Experimental study on the effect of diet on fatty acid and stable isotope profiles of the squid Lolliguncula brevis

Fatty acid and stable isotope analyses have previously been used to investigate foraging patterns of fish, birds, marine mammals and most recently cephalopod species. To evaluate the application of these methods for dietary studies in squid, it is important to understand the degree to which fatty acid and stable isotope signatures of prey species are reflected in the squids' tissue. Four groups of Lolliguncula brevis were fed on prey species with distinctly different fatty acid and stable isotope profiles over 30 consecutive days. One group of squid were fed fish for fifteen days, followed by crustaceans for a further fifteen days. A second and third group were fed exclusively on fish or crustaceans for thirty days. And a fourth group was fed on a mixture of fish and crustaceans for thirty days. Analysis of squid tissue showed that, after 10 days of feeding, fatty acid profiles of squid tended to reflect those of their prey. Squid that fed on a single prey type, i.e. fish or crustacean, showed only minor modifications in fatty acid proportions after the initial change and fatty acid profiles were clearly distinguishable between the two feeding groups. Shifts in fatty acid proportions towards respective prey profiles could clearly be observed in squid the diet of which was swapped after 15 days. Clear differences could also be seen in fatty acid profiles of squid feeding on a mixed diet with trends towards either fish or crustacean fatty acid signatures. Stable isotope signatures of squid tissues clearly distinguished between animals feeding on different diets and supported findings from fatty acid analysis, thus indicating both methods to be viable tools in feeding studies on squid species.     

台湾海峡游泳动物种类组成及其多样性

根据2006-2007年在台湾海峡进行的四个季度航次定点底拖网调查资料,分析了台湾海峡游泳动物的种类组成、数量分布、优势种和多样性等特征。结果表明,调查海域共鉴定出游泳动物373种,其中鱼类273种,甲壳类81种,头足类19种;渔获物组成以鱼类为主,占渔获物总重量的65.6%,其次为甲壳类和头足类,分别占21.1%和13.3%,所有调查站位游泳动物的年平均生物量密度指数为24.91kg/h,主要优势种类为带鱼(Trichiurus japoni-cus)、拥剑梭子蟹(Portunus haanii)、二长棘鲷(Parargyrops edita)、龙头鱼(Harpadon nehereus)、竹筴鱼(Trachurus japonicus)、火枪乌贼(Loligo beka)等。对多样性的分析显示,台湾海峡游泳动物物种多样性指数(H′)变化范围为1.45-3.21,平均为2.47,其中秋季最高,夏季最低,且呈现南高北低的特点。与历史资料相比,目前台湾海峡游泳动物种类数明显减少,尤其是闽东和闽南—台湾浅滩海域表现最为突出;优势种类个体呈现小型化和低龄化趋势,表明台湾海峡游泳动物资源衰退明显。     

Parasites of recruiting coral reef fish larvae in New Caledonia

Recruiting coral reef fish larvae from 38 species and 19 families from New Caledonia were examined for parasites. We found 13 parasite species (Platyhelminthes: Monogenea, Cestoda and Trematoda) but no acanthocephalan, crustacean or nematode parasites. Over 23% of individual fish were infected. Didymozoid metacercariae were the most abundant parasites. We conclude that most of the parasites are pelagic species that become ‘lost’ once the fish larvae have recruited to the reef. Larval coral reef fish probably contribute little to the dispersal of the parasites of the adult fish so that parasite dispersal is more difficult than that of the fish themselves.     

Diet composition of bigeye tuna (Thunnus obesus) and yellowfin tuna (Thunnus albacares) caught on aggregated schools in the western equatorial Atlantic Ocean

