Sandeel Ammodytes Marinus Research Articles

Spatio-temporal variation in the zooplankton prey of lesser sandeels: species and community trait patterns from the Continuous Plankton Recorder

Abstract The phenology, distribution, and size composition of plankton communities are changing rapidly in response to warming. This may lead to shifts in the prey fields of planktivorous fish, which play a key role in transferring energy up marine food chains. Here, we use 60 + years of Continuous Plankton Recorder data to explore temporal trends in key taxa and community traits in the prey field of planktivorous lesser sandeels (Ammodytes marinus) in the North Sea, the Faroes and southern Iceland. We found marked spatial variation in the prey field, with Calanus copepods generally being much more common in the northern part of the study area. In the western North Sea, the estimated amount of available energy in the prey field has decreased by more than 50% since the 1960s. This decrease was accompanied by declining abundances of small copepods, and shifts in the timing of peak annual prey abundances. Further, the estimated average prey community body size has increased in several of the locations considered. Overall, our results point to the importance of regional studies of prey fields, and caution against inferring ecological consequences based only on large-scale trends in key taxa or mean community traits.

Long‐term within‐season changes in the diet of Common Guillemot (Uria aalge) chicks at a North Sea colony: implications for dietary monitoring

Over four decades (1982–2019) there were pronounced within‐season changes in the proportion of a key prey species (Lesser Sandeel Ammodytes marinus) in Common Guillemot Uria aalge chick diet. As Sandeels became scarcer their occurrence was largely confined to the early part of the chick period. Consequently, the mean annual proportion of Sandeels was poorly estimated if sampling occurred within a short time window, particularly if this was early or late in the season. Within‐season variation is rarely considered in diet monitoring but our results highlight the need for further analyses across other species and sites to develop a deeper understanding of how best to optimize sampling protocols.

A verified distribution model for the lesser sandeel Ammodytes marinus

The lesser sandeel Ammodytes marinus is a key component of the North East Atlantic ecosystem but little is known about its distribution outside of fished areas. In this study, species distribution models were developed to predict the occurrence and density of sandeels in parts of the North Sea and Celtic Seas regions. A hurdle model was found to be the best fitting model with the highest predictive performance; model evaluation with independent data demonstrated that it had significant discrimination ability across the study region. Percentage silt was the most important variable in predicting occurrence, and percentage sand had a strong influence on density, consistent with past local studies. Slope was also a significant explanatory variable, especially for predicting density, as buried sandeels avoided strongly sloping areas such as the edges of sand banks. A predicted preferred depth range of 30-50 m was consistent with many previous studies, although the depth response did appear partially biased by the depth range investigated in the training data set. Overall, the predicted distribution did not indicate that there were large areas of unexploited habitat. However, some small areas known to be important to sandeel predators were identified by the model. The distribution model helps refine past inferences about sandeel availability to predators and indicates to marine planners potential areas where anthropogenic impacts should be considered.

Spatial synchrony of breeding success in the blacklegged kittiwake Rissa tridactyla reflects the spatial dynamics of its sandeel prey

Synchrony in demographic rates between spatially disjunct populations is a widespread phenomenon, although the underlying mechanisms are often not known. This synchrony and its spatial patterns can have important consequences for the long-term persistence of metapopulations and can also be used to infer drivers of population dynamics. Here, we examined spatial patterns of synchrony in the breeding success of black-legged kittiwakesRissa tridactylain the UK, using an extensive dataset on kittiwake breeding success and 2 different ways of measuring synchrony: one reflecting synchrony in inter-annual fluctuations only (rdiff) and one reflecting synchrony in both inter-annual fluctuations and long-term trends (r). We found that between-colony synchrony in breeding success decreased with distance up to just over 200 km but that some colony pairs showed stronger or weaker synchrony than expected based on distance. This was also reflected in the configuration of spatially coherent clusters of kittiwake colonies with synchronous breeding success. Further, we compared the support for different drivers of these spatial patterns, including trophic interactions and weather conditions. We found that the spatial dynamics of the kittiwakes’ main prey in this region, the lesser sandeelAmmodytes marinus, appeared to play some role in generating synchrony in long-term patterns, but their role in generating synchrony in inter-annual fluctuations was less clear. The study shows that examining spatial patterns in synchrony can provide useful information for inferring potential drivers and the spatial scale over which they are acting.

