123,678 research outputs found
The diet and feeding ecology of harbour seals around Britain
No full textSince 2000, there has been a marked decline in the number of harbour seals in some regions around Britain; one possible contributing cause is competition for prey with sympatric grey seals. To explore one important aspect of this interaction, in this thesis the diet of harbour seals is estimated using analysis of hard prey remains recovered from faeces and compared with equivalent results for grey seals. To estimate coefficients to account for partial and complete digestion of hard prey remains, 100 whole prey feeding trials were conducted with six harbour seals and 18 prey species. Differences were found among prey species and between harbour and grey seals highlighting the importance of applying predator- and prey-specific digestion correction factors when reconstructing diet. In a comprehensive exploration of the diet of harbour seals around Britain, sandeel and flatfish dominated in the North Sea and large gadoids dominated on the Scottish west coast with seasonal pulses of pelagic prey. Variation in diet was linked to regional and seasonal differences in prey distribution and abundance. Sex-specific variation in harbour seal diet was examined in four regions. The main difference detected was in The Wash, where female diet quality was significantly higher than males in winter, which appeared to be driven by greater consumption of pelagic prey by female seals associated with seasonal energetic requirements of their annual life cycle. Comparison of the diet of harbour and grey seals revealed regional differences in diet composition, diversity and quality between the two species. However, there was no consistent pattern in this variation in relation to regional variation in harbour and grey seals population trajectories and no clear evidence for interspecific competition for prey. Future work should focus on an integrated investigation of prey abundance and distribution, and seal diet and foraging behaviour/distribution
Variation in habitat preference and distribution of harbour porpoises west of Scotland
No full textThe waters off the west coast of Scotland have one of the highest densities of harbour porpoise
(Phocoena phocoena) in Europe. Harbour porpoise are listed under Annex II of the EU Habitats
Directive, requiring the designation of Special Areas of Conservation (SACs) for the species’
protection and conservation.
The main aim of this thesis is to identify habitat preferences for harbour porpoise, and key
regions that embody these preferences, which could therefore be suitable as SACs; and to
determine how harbour porpoise use these regions over time and space. Designed visual and
acoustic line-transect surveys were conducted between 2003 and 2008. Generalised Estimating
Equations (GEEs) were used to determine relationships between the relative density of harbour
porpoise and temporally and spatially variable oceanographic covariates.
Predictive models showed that depth, slope, distance to land and spring tidal range were all
important in explaining porpoise distribution. There were also significant temporal variations in
habitat use. However, whilst some variation was observed among years and months, consistent
preferences for water depths between 50 and 150 m and highly sloped regions were observed
across the temporal models. Predicted surfaces revealed a consistent inshore distribution for the
species throughout the west coast of Scotland. Regional models revealed similar habitat
preferences to the full-extent models, and indicated that the Small Isles and Sound of Jura were
the most consistently important regions for harbour porpoise, and that these regions could be
suitable as SACs.
The impacts of seal scarers on distribution and habitat use were also investigated, and there
were indications that these devices have the potential to displace harbour porpoise.
These results should be considered in the assessment of sites for SAC designation, and in
implementing appropriate conservation measures for harbour porpoise
Investigating monitoring options for harbour seals in Special Areas of Conservation in Scotland
No full textManaging a wild population effectively requires knowledge of the abundance and behaviour of the species. Harbour seals (Phoca vitulina) are usually counted when they come ashore at haul-out sites, and so it is important to understand how the number of seals counted at this time relates to total population size. Satellite telemetry studies confirmed that harbour seals on the west coast of Scotland showed a degree of site fidelity and coastal foraging. Most trips taken by tagged animals involved travelling only 10-30 km from haul-outs and lasted less than a day (mean 21.07 hours, SE = 0.54), although some seals travelled over 100 km. Eighteen percent of the time these tagged seals spent hauled out was in the Special Area of Conservation where they were caught.
