1,721,059 research outputs found
Trophic ecology of black scabbardfish, Aphanopus carbo in the NE Atlantic—Assessment through stomach content and stable isotope analyses
No full textThe black scabbardfish is a deep water species of high commercial interest in the NE Atlantic. Specimens were collected from commercial trawls to the west of the British Isles and from longliners operating near Madeira between September 2008 and May 2010. Stomach content analysis was confined to samples from the northern area, because of a high number of empty stomachs from Madeira. Stable isotope analyses identified that black scabbardfish feeds on species with epipelagic and benthopelagic affinities. For the west of British Isles, the ?N values were significantly different between seasons suggesting a change in the diet throughout the year. Black scabbardfish have higher ?N and ?C values compared with other co-occurring benthopelagic feeders and lower nitrogen values than the true benthic predators and/or scavengers. Comparison with stable isotope analysis in samples from Madeira indicated that black scabbardfish feed at a similar trophic level and has the same trophic niche width in both areas, assuming similar baseline isotope compositions. The diet in the northern area comprised fish (68% N), crustaceans (22% N) and cephalopods (15% N) with blue whiting (Micromesistius poutassou) constituting 40% of the prey. Seasonal shift in diet was observed, with a predominance of blue whiting (70%) in the first quarter of the year, shifting to a more diverse diet in the remainder of the year. These results indicate that the diet of black scabbardfish is closely linked with the seasonal migration of blue whiting and that they likely select prey in proportion to availability. This study demonstrates that the combined used of both methods can elucidate the trophic ecology of black scabbardfish, in situations where conventional methods alone provide insufficient data
Fine-scale population structure in a deep-sea teleost (orange roughy, Hoplostethus atlanticus)
No full textMicrosatellite and otolith chemistry variability were analysed to assess fine scale genetic structure in the deep-sea teleost orange roughy (Hoplostethus atlanticus). The Porcupine Bank located on the continental shelf west of Ireland, comprises a complex system of mounds and flat areas that are broken up by canyons. Orange roughy form spawning aggregations on mounds and flat areas, and were heavily fished until the resource was depleted. By analysing adults in spawning condition and juvenile orange roughy from six mounds and one flat area, shallow but significant genetic population structure was evident (FST=0.0031, Dest across loci=0.0306 and G-test). Most of the structure was accounted for by inclusion of a sample from the flats (six of ten significant pairwise FST estimates and G-tests, and five of the highest Dest estimates included the flat sample). While the flat sample contributed most to the genetic structure, there was still significant (albeit weaker) structure among mound samples. The observed structure was supported by otolith analyses. Fish caught as late juveniles in either the flat or mound areas showed consistent differences in chemistry at the otolith core throughout the initial 10 years of growth, which could indicate site fidelity. We hypothesise that seafloor topographic structures (mounds and flats) may provide discrete spawning areas for orange roughy and that the limited gene flow between these spawning areas is insufficient to counteract genetic drift
The life history and ecology of black scabbardfish (Aphanopus carbo Lowe 1839) in the north-east Atlantic
No full textThe black scabbardfish is a deep water species that supports commercial fisheries across a large area of the NE Atlantic shelf. The life history of black scabbardfish is poorly understood and a major unresolved issue is population structure. In this study it was used a combination of methodologies to get further knowledge in the life history and population structure of A. carbo over its wide distribution range in the Northeast Atlantic. The new knowledge acquired during this study, will increase our ability to better manage this species in the NE Atlantic. It has been postulated that fish caught to the west of the British Isles are pre-adults that migrate further south (to Madeira) for spawning, implying a single panmictic population. In this study, specimens of Aphanopus carbo were sampled between September 2008 and May 2010 from two different areas: NW Scotland (French trawlers and deep water surveys) and Madeira Islands (longliners commercial landings). Geographical differences in reproductive state of scabbardfish were evident, supportive of a north-south migration theory. In the northern area, all specimens found were immature, while in Madeira all maturity stages were observed. In Madeira, spawning occurred during the fourth quarter, with peak maturity in October (males) and in November (females). The age of this species has proven difficult and has led to different and contradictory age and growth estimates. For this study, we used two reading interpretations to determine age and estimate the growth parameters. To the west of the British Isles, specimens reached a lower maximum age and had a higher growth rate than those