The present study aims to characterize and compare the diet of bigeye and yellowfin tunas caught on aggregated schools in the western equatorial Atlantic Ocean. The samples were collected from January 2011 to June 2016. The tunas were measured on board and the stomachs were removed after evisceration. The stomachs were analyzed regarding their Index of Fullness and the importance of each prey in the diet was estimated by the Index of Relative Importance (IRI). The diet overlap was assessed by the Morisita‐Horn's Index, Non‐Metric Multidimensional Scale (NMDS), and Analysis of Similarity (ANOSIM). The feeding strategy was determined by the Costello's Diagram. The 195 bigeye and 212 yellowfin tunas ranged in fork length from 51 to 137 cm and 43 to 174 cm, respectively. The diet of bigeye tuna was composed of 10 families of fish, three cephalopod families, and four crustacean orders. The diet of yellowfin tuna was composed of 11 families of fish, three cephalopod families, and three crustacean orders. The yellowfin tuna seems to feed upon more abundant prey species near the surface like flying fish, which have the concentration enhanced by the light attractors on the boat, and occasionally on other prey from deeper habitats like lanternfish, squids, and pomfret. Bigeye tuna feed mainly at prey that commonly occurs in deeper habitats like squids, drift fish, lanternfish, and pomfret.     

Food habits of fishes in the surf zone of a sandy beach at Sanrimatsubara, Fukuoka Prefecture, Japan

To clarify the feeding habits of fishes in surf zones, the gut contents of 19 fish species collected in the surf zone of a sandy beach at Sanrimatsubara, western Japan, were examined. Ontogenetic changes in food preference were recognized in seven species (Mugil cephalus cephalus, Lateolabrax latus, Sillago japonica, Paralichthys olivaceus, Paraplagusia japonica, Takifugu poecilonotus, and Takifugu niphobles). A cluster analysis based on dietary overlaps showed that the surf zone fish assemblage comprised six trophic groups (zooplankton, benthic and epiphytic crustacean, detritus, polychaete, fish, and insect feeders). Of these, the most abundant trophic group was zooplankton feeders, along with benthic and epiphytic crustacean feeders.     

福建三都澳游泳动物种类组成及群落结构稳定性

利用2012-2013年三都澳渔业资源的定置张网调查资料, 应用物种多样性指数、数量生物量比较曲线(ABC曲线)及鱼类分类多样性指数等方法分析三都澳游泳动物种类组成特征和群落结构的稳定性。调查中共出现游泳动物195种, 隶属于17目64科125属, 其中鱼类143种, 甲壳类47种, 头足类5种。大黄鱼(Larimichthys crocea)在三都澳4个航次的调查中都是最主要的优势种类, 其他优势种类还包括叫姑鱼(Johnius belengerii)、白姑鱼(Argyrosomus argentatus)、虾虎鱼类和一些甲壳类。大黄鱼多为养殖群体, 其他优势种类的共同特征是个体小, 繁殖周期短, 生物量季节或年际间波动剧烈。物种多样性分析表明, 三都澳游泳动物群落平均Shannon-Wiener多样性指数为2.61, 9、10月高, 1、5月低。ABC曲线分析表明, 4次调查中群落结构存在明显的变化, 繁殖群体的补充、个体生长、捕捞、伏季休渔等是影响群落结构稳定性的因素。本次研究表明, 大黄鱼生物量的比例与Shannon-Wiener多样性指数呈极显著负相关(P < 0.01, R = -0.890), 与种类数呈显著负相关(P < 0.05, R = -0.563)。结合近年来的调查数据, 统计得到三都澳的现存鱼类约224种, 其平均分类差异指数(△⁺)为59.5, 分类差异变异指数(∧⁺)为260.8。相对于中国沿海其他海域, 三都澳鱼类群落分类学范围较小, 且群落间的分类地位关系极不均匀, 群落抗干扰的能力较差。     

