Feeding Ecology of Northeast Atlantic Mackerel,Norwegian Spring-Spawning Herring and Blue Whiting in the Norwegian Sea

The Norwegian spring-spawning (NSS) herring (Clupea harengus), blue whiting (Micromesistius poutassou) and Northeast Atlantic (NEA) mackerel (Scomber scombrus) are extremely abundant pelagic planktivores that feed in the Norwegian Sea (NS) during spring and summer. This study investigated the feeding ecology and diet composition of these commercially important fish stocks on the basis of biological data, including an extensive set of stomach samples in combination with hydrographical data, zooplankton samples and acoustic abundance data from 12 stock monitoring surveys carried out in 2005–2010. Mackerel were absent during the spring, but had generally high feeding overlap with herring in the summer, with a diet mainly based on calanoid copepods, especially Calanus finmarchicus, as well as a similar diet width. Stomach fullness in herring diminished from spring to summer and feeding incidence was lower than that of mackerel in summer. However, stomach fullness did not differ between the two species, indicating that herring maintain an equally efficient pattern of feeding as mackerel in summer, but on a diet that is less dominated by copepods and is more reliant on larger prey. Blue whiting tended to have a low dietary overlap with mackerel and herring, with larger prey such as euphausiids and amphipods dominating, and stomach fullness and feeding incidence increasing with length. For all the species, feeding incidence increased with decreasing temperature, and for mackerel so did stomach fullness, indicating that feeding activity is highest in areas associated with colder water masses. Significant annual effects on diet composition and feeding-related variables suggested that the three species are able to adapt to different food and environmental conditions. These annual effects are likely to have an important impact on the predation pressure on different plankton groups and the carrying capacity of individual systems, and emphasise the importance of regular monitoring of pelagic fish diets.     

Coexistence of Fish Species in a Large Lowland River: Food Niche Partitioning between Small-Sized Percids,Cyprinids and Sticklebacks in Submersed Macrophytes

In the spring and summer of each year, large patches of submersed aquatic macrophytes overgrow the bottom of the alluvial Warta River downstream of a large dam reservoir owing to water management practices. Environmental variables, macroinvertebrates (zoobenthos and epiphytic fauna, zooplankton) and fish abundance and biomass were assessed at this biologically productive habitat to learn intraseasonal dynamics of food types, and their occurrence in the gut contents of small-sized roach, dace, perch, ruffe and three-spined stickleback. Gut fullness coefficient, niche breadth and niche overlap indicated how the fishes coexist in the macrophytes. Chironomidae dominated in the diet of the percids. However, ruffe consumed mostly benthic chironomids, while perch epiphytic chironomids and zooplankton. The diet of dace resembled that in fast flowing water although this rheophilic species occurred at unusual density there. The generalist roach displayed the lowest gut fullness coefficient values and widest niche breadth; consequently, intraspecific rather than interspecific competition decided the fate of roach. Three-spined stickleback differed from the other fishes by consuming epiphytic simuliids and fish eggs. The diet overlap between fishes reaching higher gut fullness coefficient values was rather low when the food associated with the submersed aquatic macrophytes was most abundant; this is congruent with the niche overlap hypothesis that maximal tolerable niche overlap can be higher in less intensely competitive conditions.     

