Capelin Research Articles

Temporal dynamics of top predators interactions in the Barents Sea.

The Barents Sea system is often depicted as a simple food web in terms of number of dominant feeding links. The most conspicuous feeding link is between the Northeast Arctic cod Gadus morhua, the world's largest cod stock which is presently at a historical high level, and capelin Mallotus villosus. The system also holds diverse seabird and marine mammal communities. Previous diet studies may suggest that these top predators (cod, bird and sea mammals) compete for food particularly with respect to pelagic fish such as capelin and juvenile herring (Clupea harengus), and krill. In this paper we explored the diet of some Barents Sea top predators (cod, Black-legged kittiwake Rissa tridactyla, Common guillemot Uria aalge, and Minke whale Balaenoptera acutorostrata). We developed a GAM modelling approach to analyse the temporal variation diet composition within and between predators, to explore intra- and inter-specific interactions. The GAM models demonstrated that the seabird diet is temperature dependent while the diet of Minke whale and cod is prey dependent; Minke whale and cod diets depend on the abundance of herring and capelin, respectively. There was significant diet overlap between cod and Minke whale, and between kittiwake and guillemot. In general, the diet overlap between predators increased with changes in herring and krill abundances. The diet overlap models developed in this study may help to identify inter-specific interactions and their dynamics that potentially affect the stocks targeted by fisheries.

Seabird diet changes in northern Hudson Bay, 1981-2013, reflect the availability of schooling prey

Ongoing climate change is altering Arctic marine ecosystems with major conse- quences for food-webs. Seabirds, by foraging over large marine areas but returning regularly to their breeding colonies, provide a good medium for tracking such changes. We studied the prey delivered to nestling thick-billed murres Uria lomvia at a colony in northern Hudson Bay, Canada, over the period 1981−2013. During that period, ice conditions in the region altered substantially, with earlier break-up and clearance. This change was not gradual but mainly occurred in the mid- 1990s. Breeding chronology also advanced, but not as fast as early summer ice clearance advanced. Ice conditions strongly affected diet, presumably reflecting the change in the timing of breeding relative to ice clearance. Of the dominant species in the diet, the proportion of Arctic cod Boreogadus saida decreased and the proportion of capelin Mallotus villosus increased over the 33 yr period, even after ice effects were taken into account, suggesting a progressive and cumu- lative effect of environmental change on the marine community. Those cumulative changes were manifested primarily in the diet representation of the most frequent taxa (cod and capelin), with variation in secondary diet components being driven by the availability of the dominant taxa. Diet diversity, representing an increase in the proportion of benthic fish (stichaeids, zoarcids, pholids and sculpins) and invertebrates (squid, amphipods and crustaceans), increased when ice cover was low, and hatching was late relative to ice break-up. Chick growth rates were low when the proportion of benthic fish was high. Hence, although it appears that growth rates are influenced by diet composition, it is more likely that they reflect the availability of the dominant schooling prey species, rather than any nutritional deficiency in benthic species.

A retrospective evaluation of the Barents Sea capelin management advice

Since 1998, the assessment model framework Bifrost/Captool has been used for advice on total allowable catch for the Barents Sea capelin (Mallotus villosus) stock. However, since the management is based on a target escapement strategy, and most capelin die after spawning, viewed in retrospect, there is hardly any possibility of checking whether the forecast underpinning the quota was actually realistic. The forecast using Captool for the period from 1 October up to capelin spawning time at 1 April relies on a forecast of cod abundance during this period. This estimate of cod abundance is, in turn, based on a cod assessment from the previous spring. By rerunning the Captool model, where the cod forecast is replaced with the actual amount of cod from the cod assessment model run later in time, we show that considerably smaller annual quotas would have been advised if the true amount of cod had been known when the capelin quota was set. We discuss this fact in light of the present knowledge about recruitment success of capelin during the period. Our conclusion is that either the acoustic stock size estimates of capelin have been consistently underestimating the true stock size, the predation model overestimates the natural mortality of capelin during winter, the minimum spawning stock size considered necessary to uphold normal recruitment (Blim) built into the harvest control rule is higher than needed to secure good recruitment, or a combination of these.

The role of harp seals, fisheries and food availability in driving the dynamics of northern cod

The Atlantic cod Gadus morhua population off Newfoundland collapsed in the early 1990s due to over-exploitation, and despite marked reduction in fishing effort the stock remains depressed. Harp seal Pagophilus groenlandicus predation has been repeatedly proposed as an explanation for this lack of recovery, but other hypotheses include reduced prey availability and/or food quality (i.e. lack of capelin Mallotus villosus), as well as fisheries catches and environ- mental effects. Using a bioenergeticsallometric model, we gauged the relative contributions of these drivers on the lack of recovery and dynamics of the northern cod stock. Biomass dynamics were best explained by a combination of fisheries removals and capelin availability, whereas seal consumption was found not to be an important driver of the northern cod stock. Prey availability was linked to reduced somatic condition during the 1990s and 2000s. We discuss evidence that suggests that cod may be experiencing depensatory dynamics, but not related to a 'predator pit effect'. Our study suggests that trophic control is bottom-up, and that a depressed capelin stock could be a serious impediment for cod rebuilding.