caught off Madeira. These differences are consistent with the theory of a single population of black scabbardfish in the NE Atlantic, highly segregate, with smaller, immature and younger fish caught to the west of the British Isles and bigger and mature caught in Madeira Islands. The feeding ecology showed strong evidence that the diet of black scabbardfish is associated with the spawning migration of blue whiting, which may support a northerly feeding migration theory for black scabbardfish. The stable isotope analyses in the muscle of black scabbardfish identified that black scabbardfish feeds on species with epipelagic and benthopelagic affinities. Comparison with stable isotope analysis in Madeira samples indicated that black scabbardfish feed at a similar trophic level and has the same trophic niche width in both areas, assuming similar baseline isotope compositions. Otolith stable isotopes (oxygen - δ18O and nitrogen - δ15N) analyses were used as a tool to clarify migratory behaviour. Otolith isotope ratios can provide insight into whether adults caught around Madeira fed in an isotopically depleted northerly ecosystem (NW Scotland) during their pre-adult period and then migrate towards south to spawn. Overall, the results support a south-north migration of pre adult fish from spawning areas around Madeira and a north-south migration from the west of Scotland to the spawning areas. Given its life cycle there is an urgent need that the management process recognizes the existence of a continuous widely distributed stock of black scabbardfish between the west of the British Isles and Madeira. The results highlight large scale dispersal in this species which needs to be treated as a highly migratory species and be managed as a single population
Trophic role of small cetaceans and seals in Irish waters
No full textUnderstanding the role of marine mammals in specific ecosystems and their interactions with fisheries involves, inter alia, an understanding of their diet and dietary requirements. In this thesis, the foraging ecology of seven marine mammal species that regularly occur in Irish waters was investigated by reconstructing diet using hard parts from digestive tracts and scats. Of the species examined, two (striped and Atlantic white-sided dolphin) can be considered offshore species or species inhabiting neritic waters, while five others usually inhabit more coastal areas (white-beaked dolphin, harbour porpoise, harbour seal and grey seal); the last species studied was the bottlenose dolphin whose population structure is more complex, with coastal and offshore populations. A total of 13,028 prey items from at least 81 different species (62 fish species, 14 cephalopods, four crustaceans, and a tunicate) were identified. 28% of the fish species were identified using bones other than otoliths, highlighting the importance of using all identifiable structures to reconstruct diet. Individually, each species of marine mammal presented a high diversity of prey taxa, but the locally abundant Trisopterus spp. were found to be the most important prey item for all species, indicating that Trisopterus spp. is probably a key species in understanding the role of these predators in Irish waters. In the coastal marine mammals, other Gadiformes species (haddock, pollack, saithe, whiting) also contributed substantially to the diet; in contrast, in pelagic or less coastal marine mammals, prey was largely comprised of planktivorous fish, such as Atlantic mackerel, horse mackerel, blue whiting, and mesopelagic prey. Striped dolphins and Atlantic white-sided dolphins are offshore small cetaceans foraging in neritic waters. Differences between the diet of striped dolphins collected in drift nets targeting tuna and stranded on Irish coasts showed a complex foraging behaviour; the diet information shows that although this dolphin forages mainly in oceanic waters it may occasionally forage on the continental shelf, feeding on available prey. The Atlantic white-sided dolphin diet showed that this species prefers to feed over the continental edge, where planktivorous fish are abundant. Some resource partitioning was found in bottlenose dolphins in Irish waters consistent with previous genetic and stable isotope analysis studies. Bottlenose dolphins in Irish waters appears to be generalist feeders consuming more than 30 prey species, however most of the diet comprised a few locally abundant species, especially gadoid fish including haddock/pollack/saithe group and Trisopterus spp., but the contribution of Atlantic hake, conger eels and the pelagic planktivorous horse mackerel were also important. Stomach content information suggests that three different feeding behaviours might occur in bottlenose dolphin populations in Irish waters; firstly a coastal behaviour, with animals feeding on prey that mainly inhabit areas close to the coast; secondly an offshore behaviour where dolphins feed on offshore species such as squid or mesopelagic fish; and a third more complex behaviour that involves movements over the continental shelf and close to the shelf edge. The other three coastal marine mammal species (harbour porpoise, harbour seal and grey seal) were found to be feeding on similar prey and competition for food resources among these sympatric species might occur. Both species