Individual seals can be recognised from their unique pelage patterns using computer-assisted photo-identification. Capture histories for adult harbour seals at a site in north-west Scotland indicated that the number of seals using the study area between April and October was 3.4 times higher than the number counted during an aerial survey made during the August moult. In the UK, aerial surveys of harbour seals are usually conducted during the first three weeks of August, when seals are moulting. These counts have a coefficient of variation of around 15%. Land-based counts made at study sites on the north-west coast of Scotland indicated that the number of seals hauled out was most consistent during the moult, but highest counts were from the pupping period. Analysis of moult counts indicated that starting surveys one week earlier (on 7th August) and surveying 1½ hours earlier in the tidal cycle would reduce the count variation. There was spatial, seasonal, diurnal and sex-related variation in the proportion of time harbour seals hauled out. Thus the relationship between counts and total population size is likely to vary spatially and temporally. This variation should be included in the estimates of the CV of correction factors.
A 5% annual change in harbour seal population size was predicted to take around 14 years to detect based on annual surveys and a CV = 0.15. This detection period increases when monitoring methods with lower precision are used, or surveys are made less frequently. Trends in seal abundance at pairs of haul-out sites were not synchronous and so it is unlikely that counts from small land-based protected areas, such as Special Areas of Conservation, can be used to monitor overall population status
Estimating the impact of bycatch and calculating bycatch limits to achieve conservation objectives as applied to harbour porpoise in the North Sea
No full textIncidental catch, or bycatch, of harbour porpoise (Phocoena phocoena) in fishing operations is an international conservation issue. The main objective of this thesis was to develop methods for determining the impact of bycatch on the state and dynamics of porpoise populations and for calculating bycatch limits that will achieve conservation objectives in the future. I applied these methods to the North Sea as a case study. First, I analysed sighting rates of harbour porpoise on seabird surveys in the North Sea during 1980-2003 to determine whether these data could provide informative time-series of relative abundance. Some general patterns and trends in sighting rates were consistent with previous studies. However, the standardised indices of abundance were relatively imprecise and thus have limited value for a monitoring framework that relies on statistical detection of trends. Second, I used a population model to integrate available data on harbour porpoise in the North Sea and to assess the dynamics of the population during 1987-2005. There was a high probability that bycatch resulted in a decrease in abundance. The estimated life history parameters suggested a limited scope for population growth even in the absence of bycatch. The model and data were not informative about maximum population growth rate or carrying capacity. The model suggested that dispersal was the most plausible explanation for observed changes in distribution within the North Sea. Third, I considered management procedures for calculating bycatch limits. I performed simulations to compare the behaviour of the procedures, to tune the procedures to specific conservation objectives and to test the robustness of the procedures to a range of uncertainties regarding population dynamics and structure, the environment, observation and implementation. Preliminary annual bycatch limits for harbour porpoise in the North Sea ranged from 187-1685 depending on the procedure, tuning and management areas used
Distribution and density of harbour popoises in Dutch North Sea waters
No full textAerial surveys were conducted to investigate harbour porpoise density and distribution in Dutch waters. Surveys were conducted following standard line transect distance sampling methodology on tracklines providing a representative coverage of the study area which ranged from the Dutch coast to about 120 km offshore thus covering about half of the Dutch EEZ. Within this overall study area two sub-areas were defined. One sub-area (from Texel to the German border) was covered in on 29 November 2008 and 3 April 2009. Density was 1.02 animals per km² during the November survey and 0.52 animals per km² during the April survey. An overall survey, covering both sub-areas, was conducted on 3 February, 18 March and 3 April 2009. The resulting density was 1.12 animals per km². This corresponds to an estimate of harbour porpoise abundance for this study area of 36 825 animals (95% C.I. 19 090 – 68 130; 0.33 C.V.). Distribution patterns of porpoises in the surveys waters were patchy and seemed variable between surveys. Applying this abundance estimate, a range of potential mortality limits were calculated for the Dutch harbour porpoises
The hydrodynamics of the southern basin of Tauranga Harbour
