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1.
Benthic macroinvertebrates were collected and the diets of shortfinned eels (Anguilla australis) and longfinned eels (Anguilla dieffenbachii) inhabiting a small coastal New Zealand stream were examined to investigate intraspecific and interspecific trophic partitioning and prey selection. Our results showed intraspecific segregation of preferred prey among three size classes of juvenile shortfinned eels, but there was significant overlap between different size classes of longfinned eels. All size classes of both species of eel fed nocturnally on similar prey, and so there was no indication of temporal or trophic segregation. Therefore, habitat separation is assumed to be the main mechanism to reduce interspecific competition in these two co‐occurring species of eels.  相似文献   

2.
The food habits of 10 species of grenadier collected from the upper continental slope off South Africa's west coast and Agulhas Bank are described. Three feeding strategies were identified. Members of the demersal micro- or mesocarnivore feeding guild and grazer feeding method include Caelorinchus braueri, C. simorhynchus, juvenile Coryphaenoides striaturus, Lucigadus ori, Malacocephalus laevis, Nezumia brevibarbata, N. micronychodon and N. umbracincta. A second strategy, that of Caelorinchus matamua and adult Coryphaenoides striaturus, involved switching approximately equally from demersal grazing to midwater picking or stalking. The deep-pelagic Mesobius antipodum displayed a third strategy, that of a midwater mesocarnivore picking or stalking. Ontogenetic dietary shifts were noted for the primarily demersal grazers Caelorinchus braueri, C. simorhynchus, Coryphaenoides striaturus and Malacocephalus laevis. Mesopelagic fish, shrimps and squid formed part of the diet of all species. These prey, taken at the bathyal/deep-pelagic interface, are an important source of energy transport from productive surface waters to the deep benthos.  相似文献   

3.
The stomach contents of 36 South African fur seals beached over a 20 year period along the south-east coast of South Africa were examined. In all, 15 fish and nine cephalopod prey types were identified. Five species of fish (Merluccius capensis, Trachurus trachurus capensis, Cynoglossus zanzibarensis, Pterogymnus laniarius, Austroglossus pectoralis) and two cephalopods (Loligo vulgaris reynaudii, Octopus sp.) were of major importance in the diet. The proportion of demersal species in the diet is higher than previously reported, suggesting that the seals forage extensively on the sea floor. The most important fish species in the diet was M. capensis, and the most important cephalopod was L. v. reynaudii. Male and female seals showed distinct prey selection, suggesting possible intraspecific resource partitioning. There is no evidence of competition between seals and other top predators.  相似文献   

4.
During intensive biannual demersal fish-sampling cruises since January 1983 over the South African west coast shelf region (Orange River to Cape Agulhas, coast to 500-m isobath), feeding studies on both species of Cape hake (Merluccius capensis and M. paradoxus) were undertaken. These studies were of two forms, random sampling of the dietary preference and constituents of the hake caught during daylight only and intensive sampling of stomachs with food throughout a 28-hour cycle. From the index of relative importance, crustaceans were shown to be most important in the majority of length classes of hake studied, with mesopelagics (fish and cephalopods) and other hake also important. Differences by hake species, by predator size, by geographical location and by season were evident. The Cape hakes, which constitute some three-quarters of the demersal fish biomass in the area, are deduced to play a major role in the marine faunal environment, both as predators and prey, and some base-line figures of the quantities of different food items consumed by the resource are presented. Hake are largely opportunistic feeders and it is concluded that they can adapt to perturbations in the availability of prey, whether they be triggered by environmental cause or by, for example, purse-seining of particularly mesopelagic fish.  相似文献   

