Shannon Estuary Research Articles

The rise and fall of the Clann Éinrí Aimhréidh Uí Néill: dynastic feuding and geopolitics in the late medieval Irish Sea world

AbstractDuring the late fourteenth and early fifteenth centuries, the Ulster lordship of Tír Eoghain was bitterly contested between two rival branches of the Uí Néill dynasty: the Clann Éinrí Aimhréidh and the Clann Briain Catha an Dúin. Traditionally, historians have focused mainly on the local origins and ramifications of this feud and have paid only cursory attention to how events ranging from the Shannon Estuary through to the Outer Hebrides shaped the course of this struggle. For instance, throughout the later fourteenth and early fifteenth centuries a range of different regional players from across this wider ‘Irish Sea world’ became drawn into pulled into this conflict, each possessing a vested interest in the outcome of the Uí Néill successional war. By drawing upon a rich corpus of primary sources, including Irish, Scottish and English material, this article locates the Uí Néill feud within a wider dynastic and geopolitical context. Ultimately, the article argues for the necessity of exploring this feud from within a wider geographic and dynastic framework of interpretation, and paying closer attention to how events within the Irish Sea world could impact and impinge upon the politics of the wider archipelago.

A methodology for cost-effective analysis of hydrokinetic energy projects

The cost-effective analysis (CEA) of hydrokinetic farms is typically based on simplistic assumptions regarding the performance and cost structure of hydrokinetic energy converters (HECs) and, in consequence, may lead to ill-informed decision-making. In this work, a novel approach to selecting the most appropriate combination of HEC and site within a coastal area is developed, with the accurate computation of the CEA parameters as the cornerstone. The approach, which is illustrated through a case study in the Shannon Estuary (W Ireland), encompasses four models, namely: (i) HEC-site selection model, (ii) energy production model, (iii) CAPEX model, and (iv) OPEX model. By avoiding simplistic assumptions, the proposed approach improves on current procedures and enables developers to accurately compute any cost-effective parameter of interest. In particular, operation and maintenance costs are considered, along with economies of scale, which are typically disregarded in existing procedures. Beyond the interest of the results of the Shannon case study, the approach can be implemented in other regions with potential for hydrokinetic energy conversion.

A note on long-distance matches of bottlenose dolphins (Tursiops truncatus) around the Irish coast using photo-identification

Images of 120 individual bottlenose dolphins from around the Irish coast were obtained from three photo-identification catalogues. Twenty three individuals were subsequently re-sighted, which is a re-sighting rate of 19%. The distance between re-sightings ranged from 130 to 650km and the duration from 26 to 760 days. Images were also compared to a catalogue of resident dolphins from the Shannon Estuary candidate Special Area of Conservation and from Wales but no matches were found. This short study provides strong evidence that bottlenose dolphins in Irish coastal waters are regularly undertaking large movements around the entire Irish coast and must be considered highly mobile and transient. These results have important implications for the conservation and management of this species.

Discrete or not so discrete: long distance movements by coastal bottlenose dolphins in UK and Irish waters

The potential for long distance movements in common bottlenose dolphins (Tursiops truncatus) from six UK and Irish study sites was examined using photographs of natural markings. Here we provide the first evidence for long-term re-sightings between the Moray Firth, Inner Hebrides and across international borders to the Republic of Ireland as determined for eight individuals over a ten year period from 2001 to 2010. Minimum dispersal distances of up to 1,277km were resolved providing a new distance record for the species in European waters. Although none of the sightings were made within protected areas, several were made in waters used by animals from a Special Area of Conservation (SAC) revealing some evidence for connectivity between areas previously regarded as discrete. Our findings highlight the need to mitigate broader-scale anthropogenic impacts affecting these dolphins across multiple sites throughout their coastal range. Accordingly, we underline the importance of developing wider conservation measures for this species in UK and Irish waters, but particularly in prospective corridor areas potentially linking designated SACs in the Moray Firth, Cardigan Bay and Shannon Estuary.