马鞍列岛岩礁生境鱼类群落结构时空格局

基于2009年马鞍列岛潮下带岩礁生境的多网目三层组合刺网逐月调查数据,对鱼类群落月相和季度间的变化、区域尺度上的空间差异和群落的稳态进行了探讨,应用优势种相对丰度和生物量、定居性鱼类和洄游种的季节动态、非度量多维标度(nMDS)和生物量丰度曲线(ABC)分析方法对群落时空格局进行了分析。结果显示:季节性洄游种集中出现在夏秋季,但对岩礁生境的利用表现出不同区域的强度差异;小黄鱼Larimichthys polyactis和黄姑鱼Nibea albiflora周年利用岩礁生境,但强度有别,尤其在冬季;定居性鱼类褐菖鲉Sebastiscus marmoratus、斑头鱼Agrammus agrammus和大泷六线鱼Hexagrammos otakii在春末夏初的种群密度最高,同样表现出某些或大部分月份的区域差异;而河口种中国花鲈Lateolabrax maculatus则更多地选择秋冬季出现在岩礁生境。多元分析结果揭示了当地岩礁生境鱼类群落格局上显著的季节和区域差异,这是定居性鱼类对岩礁生境利用的阶段性变化和区域差异、结合洄游种季节迁移和选择性分布等因素作用下共同形成的格局。ABC分析进一步发现,丰富的鱼类生态类型形成了夏季岩礁生境更为稳定的群落状态,而冬季相反;同时各季度A区的群落干扰明显强过B区。研究表明,产卵季节海域西北部的岩礁生境很可能起着主要的产卵场功能,而东南部区域各季度皆侧重于幼鱼育肥场的功能表达。丰富的种类区系加之优势种的季节性交替出现,共同塑造了岩礁生境极具动态的鱼类群落格局,对维持岛礁海域鱼类多样性以及局部区域生态系统的稳定性起着非常重要的作用。     

Schistocephalus solidus parasite prevalence and biomass intensity in threespine stickleback vary by habitat and diet in boreal lakes

Trophically-transmitted parasites can affect intermediate host behaviors, resulting in spatial differences in parasite prevalence and distribution that shape the dynamics of hosts and their ecosystems. This variability may arise through differences in physical habitats or biological interactions between parasites and their hosts, and may occur on very fine spatial scales. Using a pseudophyllidean cestode (Schistocephalus solidus) and the threespine stickleback (Gasterosteus aculeatus) as a model parasite–host complex, we investigated the association of infection with host diet composition and stomach fullness in different habitats of two large lakes in southwest Alaska. To become infected, the fish must consume pelagic copepods infected with the parasite’s procercoid stage, so we predicted higher infection rates of fish in offshore habitats (where zooplankton are the primary prey) compared to fish from the littoral zone. Sticklebacks collected from the littoral and limnetic zones were assayed for parasites and their stomach contents were classified, counted, and weighed. Contrary to our prediction, permutational multivariate analysis of variance and principal components analysis revealed that threespine sticklebacks in the littoral zone, which consumed a generalist diet (pelagic zooplankton and benthic invertebrates), had higher parasite prevalence and biomass intensity than conspecifics in the limnetic zone, which consumed zooplankton. These results, consistent in two different lakes, suggest that differences in parasite prevalence between habitats may have been determined by a shift in host habitat due to infection, differential host mortality across habitats, differential procercoid prevalence in copepods across habitats, or a combination of the three factors. This paradoxical result highlights the potential for fine spatial variability in parasite abundance in natural systems.     

Lipid‐rich zooplankton subsidise the winter diet of benthivorous Arctic charr (Salvelinus alpinus) in a subarctic lake

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River flow,zooplankton and dominant zooplanktivorous fish dynamics in a warm‐temperate South African estuary

The possible links between river flow, zooplankton abundance and the responses of zooplanktivorous fishes to physico‐chemical and food resource changes are assessed. To this end, the seasonal abundance, distribution and diet of the estuarine round‐herring Gilchristella aestuaria and Cape silverside Atherina breviceps were studied in the Kariega Estuary. Spatio‐temporal differences were determined for selected physico‐chemical variables, zooplankton abundance and zooplanktivorous fish abundance and distribution. Results indicated that, following a river flood event in winter (>30 m³ s^?1), altered physico‐chemical conditions occurred throughout the estuary and depressed zooplankton stocks. Abundance of G. aestuaria was highest in spring, with this species dominant in the upper and middle zones of the estuary, while A. breviceps was dominant in summer and preferred the middle and lower zones. The catch per unit of effort of both zooplanktivores also declined significantly following the flooding, thus suggesting that these fishes are reliant on zooplankton as a primary food source for healthy populations. Copepods dominated the stomach contents of both fish species, indicating a potential for strong interspecific competition for food, particularly in the middle reaches. Temporal differences were evident in dietary overlap between the two zooplanktivorous fish species and were correlated with river flow, zooplankton availability and fish distribution. The findings of this study emphasize the close trophic linkages between zooplankton and zooplanktivorous fishes under changing estuarine environmental conditions, particularly river flow and provide important baseline information for similar studies elsewhere in South Africa and the rest of the world.     

