Sandeel Abundance Research Articles

Effect of timing and abundance of lesser sandeel on the breeding success of a North Sea seabird community

Understanding the responses of seabirds to climate-induced variations in phenology and abundance of their prey is key to developing ecosystem-based fisheries management measures that benefit higher trophic levels. The match/mismatch hypothesis (MMH) emphasizes the need to consider synchrony in the seasonal cycles of predators and prey, while the match/mismatch/abundance hypothesis (MMAH) proposes that prey abundance may reinforce/compensate mismatch effects. This study considers the effects of both variations in seasonal availability and abundance of lesser sandeel Ammodytes marinus on hatching, fledging and breeding success of 5 seabird species: black-legged kittiwake Rissa tridactyla, Atlantic puffin Fratercula arctica, razorbill Alca torda, common guillemot Uria aalge and European shag Gulosus aristotelis. Consistent with MMH, temporal asynchrony between sandeel availability and seabird breeding schedules affected productivity in 4 species. The effects of trophic asynchrony were either reinforced or compensated by sandeel abundance for some species, supporting MMAH. Breeding success in the late-breeding kittiwake was high when conditions favoured both high sandeel abundance and temporal synchrony while the cost of asynchrony could be compensated by high sandeel abundance in the earlier-breeding puffin. Differential effects of sandeel abundance and trophic synchrony at different stages of the seabird breeding season suggest that distinct mechanisms are involved. The effects were most evident in the most sandeel-reliant seabirds. As further disruption of sandeel phenology and abundance is anticipated under the current climate crisis, the present study is an important step towards understanding bottom-up effects of environmental change on higher trophic levels.

Effects of a fishery closure and prey abundance on seabird diet and breeding success: Implications for strategic fisheries management and seabird conservation

Industrial forage fish fisheries may reduce prey availability affecting diet and breeding success of marine predators. However, evidence for fisheries effects on predator demography remains rare, hindering evaluation of their impact on populations. Using 25 years of data on the commercial lesser sandeel fishery in the north-western North Sea, we evaluated the effectiveness of the closure in safeguarding breeding success of four seabird species - black-legged kittiwake, common guillemot, Atlantic puffin and razorbill. We also tested for effects of a scientific fishery in the closed area on breeding success. We quantified how changes in the diet of chicks for the four seabird species were influenced by the abundance of sandeels and the alternative prey species, European sprat, and the potential prey behavioural disturbance effects of sandeel fishing on the prey. Finally, we examined how changes in chick diet and prey abundance have shaped long-term variation in seabird breeding success. The period of fishery operation was associated with a decline in kittiwake breeding success in colonies with foraging ranges overlapping the closed area, from 52 % of young fledged pre-fishery to 23 % during fishery operation. Breeding success increased by approximately 10 % in the period following fishery closure to 2018. We document wide uncertainty around this increase in breeding success, partly driven by variation in the responses of individual colonies. For guillemot, razorbill and puffin we found no evidence for negative effects of the fishery on breeding success, nor for positive effects arising from its closure. We found no evidence for an impact on breeding success of the scientific fishery. The proportion of sandeel in chick diet was positively associated with breeding success in the four species, albeit with only weak evidence for puffin. Fishing effort was associated with a decreased proportion of sandeel in puffin diet, a lower proportion of the sandeel component of the diet consisting of 0-group in kittiwake, razorbill and puffin, and with decreased kittiwake breeding success. Our findings provide quantitative evidence for how forage fish fisheries may impact seabird demography, highlighting the species-specific nature of responses, and the difficulties in teasing apart drivers amongst ongoing environmental change. Time-area fisheries closures show promise as a tool for positively affecting productivity in some seabird species. However, we identify important caveats around its effectiveness for strategic seabird conservation and aspirations of net gain.