No full textThe circulation of the southern basin of Tauranga Harbour was simulated using a 3-D hydrodynamic model ELCOM. A 9-day field campaign in 1999 provided data on current velocity, temperature and salinity profiles at three stations within the main basin. The tidal wave changed most in amplitude and speed in the constricted entrances to channels, for example the M2 tide attenuated by 10% over 500 m at the main entrance, and only an additional 17% over the 15 km to the top of the southern basin. The modelled temperature was sensitive to wind mixing, particularly in tidal flat regions. Residence times ranged from 3 to 8 days, with higher residence times occurring in sub-estuaries with constricted mouths. The typical annual storm events were predicted to reduce the residence times by 24%–39% depending on season. Model scenarios of storm discharge events in the Wairoa River varying from 41.69 m3/s to 175.9 m3/s show that these events can cause salinity gradients across the harbour of up to 4 PSU
The relationship between developmental stability, Ggenomic diversity and environmental stress in two cetacean species:: the Harbour Porpoise (Phocoenaphocoena) and The Bottlenose Dolphin (Tursiops truncatusl)
No full textThe relationship between developmental stability, genomic diversity and environmental stress in three eastern North Atlantic populations of the harbour porpoise {Phocoena phocoena), and in two populations of the western North Atlantic and one from the Gulf of California of the bottlenose dolphin {Tursiops truncatus) was investigated. In addition, the population structure for the two species from the study areas mentioned was also assessed. Population structure was determined using discriminant function analysis for morphological characters and a Bayesian analysis for microsatellite loci. Consistency of the results was assessed with pairwise comparisons between populations using two indices of population differentiation (F(_st) and Rho(_st)). For the harbour porpoises classification was made into three putative populations: Norwegian, British and Danish. For the bottlenose dolphin significant differentiation was found for the three populations studied. Population differentiation between the two western North Atlantic parapatric populations was the highest among the pairwise comparisons. This result highlights the importance of resource specialisation of bottlenose dolphins in causing population structure for parapatric populations. Developmental stability was assessed by fluctuating asymmetry (FA) measured on morphological traits. Genomic diversity was determined by five indices (mean cf, scaled mean cF, multilocus individual heterozygosity, standardised heterozygosity and internal relatedness). Environmental stress was assessed by the concentration of chemical pollutants in tissues, and from the literature published for chemical pollutants, by-catch rate, parasite load and mean surface ocean temperature. Significant relationships between FA and the indices of genomic diversity were found. The Norwegian population of harbour porpoises and the coastal population of the western North Atlantic of bottlenose dolphin showed the highest level of FA. Both populations also showed the least genetically diverse animals. However, no clarity was obtained in respect of the relationship between FA and environmental stress. British and Norwegian harbour porpoises did not show significant correlations between the concentration of several chemical pollutants in tissues and FA. In addition, the Norwegian population of harbour porpoise inhabits the least impacted areas in respect to the concentration of chemical pollutants in tissues, parasite load and by-catch rates. Environmental stress was difficult to assess on the bottlenose dolphins populations due to the scarcity of data. These results show the influence of genetic diversity on the disruption of developmental stability and they also show the importance of conservation practices in maintaining genetic diversity as an important factor for the subsistence of natural populations
Pup mortality in a rapidly declining harbour seal (Phoca vitulina) population
No full textThis research was funded by the Scottish Government (www.scotland.gov.uk), Scottish Natural Heritage (www.snh.gov.uk) and the Natural Environment Research Council (www.nerc.ac.uk). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.The harbour seal population in Orkney, off the north coast of Scotland, has reduced by 65% between 2001 and 2010. The cause(s) of this decline are unknown but must affect the demographic parameters of the population. Here, satellite telemetry data were used to test the hypothesis that increased pup mortality could be a primary driver of the decline in Orkney. Pup mortality and tag failure parameters were estimated from the duration of operation of atellite tags deployed on harbour seal pups from the Orkney population (n = 4) and from another population on the west coast of Scotland (n = 24) where abundance was stable. Survival probabilities from both populations were best represented by a common gamma distribution and were not different from one another, suggesting that increased pup mortality is unlikely to be the primary agent in the Orkney population decline. The estimated probability of surviving to 6 months was 0.390 (95% CI 0.297 – 0.648) and tag failure was represented by a Gaussian distribution, with estimated mean 270 (95% CI = 198 – 288) and s.d. 21 (95% CI = 1 – 66) days. These results suggest that adult survival is the most likely proximate cause of the decline. They also demonstrate a novel technique for attaining age-specific mortality rates from telemetry data.Peer reviewe