Weak genetic structure despite strong genomic signal in lesser sandeel in the North Sea.

Sandeels are an ecologically important group of fishes; they are a key part of the food chain serving as food for marine mammals, seabirds and fish. Sandeels are further targeted by a large industrial fishery, which has led to concern about ecosystem effects. In the North Sea, the lesser sandeel Ammodytes marinus is by far the most prevalent species of sandeel in the fishery. Management of sandeel in the North Sea plus the Kattegat is currently divided into seven geographical areas, based on subtle differences in demography, population dynamics and results from simulations of larval dispersal. However, little is known about the underlying genetic population structure. In this study, we used 2,522 SNPs derived from restriction site‐associated DNA sequencing (RADseq) typed in 429 fish representing four main sandeel management areas. Our main results showed (a) a lack of a clear spatially defined genetic structure across the majority of genetic markers and (b) the existence of a group of at least 13 SNPs under strong linkage disequilibrium which together separate North Sea sandeel into three haplotype clusters, suggestive of one or more structural variants in the genome. Analyses of the spatial distribution of these putative structural variants suggest at least partial reproductive isolation of sandeel in the western management area along the Scottish coast, supporting a separate management. Our results highlight the importance of the application of a large number of markers to be able to detect weak patterns of differentiation. This study contributes to increasing the genetic knowledge of this important exploited species, and results can be used to improve our understanding of population dynamics and stock structure.

From days to decades: short- and long-term variation in environmental conditions affect offspring diet composition of a marine top predator

Long-term changes in climate are affecting the abundance, distribution and phenology of species across all trophic levels. Short-term climate variability is also having a profound impact on species and trophic interactions. Crucially, species will experience long- and short-term variation simultaneously, and both are predicted to change, yet studies tend to focus on only one of these temporal scales. Apex predators are sensitive to long-term climate-driven changes in prey populations and short-term effects of weather on prey availability, both of which could result in changes of diet. We investigated temporal trends and effects of long- and short-term environmental variability on chick diet composition in a North Sea population of European shags Phalacrocorax aristotelis between 1985 and 2014. The proportion of their principal prey, lesser sandeel Ammodytes marinus, declined from 0.99 (1985) to 0.51 (2014), and estimated sandeel size declined from 104.5 to 92.0 mm. Concurrently, diet diversification increased from 1.32 (1985) to 11.05 (2014) prey types yr-1, including members of the families Pholidae, Callionymidae and Gadidae. The relative proportion of adult to juvenile sandeel was greater following low sea surface temperatures (SSTs) in the previous year. In contrast, the proportion of Pholidae and prey richness were higher following high SST in the previous year. Within a season, the proportion of sandeel in the diet was lower on days with higher wind speeds. Crucially, our results showed that diet diversification was linked to trends in SST. Thus, predicted changes in climate means and variability may have important implications for diet composition of European shags in the future, with potential consequences for population dynamics.

Influence of diet and foraging strategy on reproductive success in two morphologically similar sympatric seabirds

ABSTRACTCapsule: Morphologically similar sympatrically breeding species differ in diet and foraging strategies, which could explain interspecific variation in breeding success and reproductive output.Aims: To compare provisioning rate and diet of nestling Arctic (Sterna paradisaea) and Common Terns (Sterna hirundo), and examine how variation in provisioning behaviour influences reproductive parameters.Methods: Arctic and Common Tern nests were observed from June to July 2011 on Coquet Island, northeast England. We compared chick provisioning rate, diet and energy delivery rate between species, and examined whether these parameters were associated with interspecific differences in chick growth and survival, and total number of chicks fledged.Results: Arctic Terns delivered higher percentages of smaller Sandeels (Ammodytes marinus) and juvenile fish to chicks than did Common Terns, which delivered comparatively high percentages of larger Sprats (Sprattus sprattus). Although chick growth rate and survival were not significantly different between species, Common Terns fledged more chicks than Arctic Terns due to a tendency for larger clutch sizes.Conclusion: Our study suggests that interspecific differences in diet and foraging strategies can support total reproductive output in morphologically similar species.