Effect of electrical stimulation used in the pulse trawl fishery for common sole on internal injuries in sandeels

Abstract Electric stimulation was used in the North Sea beam trawl fishery for common sole to reduce its environmental impact. Because electrical stimulation may cause internal injuries in fish, a laboratory experiment was conducted to study the effect of pulse exposure on lesser sandeel (Ammodytes tobianus) and greater sandeel (Hyperoplus lanceolatus), important mid-trophic species in the North Sea ecosystem. We exposed 244 sandeels between two electrodes to a pulsed bipolar current for 2 s in an experimental cage with 5 cm sediment; 221 control fish were handled similarly but not exposed. The occurrence of spinal injuries and internal haemorrhages were scored using X-radiography and dissection. None of the sandeels exposed to a field strength of up to 600 V m–1 showed spinal injury or haemorrhage. Equal numbers of minor spinal abnormalities were found in exposed and control fish. In the absence of spinal injuries, we estimated by bootstrapping the field strength below which spinal injuries are unlikely to occur, i.e. the lower limit threshold, and the corresponding limit dose–response relationship between field strength and injury probability. We conclude that it is unlikely that pulse trawl fishery will have an ecologically significant adverse effect on the population abundance of sandeels, because of the low probabilities of exposure and injury.

Temperature and body size affect recruitment and survival of sandeel across the North Sea

Abstract Climate effects on marine fish depend on life stage, particularly when life stages differ in habitat utilization. In the present study, we investigated life stage-dependent responses of lesser sandeel (Ammodytes marinus) to temperature at contrasting geographical scales. We related population density and individual growth to temperature and found different temperature responses between the first and the second years of life. During the first year of life, fish size was the single most important factor influencing sandeel abundances, indicating a positive relationship between growth and survival. In contrast, during the second year of life, autumn bottom temperature was negatively correlated with sandeel abundance, suggesting elevated mortality in warm years. Southerly areas, experiencing higher temperatures in general, were also the areas showing the strongest response to temperature. This study sheds light on how warming impacts population dynamics of one of the most important forage fishes in the North Sea and supports the discussion of underlying mechanisms.

Trends in Sandeel Growth and Abundance off the East Coast of Scotland

Sandeels Ammodytes marinus are a crucial forage fish species in the North Sea, transferring zooplankton energy to higher trophic levels. However, there has been a sustained decline in sandeel abundance in the northwestern North Sea since 2000. Here we use field data to analyze year-to-year changes in A. marinus growth rate between 1997 and 2009 and assess whether variation in growth rate corresponded with variation in abundance. The signature of the reduction in abundance between 2000 and 2009 was a decline in age 1 sandeels, while no other age class declined. Analysis of age-length data showed that the decline in abundance coincided with a period of low growth. Growth performance indexes were correlated with zooplankton and phytoplankton biomass but not temperature. Further, we observed a significant correlation between larval growth rate and 0-group sandeel length during a period when hatch dates were relatively fixed; suggesting recent changes in length were influenced by food availability.

Pronounced long-term trends in year-round diet composition of the European shag Phalacrocorax aristotelis

Populations of marine top predators are exhibiting pronounced demographic changes due to alterations in prey availability and quality. Changes in diet composition is a key potential mechanism whereby alterations in prey availability can affect predator demography. Studies of long-term trends in diet have focused on the breeding season. However, long-term changes in non-breeding season diet is an important knowledge gap, since this is generally the most critical period of the year for the demography of marine top predators. In this study, we analysed 495,239 otoliths from 5888 regurgitated pellets collected throughout the annual cycle over three decades (1985–2014) from European shags Phalacrocorax aristotelis on the Isle of May, Scotland (56°11′N, 02°33′W). We identified dramatic reductions in the frequency of lesser sandeel Ammodytes marinus occurrence over the study, which was more pronounced during the non-breeding period (96% in 1988 to 45% in 2014), than the breeding period (91–67%). The relative numerical abundance of sandeel per pellet also reduced markedly (100–13% of all otoliths), with similar trends apparent during breeding and non-breeding periods. In contrast, the frequencies of Gadidae, Cottidae, Pleuronectidae and Gobiidae all increased, resulting in a doubling in annual prey richness from 6 prey types per year in 1988 to 12 in 2014. Our study demonstrates that the declining importance of the previously most prominent prey and marked increase in diet diversity is apparent throughout the annual cycle, suggesting that substantial temporal changes in prey populations have occurred, which may have important implications for seabird population dynamics.