Feeding ecology of wintering terns in Guinea-Bissau

We studied the feeding ecology of Little Terns Sterna albifrons , Sandwich Terns S. sandvicensis and Royal Terns S. maxima in the Archipélago dos Bijagós (11°40'N, 15°45'W) in Guinea-Bissau (West Africa) during the winter of 1992/1993. More than 95% of all prey taken by these terns were roundfish, ranging in weight from 0.3 to 40 g. Birds usually fed alone, but sometimes they were observed feeding in mixed-species flocks consisting of 15–200 individuals. Capture rate ( n fish per hour foraging) in these flocks was higher than that of solitary birds. However, smaller fish were caught by birds foraging in flocks, so food intake rate (g/h) did not differ between solitary and flock-feeding birds. The relationships between foraging behaviour of the three tern species and abiotic factors, such as time, tide and water clarity, have been investigated. Capture rate of Royal Terns increased with water clarity. For Little Terns and Sandwich Terns, food intake rate was lower in the most turbid waters compared to clearer waters. There was very little foraging activity during high tide. For Little Terns and Royal Terns, food intake rate was about twice as high during receding and low tides as during an incoming tide. Food intake rate averaged 8 g/h in Little Terns, 60 g/h in Sandwich Terns and 45 g/h in Royal Terns. With a rough model, we estimate the maximum rate of daily energy expenditure of terns wintering in the tropics at 3 × BMR (defined as energy expenditure of inactive bird at thermoneutrality in a post-absorptive state during the resting phase of the daily cycle). From an energetic viewpoint, wintering Sandwich Terns in Guinea-Bissau seem to have an easy living.     

Stable isotope analysis as a tool to monitor dietary trends in little penguins Eudyptula minor

Long‐term dietary monitoring of seabirds can be used to relate population fluctuations to at‐sea events. Stomach flushing is a conventional dietary monitoring technique, but has a number of disadvantages. Stable isotope analysis (SIA) is a less invasive method that provides unbiased dietary information over a longer period. We evaluated stable isotope analysis as a potential tool for monitoring long‐term little penguin Eudyptula minor diet. We determined diet composition during the chick feeding stage using stomach flushing and SIA at three separate colonies, using spatial variation in diet as a surrogate for potential temporal variation. Bayesian isotopic mixing models were generated for blood and feathers to evaluate their ability to discriminate broad‐scale (fish, squid, crustaceans) and fine‐scale (individual prey species) diet composition. Differences in stable carbon and nitrogen isotope ratios were found between colonies: broad‐scale isotopic mixing models predicted different proportional contributions of broad taxa (fish, cephalopod, crustacean) to diet than was indicated by stomach samples, reflecting the bias incurred by one‐off stomach contents analysis. Fine‐scale isotopic mixing models predicted proportional contributions of prey items with less certainty. Blood isotopic mixing models had narrower confidence intervals than models for feathers, but trends in δ¹⁵N for feathers mirrored those for blood. Our results suggest that relying on stomach contents analysis to detect shifts in prey consumption in little penguins could be very misleading, resulting in a less‐than‐complete idea of total prey consumption. SIA of little penguin tissues could be used to monitor dietary shifts across dissimilar taxa that may affect population numbers, but would fail to detect shifts between fish species.     

Cephalopod and Groundfish Landings: Evidence for Ecological Change in Global Fisheries?

Cephalopod fisheries are among the few still with some local potential for expansion; in fact, as groundfish landings have declined globally, cephalopod landings have increased. We propose the hypothesis that, although increased cephalopod landings may partly reflect increased market demand, overfishing groundfish stocks has positively affected cephalopod populations. Data from 15 key FAO areas reveal that, with the exception of the north- east Atlantic, cephalopod landings have increased significantly over the last 25 years while groundfish have risen more slowly, remained stable, or declined. In terms of volume, cephalopods have not replaced groundfish. This is hypothesized as owing to the shorter life cycle of cephalopods, and rapid turnover and lower standing stocks than for longer-lived finfish species. Under high fishing pressure, groundfish are probably poor competitors, having less opportunity for spawning and replacement. In West Africa, the Gulf of Thailand and Adriatic there is strong circumstantial evidence that fishing pressure has changed ecological conditions and cephalopod stocks have increased as predatory fish have declined. We recommend that this hypothesis be tested thoroughly in other areas where suitable data exist. Most coastal and shelf cephalopod fisheries are likely to be fully exploited or overexploited, and current annual fluctuations in cephalopod landings are probably largely environmentally-driven.     