Distribution of the larvae of capelin Mallotus villosus and lesser sandeel Ammodytes marinus in the White Sea

The early developmental stages of capelin Mallotus villosus and lesser sandeel Ammodytes marinus were the major representatives of the fish larvae in the ichthyoplankton of the open waters of the White Sea in June 2007 and 2010 and in July 2010 and 2011. The larvae of these two species were widely distributed in the White Sea and have been registered in the large bays and in the other parts of the sea. The larvae of capelin and lesser sandeel were the most abundant in Onega Bay and in Dvina Bay and in Gorlo Strait of the White Sea; the larvae of lesser sandeel have also been found in the coastal waters of Kandalaksha Bay. The schooling of the larvae of these two species were characterized by a relatively permanent localization that referred to the spawning grounds; the shape and the location of the schoolings usually depend on the presence and configuration of the areas of the pronounced gradients of the hydrophysical parameters in these areas.

The winter diet of theAtlanticPuffinFratercula arcticaaround theFaroeIslands

Most mortality of Atlantic Puffins occurs outside the breeding season but little is known about the species’ diet at that time. The stomach contents of 176 Puffins shot legally for food around the Faroe Islands between October and January in three winters were examined. The remains of 20 species of fish, six species of crustacea and single species of polychaete, chaetognathid and squid were identified. The most frequently recorded prey in terms of frequency of occurrence were 0 group (< 1 year old) Lesser SandeelAmmodytes marinus(82% of stomachs), followed by mesopelagic fish (52%), nereid worms (41%), Silver RocklingGaidropsarus argentatus(36%), crustacea (35%), large sandeel (32%) and other large fish (32%). In terms of calculated biomass, nereids (41%), large sandeel (23%) and other large fish (17%) made up the bulk of the diet but the latter two prey types were most important in energetic terms (46% despite accounting for only 9% of items). Stomach contents collected on the same day and location were significantly more similar than those collected on different dates and locations, suggesting that during the winter, Puffins are generalists, taking any prey they encounter.

Effects of copepod size on fish growth: a model based on data for North Sea sandeel

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 520:235-243 (2015) - DOI: https://doi.org/10.3354/meps11092 Effects of copepod size on fish growth: a model based on data for North Sea sandeel Mikael van Deurs1,3,*, Christian Jørgensen2, Øyvind Fiksen2 1DTU Aqua National Institute of Aquatic Resources, Technical University of Denmark (DTU), Jægersborg Alle 1, Charlottenlund Castle, 2920 Charlottenlund, Denmark 2Thormøhlensgate 53B 3rd floor, Department of Biology, University of Bergen, PO Box 7803, 5020 Bergen, Norway 3Present address: Lund University, Sölvegatan 37, International Postal Code 50, Lund, Sweden *Corresponding author: mvd@aqua.dtu.dk ABSTRACT: In productive marine off-shore ecosystems, the flow of energy from zooplankton to large predators is channeled through a few species of short-lived, highly abundant schooling planktivorous fish. There are indications that these species respond to qualitative and phenological changes in the zooplankton. If so, the climate-induced alterations of the local copepod communities that we see in temperate and arctic regions may influence the energy flux in marine food chains. In order to investigate how different processes contribute to the relationship between copepod size and fish growth, we merged 2 mechanistic models from relevant data: (1) a model of the bioenergetics and stomach filling/evacuation dynamics, and (2) a Holling type II functional response model that encompasses visual range from basic principles. The model predicts that going from a situation where large Calanus copepods (2 mm) dominate the prey field of lesser sandeel Ammodytes marinus in the central North Sea to a situation where only relatively small (1 mm) and less energy-rich copepods are available roughly halves the energy intake of sandeels even if prey biomass concentration remains constant. Visual constraint on foraging was the most important factor, followed by handling time limitation and prey energy content. These limitations became stronger with increasing fish length, showing that copepod size and energy content have a strong effect on the specific growth potential of these fish. KEY WORDS: Prey preference · Bioenergetics · Optimal foraging · North Sea regime-shift · Climate change · Ammodytes · Holling disc · Calanus · Handling time limitation · Food quality Full text in pdf format PreviousNextCite this article as: van Deurs M, Jørgensen C, Fiksen Ø (2015) Effects of copepod size on fish growth: a model based on data for North Sea sandeel. Mar Ecol Prog Ser 520:235-243. https://doi.org/10.3354/meps11092 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 520. Online publication date: February 03, 2015 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2015 Inter-Research.

