Ammodytes Marinus Research Articles

DIFFERENTIAL EFFECTS OF A LOCAL INDUSTRIAL SAND LANCE FISHERY ON SEABIRD BREEDING PERFORMANCE

Fisheries management across the world is moving toward an ecosystem-based approach, implying that fishery effects on nontarget species should be taken into account. However, such effects are often not well understood, partly because, they can be difficult to distinguish from impacts of environmental fluctuations. We evaluated the effects of an industrial sand lance (Ammodytes marinus) fishery off the North Sea coast of the United Kingdom, which has been opened and closed in a quasi-experimental fashion, on sand-lance-dependent breeding seabirds. Controlling for environmental variation (sea surface temperature, abundance of larval sand lance, and size of adult sand lance), we found that, when the fishery was operating, breeding productivity in the intensively studied seabird colony on the Isle of May was significantly depressed for one surface-feeding seabird species, the Black-legged Kittiwake (Rissa tridactyla), but not for four diving species. Analyzing Kittiwake data from 12 colonies inside and outside the closure zone in a replicated before-after control-impact design, we again found that breeding productivity was significantly depressed in the closure zone when the fishery was active, whereas no effect was found in the control zone. Furthermore, Kittiwake breeding productivity was negatively correlated with fishery effort during the fishery period in the closure zone, but not in the control zone. The contrasting findings in the two zones could be related to environmental differences or to the fact that only one study colony in the control zone was exposed to high fishery effort within the typical foraging range of Kittiwakes during the breeding season. The strong impact on Kittiwakes, but not on diving species, could result from (1) inherently high sensitivity to reduced prey availability, (2) changes in the vertical distribution of sand lance at lower densities, (3) sand lance showing avoidance behavior to fishery vessels, or a combination of some or all of these factors. These findings indicate that local fishery closures can benefit sensitive predators and should be considered as a tool for future ecosystem-based 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.

The diet of European Shag Phalacrocorax aristotelis, Black-legged Kittiwake Rissa tridactyla and Common Guillemot Uria aalge on Canna during the chick-rearing period 1981–2007

Chick diet of European Shags Phalacrocorax aristotelis, Black-legged Kittiwakes Rissa tridactyla and Common Guillemots Uria aalge at Canna was investigated over a 27- year period. The diet was mainly composed of Sprats Sprattus sprattus, Lesser Sandeels Ammodytes marinus and members of the Gadidae (a variety of species but mainly Trisopterus spp. and Whiting Merlangius merlangus). Other groups (ten families of fish, crustaceans, cephalopod molluscs and polychaete worms) were of minimal importance. Lesser Sandeels dominated the diet of young Black-legged Kittiwakes and European Shags, Sprats the diet of young Common Guillemots, whereas gadid otoliths were by far the commonest items found in pellets regurgitated by older European Shags. There were few significant temporal changes in species composition or the size of prey taken over the 27 years and the results confirm earlier findings that gadids are a normal and important part of the diet of seabirds at this colony.

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.

Hydrodynamic backtracking of fish larvae by individual-based modelling

We discuss methodological and implementation issues of spatial, temporal and com- bined spatio-temporal backtracking and illustrate larval backtracking for North Sea lesser sandeel Ammodytes marinus larvae, using a combined hydrodynamical and individual-based model. It was found that dispersal effects are important for larval backtracking predictions. Our results show large differences in average transport distance, as well as in shape and extent of predicted hatch areas, when backtracking advected larval cohorts in different regions of the North Sea, thus emphasizing the importance of using realistic, spatially and temporally resolved diffusivity fields in simulations of larval transport. In all cases, biologically likely hatching areas have been predicted. We discuss issues of methodological consistency and present a new scheme for including life-history stochasticity effects on growth in backtracking in a consistent way, as well as procedures for assessing the effects of larval mortality. Finally, fundamental limitations of larval backtracking are clarified, most importantly the time horizon and spatial resolution limit for backward prediction.

