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Kittiwakes have been studied in detail at North Shields, Tyne and Wear, England since 1954. I investigated die effect of mate change (due to divorce or mate death) on reproductive performance. Below average productivity in the year of divorce and in the preceding year, coupled with a low adult survival rate in the year following divorce, suggested birds which divorced were poorer quality individuals than birds which retained their mate. Productivity was reduced if one or both members of a pair were in their last year of life and was indicative of a decline m fitness. Dispersal, breeding and the importance of nest site tenacity to mate retention were studied when kittiwakes were prevented from returning to their original nest sites in 1991. In 1991, extensive non-breeding (57%) and low productivity resulted. Of die birds which bred, 54 (83%) nested in the immediate colony area and only 11 moved to other colonies. Despite moving site, many birds retained their mate of the previous breeding season. In the following year, a further 61 kittiwakes moved and nested at other colonies and about a third retained theu" mate. This, and other evidence, suggests that individual recognition is important in mate retention. Reproductive performance, in relation to nest position in the colony and proxunity to other nesting pairs, was compared with a kittiwake colony at Marsden, NE England. Productivity was highest at the centre of the colonies and, at the edge, was highest for pairs which nested adjacent to another pair. It is suggested that social stimulation, arising from nesting adjacent to another pair, advanced the date of laying. Adult attendance at the nest during chick-rearing was monitored at Marsden in three years. During comparable time periods ui 1991 and 1993,93% and 75% of die broods, respectively, were attended by an adult, compared to only 51% during the same period in 1992. Attendance decreased in relation to hatching date, chick age and brood size and increased with parental age and/or quality.

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Northern fulmars and Manx shearwaters are pelagic seabirds of the Order Procellariiformes, a group that is characterised by extreme life-history traits. Many of these traits have been associated with the unpredictability of marine food sources. However, fulmars and Manx shearwaters feed their chicks at relatively frequent intervals compared with other procellariiforms, and the life-history implications of this strategy are poorly understood. In this thesis I examined food provisioning and chick growth strategies in fulmars and Manx shearwaters, and discussed these strategies in the context of life history - environment interactions. 1 tested the efficacy of a periodic weighing method for assessing food provisioning, and found that this gave a very similar estimate of the frequency and size of feeds compared to periodic weighing combined with data on parental attendance, determined by radio tracking. However, periodic weighing was much less effective at distinguishing meals from one or two parents. In Manx shearwaters, chick growth was highly correlated with food provisioning rate, and both variables showed significant annual variation. Both individual and environmental effects contributed to this variation, and in particular, peak mass showed highly significant repeatability coefficients. Fulmars showed significant variation in breeding success, diet and chick growth between two years, but chicks were apparently heavier in a very poor year. This was caused by differential mortality of chicks in poor condition. In Manx shearwaters, male parents visited the nest more frequently and made a greater contribution to food provisioning than females, a strategy that has seldom been reported in sexually monomorphic seabirds. I used a cross-fostering experiment to examine the parent-chick interactions responsible for the mass recession period prior to fledging in Manx shearwaters. Both parents and chicks had an active role in controlling food intake, and the results indicated that mass recession was not caused by parental desertion as previously thought.