Feeding of grey gurnard Eutrigla gurnardus (Triglidae) in the area of the Rockall Seamount

Specific features of feeding of grey gurnard Eutrigla gurnardus depending on vertical distribution and habitat conditions in the area of the Rockall Seamount in 2000 were considered. The intensity of feeding of grey gurnard from April to September decreased by several times. The main food of this species in spring are euphausiids and that in autumn are fish. Males feed slightly more intensively than females. The intensity of feeding, distribution, and behavior of grey gurnard in different seasons and at different depths near bottom and in the pelagial noticeably differ and depend on the composition of distribution and numbers of dominant food items (euphausiids, sand eel Ammodytes marinus, fish juveniles).

Patchy zooplankton grazing and high energy conversion efficiency: ecological implications of sandeel behavior and strategy

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 487:123-133 (2013) - DOI: https://doi.org/10.3354/meps10390 Patchy zooplankton grazing and high energy conversion efficiency: ecological implications of sandeel behavior and strategy Mikael van Deurs*, Asbjørn Christensen, Anna Rindorf DTU Aqua National Institute of Aquatic Resources, Technical University of Denmark (DTU), Jægersborg Alle 1, Charlottenlund Castle, 2920 Charlottenlund, Denmark *Email: mvd@aqua.dtu.dk ABSTRACT: Sandeels display strong site fidelity and spend most of their life buried in the seabed. This strategy carries important ecological implications. Sandeels save energy when they are not foraging, but in return are unable to move substantially and may therefore be sensitive to local depletion of prey. We studied zooplankton consumption and energy conversion efficiency of the lesser sandeel Ammodytes marinus in the central North Sea, using stomach data, length and weight-at-age data, bioenergetics, and hydrodynamic modeling. The results suggested the following. (1) Lesser sandeels in the Dogger area depend largely on relatively large copepods in early spring. (2) The lesser sandeel is an efficient converter, making secondary production into fish tissue available for higher trophic levels. Hence, changes in species composition towards a more herring-dominated system, as seen in recent times, may lead to a decrease in system transfer efficiency. (3) Sandeels leave footprints in the standing copepod biomass as far as 100 km from the edge of their habitat, but smaller and more isolated sandeel habitat patches have a much lower impact than larger patches, suggesting that smaller habitats can sustain higher sandeel densities and growth rates per area than larger habitats. We conclude that sandeel behavior and strategy have ecosystem implications. KEY WORDS: Sand lance · Food web · Trophic transfer efficiency · Bioenergetics · Growth · Food consumption · North Sea · Dogger Full text in pdf format PreviousNextCite this article as: van Deurs M, Christensen A, Rindorf A (2013) Patchy zooplankton grazing and high energy conversion efficiency: ecological implications of sandeel behavior and strategy. Mar Ecol Prog Ser 487:123-133. https://doi.org/10.3354/meps10390 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 487. Online publication date: July 30, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.

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.