Assessment of the environmental drivers of European glass eel (Anguilla anguilla) recruitment in transitional waters

The European eel (Anguilla anguilla) has undergone an unprecedented population decline since the 1980s, with current recruitment levels fluctuating from 3 to 15% of historical levels for the last 20 years. Monitoring of glass eels and elvers as 0 + recruitment is an essential step in helping to understand the trend in recruitment and to better quantify the current recruitment time series. Two locations within the Shannon estuary on the west coast of Ireland were monitored for glass eel recruitment from January to April in 2017 and 2018. This study used a generalised linear mixed model to examine a range of environmental variables impacting on glass eel abundance in transitional waters. Results found that water temperature and moon phase were the most important variables. Tidal height and cloud cover also influenced the abundance of glass eels but to a lesser extent. This study found that focussing survey efforts on nights around the full moon when water temperatures exceed 5℃ will allow a catch which is representative of the population in an estuary. Glass eel monitoring needs a long-term sampling plan in order to account for annual fluctuations apparent in glass eel recruitment.

A holistic methodology for hydrokinetic energy site selection

Hydrokinetic energy can contribute to diversify and decarbonise the energy mix in many coastal regions, in particular estuaries. These are typically areas of high environmental value and with intense socioeconomic activity. The aim of this work is to provide a comprehensive methodology for selecting the optimum locations for hydrokinetic energy exploitation, by considering all the relevant aspects which affect the decision-making process, and improve the current available procedures. The methodology is centred around a novel holistic index, the Integrated Hydrokinetic Energy (IHE) index, which considers: (i) the exploitable resource, (ii) the costs of installation, and (iii) the socioeconomic and environmental aspects. The approach is illustrated through a case study in the Shannon Estuary, on the west coast of Ireland. It is shown that the application of this methodology facilitates the planning and reduces the uncertainties in the development of a hydrokinetic farm project.

Tidal stream energy potential in the Shannon Estuary

The tidal and river in-stream energy resource in the Shannon Estuary (W Ireland) is investigated using of high-resolution numerical modelling and spatial analysis. Although freshwater discharges are large, their influence on the available resource is found to be all but negligible, the tide being the main driver of estuarine circulation. The Tidal Stream Exploitability (TSE) index is adapted to the analysis of estuaries with non-depth-limited areas (TSEndl), such as the Shannon Estuary, and then used to select the hotspots with potential for a tidal stream farm. For this purpose, a new depth penalty-limiting function is defined to avoid overestimating the available energy potential in areas with depths greater than those required for tidal energy converter operation. Seven hotspots are identified based on the revised index. The approach followed in this study illustrates the applicability of high-resolution numerical modelling and spatial analysis for identifying the most appropriate areas for tidal stream energy conversion. Finally, the potential of tidal stream energy to contribute to the much-needed decarbonisation of the energy mix in Ireland is emphasized.

The Scattering: a Family History for a Floating World

Abstract This essay is an experiment in family history, inspired by a journey to scatter my father’s ashes on Scattery – the island in the Shannon estuary where my grandmother was born and raised. It explores how my family’s story illuminates the history of small Irish islands and of two much bigger islands, Ireland and Britain. Island stories replay in microcosm, and with great intensity, broader narratives of Irish and British history since the famine. But they also muddy these narratives with the idiosyncratic, granular experiences of a precise and bounded place. They put human flesh and bones on abstract nouns like family, community, modernity, emigration and exile. In every island story – Scattery as my father’s idyllic land of endless summer, Ireland as the home of sturdy children and happy maidens, Britain as proud island nation taking back control of its borders – lies a fantasy of homogeneity and readability. Even the smallest islands have multilayered histories; and then, as they disperse their peoples across the world as small islands do, those histories keep multiplying. Our journey back to the island may have begun as a search for origins but it ended up revealing the heterogeneity and unrecoverability of the past.