Exploring the Influence of Food and Temperature on North Sea Sandeels Using a New Dynamic Energy Budget Model

The zooplanktivorous schooling fish sandeels A. marinus comprise a quarter of North Sea fish biomass and are essential food for a number of marine mammals and birds. However, in recent decades there has been a decline in the abundance of older sandeels, with increased overwinter mortality proposed as a contributor. To survive winter animals require a minimum energy reserve which is determined by temperature, prey abundance, and possibly prey size. Here a new dynamic energy budget model is created to determine the influence of food and temperature on sandeel energy dynamics. The model hindcasts changes in energy and survival between 2000 and 2008, a period of pronounced stock decline in the northwestern North Sea. Overwinter starvation mortality was a large contributor towards a recent decline in sandeels in northern UK waters. Highest over-winter mortality rates were recorded for juveniles and not individuals aged 1 or over due to the effect of weight-specific metabolism. However, a sensitivity analysis of the model suggests that mortality rates are more sensitive to changes in copepod abundance in the build up to overwintering rather than temperature during overwintering. Further, projections show that temperature rises are negated by increases in large, but not small copepods. The conclusion is that food-driven size-selective starvation mortality contributed to the northwestern North Sea stock decline and that indirect food web effects of climate change are greater than direct physiological effects on sandeels.

Are simple environmental indicators of food web dynamics reliable: Exploring the kittiwake–temperature relationship

This study examined the inter-relationships between kittiwake breeding success and sandeel abundance, Calanus copepods, chlorophyll and temperature. The validity of past proxies of sandeel prey (Calanus and temperature) suggested in the literature was also examined. Winter temperature was not found to be a reliable indicator of the abundance of sandeel or lower trophic levels, although the present study did support past evidence for a dependence of kittiwake breeding success on local sandeel abundance as, with the exception of two years, there was a linear relationship with log age-0 sandeel abundance. The abundance of sandeel was positively linked to the dates of predicted peak egg abundance in C. finmarchicus and C. helgolandicus. This supported earlier evidence that the match with prey timing is important to sandeel recruitment. Neither Calanus species was associated with temperature in the February to March period nor in the April–May period, which may explain the lack of a temperature effect that propagates through the trophic levels. Consequently, although kittiwake breeding success appears to show some sensitivity and specificity to changes in their prey, this responsiveness was not found to extend to the lowest trophic level (Calanus abundance) or to temperature. As such kittiwake breeding success was not a reliable indicator of climate-driven changes in the local food web.

Distribution, abundance, and feeding ecology of baleen whales in Icelandic waters: have recent environmental changes had an effect?

The location of Iceland at the junction of submarine ridges in the North-East Atlantic where warm and cold water masses meet south of the Arctic Circle contributes to high productivity of the waters around the island. During the last two decades, substantial increases in sea temperature and salinity have been reported. Concurrently, pronounced changes have occurred in the distribution of several fish species and euphausiids. The distribution and abundance of cetaceans in the Central and Eastern North Atlantic have been monitored regularly since 1987. Significant changes in the distribution and abundance of several cetacean species have occurred in this time period. The abundance of Central North Atlantic humpback and fin whales has increased from 1,800 to 11,600 and 15,200 to 20,600, respectively, in the period 1987-2007. In contrast, the abundance of minke whales on the Icelandic continental shelf decreased from around 44,000 in 2001 to 20,000 in 2007 and 10,000 in 2009. The increase in fin whale abundance was accompanied by expansion of distribution into the deep waters of the Irminger Sea. The distribution of the endangered blue whale has shifted northwards in this period. The habitat selection of fin whales was analyzed with respect to physical variables (temperature, depth, salinity) using a generalized additive model, and the results suggest that abundance was influenced by an interaction between the physical variables depth and distance to the 2000m isobaths, but also by sea surface temperature and sea surface height, However, environmental data generally act as proxies of other variables, to which the whales respond directly. Overall, these changes in cetacean distribution and abundance may be a functional feeding response of the cetacean species to physical and biological changes in the marine environment, including decreased abundance of euphausiids, a northward shift in summer distribution of capelin and a crash in the abundance of sand eel.