Temporal and spatial variability of mobile fauna on a submarine cliff and boulder scree complex: a community in flux

The mobile component of a community inhabiting a submarine boulder scree/cliff was investigated at Lough Hyne, Ireland at dawn, midday, dusk and night over a 1-week period. Line transects (50 m) were placed in the infralittoral (6 m) and circumlittoral (18 m) zones and also the interface between these two zones (12 m). The dominant mobile fauna of this cliff consisted of echinoderms (6 species), crustaceans (10 species) and fish (23 species). A different component community was identified at each time/depth interval using Multi-Dimensional Scaling (MDS) even though both species diversity (Shannon–Wiener indices) and richness (number of species) remained constant. These changes in community composition provided indirect evidence for migration by these mobile organisms. However, little evidence was found for migration between different zones with the exception of the several wrasse species. These species were observed to spend the daytime foraging in the deeper zone, but returned to the upper zone at night presumably for protection from predators. For the majority of species, migration was considered to occur to cryptic habitats such as holes and crevices. The number of organisms declined during the night, although crustacean numbers peaked, while fish and echinoderms were most abundant during day, possibly due to predator-prey interactions. This submarine community is in a state of flux, whereby, community characteristics, including trophic and energetic relationships, varied over small temporal (daily) and spatial (m) scales.     

Altered predation susceptibility of mosquitofish infected with Eustrongylides ignotus

Eustrongylides ignotus is a parasitic nematode whose definitive hosts are often piscivorous wading birds (Ciconiiformes). Several species of small fishes are intermediate hosts, while larger predatory fish may be paratenic (transport) hosts. We examined predation susceptibility of infected mosquitofish (Gambusia holbrooki) to three species of predatory fishes, including juvenile largemouth bass (Micropterus salminoides), warmouth (Lepomis gulosus), and bluegill (Lepomis macrochirus). A 250 L aquarium with removable plexiglass divider and remote observation windows was constructed. Aquatic macrophytes were placed in the tank to provide refuge for the fishes. Predatory fish were allowed to acclimate to one half of the tank, while one infected and one uninfected mosquitofish were placed in the other. The divider was removed and an observer recorded the number of capture attempts and time required for capture. Predators were observed for behavioral alterations for 4 days after ingestion of infected mosquitofish, then examined at necropsy. Infected prey were selected preferentially in 31 of 38 (82%) trials. The number of capture attempts was 2.7+/-0.2 (x +/- SE) for infected fish and 3.9+/-0.4 for uninfected fish. Mean time of capture was 12.4+/-1.6 min for infected fish and 21.7+/-2.9 for uninfected fish. Because of these differences, infected mosquitofish were more susceptible to predation (P < 0.01) than uninfected fish. Aberrant behavior including lethargy, convulsions, and buoyancy abnormalities was observed in eight (67%) predatory fish. At necropsy, larvae of E. ignotus were found in the coelomic cavity, viscera, and swim bladders of predators. Parasite-induced behavior modification of intermediate hosts may predispose them to predation by wading birds and thereby facilitate the transmission of this nematode in natural populations.     

Impact of hard-bottom substrata on the small-scale distribution of fish and decapods in shallow subtidal temperate waters

The micro-scale spatial distribution patterns of a demersal fish and decapod crustacean assemblage were assessed in a hard-bottom kelp environment in the southern North Sea. Using quadrats along line transects, we assessed the in situ fish and crustacean abundance in relation to substratum types (rock, cobbles and large pebbles) and the density of algae. Six fish and four crustacean species were abundant, with Ctenolabrus rupestris clearly dominating the fish community and Galathea squamifera dominating the crustacean community. Differences in the substratum types had an even stronger effect on the micro-scale distribution than the density of the dominating algae species. Kelp had a negative effect on the fish abundances, with significantly lower average densities in kelp beds compared with adjacent open areas. Averaged over all of the substrata, the most attractive substratum for the fish was large pebbles. In contrast, crustaceans did not show a specific substratum affinity. The results clearly indicate that, similar to other complex systems, significant micro-scale species–habitat associations occur in northern hard-bottom environments. However, because of the frequently harsh environmental conditions, these habitats are mainly sampled from ships with sampling gear, and the resulting data cannot be used to resolve small-scale species–habitat associations. A detailed substratum classification and community assessment, often only possible using SCUBA diving, is therefore important to reach a better understanding of the functional relationships between species and their environment in northern temperate waters, knowledge that is very important with respect to the increasing environmental pressure caused by global climate change.     