of seals were found to have a high overlap (more than 80%) in their diet composition, but while grey seals feed on large fish (>110mm), harbour seals feed mostly on smaller fish (<110mm), suggesting some spatial segregation in foraging. Harbour porpoises and grey seals are potentially competing for the same food resource but some differences in prey species were found and some habitat partitioning might occur. Direct interaction (by catch) between dolphins and fisheries was detected in all species. Most of the prey found in the stomach contents from both stranded and by catch dolphins were smaller sizes than those targeted by commercial fisheries. In fact, the total annual food consumption of the species studied was found to be very small (225,160 tonnes) in comparison to fishery landings for the same area (~2 million tonnes). However, marine mammal species might be indirectly interacting with fisheries, removing forage fish. Incorporating the dietary information obtained from the four coastal species, an ECOPATH food web model was established for the Irish Sea, based on data from 2004. Five trophic levels were found, with bottlenose dolphins and grey and harbour seals occurring at the highest trophic level. A comparison with a previous model based on 1973 data suggests that while the overall Irish Sea ecosystem appears to be “maturing”, some indices indicate that the 2004 fishery was less efficient and was targeting fish at higher trophic levels than in 1973, which is reflected in the mean trophic level of the catch. Depletion or substantial decrease of some of the Irish Sea fish stocks has resulted in a significant decline in landings in this area. The integration of diet information in mass-balance models to construct ecosystem food-webs will help to understand the trophic role of these apex predators within the ecosystem
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Habitat preferences and movement patterns of bottlenose dolphins at various spatial and temporal scales
Full text linkQuantifying marine mammal abundance, site occupancy, and habitat use patterns is fundamental for the correct design and implementation of conservation and management schemes. Bottlenose dolphins in Irish waters form at least three distinct populations, two coastal and one pelagic, each ranging in different areas over unequal scales. While the abundance of all three has been estimated and core areas of use have been previously identified for the coastal populations, their habitat preferences have not yet been investigated sufficiently. In this thesis, generalised additive models were used to describe the habitat use of each population in relation to a suite of static and dynamic environmental parameters, over a range of temporal scales. Mixed models and generalised estimating equations were implemented to account for spatial and temporal autocorrelation when necessary. The habitat use of the pelagic population was modelled using two seasons (Summer and Winter) of aerial survey data of the greater part of the Irish EEZ and the models’ predictive capacity was tested on observations from two separate seasons. The interaction of environmental covariates with a habitat classifier was also tested to elucidate dolphin habitat use changes depending on whether they are in shelf, slope, or abyssal waters. The site occupancy of the coastal mobile population was modelled using five years of passive acoustic monitoring (C-POD) data from two locations on the west coast at an hourly, daily, and monthly scale. The second coastal population is resident in the outer Shannon estuary Special Area of Conservation and its abundance has been sporadically monitored for nearly two decades using boat-based photo-identification surveys. Encounter data from these surveys were used to model habitat use by incorporating a two-dimensional geographic coordinate term and an interaction with tidal phases. Given the irregular frequency of standardised surveys, I also assessed the potential of using a dolphin-watching boat operating in the same area as an alternative platform from which to derive a robust abundance estimate, using mark-recapture techniques. Different environmental covariates proved significant at each spatial scale, with dolphins showing season-, habitat-, and site-specific responses to each parameter. A higher probability of dolphin presence was predicted over the continental shelf and slope in the winter and in two primary areas in the summer, the southwest coast and the Porcupine Basin. Sea surface temperature and primary productivity were significant predictors of dolphin presence for both the pelagic and mobile coastal population, but not for the resident coastal population. Tidal level had a significant effect on dolphin detection in the coastal mobile population, with the likelihood of detections increasing at higher water levels. Tidal phase was also a significant predictor of dolphin presence for the resident population, with higher probabilities being predicted closer to a bottleneck feature during ebb tides. The abundance estimate generated from the dolphin-watching boat observations compared favourably to an estimate generated from a standardised survey the previous year. This indicates that, in years when standardised surveys do not take place, the dolphin-watching boat may provide a suitable interim platform for more frequent and efficient monitoring of this population. The results presented here highlight the importance of investigating habitat use at different spatial and temporal scales, provide valuable insights regarding areas used at different times by bottlenose dolphins, and form a baseline upon which to build further, more targeted investigations of the habitat preferences, demographic parameters, and abundance of each population, ultimately advancing our efforts at conservation and facilitating marine spatial planning