Spring-neap cycle as a major driver of temporal variations in feeding of intertidal fishes: Evidence from the sea catfish Sciades herzbergii (Ariidae) of equatorial west Atlantic mangrove creeks

On macrotidal coasts, short- to medium term variations in feeding of intertidal fishes are influenced by several interacting time scales. To identify the driver of major variations in the feeding habits of intertidal fish, we used the pemecou sea catfish Sciades herzbergii (Ariidae), an abundant intertidal benthic second order consumer, as a model species. We analyzed the influence of the spring-neap and the day-night cycle on intertidal abundance, stomach fullness, diet composition and food consumption of S. herzbergii using block nets set at slack high tides in two mangrove creeks in north Brazil. At spring tides, intertidal abundance, stomach fullness, and total daily consumption of S. herzbergii were on average 8.8, 1.9, and 3.8 times higher than at neap tides, respectively. At spring tides, Uca spp. and Grapsidae (mostly Pachygrapsus gracilis) dominated the diet, irrespective of the time of day. Other important food items were Insecta and the semiterrestrial crab Ucides cordatus. At neap tides, Capitellidae contributed to the diet of nightly inundations while no specimens were caught at daytime. Creek location had no effect on any variable. Results from our study area and evidence from other studies suggest that the spring-neap tide pulse is likely the major driver of short- to medium term variations in feeding of intertidal fishes. This has important implications for feeding-related issues on macro- and probably also on mesotidal coasts: (i) juvenile fishes may have fortnightly growth spurts, (ii) intertidal prey populations may suffer regular fluctuations in mortality, (iii) studies of the feeding ecology of intertidal fishes should cover the combined effects of the tidal, diel, lunar and seasonal cycles, and (iv) the modeling of food webs should consider the differences between highly dynamic spring tide and quieter neap tide conditions.     

Temporal and spatial patterns in littoral-zone fish assemblages of a reservoir (Lake Texoma,Oklahoma-Texas,U.S.A.)

Synopsis We sampled the littoral-zone fish fauna of Lake Texoma reservoir by electrofishing from January through December 1986 to examine species abundance, species associations and assemblage structure. Although total fish abundance differed significantly across seasons, only one common species (Dorosoma cepedianum) exhibited significant seasonal movement into or out of the littoral zone. Overall littoral-zone assemblage structure (based on rank order of species abundance) was concordant across seasons and habitat types, (vegetation, wood, open). However, within individual seasons and habitat types, assemblage structure was likely influenced by temporal and spatial differences in habitat availability and physicochemical conditions. Associations characteristic of species in natural aquatic environments were not well developed among species in this partly artificial, evolutionarily short-lived reservoir assemblage. Conditions related to water-level fluctuation appeared to deter the formation of persistent species associations and assemblage structure, especially in vegetation and open littoral zone habitats of this multi-purpose reservoir.Senior author     

Food and habitat partitioning between young-of-year alewives and rainbow smelt in southeastern Lake Ontario