Seabirds maintain offspring provisioning rate despite fluctuations in prey abundance: a multi‐species functional response for guillemots in the North Sea

Summary Seabirds that consume more than one prey type may adjust their foraging to maintain provisioning rates for their chicks. How energetically effective are these strategies, and what are the implications for the management of seabirds and their marine habitat? A multi‐species functional response links consumption rates to the availability of multiple prey types, but fitting multi‐species functional responses to field data can be difficult, requiring consumption measurements over a range of different prey abundances. Such detailed data may be especially difficult to obtain in marine ecosystems. We used annual time‐series data on chick provisioning for the common guillemot Uria aalge together with abundance indices for its two main prey (lesser sandeel Ammodytes marinus and sprat Sprattus sprattus) to parameterize a multi‐species functional response for parents provisioning chicks at a major North Sea colony from 1992 to 2005. The fitted model reproduced changes in diet and consumption rate which were consistent with changes in local prey abundance including a long‐term decline in sandeels. The model predicted that energy intake by chicks would be more sensitive to changes in sprat abundance than sandeel abundance. Guillemots appeared able to adjust their foraging tactics over a wide range of prey abundances to maintain a consistent energetic intake rate for chicks. Synthesis and applications. Our results suggest guillemot chicks obtain adequate calorific intake from their parents despite fluctuating prey abundances, conferring some resilience in the face of environmental variation. The parameterized multi‐species functional response model can be used to estimate levels of severe prey shortage that compromise provisioning. It also enables us to interpret predator consumption rates so that these can be used as a metric of prey availability. Further, quantifying trophic links between marine prey and apex predators is needed to support the development of multi‐species models in which the predators can be included. Such models are needed as tools to effectively manage the marine ecosystem, taking into account the objectives of fishing, conservation and the need to maintain Good Environmental Status.

Spatial patterns and trends in abundance of larval sandeels in the North Sea: 1950–2005

Abstract Lynam, C. P., Halliday, N. C., Höffle, H., Wright, P. J., van Damme, C. J. G., Edwards, M., and Pitois, S. 2013. Spatial patterns and trends in abundance of larval sandeels in the North Sea: 1950–2005 – ICES Journal of Marine Science, 70: 540–553. Early recruitment indices based on larval fish data from the Continuous Plankton Recorder (CPR) have the potential to inform stock assessments of Ammodytes marinus in the North Sea. We evaluate whether the CPR data are reliable for sandeel larvae. Spatially, CPR larval data were comparable with catches by dedicated larval samplers (Gulf and bongo nets) during ICES coordinated surveys in 2004 and 2009. ICES data are also used to explore environmental influences on sandeel distributions. Temporally, CPR data correlate with larval data from plankton surveys off Stonehaven (1999–2005), with sandeel 0-group trawl data at the east Fair Isle ground (since 1984), and with recruitment data (since 1983) for the Dogger Banks stock assessment area. Therefore, CPR data may provide an early recruit index of relative abundance for the Dogger Banks assessment area, where the majority of the commercial catch of A. marinus is taken, and the Wee Bankie area that is particularly important for seabird foraging. While warm conditions may stimulate the production of sandeel larvae, their natural mortality is typically greater, in the Dogger Banks and Wadden Sea areas, when the larvae are hatched in warm years and/or with abundant 1-year-old sandeel that are likely to be cannibalistic.