Tissue-specific turnover rates and trophic enrichment of stable N and C isotopes in juvenile Atlantic cod Gadus morhua fed three different diets

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 461:197-209 (2012) - DOI: https://doi.org/10.3354/meps09871 Tissue-specific turnover rates and trophic enrichment of stable N and C isotopes in juvenile Atlantic cod Gadus morhua fed three different diets Torben Ankjærø, Jens Tang Christensen, Peter Grønkjær* Department of Bioscience, Marine Ecology, Aarhus University, 8000 Aarhus C, Denmark *Email: peter.groenkjaer@biology.au.dk ABSTRACT: A 150 d laboratory diet-shift study was conducted on juvenile Atlantic cod Gadus morhua L. to examine (1) stable nitrogen and carbon isotope turnover rates, (2) the tissue-specific relative contribution of metabolism and growth to isotopic change, and (3) diet−tissue enrichment of the isotopes in white muscle, heart, whole blood, and cranial bone collagen. Time- and growth-based models described the change in δ15N and δ13C of the tissues following a diet shift from pelleted food to either blue mussels Mytilus edulis L., sandeel Ammodytes marinus Raitt., or whiting Merlangius merlangus L. diets. Cod growth rates ranged from 1.5 to 2.0% d−1, with the exception of whiting-fed cod that experienced a cessation in growth after Day 86. Isotope turnover rates, expressed as half-lives (T½), differed little between tissues as expected in fast-growing fish. For δ15N, heart tissue had the shortest T½ while muscle had the longest (30.7 to 34.8 versus 35.7 to 77.9 d−1; range among diets). Heart tissue also had the shortest δ13C T½, whereas blood had the longest (25.5 to 38.5 versus 49.5 to 60.3 d−1; range among diets). Diet-tissue enrichment varied between 0.8 and 5.1‰ (Δδ15N) and between 0.7 and 2.2‰ (Δδ13C). Growth accounted for most of the isotopic change, except in heart tissue of all cod and in all tissues of whiting-fed cod, where there was a significant effect of metabolism on isotopic change. Despite variability in enrichment among diets and tissues, fish feeding on the 3 diets could be distinguished based on their tissue-specific isotopic signatures. KEY WORDS: Isotopic turnover · Diet shift · 15N · 13C · Nitrogen · Carbon · Growth · Metabolism Full text in pdf format PreviousNextCite this article as: Ankjærø T, Christensen JT, Grønkjær P (2012) Tissue-specific turnover rates and trophic enrichment of stable N and C isotopes in juvenile Atlantic cod Gadus morhua fed three different diets. Mar Ecol Prog Ser 461:197-209. https://doi.org/10.3354/meps09871 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 461. Online publication date: August 08, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Survival of breeders in a Danish Black-legged Kittiwake Rissa tridactyla colony - a capture-mark-recapture study

The Black-legged Kittiwake Rissa tridactyla is one of the most numerous seabirds in the North Atlantic, but during the last couple of decades there have been reports of widespread large declines in breeding populations. In some areas, these declines are believed to be linked to lack of prey (Lesser Sandeel Ammodytes marinus) due to industrial fishing and increasing sea surface temperatures. In this paper, we explore the effect of sea surface temperature and age on survival of adult breeders in a small and relatively stable Danish colony of Black-legged Kittiwakes from 1992 to 2010. We found that survival did not vary significantly over the study period (mean 0.82), but was lower than reported from other studies. This could be due to a trade-off between reproduction and survival, leading to a lower survival, or it could be due to a high emigration leading to a too low estimate. Sea surface temperature had no effect on survival, contrary to other studies. Danish Black- legged Kittiwakes may rely on a food source which is not affected by the sea temperatures, either other species of fish or fishery discards. Finally, we found that survival decreased with age, in line with other studies.