Survival Rates and Capture Heterogeneity of Bottlenose Dolphins (Tursiops truncatus) in the Shannon Estuary, Ireland

Adult survival is arguably the most important demographic parameter for long-lived species as it has a large impact on population growth, and it can be estimated for cetacean populations using natural markings and mark-recapture (MR) modelling. Here we describe a 26-year study of a genetically discrete, resident population of bottlenose dolphins in the Shannon Estuary, Ireland, conducted by an NGO using multiple platforms. We estimated survival rates (SRs) using Cormack-Jolly-Seber models and explored the effects of variable survey effort, multiple researchers, and changes in camera equipment as well as capture heterogeneity induced by changes in marks and site fidelity variation, all common issues affecting longitudinal dolphin studies. The mean adult SR was 0.94 (±0.001 SD) and thus comparable to the estimates reported for other bottlenose dolphin populations. Capture heterogeneity through variation in mark severity was confirmed, with higher capture probabilities for well-marked individuals than for poorly marked individuals and a “transience” effect being detected for less well-marked individuals with 43% only recorded once. Likewise, both SR and capture probabilities were comparatively low for individuals with low site fidelity to the Shannon Estuary, and SR of these individuals additionally decreased even further toward the end of the study, reflecting a terminal bias. This bias was attributed to non-random temporal migration, and, together with high encounter rates in Brandon Bay, supported the hypothesis of range expansion. Our results highlight the importance of consistent and geographically homogenous survey effort and support the differentiation of individuals according to their distinctiveness to avoid biased survival estimates.

Foraging Behavior of Bottlenose Dolphins in the Shannon Estuary, Ireland as Determined through Static Acoustic Monitoring

The Shannon Estuary in Ireland is home to a resident population of bottlenose dolphins (Tursiops truncatus) and is designated as a Special Area of Conservation under the EU Habitats Directive. It is an important industrial area, with numerous deep-water berths for shipping. Despite its high conservation value, there are few published studies on habitat use or foraging behavior of the Shannon dolphins throughout the year. The present study assessed the year-round presence and foraging activity of bottlenose dolphins at different locations in the middle and inner estuary using static acoustic monitoring. Dolphin presence was found to decrease with increased distance from the estuary mouth, i.e., where the estuary meets the Atlantic Ocean, while at the same time, foraging was found to be considerably higher in the upriver areas, suggesting the inner estuary was an important foraging area. Model predictions for seasonal, tidal and diel foraging were highly variable across locations, indicating that changes in dolphin behavior occurred over relatively small geographical scales. These results indicate that conservation efforts should consider the Shannon Estuary as a dynamic aggregation of habitats and future development initiatives should attempt to mitigate disturbance to the dolphins during important foraging periods on seasonal and diel scales.

Population Viability Analysis and Comparison of Two Monitoring Strategies for Bottlenose Dolphins (Tursiops truncatus) in the Shannon Estuary, Ireland, to Inform Management

Population Viability Analysis and Comparison of Two Monitoring Strategies for Bottlenose Dolphins (Tursiops truncatus) in the Shannon Estuary, Ireland, to Inform Management

Fine‐scale population structure and connectivity of bottlenose dolphins, Tursiops truncatus, in European waters and implications for conservation