Body condition of predatory fishes linked to the availability of sandeels

Lesser sandeels Ammodytes marinus are eaten by a range of predatory fishes including commercially fished species, but are also exploited at large scale by industrial fisheries. Is availability of sandeels, as key prey source, linked to the body condition of predatory fishes? In the North Sea, the largest sandeel biomass is concentrated in the Dogger Bank region. Here we studied predator–sandeel interactions at two sites differing widely in sandeel abundance and local sandeel fishing effort. Surveys took place in 2004, 2005, and 2006, years when local sandeel densities observed at these sites were low, intermediate, and high, respectively. Five predator species––whiting, lesser weever, grey gurnard, plaice, and haddock––showed better body condition indices in either the years or study area (or both) characterised by higher local sandeel densities, when compared to sandeel-poorer conditions. Moreover, whiting, weever, and gurnard condition was better for those individuals actually observed to have eaten sandeels (based on stomach contents) than for those that had not. As body condition relates to growth, reproduction, and survival, predators in sandeel-rich conditions may be inferred to have a higher fitness. These links between sandeel availability, sandeel consumption, and predator condition hint that, if large-scale localised depletions of sandeels were to occur, negative indirect effects on predatory fish might become apparent, underlining the importance of considering the sandeel fishery in an ecosystem context.

Sandeel as a link between primary production and higher trophic levels on the Faroe shelf

A good correlation has previously been established between primary production and production in higher trophic levels in the marine ecosystem on the Faroe shelf, but identification of potential intermediate species has been missing. Sandeel Ammodytes spp. is known to be of great ecological importance in other areas; thus, we investigated the relationship between primary and sandeel production on the Faroe shelf. Juvenile sandeels have been sampled on the annual Faroese 0-group survey in late June to early July with a standardized procedure since 1982. Measurements on primary production, i.e. estimates of accumulated new primary production and chlorophyll a concentration, have been carried out during spring and summer on the Faroe shelf since 1990 and 1997, respectively. We found positive correlations between the primary production and the mean length and abundance of juvenile sandeels on the Faroe shelf in the period investigated. There was also a highly significant relationship between primary production and an index of juvenile sandeel biomass. Two simple models based on starvation mortality and length-dependent predation mortality, respectively, fitted the data well. These findings verify a clear, almost instantaneous, and rather unique link from primary producers to top predators.

Inferring the location and scale of mixing between habitat areas of lesser sandeel through information from the fishery

Abstract Jensen, H., Rindorf, A., Wright, P. J., and Mosegaard, H. 2011. Inferring the location and scale of mixing between habitat areas of lesser sandeel through information from the fishery. – ICES Journal of Marine Science, 68: 43–51. Sandeels are small pelagic fish that play an important role in the diet of a range of natural predators. Because of their limited capture by traditional survey gear, little is known about their large-scale distribution or the degree of mixing between habitat areas. Detailed information collected directly from the fishery was used to map fishing grounds, which were then assumed to reflect the foraging habitat of the species. Length distributions from individual hauls were used to assess differences in the distributions as a function of distance between samples. Sandeel foraging habitat covered some 5% of the total area of the North Sea. Mixing between neighbouring fishing grounds was too low to eliminate differences in length distributions at distances between grounds down to 5 km. Within fishing grounds, mixing was sufficient to eliminate differences in length distributions at scales <28 km but insufficient at greater distances. The lack of mixing between grounds may result in large differences in sandeel abundance among adjacent fishing grounds. Further, notable abundance at one end of an extensive fishing ground is not necessarily indicative of similar abundance at its other end.

Spring distribution and density of minke whale Balaenoptera acutorostrata along an offshore bank in the central North Sea

