或按地理区域和季节细分的数据。各种数据集都确定了类似的营养群（簇），这表明营养结构的结果是稳健的。包括大小信息在内的营养群体与之前发现的在物种水平上平均数据的群体大致相似。层次聚类产生不同饮食差异水平的营养组（或营养行会）的层次结构。在确定的 12 个簇中，其中一个簇以鱼类为主要猎物，另外 5-6 个簇以浮游生物或底栖生物为主要猎物。这些簇往往是不同且同质的，在平均饮食中具有一种主要的猎物类别（通常> 60%）。对于浮游生物群来说尤其如此，桡足类、磷虾类、超甲类片脚类或胶状浮游动物是 4 个营养组中每一个的主要猎物。底栖动物群的相似性往往较小，饮食成分重叠较多，群中以硬壳动物（棘皮动物和软体动物）或较软的猎物（多毛类和甲壳类动物）为主。鱼类饮食存在明显的个体发生变化模式。 体型较大时聚集为食鱼动物的鱼往往会在体型较小时从食浮游动物成长为食鱼动物。较小的浮游动物或底栖动物在营养组中的位置发生了变化，但仍分别属于浮游动物或底栖动物类别。对于解释不同鱼类捕食者群体的饮食构成而言，分类（物种）往往比大小更重要。