Abstract Protecting species often involves the designation of protected areas, wherein suitable management strategies are applied either at the taxon or ecosystem level. Special Areas of Conservation (SACs) have been created in European waters under the Habitats Directive to protect bottlenose dolphins, Tursiops truncatus, which forms two ecotypes, pelagic and coastal. The SACs have been designated in coastal waters based on photo‐identification studies that have indicated that bottlenose dolphins have relatively high site fidelity. However, individuals can carry out long‐distance movements, which suggests potential for demographic connectivity between the SACs as well as with other areas. Connectivity can be studied using genetic markers. Previous studies on the species in this area used different sets of genetic markers and therefore inference on the fine‐scale population structure and demographic connectivity has not yet been made at a large scale. A common set of microsatellite markers was used in this study to provide the first comprehensive estimate of genetic structure of bottlenose dolphins in European Atlantic waters. As in previous studies, a high level of genetic differentiation was found between coastal and pelagic populations. Genetic structure was defined at an unprecedented fine‐scale level for coastal dolphins, leading to identification of five distinct coastal populations inhabiting the following areas: Shannon estuary, west coast of Ireland, English Channel, coastal Galicia, east coast of Scotland and Wales/west Scotland. Demographic connectivity was very low among most populations with <10% migration rate, suggesting no demographic coupling among them. Each local population should therefore be monitored separately. The results of this study have the potential to be used to identify management units for bottlenose dolphins in this region and thus offer a significant contribution to the conservation of the species in European Atlantic waters. Future studies should prioritize obtaining biopsies from free‐living dolphins from areas where only samples from stranded animals were available, i.e. Wales, west Scotland and Galicia, in order to reduce uncertainty caused by sample origin doubt, as well as from areas not included in this study (e.g. Iroise Sea, France). Furthermore, future management strategies should include monitoring local population dynamics and could also consider other options, such as population viability analysis or the incorporation of genetic data with ecological data (e.g. stable isotope analysis) in the designation of management units.

Optimisation of tidal turbine array layouts whilst limiting their hydro-environmental impact

The economic viability of tidal energy projects will likely require large-scale deployment, with tens, or even hundreds, of turbines positioned in an array. There is limited published research available on the viability of large-scale deployments, which will depend on both the expected energy yield and potential adverse hydro-environmental impacts. This leads to the question of how best to position turbines in large-scale arrays for maximum energy capture with minimal associated hydro-environmental impacts. The primary aim of this research was the further development of an existing two-dimensional tidal flow model for optimising tidal turbine arrays relative to both power output and potential hydro-environmental impacts. Turbine impacts are simulated using a momentum sink approach and an optimisation algorithm was implemented, which determines an optimal array configuration for maximum energy capture, whilst employing spatial and environmental impact constraints. Application of the developed model to an idealised test case demonstrated that a staggered array is optimal, if one considers maximising power capture alone, while a fence layout was optimal, when considering both power output and associated impacts. In both the scenarios, the optimised configurations produced higher efficiencies than symmetrical inline arrays. To demonstrate the model’s applicability to a real tidal environment, it was applied to a case study site; the Shannon Estuary, along the West Coast of Ireland. To the authors’ knowledge, this is the first automated array optimisation model to incorporate hydro-environmental impact constraints with the aim of determining specific optimised array configurations with quantifiable efficiencies. The approach could be extremely useful for determining the economic viability of proposed arrays, enabling determination of ‘environmentally acceptable’ levels of tidal energy extraction, and thereby allowing the completion of realistic and accurate early stage cost–benefit analyses for tidal energy projects. The model is therefore, potentially, a very valuable tool for tidal energy researchers, developers and planners.

Fine‐scale sociality reveals female–male affiliations and absence of male alliances in bottlenose dolphins (Tursiops truncatus) in the Shannon Estuary, Ireland

AbstractKnowledge of social behavior at an individual level is central to our understanding of complex mammalian societies. In this study, we analyzed the fine‐scale sociality of wild bottlenose dolphins in the Shannon Estuary, Ireland, by examining associations between members of the whole population and between specific female and male dolphins. We carried out 51 boat‐based individual focal follows on 18 identifiable bottlenose dolphins over 90.8 hr (39 days) between 2014 and 2016. Additionally, we conducted 353 boat‐based surveys (with 607 sightings) between 2012 and 2015, and identified 121 distinct adult/juvenile dolphins. The mean group size of focal dolphin groups was 7.2 ± 4.1 (range = 1–20) and the mean fission‐fusion rate was 3.06 ± 1.35 changes/hr. The most frequent composition of within‐group affiliate pairs was female–male. Focal males spent more time with female nearest‐neighbors than male nearest‐neighbors (p = .013). Differences between female and male activity budgets were not strongly supported (p = .13). There was no evidence for male alliance formation in the Shannon Estuary population, and all of the known‐sex top‐ranked associates (7) of known males (n = 10) were females. This research reveals a distinct bottlenose dolphin society with female–male affiliations and an absence of male alliances.