Diel and seasonal patterns of food intake and prey selection by Coregonus sp. in re-oligotrophicated Lake Lucerne, Switzerland

Feeding intensity by whitefish Coregonus sp., in oligotrophic Lake Lucerne in Switzerland was high during dusk when the bulk of potential prey items were in the depth zone occupied by the fish. Diet composition was fairly uniform throughout the day but changed substantially over the seasons. The fish fed opportunistically; differences between seasons reflected changes in prey availability. During the intensive feeding and growing period (May-September), fish were found in the upper 20 m of the lake feeding primarily on cladocerans. Large and non-evasive species, Daphnia spp. and Bythotrephes longimanus , were the most numerous and frequent organisms in the diet during the major part of the growing season. Smaller ( Bosmina spp.) as well as evasive species (cyclopoid copepods) were consumed in large numbers when larger, non-evasive species were rare in the lake. The fish showed strong preference for the least abundant crustacean, B. longimanus , while the most abundant crustaceans, calanoid copepods, were rare in the diet. The fish not only selected particular species but, within each species, selected the larger individuals. Diel vertical migration of the prey items in this lake could be, at least in part, attributed to fish predation pressure. The observed selectivity patterns shown by the fish are explained in terms of prey visibility, escape ability, the overlap in distribution of predators and prey in time and space, the profitability of the prey and the present trophic state of the lake.     

Microchemical provenancing of prey remains in cormorant pellets reveals the use of diverse foraging grounds

Piscivorous birds in aquatic ecosystems exert predation pressure on fish populations. But the site-specific impact on fish populations, including stocked and commercially used fish species, remains disputed. One of the key questions for the management of piscivorous birds and fish is determining the origin of prey and thus which fish populations are targeted by the birds. We addressed this question by provenancing otoliths (earstones) of fish obtained from regurgitated pellets of piscivorous birds by otolith microchemistry analysis. We retrieved otoliths from regurgitated pellets of great cormorants (Phalacrocorax carbo sinensis) collected every 2 weeks for 2 years from breeding and roosting colonies at Chiemsee in Bavaria, Germany, and classified them according to family or species. We collected water samples from Chiemsee and potential surrounding foraging grounds. We measured the strontium (Sr) ⁸⁷Sr/⁸⁶Sr isotope ratio and Sr mass fraction of water and otoliths using (laser ablation) inductively coupled plasma-mass spectrometry. We assigned otoliths from regurgitated pellets to habitat clusters of origin by comparing the Sr isotopic and elemental composition of otoliths and waterbodies. In 36% of cormorant pellets collected at Chiemsee, prey was assigned to waterbodies distinct from Chiemsee. Furthermore, cormorants used different foraging sites during 1 day. Microchemical provenancing of prey remains can contribute to identifying foraging sites of piscivorous birds and to what extend the birds switched among foraging sites.     

Eye morphology and optics of the double-eyed mysid Euchaetomera typica

The structure and optics of the mesopelagic double-eyed mysid crustacean Euchaetomera typica Sars, 1884 are described for the first time. The lateral eye is a typical refracting superposition eye with a wide field of view (172°) and low resolution (interommatidial angle of 7.3°). The antero-dorsal part of the eye is elongated due to the extension of the clear zone. This dorsal eye has a restricted field of view (33°) but much higher resolution (1.5°). The dorsal eye also uses refracting superposition optics, although the optical array is unusual as many of the peripheral ommatidia lack crystalline cones. The centre of curvature of the cornea is in front of the flattened rhabdom layer whereas the axes of the crystalline cones are centred on a point about twice as deep as the rhabdom layer. This results in a well-focused eye, free of spherical aberration. There is a remarkable similarity in eye structure between this species and some mesopelagic double-eyed euphausiid crustaceans.     