Harnessing Marine Renewable Energy from Poole Harbour: Case Study
No full textGlobal warming and its impact on our environment, society, economies and security is one of the fundamental concerns of our time. In response, the United Kingdom government has put in place a legally binding target of an 80% reduction in greenhouse gas emissions on 1990 levels by 2050. The United Kingdom will need to achieve a tenfold expansion of energy supply from renewable sources by 2020 to meet its share of the European Union renewable energy target. The marine and coastal environment’s renewable energy potential in Britain is high. It is estimated that it has 50% of the tidal energy, 35% of wave and 40% of wind resources in the European Union. Use of geothermal resources using heat pump technology is the least evolved sector, but in 2010 contributed to 0.7 TWh of energy and it is believed that non domestic heat pumps could contribute up to 22 TWh by 2020. In the Southwest of England, Poole Harbour has been recognised as a potential, highly predictable source of tidal and heat energy. Local groups are embarking on a feasibility study for harnessing this energy for the benefit of the community. The purpose of this article is to examine the potential conflict of interest between the laudable aims of promoting the use of renewable energy and of safeguarding ecosystems and their biodiversity. Using Poole Harbour as a case study, it will consider the environmental and economic costs and benefits of a Community Renewable Energy project (the Poole Tidal Energy Partnership) in the context of an area subject to a number of statutory and non-statutory designations to protect nationally and internationally important habitats and species. The paper identifies key environmental legislation, including spatial planning law and policy, which will facilitate exploring whether there is potential for reconciling what may be perceived as competing objectives for sustainable development
Hydrodynamic impacts of tectonics in prehistoric Ohiwa Harbour, North Island, New Zealand
No full textOhiwa Harbour is an estuarine lagoon located in the eastern Bay of Plenty, North Island, New Zealand. Ohiwa Harbour is bounded by two sand spits, Ohope and Ohiwa Spits.
This study assessed the likelihood of a resistant barrier underlying Ohiwa Spit, which would control the inlet and spit locations. The observed depths of layers unable to be penetrated by a vibrocorer on Ohiwa Spit supported this idea, along with the discovery of a rock outcrop on the eastern harbour entrance using sidescan SONAR.
Vibrocoring on Ohiwa Spit added to the knowledge of the prehistoric evolution of Ohiwa Harbour, and an attempt to infer various subsidence events on Ohiwa Spit were made. Fining upwards coarse sand sequences with dominant shell material were found in the cores. These sequences could be related to a change in harbour hydrodynamics, or recent subsidence events in Ohiwa Harbour, such as the 0.6m subsidence of the Waimana Fault 636 to 575cal yrs BP. A sharp change in the core profile was observed at 1.4m in core C and 1.7m in core C2, marked by increased grain size and an abundance of shell material, mostly Austrovenus stutchburyi. This could be related to a change in wave energy in the harbour or an erosional contact associated with subsidence of Ohiwa Spit. Comparison of radiocarbon dated shells in this study with Murdoch (2005) on Ohope Spit suggests that more subsidence has occurred at Ohiwa Spit than Ohope Spit; this may be associated with a fault through the harbour entrance.
Subsidence associated with earthquakes, and erosion associated with at least four tsunami events in the last 6000 years has increased the depth and extent of Ohiwa Harbour, increasing its volume. This study used numerical modeling to determine the hydrodynamic impacts of past catastrophic events (earthquake related subsidence and volcanic eruptions) on Ohiwa Harbour. Ten scenarios along with present conditions were modelled.
• In scenarios where sea level was modified only (scenarios 1-5 and 8), tidal range and surface elevation increased within the harbour, but not at the harbour entrance. The entrance hydrodynamics were also influenced by its width; as Ohope Spit accreted, the surface elevation and flow velocities increased within the tidal inlet
• Flow speeds increased at the harbour entrance by up to 50% following subsidence in scenarios 9 and 10
• A drop in sea level during subsidence (scenario 6) resulted in a smaller tidal prism and hence reduced flow velocities at the inlet, despite the subsidence
• Scenario 7 involved subsidence and the breaching of Ohope Spit, which would divert flow away from the entrance and result in reduced flow velocities at the entranc
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