Quantifying dispersal between marine protected areas by a highly mobile species, the bottlenose dolphin, Tursiops truncatus.

The functioning of marine protected areas (MPAs) designated for marine megafauna has been criticized due to the high mobility and dispersal potential of these taxa. However, dispersal within a network of small MPAs can be beneficial as connectivity can result in increased effective population size, maintain genetic diversity, and increase robustness to ecological and environmental changes making populations less susceptible to stochastic genetic and demographic effects (i.e., Allee effect). Here, we use both genetic and photo‐identification methods to quantify gene flow and demographic dispersal between MPAs of a highly mobile marine mammal, the bottlenose dolphin Tursiops truncatus. We identify three populations in the waters of western Ireland, two of which have largely nonoverlapping core coastal home ranges and are each strongly spatially associated with specific MPAs. We find high site fidelity of individuals within each of these two coastal populations to their respective MPA. We also find low levels of demographic dispersal between the populations, but it remains unclear whether any new gametes are exchanged between populations through these migrants (genetic dispersal). The population sampled in the Shannon Estuary has a low estimated effective population size and appears to be genetically isolated. The second coastal population, sampled outside of the Shannon, may be demographically and genetically connected to other coastal subpopulations around the coastal waters of the UK. We therefore recommend that the methods applied here should be used on a broader geographically sampled dataset to better assess this connectivity.

Specification of the thrust coefficient when using the momentum sink approach for modelling of tidal turbines

A common method for simulating tidal turbines in far-field coastal models is the momentum sink approach, where the thrust induced by a tidal turbine is included as an additional external force in the momentum equations. A value close to 1 is commonly used for the turbine thrust coefficient (CT), but this value is based on a relationship between turbine thrust and undisturbed free-stream flow. Implementation of the momentum sink approach usually means that the thrust is calculated using the flow at the turbine grid cell as opposed to the undisturbed upstream flow speed. This research found that adopting the typical thrust coefficient value in the range of 0.8–1.0 in combination with the local velocity at the turbine can lead to underestimation of the energy extraction and hydrodynamic impacts of a tidal turbine, particularly for finer resolution models. This research implements the momentum sink approach using a local thrust coefficient (C′T) which has appropriate values greater than 1. C′T was shown to be dependent on the turbine blockage (ratio of the turbine area to the grid cell area), and a relationship between the two was determined using a model of an idealised channel. This allows determination of appropriate C′T values for a desired turbine efficiency of 40%. The developed relationship was used to determine appropriate C′T values for four potential tidal turbine deployments in the Shannon estuary. The results show that the use of the appropriate C′T values resulted in the desired energy removal of 40%, while the use of values less than or equal to 1 resulted in lower than desired levels of energy removal.

Bottlenose dolphin (Tursiops truncatus) social structure in the Shannon Estuary, Ireland, is distinguished by age‐ and area‐related associations

AbstractSocial and network analyses that incorporate information on individuals within a population enhance our knowledge of complex species. In this study, the social structure of wild bottlenose dolphins in the Shannon Estuary, Ireland, was analyzed by examining the dynamics of the whole population and then of individuals classed by sex, age, and area. One hundred and twenty‐one dolphins were identified during 522 sightings between 2012 and 2015. The mean half‐weight association index (HWI) of the population was 0.07 ± 0.02. The highest HWIs for individuals of known sex were for female‐male pairs. Mean within‐class HWI was significantly higher than mean between‐class HWI for both age and area classes. Ordinations and sociograms were used to visualize social networks. Permutation tests revealed nonrandom associations for the population overall and both between and within classes. Temporal analyses showed associations persisting for >1,000 d. The whole population's best fit model was for two levels of casual acquaintances. Movement analyses demonstrated the use of the inner estuary by only 25% of the population revealing a potential community division by area. The difference between mean HWI when socializing (0.09 ± 0.03) compared to foraging (0.06 ± 0.03) was significant. These results highlight the importance of localized research, reflecting the complexity found in bottlenose dolphin societies globally.