5.
根据2019年1月、4月、7月和10月四个季度10个站位定置张网调查资料, 对福建三沙湾游泳动物的种类组成及季节变化进行分析研究。结果表明: 调查共获得游泳动物209种, 隶属于3门4纲19目73科144属, 其中鱼类154种, 甲壳类48种, 头足类7种。游泳动物种类数以秋季出现最多, 四个季节共同出现的种类有42种。鲈形目种类最多, 其次是十足目。鱼类适温性以暖水性种类居多, 占71.43%, 暖温性种类次之(27.92%); 生态类型以底层、近底层鱼类居多, 两者合占75.97%。鹰爪虾(Trachypenaeus curvirostris)、大黄鱼(Larimichthys crocea)、棘头梅童鱼(Collichthys lucidus)、红星梭子蟹(Portunus sanguinolentus)和日本蟳(Charybdis japonica)等14个种类是三沙湾游泳动物的优势种类, 季节性优势种居多。三沙湾定置张网调查渔业资源质量密度为111.09 kg/km2, 尾数密度为13.72×103 ind./km2, 均以夏季最高, 春季最低。应该进一步加强对三沙湾渔业资源的合理利用和有效保护, 同时重视对外来物种的监测。  相似文献   

6.
为研究长江口日本鳗鲡玻璃鳗肠道菌群的结构与多样性特征,初步探究野生鳗鲡仔鱼的营养需求,分别采集浙江台州市、舟山市以及江苏盐城市邻近海域的玻璃鳗样品,利用16S rDNA扩增子测序技术,分析三个采样点玻璃鳗肠道优势菌群及营养代谢相关的功能差异。结果显示,三个采样点的玻璃鳗肠道菌群均以变形菌门(Proteobacteria, 68.7%～82.0%)和放线菌门(Actinobacteria,4.2%～19.0%)为主要优势菌门。在属分类水平上,不动杆菌属(Acinetobacter, 12.4%～17.3%)和假单胞菌属(Pseudomonas, 8.07%～13.03%)丰度较高,属固定优势菌属。此外,每个采样点样本中都含有丰富的独特细菌群,包括台州市的气单胞菌属(Aeromonas)、舟山市的内生单胞属(Endozoicomonas)和丙酸杆菌属(Cutibacterium)以及盐城市的嗜冷杆菌属(Psychrobacter)和稳杆菌属(Empedobacter),推测是受采样点不同水环境因素影响。不动杆菌、假单胞菌、内生单胞菌等菌属在多种鱼类肠道中有着消化蛋白质的功能,气单胞菌虽属于...  相似文献   

7.
Spatial and size/age distributions of seven teleost species are described from a series of five annual trawling surveys made over the continental shelf and upper slope (20–500 m) of the South African south coast between Cape Agulhas and Port Alfred. The catch was quantified and scaled up to an estimate of an annual biomass index for each of the principal species. The fish studied were the two species of Cape hake Merluccius capensis and M. paradoxus, kingklip Genypterus capensis, Agulhas sole Austroglossus pectoralis, Cape horse mackerel Trachurus trachurus capensis, monk Lophius vomerinus and panga Pterogymnus laniarius. Each showed varying patterns of biomass fluctuation annually, although the surveys constituted too short a data series to reveal significant trends. Nevertheless, declines in abundance of panga and kingklip supported data collected from other sources over a longer period. Interpretation of the data is tempered by a realization that species which are patchily distributed or less vulnerable to the sampling gear may have been inadequately sampled. The information can be used for more-effective management of the multi-species demersal trawl fishery of the region.  相似文献   

8.
The two sympatric species of Cape hake, Merluccius capensis and M. paradoxus, have been the main targets of bottom-trawl fisheries off Namibia for several decades. The feeding ecology of these hakes has been studied mainly using stomach content analyses and thus there remain some gaps in our knowledge about food assimilated over the longer term. In this study, we used fatty acid (FA) profiles to characterise the dietary relationships of M. capensis and M. paradoxus. Muscle samples from hake (n=110) and their known prey (n=68) were collected during trawl surveys off Namibia during 2011. Significant differences between the neutral FA profiles of the hake populations were detected in December 2011 but not in January 2011, an indication of temporal variations in diet and resource partitioning. Comparisons of the neutral FAs in hake and the total FAs of potential prey showed no clear trophic connections, with the exception of flying squid Todarodes sagittatus, which had FA profiles very similar to those of M. paradoxus in December 2011. Our results highlight the complex and temporally shifting relationships that exist between hake and the large pool of prey available to them, and between the two hake species that overlap in their feeding habits and distribution within the highly productive Benguela Current region.  相似文献   