Toxicity of Clostridium botulinum type E neurotoxin to Great Lakes fish: implications for avian botulism

Since 1999, large-scale mortalities of fish-eating birds have been observed on the Great Lakes, and more specifically on Lake Erie. Type E botulism has been established as the primary cause of death. The mechanism of type E botulism exposure in fish-eating birds is unclear. Given that these birds are thought to eat live fish exclusively, it seems likely that their prey play a key role in the process, but the role of fish as potential transport vectors of botulinum neurotoxin type E (BoNT/E) to birds has not been adequately investigated. Between June 2003 and April 2004 a methodological model for exposing fish to Clostridium botulinum was developed and used to compare the sensitivity of rainbow trout (Oncorhynchus mykiss), round goby (Neogobius melanostomas), walleye (Stizostedion vitreum), and yellow perch (Perca flavescens) to four doses (0, 800, 1,500, and 4,000 Mouse Lethal Doses) of Clostridium botulinum type E neurotoxin. Each fish species expressed unique changes in both behavior and skin pigmentation prior to death. Yellow perch survived significantly longer (P < 0.05) than the three other species at all toxin treatments. Results of this study suggest that live fish can represent a significant vector for transfer of BoNT/E to birds.     

The winter fattening model: a test at low latitude using the Clamorous Reed Warbler

Small birds at high latitudes accumulate fat during the day so that they can survive long and cold winter nights. The winter fattening model suggests that birds increase their minimum (morning) mass in cold weather, build up their mass during the day, and then rely on the energy reserves so accumulated until the morning. While data from mid and high latitudes support this model, little is known about the strategies of birds inhabiting lower latitudes (< 40°N). We use an 18-year data set to investigate whether the winter fattening model holds in a mid-latitude (32°N) population of the Clamorous Reed Warbler Acrocephalus stentoreus . We show that morning mass and fat score vary as predicted by the winter fattening model. In addition, adults appear to be better adapted to long and cold winter nights than first-year birds. A long-term trend of increased body mass may be attributable to character release following reduced interspecific competition.     

CEPHALOPODS AND FISH: THE LIMITS OF CONVERGENCE

Resemblances between cephalopods and fish 1. Modern cephalopods (coleoids < 1000 species) resemble modern fish (30,000 species) more closely than any of their ancestors did. They have not been replaced by the more diversified group in geological time. 2. The main body of the article (pp. 245–283) reviews these resemblances. They are to be found at all levels of analysis. 3. Basic physiological mechanisms of molluscs (pp. 262–5) have been incorporated into systems with performances comparable to those of vertebrate systems. For instance the cephalopod locomotory system (pp. 249–56) and hydrostatic control system (pp. 256–60), structurally very different from their fish counterparts, have similar adaptive radiation. 4. Behaviour (p. 278) and growth of the brain (p. 265) are characteristically vertebrate-like. 5. Cephalopods and fish are considered as occupying the same broad adaptive zone though modal differences (pp. 283–5)-in reproductive habits, growth rate and light-dependent behaviour where extraocular photoreceptors appear to be important - mean that they occupy different areas within that zone. (ii) Evolution of convergence 6. Evidence is presented (pp. 287–293) for considering the convergence as due not merely to similar physical demands of the marine environment, but to dynamic interactions between cephalopods and vertebrates from the late Palaeozoic onwards. 7. The convergence was set on its way when the two groups, independently of each other, acquired locomotory methods that allowed them to increase in size. 8. It is argued that reduction and eventually complete loss of the chambered shell (in all but sepiids) was an evolutionary response to the needs of increased mobility and to the need to go deeper as vertebrate predators pushed out into oceanic waters. 9. The ammonites (pp. 291–2) present a partial model of the course that coleoid ancestors may have taken. 10. Coleoids subsequently reinvaded surface and coastal waters, competing successfully in a teleost habitat. Their most striking adaptations are ones that they share with teleosts. 11. Behavioural interactions in a vertebrate-dominated environment have probably been responsible for the vertebrate-type eye of cephalopods (p. 293). 12. The conclusion that the common adaptive zone shared by cephalopods and fish has been achieved by mutual interactions between the two groups evokes no special evolutionary principles. It assumes that all cephalopod species have (at some period of their evolutionary history) been in competition for food with some vertebrate species and that vertebrates are a source of selection pressures - largely operating through visual behaviour - that maintain and promote convergence upon the ‘fish’ modal type. 13. Selection pressures also operate within behaviour space to maintain and promote the special differences that separate any competitively successful species from all others. Coleoids as a group appear to have retained adaptations associated with such molluscan features as high growth rate and rapid turnover of the population. They are still characteristically crepuscular in habits and have extensive vertical mobility.