Synopsis Thermal and depth distributions, diets and time of feeding of young-of-year (YOY) alewives and YOY rainbow smelt were compared for evidence of resource partitioning in southeastern Lake Ontario. YOY alewives were largely epilimnial during August and September, but moved toward the bottom during fall turnover. Alewives were most abundant in the warmest available water. YOY rainbow smelt were concentrated at depths between 10 and 30 m in August and September, but moved into deeper water at fall turnover. Depth distribution of YOY smelt was correlated with temperatures of 8–12°C Both species fed predominantly during day on zooplankton during August and September. Cyclopoid copepods were the most common prey, but bosminids, eubosminids, and occasionally calanoid copepods were frequently eaten. As YOY rainbow smelt grew (> 60 mm), they consumed more Mysis relicta and amphipods, which became the major prey of rainbow smelt by November. YOY alewives consumed mostly zooplankton in all months. Diet overlap of the two species was greatest in warm water (> 12.0° during October (94.3% similarity) and August (80.0% similarity) and lowest in November (16.9% similarity). Positive size-selection on zooplankton was found in all months for YOY rainbow smelt, but only in late September through November for YOY alewives. Thus, during thermal stratification, the species were spatially segregated by water temperature but had a high degree of overlap in time of feeding and types of prey eaten. In contrast, after fall turnover there was a greater separation in diet but a higher overlap in habitat use.     

Diet of an invading clupeid along an urban neotropical reservoir: responses to different environmental conditions

The river plate sprat Platanichthys platana (Regan, 1917) is a small clupeid fish of South American fresh and brackish waters which was introduced outside of its native range, becoming widespread in the Billings Complex, a highly eutrophic urban reservoir located in the metropolitan area of São Paulo city, Upper Tietê River Basin (São Paulo State, Brazil). To better understand some aspects related to the invasion of this species in the reservoir, we assessed its diet through the analysis of stomach contents, niche breadth and feeding selectivity. Simultaneously to fish catches, zooplankton samples were collected at three reservoir arms with different anthropic influences during the dry and rainy seasons of 2014. Zooplankton diversity and dominance varied between sites, while composition at the genus level was similar. Sprat fed predominantly on zooplankton (68.3%), consuming a broad diversity of prey (Bosmina, Lecane , Chydoridae, Cyclopoida and Harpacticoida copepods), which were selectively predated. Consumed species varied according to site, season and fish size, with Cladocera being dominant at the most eutrophic site (Bororé). Considering spatial differences in the consumed zooplankton, the analysis of percentage similarity (SIMPER) indicated the highest dissimilarity (95.3%) between the Bororé (hypereutrophic) and Grande River Reservoir (supereutrophic) sites, while trophic niche width increased from the most impacted (Bororé) to the most preserved site (Capivari). The high captures of the sprat in the Billings Complex reported by local fishermen, indicated the adaptability of this invasive fish to the new habitat, suggesting that it may possess a central role as the dominant zooplankton predator in the system.     

Assessing the statistical power of genetic analyses to detect multiple mating in fishes

Blue catfish Ictalurus furcatus and channel catfish Ictalurus punctatus , two large-bodied piscivore-omnivores in Lake Texoma, Texas-Oklahoma, U.S.A., showed very high overlap in food use, but substantial differences in use of habitat during the year. Both species primarily ate fishes, aquatic insects, vegetation and detritus, terrestrial insects, seeds and zooplankton, with overall overlap = 98%. Diet breadth indices were very similar (blue catfish=4.31, channel catfish = 4.53). Quantitative and qualitative feeding varied seasonally and food habits changed ontogenetically. Feeding intensity was greatest in winter and lowest in late summer. Aquatic insects were eaten more from May to October and fishes more in winter. At body sizes from 100 to 299 mm L_s , both species primarily ate aquatic insects, terrestrial insects, fishes or zooplankton, whereas the diets of individuals >300 mm L_s of both species were dominated by fishes. Overall, their overlap in distribution across major habitat types was only 58%, with blue catfish most abundant in deep water offshore, and channel catfish more common in shallow cove habitats. Blue catfish that did occur in coves were in the deeper parts of those habitats, essentially not occurring in the littoral zone. In lakes without blue catfish, channel catfish are widely dispersed in various habitats and it is suspected that displacement of channel catfish by blue catfish may influence habitat differences of the two species in Lake Texoma. Because the spatial separation of the species also reflects their typical interspecific differences in unimpounded drainages, however, the habitat differences observed in Lake Texoma probably also reflect evolved, historical differences in ecology of the two species.     