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 408:265-274 (2010) - DOI: https://doi.org/10.3354/meps08598 Spring distribution and density of minke whale Balaenoptera acutorostrata along an offshore bank in the central North Sea Marijke N. de Boer* Wageningen IMARES, Institute for Marine Resources and Ecosystem Studies, Postbus 167, 1790 AD Den Burg, The Netherlands *Email: seven.seasmc@yahoo.co.uk ABSTRACT: Minke whales were recorded in the central North Sea in an area characterised by frontal features and high productivity northeast of the Dogger Bank (4677 km2). Survey efforts were carried out from 28 March to 2 July 2007, at a finer scale than in earlier studies in the region, using 2 vessels as platforms of opportunity and a dedicated line-transect survey vessel following distance sampling methods. The high density of whales indicated that this offshore bank slope is an important spring habitat for minke whales in the North Sea. In total, 77 sightings of minke whales comprising 130 individuals were recorded. The peak density of minke whales was estimated to be 0.029 whales km–2 (minimum estimate, 95% CI: 0.012 to 0.070) in May. During peak abundance, the minke whales temporarily congregated in the area, suggesting that the whales were taking advantage of the local spring abundance of sandeels. The density found was higher than previous studies have suggested for the central North Sea. The results correspond to recent observations of minke whale redistribution within the North Sea, and these may be related to a decline in sandeel availability elsewhere in the North Sea. Offshore banks that aggregate prey may therefore become increasingly important feeding habitats for minke whales and other top predators in the North Sea. The observed habitat preference of minke whales along this offshore bank appeared to be similar to that observed in coastal areas, and this suggests some degree of generality regarding the preference for this type of habitat. KEY WORDS: Minke whale · Distribution · Density · Relative abundance · Offshore bank · Platform of opportunity · Line-transect survey · Central North Sea Full text in pdf format PreviousNextCite this article as: de Boer MN (2010) Spring distribution and density of minke whale Balaenoptera acutorostrata along an offshore bank in the central North Sea. Mar Ecol Prog Ser 408:265-274. https://doi.org/10.3354/meps08598 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 408. Online publication date: June 03, 2010 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2010 Inter-Research.

Combining hydroacoustic seabed survey and grab sampling techniques to assess “local” sandeel population abundance

Abstract Greenstreet, S. P. R., Holland, G. J., Guirey, E. J., Armstrong, E., Fraser, H. M., and Gibb, I. M. 2010. Combining hydroacoustic seabed survey and grab sampling techniques to assess “local” sandeel population abundance. – ICES Journal of Marine Science, 67: 971–984. Sandeels (Ammodytes marinus) are a critical prey of many top predators in the North Sea, and have also been the target of a major industrial fishery. To quantify resource allocation between competing predators, and between natural predators and fishers, and to assess the impact of each source of mortality on sandeel population dynamics, estimates of the absolute abundance of sandeels at the spatial scale at which these interactions take place are required. In this study, hydroacoustic seabed survey and nocturnal grab surveys are combined to examine variation in the abundance of sandeels at a sandbank complex off southeast Scotland. Grab surveys provide point estimates of sandeel density and sediment composition data, which are used to define sandeel sediment preference categories. The total area of each sandeel sediment preference category is determined by hydroacoustic seabed survey. Sandeel population abundance recovered immediately following the closure of the sandeel fishery. However, simply closing the fishery was not sufficient to maintain the size of the local sandeel stock; the population is also highly dependent on good recruitment. We demonstrate how this combination of techniques might be used to examine variation in overwintering mortality rates in sandeels.

Fishing mortality versus natural predation on diurnally migrating sandeels Ammodytes marinus

Do large-scale industrial fisheries for sandeels impact 'human consumption' fishes by depriving them of food? In the North Sea, most sandeel fishing takes place on the Dogger Bank dur- ing spring. Here, we studied sandeel-fishery and sandeel-predatory fish interactions in 2 sampling grids, focussing on (1) how localised sandeels are distributed during the day (when feeding pelagi- cally) and at night (when buried in the seabed); (2) how precisely the fishery can target localised sandeel concentrations; and (3) how tightly day/night sandeel distributions are linked to the local abundance of predatory fishes and their sandeel consumption. Sandeel abundance differed widely between both grids. Within each grid, marked day/night differences in distributions indicated exten- sive diurnal migrations, with centres of gravity of day and night distributions up to 15 km apart. Fish- ing effort was tightly matched with sandeel populations during the day and was far higher in the 'high sandeel density' grid. Only at the finest scale examined, effort was concentrated at sandbanks but not significantly matched with local sandeel numbers. This suggested either insufficient know- ledge among fishers or vessel maneuverability issues, possibly relating to high mobility of sandeels. Ten predatory fishes (8 'human consumption' species) preyed on sandeels, most notably whiting and lesser weever. Spatial comparisons showed that the predominant sandeel predators were whiting during the day and lesser weever at night. Tight predator-prey interdependencies were revealed: whiting and weever exhibited 'aggregative responses' to sandeels, and most predators consumed more sandeels in the 'high sandeel density' grid. On the Dogger Bank, sandeel fishing effort is con- centrated when and where sandeels are most available, but also where these are extensively and locally preyed upon by at least 10 predatory fish species. Hence concerns that this industrial fishery may indirectly impact predatory fishes by depriving them of food might have some basis.