9.
A semi-quantitative assessment is made of the animals observed in archived videotapes taken from the research submersible Jago, during diamond mining and exploratory surveys off the mouth of the Orange River on the west coast of southern Africa (28°15′S, 29°11′S) in November 1996. The seabed environment is described and nekton associations with substratum features are identified. The area is characterized by heterogeneity to its physical and biological struture. The variety of observed nekton is low, and communities are dominated by goby Sufflogobius bibarbatus, juvenile hake Merluccius spp. and cuttlefish Sepia spp. (on soft substrata), as well as false jacopever Sebastes capensis and kingklip Genypterus capensis (on rocky substrata).  相似文献   

10.
Results are presented following a long-term study of the diet of the Cape gannet Morus capensis at Bird Island, Algoa Bay, examining 4 178 regurgitations representing 36 351 prey items collected during 12 breeding cycles from April 1979 to March 1991. In all, 32 teleost and two cephalopod species were recorded. The pelagic shoaling pilchard Sardinops ocellatus, anchovy Engraulis capensis and saury Scomberesox saurus scombroides were identified as the main prey species. The diet composition showed marked interannual fluctuations during the sampling period, which appear to be related to changes in the abundance of the main prey species. The relative abundance of pilchard, anchovy and saury was also found to change intra-annually, the first two species occurring more frequently in the diet during the breeding season and saury dominating the diet in the non-breeding season. These changes are thought to originate from temporal variation in the oceanographic regime within the foraging range of the gannets.  相似文献   

11.
Cape fur seals Arctocephalus pusillus pusillus were harvested to extirpation on the Robberg Peninsula, Plettenberg Bay, on the south-east coast of South Africa, between the 17th and early 20th centuries. Seals returned to Robberg in small numbers during the early 1990s and their numbers subsequently increased. We studied the diet of this increasing population using faecal (scat) sampling to determine: the species composition and size of prey in the diet of Cape fur seals at Robberg; to explore temporal variation in the diet; and to investigate the potential for competition between seals and the fisheries around Plettenberg Bay. Of the 445 scats collected, 90% contained hard prey remains and 15 teleost prey species were represented in the 3 127 otoliths that could be identified. The seals’ most important prey species in terms of numerical abundance, frequency of occurrence and mass in the diet, were anchovy Engraulis encrasicolus, sardine Sardinops sagax, horse mackerel Trachurus capensis, sand tongue-fish Cynoglossus capensis and shallow-water hake Merluccius capensis (in decreasing order of importance for numerical abundance). The proportion of anchovy in the diet increased during the study period (2003–2008), whereas the proportion of sardine decreased. The estimated average annual consumption of sardine by seals was higher than the average annual catch made by purse-seine fisheries in this area, suggesting resource competition between seals and purse-seiners, especially in the light of continuing growth of seal numbers in the area. However, direct competition between seals and linefisheries appeared to be minimal. Scat sampling of Cape fur seals holds potential to serve a useful and cost effective indicator of temporal changes in sardine abundance.  相似文献   

12.
Diel patterns in survey trawl catches for the Cape hakes Merluccius capensis and M. paradoxus off Namibia were studied in order to examine the effect of diel bias on catchability, and its implication for survey abundance estimation and the consistency of the survey time-series. Catch rates (numbers per haul) by species and length from summer demersal biomass surveys conducted during the period 2002–2013 were used, together with a computation of the corresponding light-level data from which the solar zenith angles were obtained. Generalised additive models were fitted to assess the relationship between the catches and a number of explanatory variables. Significant covariates were zenith angle, depth and geographical position. The final models explained 78% and 59% of the variability in catch rates of M. capensis and M. paradoxus, respectively. For M. capensis, the response to zenith angle increased sharply for values above 100°, which represents the time between sunset and sunrise. For M. paradoxus there was a moderate increase in the response to zenith angle during the night. In cases where some fishing took place at night in shallow water, the survey results for M. capensis were more greatly affected than was the case for M. paradoxus, which is related to the different depth preference of the two species. Fishing in depths shallower than 400?m outside daylight hours should therefore be avoided in order to reduce bias and ensure consistency in abundance estimates from surveys.  相似文献   