Prey density in non-breeding areas affects adult survival of black-legged kittiwakes Rissa tridactyla

In migratory birds, environmental conditions in both breeding and non-breeding areas may affect adult survival rates and hence be significant drivers of demographic processes. In seabirds, poor knowledge of their true distribution outside the breeding season, however, has severely limited such studies. This study explored how annual adult survival rates of black-legged kittiwakes Rissa tridactyla on Hornoya in the southern Barents Sea were related to temporal vari- ation in prey densities and climatic parameters in their breeding and non-breeding areas. We used information on the kittiwakes' spatiotemporal distribution in the non-breeding season gained from year-round light-based tracking devices (geolocators) and satellite transmitters, and kittiwake annual adult survival rates gained from a multistate capture-mark-recapture analysis of a 22 yr time series of colour-ringed kittiwakes. In the post-breeding period, kittiwakes concen- trated in an area east of Svalbard, in the winter they stayed in the Grand Banks/Labrador Sea area, and in the pre-breeding period they returned to the Barents Sea. We identified 2 possible prey categories of importance for the survival of kittiwakes in these areas (sea butterflies Theco- somata in the Grand Banks/Labrador Sea area in winter and capelin Mallotus villosus in the Bar- ents Sea in the pre-breeding season) that together explained 52% of the variation in adult survival rates. Our results may have important implications for the conservation of kittiwakes, which are declining globally, because other populations use the same areas. Since they are under the influ- ence of major anthropogenic activities including fisheries, international shipping and the offshore oil and gas industry, both areas should be targeted for future management plans.

Epural bones in teleost fishes: a problem of phylogenetic homology

In the past, epural bones of teleost fishes have been labeled sequentially from anterior to posterior (e.g., epural 1, epural 2, etc.) without regard to their position relative to centra and ventral elements of the caudal fin. Recent research on caudal fin development of basal teleosts (e.g., Elops saurus and Hiodon spp.) and salmonids (e.g., Thymallus thymallus and Oncorhynchus spp.) indicates that simple numbering of epural bones is not phylogenetically meaningful. Our purpose is to demonstrate that “higher” teleost fishes show a variety of patterns of epural formation and development and that some of these may be phylogenetically informative characters. We describe the early ontogeny of the caudal fin with special reference to the epurals for selected species of teleosts. Development of epurals is detailed beginning with the earliest detection of chondrocytes in growth series of various teleosts. Epurals form after notochord flexion in the examined otomorphs, salmonids, and Mallotus villosus, as well as in Chauliodus macouni and Synodus foetens. Epurals form before flexion in the examined ctenosquamates, which allows for simple association of an epural with a ventral caudal element (i.e., hypural). After notochord flexion, epurals may reposition relative to their corresponding hypurals and this is a factor that can confuse homology assessment in adult specimens. It is recommended that epurals be named using the polyural terminology according to their position relative to ventral caudal elements early in ontogeny (e.g., epural of preural segment 1 or epural of hypural 2).

Connectivity of capelin (Mallotus villosus) between regions and spawning habitats in Newfoundland inferred from otolith chemistry

Capelin (Mallotus villosus) is an important, highly migratory marine forage fish in many northern marine ecosystems. During 2009, spawning capelin were collected from beach and nearby deeper water (15–40m) spawning habitats in two regions of Newfoundland ∼200km apart (Bellevue, Trinity Bay; Lumsden, Notre Dame Bay). We used otolith chemistry to investigate connectivity by testing if age-specific chemical signatures differed between fish from different regions or spawning habitats. Trace element concentrations (strontium, barium) did not differ between regions but did between spawning habitats. Otolith strontium and barium during the larval period (i.e. pre-metamorphosis) resulted in successfully classifying fish spawning in each habitat (71–77%). This suggests that beach and deep-water spawning fish experienced different environmental conditions during the larval period and, thus, possibly represent different behavioral types or contingents within the broader capelin population. These findings are in contrast to previous studies showing a lack of population structuring between beach and deep-water spawning fish using life history, morphometric and molecular markers (i.e. microsatellites). Fisheries management should aim to maintain this intraspecific complexity to buffer against future climate change and shifting fishing practices.

Early Development of the Caudal Fin Skeleton of Capelin,Mallotus villosus(Osmeridae)

Development of the caudal fin skeleton of capelin, Mallotus villosus, is described based on observations of cleared-and-stained specimens from a wild caught growth series ranging in size from 4.2 mm notochord length (NL) to 144 mm standard length (SL). The sequence of chondrification and ossification for each element is described and compared with that of related salmonoid and esocoid fishes. Caudal fin elements are first chondrified in specimens that are 8.9 mm NL and all elements are ossified by 52 mm SL. In general, hypaxial elements (e.g., parhypural, hypurals, hemal arches and spines of preural vertebrae) develop before epaxial elements (e.g., epurals, uroneurals, neural arches and spines of preural vertebrae). Preural centra are among the last elements to form in the caudal skeleton of M. villosus. Interestingly, preural centrum 1 does not form. The caudal fin skeleton morphology of adult M. villosus is nearly identical to that of other osmerid species, and the developmental sequence of the caudal s...