Effects of body size and environment on diet-tissue δ13C fractionation in fishes

δ 13C data are often used in trophodynamic research where diet-tissue fractionation (Δ δ 13C) is assumed to be 0–1‰ per trophic level and unaffected by the size of animals or their environment. Variation in Δ δ 13C will influence conclusions about food sources, energy pathways and trophic level. To assess the effects of body size, age and environmental conditions on Δ δ 13C, European sea bass ( Dicentrarchus labrax) were reared on constant diets of dab ( Limanda limanda) or ( Ammodytes marinus) for 2years under natural environmental regimes. Bass were sampled approximately monthly to determine Δ δ 13C for muscle, heart and liver tissue and were 1.66‰, − 0.18‰, − 1.77‰ (sandeel diet) and 1.34‰, − 1.18‰, − 1.75‰ (dab diet) respectively. Arithmetic lipid correction increased Δ δ 13C to > 2‰ for muscle and liver. Δ δ 13C was dependent on body mass and experimental duration (age) and generally declined with weight or time even after correction for lipid content. For liver, increasing temperature increased Δ δ 13C. The Δ δ 13C estimates from this study were compared with all available published Δ δ 13C estimates for fish. Bass muscle Δ δ 13C was similar to previous estimates for fish white muscle Δ δ 13C (1.56 ± 1.10‰) and whole body Δ δ 13C (1.52 ± 1.13‰). Fractionations derived in this study, combined with those from the literature, support the use of diet-tissue fractionation values of between 1‰–2‰ for δ 13C, rather than the commonly used 0‰ − 1‰. For muscle Δ δ 13C, 1.5‰ is appropriate.

Regional variation in the role of bottom-up and top-down processes in controlling sandeel abundance in the 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 337:279-286 (2007) - doi:10.3354/meps337279 Regional variation in the role of bottom-up and top-down processes in controlling sandeel abundance in the North Sea Morten Frederiksen1,*, Robert W. Furness2, Sarah Wanless1 1Centre for Ecology and Hydrology, Hill of Brathens, Banchory AB31 4BW, UK 2Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, UK *Email: mfr@ceh.ac.uk ABSTRACT: The lesser sandeel Ammodytes marinus is a critically important mid-trophic species in the North Sea ecosystem. Seabirds suffered widespread breeding failures in the North Sea in 2004, due to shortages of sandeels, their principal food. Industrial sandeel fisheries also failed in 2003 to 2005. Explaining why sandeels were in short supply is thus critical to understanding and managing the North Sea ecosystem. Sandeel abundance may be controlled ‘bottom-up’ by food availability or ‘top-down’ by predation, including fisheries. The relative importance of these 2 mechanisms may vary over space and time, and failure to take account of such variation may lead to inappropriate management. We summarise the available evidence for top-down or bottom-up control of sandeel abundance in 2 well-studied North Sea regions differing in many biotic and abiotic characteristics. In Shetland, recent low abundance of sandeels coincided with record-high abundance of herring, which may have exerted a top-down predation pressure on sandeels. Off SE Scotland, where adult herrings are scarce, abundance of sandeel larvae was positively correlated with plankton abundance, indicating bottom-up control. Seabird breeding failures in this area in 2004 were linked to extremely low energy content of sandeels. Large-scale sandeel fisheries have not been operating in either area since 2000. Control of food web structure and function in the North Sea is thus likely to be complex, with pronounced regional variation. Improved cooperation between diverse research organisations will be needed to understand this complexity, and future ecosystem-based management of marine bioresources will need to take the results of such research into account. KEY WORDS: Ecosystem function · Herring · Marine food webs · Resource management · Sandeel · Trophic structure Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 337. Online publication date: May 14, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.

Comparative nutritional condition of larval dab Limanda limanda and lesser sandeel Ammodytes marinus in a highly variable environment

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 334:205-212 (2007) - doi:10.3354/meps334205 Comparative nutritional condition of larval dab Limanda limanda and lesser sandeel Ammodytes marinus in a highly variable environment Arne Michael Malzahn1,*, Catriona Clemmesen2, Karen Helen Wiltshire1, Silke Laakmann1,3, Maarten Boersma1,4 1Alfred Wegener Institute for Polar and Marine Research, Biologische Anstalt Helgoland, Ostkaje 1118, 27498 Helgoland, Germany 2Leibniz Institute of Marine Sciences (IFM-GEOMAR), Düsternbrooker Weg 20, 24105 Kiel, Germany 3University of Bremen, Bibliothekstraße 1, 28359 Bremen, Germany 4GKSS Research Centre, Institute for Coastal Research, Max-Planck-Straße 1, 21502 Geesthacht, Germany *Email: amalzahn@awi-bremerhaven.de ABSTRACT: We investigated the nutritional condition of larval fishes caught in daily ichthyoplankton hauls in the ‘Helgoland Roads’ (54°11.18’N and 07°54.00’E) from February to June 2004. We concentrated on larvae of dab Limanda limanda and lesser sandeel Ammodytes marinus in order to compare early life stages of iteroparous and nearly semelparous fish. We analysed length, weight and RNA:DNA ratios as a proxy for condition of the larvae. The relationship between larval nutritional condition and larval size provided an indication of condition-selective mortality due to a loss of larvae in poor condition from the larger size-classes. For the sandeel, larvae in good condition were present in all size-classes, whereas for the dab maximum larval condition increased with increasing size. Variability in both standard length and condition was high in the 2 species during their planktonic stage. Both species showed good nutritional condition in the early to mid portion of the recruitment period and declines in condition in late April. This was more pronounced in larval dab, which showed a higher dependency on feeding conditions than larval sandeel. Together, these findings indicate a more conservative strategy of early life stages of the nearly semelparous sandeel compared with the iteroparous dab. KEY WORDS: Larval fishes · RNA:DNA ratio · Helgoland Roads · North Sea Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 334. Online publication date: March 26, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.