Trophic niche overlap between round sardinella (Sardinella aurita) and sympatric pelagic fish species in the Western Mediterranean

The northward expansion of round sardinella (Sardinella aurita) in the Mediterranean Sea, together with declines and fluctuations in biomass and landings of European sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus) observed in recent decades, may suggest potential inter‐specific competition in the pelagic domain. The coexistence of sympatric zooplanktivorous fish species might therefore be exposed in part to trophic niche overlap and competition for food. Combining visual diet characterization under the microscope with DNA metabarcoding from stomach contents of fish collected in spring results show that predation on relatively large krill is equally important for sardinella than for the other two niche overlapping species. Furthermore, an important overlap is found in their isotopic niche, especially with anchovy, using nitrogen (δ¹⁵N) and carbon (δ¹³C) stable isotopes in muscle tissue. In fact, the three fish species are able to feed effectively in the whole prey size spectrum available during the sampled season, from the smallest diatoms and copepods to the larger prey (i.e., decapods and euphausiids), including fish larvae. Moreover, effective predation upon other large prey like siphonophores, which is observed only when multi‐proxy analyses in stomach contents are applied, might also be relevant in the diet of sardinella. The overlapping diet composition in spring, together with the effective use of food resource by sardinella, can be of special interest in potential future scenarios with warmer water temperature leading to lower zooplankton and/or higher jellyfish availability, where sardinella may take advantage over other species due to its feeding plasticity.     

Effects of season and body-size on the distribution and diet of the Iberian chub Leuciscus pyrenaicus in a lowland catchment

Seasonal and ontogenetic variations in space and food use by Leuciscus pyrenaicus were analysed in a Portuguese lowland catchment. Large fish occurred mostly in deep permanent-flowing sites whereas small fish occurred mostly in the shallowest intermittent-flowing site. No seasonal or size-related changes in feeding intensity were found, but the diet changed both across seasons and throughout ontogeny. The diet was dominated by aquatic prey over all seasons, but during winter and summer more plant material and terrestrial prey, respectively, were eaten. Throughout ontogeny fish shifted from soft-bodied to hard-shelled prey and decreased animal prey breadth. Mean prey size increased with fish size but the prey size spectrum was more variable for medium-sized fish than for either small or large fish. It is suggested that: (i) large fish avoid shallow drying areas owing to the risk of mortality, either by thermal and respiratory stresses or increased predation by mammals and birds; (ii) seasonal changes in diet are a response to differences in prey availability; and (iii) morphological constraints, prey handling costs and habitat partitioning are responsible for size-related changes in diet.     

Sex-specific differences in the seasonal habitat use of a coastal dolphin population

Understanding the factors that contribute to a population’s habitat use is important for conservation planners and managers to identify reasons behind a population’s distribution. Habitat use often differs between sexes, however few studies on sexually monomorphic species document this difference, resulting in misleading ecological interpretations and non-targeted management actions. The aim of this study was to test for sex-specific differences in the seasonal habitat use of Indo-Pacific bottlenose dolphins (Tursiops aduncus) off Bunbury, Australia. Systematic, boat-based, photographic identification dolphin surveys (n?=?587) were conducted across seasons over 6 years during 2007–2013. Generalised additive models explored relationships between the presence-absence of dolphins and sex, water depth and benthic habitat type. Results highlighted that: (i) habitat use differed seasonally for males and females, (ii) depth had a strong influence on habitat use, which differed between sexes for summer, winter and spring, and (iii) there were no sex differences in habitat use in autumn, which coincides with the peak breeding season. In summer and autumn dolphins were concentrated in shallow, near-shore waters predominantly over reef and sand, and in winter and spring dolphins had a broader distribution over reef and mud/silt with the use of deeper, offshore waters. This pattern is consistent with the seasonally-dependent dolphin abundance that has been documented for this population. Identification of sex differences in habitat use provides management agencies with insights to implement informed actions for the conservation of this coastal dolphin population which is forecast to decline by 50% in the next two decades.     