13.
The feeding patterns of 12 teleost species taken by demersal trawl from two areas of the Cape coast and which fed predominantly on benthic and epibenthic prey are described. Prey selection varied intraspecifically with growth. There was considerable overlap in prey taken by different predators, although the dominant food differed between the two coasts and according to habitat (soft substrata or hard reefs). Prey selection varied with depth, probably as a result of the influence of depth and other physical features on prey species distribution. Small crustaceans were taken by all the predators and constituted the single most important group, especially for small predators. Brachyurans were important as prey, particularly in those species inhabiting hard substrata. Fish were of minor importance as food, except in Chelidonichthys capensis, Malacocephalus laevis and Helicolenus dactylopterus. Commercially important species of fish and cephalopods were preyed on only occasionally. It appeared that prey were selected according to their abundance, size, behaviour and habitat use. The use of benthic and epibenthic prey constitutes an important pathway for energy to return from the benthos to the foodweb.  相似文献   

14.
Samples collected during four cruises on board R.S. Africana were used to study the trophic ecology and feeding behaviour of Engraulis capensis in the southern Benguela region. Previous work had indicated that this species was a non-selective filter-feeding omnivore, diatoms comprising the bulk of the diet. The results of the present study reveal that anchovies selectively feed on mesozooplankton, especially calanoid copepods and euphausiids. Investigation of the feeding behaviour of the species indicates that raptorial feeding is dominant over filter-feeding and that prey appears to be selected primarily on the basis of size.  相似文献   

15.
Food and feeding of small fish in the Rakaia River,New Zealand   总被引：1，自引：1，他引：0  
Benthic macroinvertebrates and fish species were collected at monthly intervals during a 12‐month period, from 3 areas of the lower Rakaia River. The composition and abundance of the benthos and stomach contents of the fish were analysed for seasonal trends, food niche breadth and overlap between pairs of fish species, and overlap between the benthos and the diet of each fish species. The diets of bluegilled bully (Gobiomorphus hubbsi), upland bully (G. breviceps), juvenile longfinned eel (Anguilla dieffenbachii), Galaxias brevipinnis, G. paucispondylus, and juvenile brown trout (Salmo trutta) were similar to the proportions of prey species in the benthos. Deleatidium and chironomid larvae dominated the benthos in all seasons and formed the majority of food items in the diet of these species. Food niche overlap between these species was high, indicating potential competition, but preferred habitat and feeding habit differences plus low fish population density and abundance of main prey items probably eliminate the occurrence of any serious competition. The diet of the other fish species differed from this pattern. The common bully (Gobiomorphus cotidianus) ate proportionally more chironomid larvae and fish eggs than occurred in the benthos; torrentfish (Cheimarrichthys fosteri) ate proportionally more chironomid larvae than occurred in the benthos; and quinnat salmon (Oncorhynchus tshawytscha) depended largely upon prey species of terrestial origin, such as adult Deleatidium and dipterans.  相似文献   

16.
The diets of six species of catsharks (Carcharhiniformes: Scyliorhinidae) caught between Walvis Bay and Cape Agulhas at depths between 50 and 1 016 m were analysed. The most common prey items were teleosts and crustaceans. Lanternfish (Myctophidae) were common in the diets of Apristurus microps, A. saldanha, Apristurus spp. and Holohalaelurus regani, whereas the Cape anchovy Engraulis capensis was preyed on extensively by Scyliorhinus capensis. The most common crustaceans in the diet were Parapagurus spp., Mursia cristimanus and Euphausia lucens. Cephalopods were uncommon prey items, except in A. microps, A. saldanha, Apristurus spp. and H. regani.  相似文献   