Mechanisms of long-term decline in size of lesser sandeels in the North Sea explored using a growth and phenology model

The lesser sandeel Ammodytes marinus is a key species in the North Sea ecosystem, transferring energy from planktonic producers to top predators. Previous studies have shown a long-term decline in the size of 0-group sandeels in the western North Sea, but they were unable to pinpoint the mechanism (later hatching, slower growth or changes in size-dependent mortality) or cause. To investigate the first 2 possibilities we combined 2 independent time series of sandeel size, namely data from chick-feeding Atlantic puffins Fratercula arctica and from the Continuous Plankton Recorder (CPR), in a novel statistical model implemented using Markov Chain Monte Carlo (MCMC). The model estimated annual mean length on 1 July, as well as hatching date and growth rate for sandeels from 1973 to 2006. Mean length-at-date declined by 22% over this period, corresponding to a 60% decrease in energy content, with a sharper decline since 2002. Up to the mid-1990s, the decline was associated with a trend towards later hatching. Subsequently, hatching became earlier again, and the continued trend towards smaller size appears to have been driven by lower growth rates, particularly in the most recent years, although we could not rule out changes in size-dependent mortality. Our findings point to major changes in key aspects of sandeel life history, which we ­consider are most likely due to direct and indirect temperature-related changes over a range of biotic factors, including the seasonal distribution of copepods and intra- and inter-specific competition with planktivorous fish. The results have implications both for the many predators of sandeels and for age and size of maturation in this aggregation of North Sea sandeels.

Estimation of feeding patterns for piscivorous fish using individual prey data from stomach contents

The problem of estimating temporal feeding patterns using stomach data is considered, where the time of ingestion for each prey item can be predicted through a gastric evacuation model. The arrival of prey is modelled as a nonhomogeneous Poisson process with known periodic intensity. A maximum likelihood approach is used to estimate the intensity, which is assumed to be the same for all predators, incorporating different uncertainties for the arrival time of each prey item. The method is applied to a case where a population of whiting ( Merlangius merlangus ) is feeding on sandeel ( Ammodytes marinus ), and peak feeding periods around dusk and dawn are identified.

Interactions with Great SkuasStercorarius skuaas a factor in the long‐term decline of an Arctic SkuaStercorarius parasiticuspopulation

Many of the UK’s seabird species have displayed high variation in breeding success since the 1980s, largely due to changes in the availability of Lesser SandeelsAmmodytes marinus, their main prey. During this time, Arctic SkuasStercorarius parasiticusexperienced a rapid decline in the UK and the species has subsequently been placed on the Red List of birds of conservation concern. Although shortage of Lesser Sandeels is likely to be an influential factor, the Arctic Skua’s breeding range overlaps with that of the Great SkuaStercorarius skua, a larger bird with a more varied diet, and interspecific interactions for nesting habitat may exert an additional pressure on Arctic Skua breeding populations. Results from four censuses, spanning 21 years, were used to model habitat use and analyse distributional change in nesting Arctic Skuas at a major colony located on Fetlar, Shetland, Scotland. The decline in Arctic Skuas was not uniform across the island and competition with Great Skuas for nest‐sites appears to have influenced localized breeding distribution. By 2006, Arctic Skuas had been almost entirely excluded from shrub heath, blanket bog and coastal heath habitats, which were identified as preferred habitat in 1986. In 2006, Arctic Skua breeding territories were mainly restricted to one core area of preferred habitat where over 90% nested in high density as this habitat became increasingly occupied by Great Skuas. The more generalist foraging habit of the Great Skua allowed the population to grow rapidly as numbers of the more specialist Arctic Skua decreased during times of low sandeel availability. Our model suggests that both interspecific competition for territories with Great Skuas and food limitation have played important roles in the decline of Arctic Skuas on Fetlar.