Ecology of the short-beaked common dolphin (Delphinus delphis) along the north-west coast of Spain
Full text linkStudying the ecology of a species requires a comprehensive approach encompassing several techniques aimed at understanding different aspects of their ecology such as distribution and habitat, their role in the ecosystem and interactions with the other species. In a constantly changing world, in which (coastal) marine ecosystems are consistently being impacted by human activities, the improved knowledge on marine top predators ecology is of key importance in order to develop effective conservation measures and management plans. In this regard, this thesis uses different approaches to better understand the ecology of a marine top predator, the short-beaked common dolphin (Delphinus delphis, Linnaeus 1758) in Galician waters, North-West Spain, and explores its conservation needs. To do so, the study combines data collected during 273 days at sea, covering a total distance of 9,417 km between March 2014 and October 2017, with information gathered by several studies conducted in the area in previous years. The data collected over four years contributed to improving our understanding of the environmental, topographic and anthropogenic factors influencing the dolphins distribution, and highlighted the areas entailing the most and least suitable habitats for the species and the areas with a higher degree of overlap with fishing activities. This information was combined with regional fisheries information to build an Ecopath with Ecosim framework to study the role of common dolphins in the ecosystem and its relationships with the other species. Furthermore, the approach provided information about the ecological impacts of fisheries on common dolphins and other cetacean species in the area. Results point out the importance of the continental shelf waters for the species and highlight the species vulnerability to direct and especially indirect impacts caused by fisheries, principally trawling activities. In this regard, the study predicts an important population decrease for common dolphins if fishing effort is increased. An interdisciplinary approach combining distribution and habitat use studies with the analysis of trophic food webs was used to explore the overlap between common dolphins and fisheries and the direct and indirect impacts caused on this cetacean species, providing new information on the indirect effects of fisheries on common dolphins, which will be of great value in the development of effective conservation measures and fishing management plans
New insights into the summer distribution of basking sharks (Cetorhinus maximus) in the northeast Atlantic
No full textControlled AccessBasking sharks, Cetorhinus maximus, have undergone widespread historic exploitation in the northeast Atlantic and are of conservation concern. A greater knowledge on their spatial and temporal habitat use in response to environmental conditions is required to better inform subsequent monitoring and management strategies. Several efforts to describe the occurrence and distribution of basking sharks have been already made, however nothing at large spatial scales. Sighting information on basking sharks was derived from three aerial survey programmes which covered extensive inshore and offshore waters within the northeast Atlantic. The occurrence of basking sharks in the area was highly seasonal, with individuals predominately observed during the summer months (May-August). Hotspots of occurrence were within the coastal waters off the south and west of Ireland, whereas areas such as southwest of England and west of Scotland, previously considered to be hotpots for basking sharks, were not aggregation sites during summer months, suggesting a seasonal change in distribution. Based on satellite-derived environmental variables and climate indices, this study revealed that distribution of basking sharks was associated with (1) lower chl-a concentrations (< 2.27 mg/m³), (2) shallow coastal waters which are most likely important summer feeding grounds; and (3) positive North Atlantic Oscillation (NAO) winter index, most likely through association with prey species. Sea surface temperature (SST) had no significant effect on the distribution of basking sharks. This study provided new insights into the seasonal occurrence of basking sharks on a large scale within the northeast Atlantic. The results produced here could be incorporated into future management frameworks for assessing the threat and conservation needs for this regionally protected species, as well as providing guidance for future research efforts
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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