Female reproductive parameters and population demographics of bottlenose dolphins (Tursiops truncatus) in the Shannon Estuary, Ireland

This study investigates the female reproductive parameters and population demographics of bottlenose dolphins (Tursiops truncatus) in the Shannon Estuary, Ireland, using long-term relational sightings and photographic databases. Data were collected between 2008 and 2016, during 654 boat-based surveys, from two dolphin-watching vessels and a research vessel. During 1018 sightings, 4231 identifications of 184 individual dolphins were recorded. The population size was charted through direct counts of known dolphins from 2011 to 2015 (mean 142, range 131–150), with 145 extant individuals in 2015: 80 adults, 25 juveniles, and 40 calves. Excluding dependent calves, 121 individuals were sighted, of whom 98% (n = 119) were sighted in multiple years, with 64% (n = 77) sighted in all 4 years (2012–2015). Between 2008 and 2016, 37 reproductive females and 69 dependent calves were recorded. Overall, 35% (n = 13) of these females were sighted with one calf, 43% (n = 16) with two calves and 22% (n = 8) with three calves. An average of seven (range 3–10) calves were born each year. Parturition peaked in July. Weaning ages ranged from 2.0 to 4.1 (mean 2.9) years. The mean inter-birth interval ranged between 2.7 ± 0.6 and 3.5 ± 1.3 years, depending on the method used. Mean annual calving rate was 0.29 young-of-year/reproductive female/year. Average crude birth rate was 0.07 ± 0.01. Fecundity was 0.26 ± 0.03. An average 11% of newborn calves were lost before age 1. These results are generally within the lower range of values reported for similar populations and provide essential data for conservation management and global bottlenose dolphin research.

An Ethogram for Bottlenose Dolphins (Tursiops truncatus) in the Shannon Estuary, Ireland

An Ethogram for Bottlenose Dolphins (Tursiops truncatus) in the Shannon Estuary, Ireland

Source organic matter analysis of saltmarsh sediments using SIAR and its application in relative sea‐level studies in regions of C4 plant invasion

The introduction of invasive Spartina grasses (C4 plant) into previously C3‐dominated saltmarshes of western Europe complicates the reconstruction of past relative sea‐level (RSL) using sediment geochemistry‐based approaches. We apply a Bayesian mixing model (SIAR – Stable Isotope Analysis in R) to identify organic carbon (Corg) source contributions to saltmarsh sediment and correct δ13C values for the contaminating influence of C4 vegetation. We first assess the performance of SIAR by simulation, producing synthetic saltmarsh sediment samples with variable contributions from three organic matter sources (C3 plants, C4 plants and particulate organic matter (POM)) and then comparing these known contributions to those determined by SIAR. For each source type, SIAR 68% credible intervals include true source contribution in 70% of calculations (n = 60) and all three sources were incorporated within credible intervals for 45% of sediment samples (n = 20). SIAR improves the mean absolute error of source contribution predictions by up to 26% compared to a conventional ternary mixing model approach. We then apply SIAR to real sediment samples recovered along transects spanning the intertidal zones at two contrasting saltmarshes in the inner and outer Shannon estuary, western Ireland. SIAR identified decreasing Corg contributions from POM with increasing elevation in the intertidal zone, reflecting differences in tidal inundation with height. Sediment δ13C values across the intertidal zones varied by 4.4‰ in the inner estuary and 9.4‰ in the outer estuary. Removal of the invasive C4 signatures reduced these differences to 0.5‰ and to 2.4‰ in the inner and outer estuary, respectively, with the larger range due to increased deposition of marine POM. Although subtle, when used in combination with additional proxies, these geochemical gradients can assist in RSL reconstruction. This will be most effective when POM from marine sources is a significant carbon source.