Recruitment of lesser sandeel Ammodytes marinus in relation to density dependence and zooplankton composition

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 381:249-258 (2009) - DOI: https://doi.org/10.3354/meps07960 Recruitment of lesser sandeel Ammodytes marinus in relation to density dependence and zooplankton composition Mikael van Deurs1,*, Ralf van Hal2, Maciej T. Tomczak1, Sigrún H. Jónasdóttir1, Per Dolmer1 1National Institute of Aquatic Resources, Technical University of Denmark, Jægersborg Alle 1, Charlottenlund Castle, 2920 Charlottenlund, Denmark 2Institute for Marine Resources and Ecosystem Studies, Wageningen IMARES, Haringkade 1, 1976CP Ijmuiden, The Netherlands *Email: mvd@aqua.dtu.dk ABSTRACT: Recent recruitment failure of lesser sandeel Ammodytes marinus, a key prey fish in the North Sea, followed by several years of low spawning stock biomass, prompted us to investigate factors influencing the recruitment of this species. We tested 2 hypotheses that relate to ecological mechanisms of recruitment regulation in lesser sandeel: (1) a positive spawning stock–recruitment relationship is decoupled in years associated with high abundances of age-1 sandeels and (2) the survival success of early larvae depends specifically on the abundance of Calanus finmarchicus and not C. helgolandicus. The findings of the present study supported both hypotheses and resulted in a multiple linear recruitment model with pronounced predictive capabilities. The model includes interactions between age-1 abundance and spawning stock biomass, plus the effect of C. finmarchicus abundance, and it explained around 65% of the inter-annual variation in recruitment in contrast to only 12% by a traditional Ricker curve. We argue that early egg production in C. finmarchicus supports the survival of larvae, and that climate-generated shifts in the Calanus species composition lead to a mismatch in timing between food availability and the early life history of lesser sandeels. KEY WORDS: Ammodytes marinus · Recruitment · Calanus finmarchicus · Match/mismatch hypothesis · Density dependency · Climate change Full text in pdf format PreviousNextCite this article as: van Deurs M, van Hal R, Tomczak MT, Jónasdóttir SH, Dolmer P (2009) Recruitment of lesser sandeel Ammodytes marinus in relation to density dependence and zooplankton composition. Mar Ecol Prog Ser 381:249-258. https://doi.org/10.3354/meps07960Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 381. Online publication date: April 17, 2009 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2009 Inter-Research.

Using inter‐colony variation in demographic parameters to assess the impact of skua predation on seabird populations

Large skuas and gulls are top predators in marine ecosystems, feeding on shoaling fish, fishery discards and facultatively on smaller seabirds. As generalist predators they may have deleterious impacts on prey populations of seabirds, particularly when alternative foods are scarce. Declines in discards and lipid‐rich shoaling fish may result in these large scavenging birds turning to prey on seabirds to meet their nutritional needs, yet we know relatively little about seabird predator–prey dynamics. Declines in Black‐legged Kittiwakes Rissa tridactyla in the UK are attributed to reductions in Sandeel Ammodytes marinus availability, but may also be due to predation by Great Skuas Stercorarius skua in some parts of their range. We investigate whether variation in two demographic parameters (breeding success and population growth rate) of Kittiwake colonies across Shetland are explained by skua population density at increasing spatial scales (rings with radii of 0–5, 5–10, 10–15, 15–20, 20–25 and 25–30 km) and Kittiwake population density. These explanatory variables do not explain a significant amount of the variation in annual population growth rate (lambda), but our estimate of population change is highly conservative and we cannot exclude the possibility of type II errors. Kittiwake breeding success is positively correlated with Sandeel availability and negatively correlated with the number of Kittiwakes at the focal colony. Having controlled for these effects the number of Great Skuas also has an influence on breeding success, being negatively correlated at the scale of 5–10 and 20–25 km, but positively correlated at the scale of 10–15 km. In addition, analysis of Kittiwake populations subdivided into exposed or protected cliffs reveals that exposed sub‐colonies declined more steeply than protected ones – presumably as a function of differences in susceptibility to Skua predation. We propose that comparing differences in demographic rates may be useful in unravelling seabird predator–prey dynamics, but only where there is a comprehensive demographic dataset, where it is possible to correct for confounding factors such as food availability, and information on habitat–predation interactions.