Year-to-year variation in larval fish assemblages of the Southern North Sea

In order to test the temporal stability within and the reproducibility of larval fish assemblages between years, the larval fish assemblage at Helgoland Roads, North Sea (NE Atlantic) was quantitatively sampled almost daily from January 2003 to December 2005. The survey resulted in a total of 462 samples containing 50,632 larval fish of at least 42 taxa. In winter the larval fish assemblage was mainly dominated by larvae emerging from demersal eggs. This changed gradually to larvae hatching from pelagic eggs. Larvae from pelagic eggs dominated the ichthyoplankton assemblage in summer. A remarkably stable seasonality in terms of dominance patterns with recurring, season-specific fish assemblages was observed over the 3 years, despite substantial variation in environmental conditions such as a temperature difference of almost 20°C between summer and winter. The lesser sandeel (Ammodytes marinus), was the only species which showed significant fluctuations in abundance between the years. After removal of this species from the analysis, the dominance patterns of the remaining fish species were almost identical between years.

Regional variation in maturation of sandeels in the North Sea

Abstract Boulcott, P., Wright, P. J., Gibb, F. M., Jensen, H., and Gibb, I. M. 2007. Regional variation in maturation of sandeels in the North Sea. – ICES Journal of Marine Science, 64: 369–376. The current assessment of lesser sandeel (Ammodytes marinus) in the North Sea assumes a single stock and a knife-edge maturity ogive. However, there is evidence that the North Sea stock consists of several reproductively isolated components, raising the possibility of demographic differences among regional aggregations. We examine regional variation in size- and age-at-maturity in four components of the North Sea stock. Surveys in 1999 indicated pronounced regional differences in length- and weight-at-age, implying a disparity in growth rate across the North Sea. Logistic regression revealed that the onset of maturity was significantly related to regional distribution, in addition to length and age, with a tendency for fish off the UK's northeast coast to mature later and smaller than elsewhere. No significant effect of year on either growth or length-at-maturity was revealed from a comparison with other data collected in 2004. The results show that important regional phenotypic variation not currently represented in stock assessments could have implications for the local sustainability of sandeel aggregations.

Effects of alternative prey on predation intensity from herring Clupea harengus and sandeel Ammodytes marinus on capelin Mallotus villosus larvae in the Barents Sea

Stomach contents from lesser sandeel Ammodytes marinus and herring Clupea harengus caught at one and three stations, respectively, were analysed to investigate predation intensity on capelin Mallotus villosus larvae. Most capelin larvae were found in the anterior sections of the stomachs close to the oesophagus, indicating that rapid digestion rates of larvae reduced the abundance in the posterior sections. The anterior sections of the stomachs had alternating layers of either copepods or capelin larvae and krill. This shows that the individual predators switched between feeding on either copepods or on krill and capelin larvae. A total of 549 capelin larvae was found in 440 fish stomachs. Capelin larvae were found in 20% of the sandeel stomachs, and 24, 34 and 62% of the stomachs from the three herring stations, respectively. Many of the predator stomachs contained more than five larvae, and up to 28 larvae were found in one herring stomach. The herring appeared to prey selectively on the largest capelin larvae, and the number of larvae per stomach was much higher in stomachs where krill had recently been eaten than where copepods were dominant. The predation intensity measured in this study is much higher than reported in earlier studies, and it is suggested that the predators were feeding using a searching image, and that the concentrations of alternative prey (copepods and krill) varied around a switching threshold.