Food and habitat partitioning among juveniles of three fish species in the pelagial of a mesotrophic lake

An analysis of the diet of 0⁺ perch, smelt and roach caught at night of the pelagial of a mesotrophic lake showed that their food was composed mainly of herbivorous and predatory cladocerans, copepods and Chaoborus larvae during summer, and of herbivorous cladocerans and copepods during October. An analysis of habitat use by juveniles revealed separation among the species: roach occurred in the upper, perch and smelt in the deeper water layers. Food and habitat were alternatively partitioned among the juveniles. In early summer the lowest food overlap between perch and smelt coincided with high habitat overlap. In October high food overlap between perch and smelt corresponded with low habitat overlap. Smelt and roach fry used common food resources throughout the season, but they were segregated in habitat.     

The diet of the Sea Eagle Haliaeetus albicilla and Golden Eagle Aquila chrysaetos in western Scotland

The diets of Sea Eagles Haliaeetus albicilla and Golden Eagles Aquila chrysaetos living sympatrically in western Scotland were studied using pellets and prey remains collected at roosts and nest sites throughout the year. Both species showed changes in diet between winter and summer, and there were differences between species in both seasons. As a rule, Sea Eagles took proportionately more seabirds, waterfowl (ducks and waders) and fish, whilst Golden Eagles took proportionately more rabbits and hares. Sea Eagles had a broader diet than Golden Eagles but a measure of dietary overlap based on taxonomic composition indicated an overlap of more than 90% between the two species.     

Spatial distribution and diet of the Neotropical otter<Emphasis Type="Italic">Lontra longicaudis</Emphasis> in the Ibera Lake (northern Argentina)

The seasonal spatial distribution and diet of the Neotropical otterLontra longicaudis (Olfers, 1818) were studied on Ibera Lake within the Esteros del Ibera, an important wetland of NE Argentina (Ramsar site no. 1162). Twelve lake perimeter sites were regularly checked for otter tracks and signs. The amount of signs was compared to environmental parameters to test their influence on otter presence and movements. A positive correlation was found between the amount of signs and the physical structure of the littoral areas, as well as vegetation structure. Lakeside otter presence decreased during the summer sampling throughout all sites. In order to determine otter diet, 205 spraints were examined. Otters fed mainly on fish (mostly Cichlidae), but also on crustaceans and molluscs. Other fish consumed were Characidae, Synbranchidae, Loricariidae and Erythrinidae. Seasonal variation was observed in diet composition: in summer, diet crustaceans and vertebrates other than fish increased. A higher percentage of benthic fish species was also observed in summer, while pelagic and benthopelagic species increased in winter. Such dietary changes may be explained by the different habitat use of otters in different seasons, from the lake coast (winter) towards more internal marshy areas of the wetland (summer).     

Impact of fish predation on cladoceran body weight distribution and zooplankton grazing in lakes during winter

