Summary1. Marine predators can be adversely affected by human activities in several potentially interacting ways. Industrial fisheries can affect predator populations adversely through competition for shared prey, and marine environmental change has also been implicated in population declines. In the North Sea, black-legged kittiwakes Rissa tridactyla have declined by > 50% since 1990, a period during which a lesser sandeel Ammodytes marinus fishery was active and profound oceanographic changes occurred. We studied the role of fisheries and oceanography in kittiwake declines on the Isle of May, southeast Scotland, where sandeels are the main prey. 2. Demographic data were collected from 1986 to 2002. We examined changes over time and correlations between population parameters, the local sandeel fishery and environmental factors, and incorporated the results in a deterministic and a stochastic matrix population model. 3. Breeding success and adult survival were low when the sandeel fishery was active (1991-98) and were also negatively correlated with winter sea temperature, with a 1-year lag for breeding success. Modelling showed that the observed changes in population parameters could explain the change in population growth rate from +8% year − 1 in the late 1980s to − 11% year − 1 in the late 1990s. An observed improvement in breeding success from 2000 onwards has been insufficient to arrest the population decline. To stabilize the population, breeding success must increase to unprecedented levels or survival needs to increase substantially. Stochastic modelling indicated that the population was unlikely to increase if the fishery was active or sea temperature increased, and that the population was almost certain to decrease if both occurred. 4. Sandeel recruitment is reduced in warm winters, and we propose that this explains the temperature effects on kittiwake survival and breeding success. The fishery also had a strong effect on demographic performance, although the exact mechanism is unclear as kittiwakes and fishermen target different sandeel age groups. 5. Synthesis and applications . Poor breeding success of kittiwakes was associated with warm winters and the presence of a local sandeel fishery. Reversing the trend towards warmer winters may be impossible and, at best, would be a very slow process. Therefore, to safeguard kittiwake populations we recommend that the current closure of the commercial sandeel fishery remain in place indefinitely. This study shows that adequate monitoring of the effect of a fishery or of environmental change on seabird populations needs to include survival as well as breeding success.

[1] Ammonia emissions were measured from two entire seabird colonies with contrasting species assemblages, to ascertain the ammonia volatilisation potentials among seabird species in relation to their nesting behaviour. Emissions were calculated from downwind plume measurements of ammonia concentration using both inverse dispersion and tracer ratio methods. Measured colony emissions ranged 1 -90 kg NH 3 hour À1 , and equated to 16 and 36% volatilization of excreted nitrogen for colonies dominated by ground/burrow nesting and bare rock nesting birds, respectively. The results were applied in a bioenergetics model with a global seabird database. Seabird colonies are found to represent the largest point sources of ammonia globally (up to $6 Gg NH 3 colony À1 year À1 ). Moreover the largest emissions occur mainly in remote environments with otherwise low NH 3 emissions. These ammonia ''hot spots'' explain significant perturbations of the nitrogen cycle in these regions and add $20% to oceanic ammonia emissions south of latitude 45°S.

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Keywords:Recent studies have shown that seabirds are an important source of ammonia (NH3) emissions in remote coastal ecosystems. Nesting behaviour, which varies between seabird species, is likely to be a major factor in determining the proportion of excreted nitrogen (N) volatilised to the atmosphere as NH3. A long-term NH3 monitoring programme was implemented at a Scottish seabird colony with a range of species and associated nesting behaviours. The average monthly NH3 concentration was measured at 12 locations over a 14-month period, to infer spatial (i.e. species-specific) and temporal (seasonal) changes in NH3 emissions from different seabird species. An emissions model of seabird NH3, based on species-specific bioenergetics and behaviour, was applied to produce spatial estimates for input to a dispersion model. Atmospheric NH3 concentrations demonstrated spatial variability as a result of differing local populations of breeding seabirds, with the highest concentrations measured above cliff nesting species such as Common guillemot Una aalge. Razorbill Alca torda and Blacklegged kittiwake Rissa tridactyla. NH3 concentrations above a colony of burrow nesting Atlantic puffin Fratercula arctica were low, considering the high number of birds. Emission of NH3 from excreted N exhibits a time lag of approximately a month. It is likely that all excreted N is lost from the colony by volatilisation as NH3 or surface run-off between breeding seasons. Modelled NH3 emissions and concentrations correlated with measured concentrations, but were much higher, reflecting uncertainties in the local turbulent characteristics. The results allow multi-species seabird population data to be used for the calculation of regional and global NH3 emission inventories, whilst improving understanding of N budgets of remote coastal ecosystems.

The telson-uropod stretch receptor in Emerita analoga belongs to a segmental array of axial-coxal receptors having sensory neurons with central somata. It consists of an elastic strand innervated by four giant, nonspiking, mechanoreceptive neurons. We examined the elastic (sensory) strand by light and electron microscopy to discover whether 1) functional differences between the four sensory neurons could be surmised from their peripheral terminations and 2) the process of mechano-electric transduction in this type of receptor might be revealed by the ultrastructure of the dendritic terminals. The elastic strand is divided into nonoverlapping domains by the mechanoreceptive neurons. We discerned no differences other than their serial order along the strand. Each neuron has three morphological zones in the periphery. In the zone of dendrite entry, the dendrite bifurcates into 40-60 microns primary branches that enter the strand at acute to right angles and turn rostrally and caudally along the strand's axis. The zone of branching consists of 4-35 microns diameter dendritic branches within the strand. Approximately 21,000 dendritic tips (diameters, 0.1-0.7 micron; lengths, 3-20 microns) per sensory neuron arise via short stubs from all levels of the zone of branching and constitute the zone of dendrite termination. The repeated bifurcations of dendrites within the zone of branching take place by radial intrusion of longitudinally oriented, partitions of extracellular matrix each of which extends the length of the pair of dendritic branches it divides. Tips project into these partitions. Since they change shape when the elastic strand is stretched, which compresses the extracellular matrix of the partitions, they are probably the site of mechanosensory transduction. Cross-sectional profiles of dendritic tips are significantly larger but less numerous in stretched than in relaxed receptors. We propose a model in which stretch compresses distal portions of tips until they are too small to be recognized. The large profiles are the proximal portions of tips that have been expanded by hydrostatic pressure. The very large number of dendritic tips/nonspiking mechanoreceptor may be what endows each neuron with 1) high sensitivity to stretch of the elastic strand and 2) ability to respond to a broader range of tensions than is usual for single sensory cells (the entire range experienced by the stretch receptor).