Black-legged kittiwakes as indicators of environmental change in the North Sea: Evidence from long-term studies

Top predators, particularly seabirds, have repeatedly been suggested as indicators of marine ecosystem status. One region currently under pressure from human fisheries and climate change is the North Sea. Standardized seabird monitoring data have been collected on the Isle of May, an important seabird colony in the northwestern North Sea, over the last 10–20 years. Over this period oceanographic conditions have varied markedly, and between 1990 and 1999 a major industrial fishery for sandlance ( Ammodytes marinus), the main prey of most seabird species, was prosecuted nearby. Sandlance fishing grounds close to seabird colonies down the east coast of the UK were closed in 2000 in an attempt to improve foraging opportunities for breeding seabirds, particularly black-legged kittiwakes ( Rissa tridactyla). Initially this closure seemed to be beneficial for kittiwakes with breeding success recovering to pre-fishery levels. However, despite the ban continuing, kittiwakes and many other seabird species in the North Sea suffered severe breeding failures in 2004. In this paper, we test the predictive power of four previously established correlations between kittiwake breeding success and climatic/trophic variables to explain the observed breeding success at the Isle of May in 2004. During the breeding season, kittiwakes at this colony switch from feeding on 1+ group to 0 group sandlance, and results up until 2003 indicated that availability of both age classes had a positive effect on kittiwake breeding success. The low breeding success of kittiwakes in 2004 was consistent with the late appearance and small body size of 0 group sandlance, but at odds with the two variables likely to operate via 1 group availability (lagged winter sea surface temperature and larval sandlance cohort strength in 2003). The reason for the discrepancy is currently unknown, but analysis of 1 group sandlance body composition indicated that lipid content in 2004 was extremely low, and thus fish eaten by kittiwakes during pre-breeding and early incubation were likely to be of poor quality. Monitoring of reproductive success of kittiwakes, although useful, was clearly not sufficient to tease apart the complex causation underlying the 2004 event. Monitoring programs such as this, therefore, need to be complemented by detailed research to identify the mechanisms involved, and to attribute and predict the effects of natural and human-induced environmental change.

Species composition and distribution of ichthyoplankton in the White Sea in July 2003

On the basis of an ichthyoplankton survey made in July 2003 in Kandalaskha Gulf, the Basin, the Gorlo Strait, and the Voronka the species composition and distribution of fish eggs and larvae are investigated. The ichtyoplankton comprises 17 fish species, of which the majority (11) were boreal forms. Other fish were represented by arctic species (2) and arctic-boreal species (4). The traits of distribution of abundantly caught species are considered in detail: larvae of the White Sea oligovertebrate herring Clupea pallasii marisabli, eggs of the dab Limanda limanda, larvae of the northern sand lance Ammodytes marinus, and of the capelin Mallotus villosus villosus. The presence of all larvae of White Sea herring only within Kandalaskha Gulf is considered to be evidence supporting the hypothesis suggested by Dmitriev (1946) on the absence of their drift beyond large gulfs of the White Sea. The natural barrier for mutual exchange with early developmental stages of fish between the White Sea and the Barents Sea in summer may be a developed hydrologic front in the boundary area of the Basin and Gorlo Strait, discovered in the course of the survey. This front causes their death by thermohaline shock in the abrupt gradient zone.

Robust digestion and passage rate estimates for hard parts of grey seal (Halichoerus grypus) prey

Application of digestion correction factors to measurements and counts of fish otoliths and cephalopod beaks recovered from seal scats is required before the size or quantity of prey consumed can be accurately estimated. We carried out 86 feeding trials with seven grey seals (Halichoerus grypus) and 18 prey species to derive estimates of digestion coefficients (to account for partial digestion), recovery rates (to account for complete digestion), and passage rates (to estimate the time between consumption and excretion of an item). Mean digestion coefficients were greatest for sandeel (Ammodytes marinus) and then less for large gadoid, flatfish, and Trisopterus spp. otoliths; and finally squid (Loligo forbesii) beaks. Recovery rates were greatest for squid beaks and then less for large gadoid, Trisopterus spp., flatfish, and sandeel otoliths. Greater than 95% of otoliths and beaks recovered were passed within 4 days (~88 h) of consumption. The large differences in partial and complete digestion rates found among prey species reinforce the importance of obtaining robust estimates of these quantities. Results from this study are the most comprehensive and systematically obtained for any species of pinniped and will allow accurate and precise estimation of the number and size of fish represented by otoliths recovered from grey seal scat samples collected in the wild.