1. It is well accepted that fish, if abundant, can have a major impact on the zooplankton community structure during summer, which, particularly in eutrophic lakes, may cascade to phytoplankton and ultimately influence water clarity. Fish predation affects mean size of cladocerans and the zooplankton grazing pressure on phytoplankton. Little is, however, known about the role of fish during winter. 2. We analysed data from 34 lakes studied for 8–9 years divided into three seasons: summer, autumn/spring and winter, and four lake classes: all lakes, shallow lakes without submerged plants, shallow lakes with submerged plants and deep lakes. We recorded how body weight of Daphnia and then cladocerans varied among the three seasons. For all lake types there was a significant positive correlation in the mean body weight of Daphnia and all cladocerans between the different seasons, and only in lakes with macrophytes did the slope differ significantly from one (winter versus summer for Daphnia). 3. These results suggest that the fish predation pressure during autumn/spring and winter is as high as during summer, and maybe even higher during winter in macrophyte‐rich lakes. It could be argued that the winter zooplankton community structure resembles that of the summer community because of low specimen turnover during winter mediated by low fecundity, which, in turn, reflects food shortage, low temperatures and low winter hatching from resting eggs. However, we found frequent major changes in mean body weight of Daphnia and cladocerans in three fish‐biomanipulated lakes during the winter season. 4. The seasonal pattern of zooplankton : phytoplankton biomass ratio showed no correlation between summer and winter for shallow lakes with abundant vegetation or for deep lakes. For the shallow lakes, the ratio was substantially higher during summer than in winter and autumn/spring, suggesting a higher zooplankton grazing potential during summer, while the ratio was often higher in winter in deep lakes. Direct and indirect effects of macrophytes, and internal P loading and mixing, all varying over the season, might weaken the fish signal on this ratio. 5. Overall, our data indicate that release of fish predation may have strong cascading effects on zooplankton grazing on phytoplankton and water clarity in temperate, coastal situated eutrophic lakes, not only during summer but also during winter.     

Feeding ecology of central Baltic Sea herring and sprat

A unique dataset of stomach contents sampled between 1977 and 1999 in the central Baltic Sea was used to perform a comprehensive study of the feeding ecology of Central Baltic herring Clupea harengus and sprat Sprattus sprattus . Both fish species were mainly preying upon calanoid copepods with Pseudocalanus sp. dominating the diet of herring, whereas sprat generally preferred Temora longicornis . Sprat preyed upon older copepodite stages, indicating size‐selective particulate feeding, whereas herring additionally fed on smaller copepodite stages, indicating occasional low food supply inducing filter‐feeding. Additional food sources other than copepods were mysids in winter and autumn for medium to large herring, as well as cladocerans for sprat in spring and summer, determined by the seasonal occurrence of these plankton species. Seasonally the highest feeding activity of both fishes species occurred in spring and summer, the main reproductive periods of calanoid copepods. The most important food item for both predators in spring was Pseudocalanus sp. In summer sprat switched to T. longicornis and Acartia spp. Since the late 1970s, the total stomach fullness decreased and the fraction of empty stomachs increased. In parallel the amount of Pseudocalanus sp. in the diets of both fish species decreased. Further, a considerable dietary overlap between both species in spring indicated considerable competition for food resources, especially due to an enlarged sprat stock. The results of this study support the hypothesis that growth reductions observed in Baltic herring and sprat are due to combination of a change in food availability and an increase in density‐dependent competition.     

长江口棘头梅童鱼食物组成和摄食习性的季节变

棘头梅童鱼是长江口水域的常见小型经济鱼类,具有一定的捕捞价值.为了解长江口棘头梅童鱼食物组成和摄食习性的季节变化,本研究利用胃含物分析法对2013年11月—2014年8月在长江口水域捕获的棘头梅童鱼样本进行了分析.结果表明：长江口棘头梅童鱼全年摄食的饵料生物有8目30种,其中虾类(游泳亚目)是主要饵料生物,相对重要性指数百分比(IRI%)为38.5,优势指数(Ip)为79.1;其次为糠虾目和磷虾目.全年饵料生物中的主要优势种类为葛氏长臂虾、安氏白虾、脊尾白虾、长额刺糠虾、短额刺糠虾、光背节鞭水虱和中华哲水蚤等.饵料生物优势种存在季节差异,春季和夏季的主要优势种均为葛氏长臂虾、安氏白虾和短额刺糠虾,秋季主要优势种为长额刺糠虾、短额刺糠虾和脊尾白虾,冬季主要优势种为葛氏长臂虾、中华哲水蚤和中华假磷虾.长江口棘头梅童鱼全年空胃率为10.4%,冬季最高,秋季最低;全年平均胃饱满系数为0.6%,冬季最低,春季最高,摄食习性存在季节变化.