17.
Information on hake stomach contents collected during research cruises off the west coast of South Africa between 1988 and 1990 is analysed. Estimates of the annual consumption and daily ration of the Cape hakes Merluccius capensis and M. paradoxus are obtained. Coefficients of variation (CVs) for these estimates are estimated by a bootstrap variance-estimation procedure. Cape hakes are opportunistic feeders. Juveniles feed mainly on crustaceans and the diet becomes increasingly piscivorous with age. Anchovy were the dominant dietary item of juvenile M. capensis, although this may be a reflection of the fact that anchovy were readily available at the time of the surveys. The large number of anchovy found in the diet during this study highlights the dangers of extrapolating consumption estimates for opportunistic feeders to other time periods. Pooling of data across geographic and seasonal strata introduces substantial bias in estimates of consumption and daily ration for only the pelagic prey species. Estimates of annual consumption are highly sensitive to the cruise selected to provide the estimates of numbers-at-length, because these latter estimates vary substantially between cruises. Furthermore, estimates of annual consumption and daily ration by prey species are very imprecise due to the effects of small sample sizes, the opportunistic nature of and natural variability associated with feeding. This implies that it is unlikely that model-estimation procedures which utilize these data will be able to provide particularly precise predictions. Therefore, before any larger-scale stomach collection exercise is undertaken, it is advisable to perform simulation studies to assess the sampling intensity required to achieve the desired levels of accuracy and precision for predictions from multispecies model-estimation procedures which make use of such data.  相似文献   

18.
Six species of skates were trawled commonly on the continental shelf off the Southern Cape during routine surveys of demersal fish between 1986 and 1990. Raja miraletus is a small skate found principally in shallow (<50 m) water that feeds mainly on small crustaceans, such as mysids and macrurans. The large Raja alba occurs over most of the continental shelf, is a piscivore throughout its life and preys heavily on flatfish, especially Cynoglossus zanzibarensis. R. cf. clavata is ubiquitous on the shelf but most abundant between 50 and 150 m deep. Feeding predominantly on crustaceans, this skate switches from carids, penaeids and mysids when small to brachyurans and small benthic fish when larger. R. pullopunctata is found over a similar depth range but attains a much larger size. It eats small mysids and macrurans when small, but brachyurans and fish become more important in the diet with increasing size of the predator. R. wallacei is most commonly taken at depths of 80–>200 m, feeds initially on small crustaceans, but switches to fish, including eels, as it grows. The small Cruriraja parcomaculata is found at the edge of the continental shelf and over the upper slope; it preys on small crustaceans, including mysids, isopods and macrurans. The distribution pattern of the skates and their prey suggest overlap in prey taken, the overlap being greatest in those species which feed on crustaceans. The large biomass of skates in the area suggests that they are an important component of the demersal faunal assemblage of the continental shelf there, and also that they may have a significant impact on the benthic fauna.  相似文献   

19.
Scavengers perform an important role in deep-sea ecosystems, recycling carrion. However, scavenged material can be difficult to discern from predation. The synaphobranchid eel Diastobranchus capensis Barnard, 1923, is common bycatch in deep-water fisheries for orange roughy (Hoplostethus atlanticus Collett, 1889) in New Zealand waters. Despite anecdotal reports of scavenging in D. capensis, their ecology and feeding are little known. Scavenged material was estimated to be approximately 39 per cent (by weight) of the diet of D. capensis from northeastern Chatham Rise, New Zealand, from water depths of 1062–1196 m. Scavenged material was defined as fragmentary food items from animals and plants either not normally available to the eel, or from animals larger than the eel consuming them (e.g., fish heads and tails, spent squid spermatophores, beaks and tentacle crowns, and seaweed). D. capensis were primarily piscivorous, with the diet supplemented by squid, natant decapods and mysids. The weight or number of food items did not increase with the size of the eel, nor was there any major ontogenetic shift in the composition of the diet. D. capensis probably plays an important role in mid-slope communities, recycling carrion.  相似文献   

20.
In this study demersal survey data for the period 1990–1999 are used to investigate the average distribution of the Cape hake Merluccius capensis and M. paradoxus off Namibia in terms of density and mean length. Further, biomass estimates are compared on the basis of depth and density stratification. The main distribution of M. capensis was north of 27°S and that of M. paradoxus south of 24°S. M. paradoxus was deeper than M. capensis. For both species, average length increased with depth. M. paradoxus expanded its range to the north through the 1990s as its population size (off South Africa and Namibia) increased. In Namibian waters, small M. paradoxus were found only south of 25°S. Mean length of M. capensis increased north of 21°S, largely as a result of decreased numbers of small fish in shallower water. Abundance estimates stratified by depth were no different from those post-stratified on similar densities.  相似文献   

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