Climate change and fisheries have affected marine environments worldwide leading to impacts on ecosystem structure and functioning. However there is clear evidence of spatial variability in the response of these impacts both within and among marine ecosystems. Although several studies have tried to explain the effect of these impacts on marine food webs, it is unclear how they interact, and how they may affect marine ecosystems remains an important unanswered question. This suggests the urgent need for multiple-trophic level and ecosystem-based management approaches to account for both fisheries and climate change impacts at ocean basins across the globe. Marine apex predators, such as seabirds, are vulnerable to the effects of both climate and fishing impacts, and can be used as reliable and sensitive bio-indicators of the status of the marine ecosystem. The Celtic Sea ecosystem is a productive shelf region in the Northeast Atlantic. It is characterized by high fish and invertebrate biodiversity. In addition, internationally important numbers of seabirds, such as Northern gannet Morus bassanus (L.), Manx shearwater Puffinus puffinus (B.), Common guillemot Uria aalge (P.) and Black-legged kittiwake Rissa tridactyla (L.), breed along the Celtic Sea coasts. In recent years, fisheries from across Europe have intensively exploited the Celtic Sea, leading to changes in stock structure. Moreover, the increase in annual average Sea Surface Temperature by 0.67 oC over the past two decades has altered the composition of plankton communities. These impacts, independently and in tandem, are likely to have had dramatic effects upon the Celtic Sea food web emphasizing the need to enhance our understanding of this important marine ecosystem. In this thesis the effects of climate change and fisheries on the Celtic Sea pelagic food web are evaluated, in particular focussing on the response of seabird populations. This is in part because of recent declines in the breeding success of many seabird colonies in the northeast Atlantic, particularly around the North Sea. Long-term data across four trophic levels (phytoplankton, zooplankton, mid-trophic level fish and seabirds) and different modelling approaches are used to determine factors influencing seabird productivity at different geographical scales. First, I review the direct and indirect effects of climate change and fisheries upon marine ecosystems, as well as their impacts upon marine birds. Second, I use data collected during 1986-2007 from a single seabird colony, across four trophic levels, to investigate long-term direct and indirect climate effects. The results suggest only a weak climate signal in the Celtic Sea, and this is only evident between mid-trophic level fish and certain species of seabird. Third, a similar multi-trophic level approach across three nearby regions in the southwest UK (Irish Sea, Celtic Sea, and English Channel) reveal no evidence of a bottom-up signal during the period 1991-2007. These findings are in contrast with the nearby North Sea region, where a strong bottom-up effect was found to affect seabird populations, highlighting the importance of regional-based studies across multiple trophic levels. Finally, to provide a more complete picture of the Celtic Sea, and how it might respond to changes in fisheries management and climatic variation, I use the complex tropho-dynamic ecosystem model Ecopath with Ecosim. The main focus is on how seabird biomass changes in response to the application of different fisheries regimes likely to be implemented under forthcoming reforms to the Common Fisheries Policy (e.g. the application of quotas and discard bans), as well as future climate change scenarios, in order to provide guideline support for resource management and seabird conservation in the Celtic Sea. The results suggest that some seabird guilds (gulls and some other scavengers) may be negatively affected by a reduction in discards, while other species (offshore divers) will benefit from a decrease in the fishing of pelagic fish species. Climate change is likely to have a negative impact across all trophic levels with a strong negative impact upon seabird populations. Therefore seabirds are likely to show species-specific responses to both climate variation (bottom-up effect) and changes in fishing practices, in particular our findings suggest that for some species climate may outweigh the fisheries impacts even when fisheries pressure is reduced by 50%. In summary, this study suggests that despite the generally negative impact of climate described for some regions in the Northeast Atlantic, the Celtic Sea ecosystem seems to be more resilient. However, both climate and fisheries and the interactions between these factors should be taken into account in the formulation of future management plans for the Celtic Sea ecosystem. The use of multiple-trophic level and ecosystem-based approaches over multiple spatial and temporal scales has helped to elucidate possible trophic mechanisms that are the response to future fishing and climate impacts in the Celtic Sea. The results of this study could have implications for both management plans and conservation policy.

Polybrominated diphenyl ethers (PBDEs) are anthropogenic chemicals whose environmental behavior is similar to the well-known polychlorinated biphenyls (PCBs). Few studies have quantified the amount and distribution of PBDEs in the southern hemisphere and Antarctica. The analyses reported in this dissertation document the levels of PBDEs in lichens, mosses and seabird eggs collected at King George Island, Antarctic Peninsula. The analyses were carried out using Gas Chromatography/Electron Impact-Mass Spectrometry (GC/EI-MS). Employing the ion stacking technique lowered detection limits and ensured instrument selectivity and sensitivity to the compounds of interest. Lichens and mosses absorb PBDEs directly from the atmosphere and their contamination indicates that long-range transport is the primary source of these chemicals to King George Island. The congener patterns of PBDEs in plants indicate that commercial mixtures of Penta-BDE and Octa-BDE have reached Antarctica. Differences in the levels of PBDEs observed in lichens and mosses are probably due to factors that govern the uptake of PBDEs from the atmosphere. Contamination in lichens showed a positive correlation with local precipitation. Conversely, absorption of PBDEs in mosses appears to be controlled by other plant-specific factors. Marine phytoplankton-derived aerosols are hypothesized to play an important role in the atmospheric transport of PBDEs to the Antarctic environment. PBDEs in south polar skua eggs revealed much higher concentration than in penguin eggs. This is likely associated with the northward migration of these seabirds during the non-breeding season. While penguins reside year-round in Antarctica, south polar skuas migrate northward and can be seen in boreal oceans during the austral winter. Distribution of PBDEs in penguin eggs matches the pattern found in local vegetation suggesting a common source for the chemicals. In contrast, the congener pattern of south polar skuas suggests that birds breeding at King George Island are wintering in the northwestern Pacific Ocean. A potential metabolism of PBDEs in penguin eggs during the incubation period seems to be limited. Most congeners were unaltered from source material in the eggs of chinstrap and gentoo penguins. Low levels of PBDEs, short incubation periods and energy constraints may explain these observations.