The effects of environmental factors on daytime sandeel distribution and abundance on the Dogger Bank

Spring distribution and abundance of lesser sandeels during the day were linked to zooplankton densities, seabed substrate and various hydrographic factors using small scale empirical data collected in two areas on the Dogger Bank in 2004, 2005 and 2006. The results of a two-step generalized additive model (GAM) suggested that suitable seabed substrate and temperature best explain sandeel distribution (presence/absence) and that sandeel abundance (given presence) was best described by a model that included bottom temperature, difference between surface and bottom temperature and surface salinity. The current study suggests that suitable seabed substrate explains sandeel distribution in the water column. Bottom temperature and surface salinity also played an important role in explaining distribution and abundance, and we speculate that sandeels favour hydrographically dynamic areas. Contrary to our hypothesis sandeels were not strongly associated with areas of high zooplankton density. We speculate that in early spring on the western Dogger Bank plankton is still patchily distributed and that sandeels only emerge from the seabed when feeding conditions near their night-time burrowing habitat are optimal. The results also suggested that when abundance is over a threshold level, the number of sandeel schools increased rather than the schools becoming bigger. This relationship between patchiness and abundance has implications for mortality rates and hence fisheries management.

The impact of the sandeel fishery closure on seabird food consumption, distribution, and productivity in the northwestern North Sea

In the North Sea, the lesser sandeel (Ammodytes marinus) is the target of an industrial fishery and the principal prey of many top predators. Because of concerns about potential effects on predators, the sandeel fishery off eastern Scotland was closed in 2000, and local sandeel abundance increased subsequently. To examine whether closure benefitted sandeel-dependent seabirds, we compared summer sandeel consumption, at-sea distributions, and breeding success of seven species with fishery removals and abundance of older (1+ group) and young-of-the-year (0 group) sandeels from 1996 to 2003. Breeding success of black-legged kittiwake (Rissa tridactyla), a species that has declined in recent decades, was related to abundance of both 1+ group (the age class targeted by the fishery) and 0 group sandeels. The proportion of 0 group consumed by kittiwakes and proportion of the kittiwake population foraging in the area were linked to 0 group abundance. None of these parameters in the other seabird species were associated with sandeel abundance. Our results suggest that fishery closure can have a beneficial impact on top predators sensitive to variation in abundance of the target species, although environmental conditions before and after closure are also likely to be critically important.

Regional and annual variation in black-legged kittiwake breeding productivity is related to sea surface temperature

Spatiotemporal variation in seabird demographic parameters is often pronounced and may be an important source of information on the state of marine ecosystems. Black-legged kittiwakes Rissa tridactyla in Britain and Ireland show strong regional structure in breeding productivity, and both temporal and spatial variation are probably related to abundance of the principal prey of breeding kittiwakes, the lesser sandeel Ammodytes marinus. Annual regional estimates of sandeel abundance do not exist, prohibiting direct tests of this hypothesis. We examined relationships between kittiwake breeding productivity and 2 potential proxies of sandeel abundance, winter sea surface temperature (SST) and abundance of Calanus copepods, within and among 6 regions in Britain and Ireland from 1986 to 2004. Means and trends in winter SST differed among regions, with higher means and less pronounced increasing trends in western (Atlantic) regions than in eastern (North Sea) regions. A negative relationship between breeding productivity and winter SST in the previous year was found within 2 regions (East Scotland and Orkney), as well as in a cross-regional analysis. Results were inconclusive for Calanus abundance, with a positive relationship in East Scotland and negative in Orkney. These results demonstrate that although a single environmental driver (SST) is related to both within- and between-region variation in a key demographic parameter, regional heterogeneity in SST trends as well as the importance of other factors may lead to highly variable responses. Understanding this heterogeneity is critical for predicting long-term effects of climate change or other anthropogenic drivers on marine ecosystems.