Effects of body size and environment on diet-tissue δ15N fractionation in fishes

Nitrogen stable isotope natural abundance data are often used in trophodynamic research. The assumed nitrogen diet-tissue fractionation (Δ δ 15N) determines conclusions about trophic level, potential food sources and ontogenetic diet shifts. Δ δ 15N is usually assumed to be 3.0–3.4‰ per trophic level and unaffected by the size or age of animals or their environment. To assess the effects of body size, experimental duration and environmental conditions on fish tissue Δ δ 15N, two populations of European sea bass ( Dicentrarchus labrax) were reared on constant diets of dab ( Limanda limanda) muscle or sandeel ( Ammodytes marinus) for 2 years under natural light and temperature regimes. Bass were sampled at approximately monthly intervals to determine Δ δ 15N for muscle, heart and liver tissue. Mean values of Δ δ 15N were 3.83‰, 3.54‰, 2.05‰ (sandeel diet) and 3.98‰, 3.32‰, 1.95‰ (dab diet) for muscle, heart and liver tissue respectively. The assumption that fractionation was independent of body mass was upheld for muscle and heart tissue, but not for liver. Time effects on muscle Δ δ 15N were explainable by a sinusoidal function with a period of 1 year and wave height ∼ 0.3‰. Time resulted in increases in heart δ 15N and decreases in liver δ 15N which were small compared to background variation, equating to 1/6 of a trophic level over 2 years, and unlikely to have great significance in ecological studies. Heart and liver δ 15N were also affected by temperature probably reflecting the metabolic functions of these tissues and their associated rates of turnover. However in heart the explanatory power of temperature appeared tied to that of time. Although the Δ δ 15N for bass muscle on both diets approached 4‰, the Δ δ 15N values from this study, when combined with those from the literature, suggest that where fish species specific data are not available, a mean Δ δ 15N for fish muscle of 3.2‰ should be applied (mean white muscle Δ δ 15N = 3.15). The literature based mean Δ δ 15N for whole fish was lower than that of white muscle suggesting that a separate Δ δ 15N (2.9‰) should be applied when sampling whole fish.

Feeding ecology of sympatric European shags Phalacrocorax aristotelis and great cormorants P. carbo in Iceland

The feeding ecology of the European shag (Phalacrocorax aristotelis) and the great cormorant (P. carbo) in Iceland was studied. These bird species may affect their marine environment, for instance, by predating on several commercially important fish species in coastal waters. The shag and cormorant diets were studied throughout the year in the period 1996–2000 by analysing the content of about 300 stomachs from each species. The shag relies heavily on sandeel (Ammodytes marinus) in the breeding season, whereas bull-rout (Myoxocephalus scorpius) and gadoids (Gadidae) become increasingly important in autumn and winter. The main food of the cormorant in all areas and seasons is the bull-rout. Depending on location and season, secondary food consists mainly of butterfish (Pholis gunnellus), gadoids and flatfishes (Pleuronectiformes). Similarity in diets of these two co-existing bird species was least in the breeding season when overlap in the birds’ distribution was greatest. The results suggest that predation by shags and cormorants could sometimes affect the stocks of the commercially important saithe (Pollachius virens) and plaice (Pleuronectes platessa) in Iceland.

Identifying sandeel Ammodytes marinus sediment habitat preferences in the marine environment

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 303:269-282 (2005) - doi:10.3354/meps303269 Identifying sandeel Ammodytes marinus sediment habitat preferences in the marine environment Gayle J. Holland*, Simon P. R. Greenstreet, Iain M. Gibb, Helen M. Fraser, Michael R. Robertson Fisheries Research Services, Marine Laboratory, PO Box 101, Victoria Road, Aberdeen AB11 9DB, UK *Email: g.holland@marlab.ac.uk ABSTRACT: Sandeel abundance and sediment particle size data from 2886 grab samples collected during 14 surveys undertaken in the Wee Bankie/Marr Bank region of the north-western North Sea between 1998 and 2003 are analysed. Odds Ratio, an analysis that compares the proportion of all samples assigned to a particular sediment category, with the proportion of samples containing sandeels assigned to the same category, reveals clear patterns of either selection for, or avoidance of, seabed habitats containing varying proportions of 8 sediment particle size categories. As the proportion of Coarse Gravel, Fine Gravel, Fine Sand, Coarse Silt, Medium Silt and Fine Silt in the seabed habitat increases, sandeels show reduced selection for and increased avoidance of the habitat. Conversely, as the proportion of Coarse Sand and Medium Sand in the sediment increases, sandeels show reduced avoidance of and increased selection for the habitat. Classification Tree and Principal Components Analysis define 8 types of seabed habitat on the basis of their sediment particle size composition that vary in sandeel occupancy rate, sandeel density and the size of sandeels that occupy the habitat. Variation in sandeel density across these 8 habitat types is primarily influenced by the silt content in the sediment. Variation in the size of sandeels occupying each habitat type is mainly dictated by the coarseness of the sediment. The value of such results for the design of grab surveys intended to monitor variation in local sandeel abundance is discussed. KEY WORDS: Ammodytes marinus · Sandeel · Habitat preference · Sediment particle size Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 303. Online publication date: November 21, 2005 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2005 Inter-Research.

Extrinsic and intrinsic determinants of winter foraging and breeding phenology in a temperate seabird

In temperate regions, winter presents animals with a number of challenges including depressed food abundance, increased daily energy requirements, higher frequency of extreme weather events and shortened day length. Overcoming these constraints is critical for overwintering survival and scheduling of future breeding of long-lived species and is likely to be state dependent, associated with intrinsic abilities such as food acquisition rates. We examined the relationship between environmental and intrinsic factors on overwintering foraging and subsequent breeding phenology of the European shag Phalacrocorax aristotelis, a diurnal marine predator. We tested a range of hypotheses relating to overwintering foraging time and location. We found that individuals greatly increased their foraging time in winter to a peak of more than 90% of available daylight at the winter solstice. The seasonal patterns of foraging time appear to be driven by a combination of light levels and weather conditions and may be linked to the availability of the shag's principal prey, the lesser sandeel Ammodytes marinus. There was no evidence that shags dispersed south in winter to increase potential foraging time. Foraging time decreased after the winter solstice and, crucially, was correlated with subsequent breeding phenology, such that individuals that spent less time foraging in February bred earlier. The relationship was much stronger in females than males, in line with their more direct control of timing of breeding. Our results demonstrate that pre-breeding intrinsic foraging ability is critical in determining breeding phenology.

The impact of marine fish predation on Atlantic salmon smolts ( Salmo salar) in the Tana estuary, North Norway, in the presence of an alternative prey, lesser sandeel ( Ammodytes marinus)

The Tana river, in northern Norway has the largest wild Atlantic salmon stock in the world. Each summer more than 1 million smolts, representing nearly 20% of the total number of Atlantic salmon smolts produced annually in Norwegian rivers, descend through the large estuary of this river. Several marine fishes feed in the estuary during the summer months, and because the descending smolts are suitable prey, predation by these species was expected to be significant for the survival of the smolts. In 2000 (mid-June to early August), nearly 500 cod ( Gadus morhua L.), saithe ( Pollachius virens L.), whiting ( Merlangius merlangus), haddock ( Melanogrammus aeglefinus) and sea trout ( Salmo trutta) were caught by hand jigging and troll fishing in the estuary and inner part of the Tana fjord before, during and after the smolt run. Based on analyses of the fish stomach contents, lesser sandeel ( Ammodytes marinus) was found to be the dominant prey, while no remains of Atlantic salmon, including otoliths, were found. We conclude that neither marine fishes nor anadromous trout are significant predators on salmon smolts in the estuary and inner fjord, probably due to a large abundance of lesser sandeel. Sandeel may thus be a key factor for the status of the Tana river as one of the world best Atlantic salmon rivers, by reducing the high smolt and post-smolt mortality as observed in several other estuaries and fjords.

The diet and trophic ecology of anglerfish Lophius piscatorius at the Shetland Islands, UK

The diet of anglerfish (Lophius piscatorius), based on the analysis of stomach contents, was investigated in the Shetland Islands. Samples were obtained during trawling for sandeel (Ammodytidae species) and demersal trawling when mainly whitefish (gadoids) are targeted. This allowed the diets of samples collected from different areas and at different times to be compared. The diets in different length groups were also compared and niche breadth investigated.A wide range of prey types, mainly fish, were recorded but the main prey was Norway pout (Trisopterus esmarkii) and lesser sandeel (Ammodytes marinus). Diet composition varied seasonally. In samples collected during whitefish trawling the occurrence of empty stomachs decreased from the first to the third quarters and generally increased with increasing anglerfish size. Empty stomachs occurred less frequently in samples collected from areas where sandeel fishing occurred compared to areas where whitefish trawling occurred.