White-beaked dolphin distribution and association with prey in the Barents Sea

In the Barents Sea, strong top predator responses to repeated stock collapses of the forage fish capelin Mallotus villosus have been observed. The white-beaked dolphin Lagenorhynchus albirostris, a flexible predator with a diverse diet in other marine systems, has been associated with capelin in the Barents Sea. Yet, their distribution and foraging ecology in this ecosystem remain largely unknown. Here we use synoptically collected dolphin and prey spatial data to investigate the dolphins' distribution and spatial associations with potential prey species, including the spatial responses to a capelin stock collapse of 2003–2006 and recovery in 2007–2009. Since dolphin–prey associations may be scale-dependent, analyses were conducted at two spatial scales: (1) the habitat scale, by investigating spatial associations between species distributions averaged across years, and (2) the mesoscale, by investigating spatial associations within 50 × 50 km grid cells. At the habitat scale, dolphins overlapped with different prey species in different parts of their habitat. At the mesoscale, the dolphins were associated with blue whiting in southern Atlantic waters, while no prey associations were identified in the Polar Front area, where both capelin and gadoids are abundant. The poor dolphin–prey associations in this area could indicate dolphin distributions spatially constrained by physiological limitations, habitat productivity, or niche partitioning. No strong dolphin responses to capelin collapse and recovery were observed, indicating sufficient availability of alternative prey during the collapse.

Comparative ecology of widely distributed pelagic fish species in the North Atlantic: Implications for modelling climate and fisheries impacts

This paper reviews the current knowledge on the ecology of widely distributed pelagic fish stocks in the North Atlantic basin with emphasis on their role in the food web and the factors determining their relationship with the environment. We consider herring (Clupea harengus), mackerel (Scomber scombrus), capelin (Mallotus villosus), blue whiting (Micromesistius poutassou), and horse mackerel (Trachurus trachurus), which have distributions extending beyond the continental shelf and predominantly occur on both sides of the North Atlantic. We also include albacore (Thunnus alalunga), bluefin tuna (Thunnus thynnus), swordfish (Xiphias gladius), and blue marlin (Makaira nigricans), which, by contrast, show large-scale migrations at the basin scale. We focus on the links between life history processes and the environment, horizontal and vertical distribution, spatial structure and trophic role. Many of these species carry out extensive migrations from spawning grounds to nursery and feeding areas. Large oceanographic features such as the North Atlantic subpolar gyre play an important role in determining spatial distributions and driving variations in stock size. Given the large biomasses of especially the smaller species considered here, these stocks can exert significant top-down pressures on the food web and are important in supporting higher trophic levels. The review reveals commonalities and differences between the ecology of widely distributed pelagic fish in the NE and NW Atlantic basins, identifies knowledge gaps and modelling needs that the EURO-BASIN project attempts to address.

Lack of genetic divergence in capelin (Mallotusvillosus) spawning at beach versus subtidal habitats in coastal embayments of Newfoundland

Capelin (Mallotus villosus (Müller, 1776)), a focal forage fish in the north Atlantic, spawn on both beach and demersal (deep-water) sites throughout their circumpolar distribution. Although these habitats rarely occur in close proximity, demersal spawning sites within 4 km of beach spawning sites (subtidal) have recently been discovered in two coastal embayments in Newfoundland, Canada. The physical environment differs considerably between beach and subtidal spawning sites, creating the potential for local adaptation and genetic divergence of capelin from the two habitats, but this has never been investigated on a fine spatial scale. We use eight microsatellite loci to test for genetic divergence between capelin spawning at beach and subtidal sites within these two coastal regions in Newfoundland. We found no genetic differentiation between fish spawning at beach and subtidal sites or between the two regions. The results from this fine-scale study are in agreement with the lack of habitat-based structure reported in other studies examining beach and demersal sites separated by a larger geographic area. We suggest that instead of showing site fidelity and local adaptation, the facultative use of alternate spawning habitats may be a more successful strategy in an unpredictable environment.

Underwater behaviour of common murres foraging on capelin: influences of prey density and antipredator behaviour

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 501:279-290 (2014) - DOI: https://doi.org/10.3354/meps10696 Underwater behaviour of common murres foraging on capelin: influences of prey density and antipredator behaviour Kevin A. Crook, Gail K. Davoren* Department of Biological Sciences, University of Manitoba, Room 212B Biological Sciences Building, 50 Sifton Rd, Winnipeg, Manitoba R3T 2N2, Canada *Corresponding author: gail.davoren@ad.umanitoba.ca ABSTRACT: Diving behaviour of seabirds has been studied using data logging devices, but little is known about underwater predator–prey interactions during dives. We used stationary video cameras to investigate how the underwater foraging behaviour of common murres Uria aalge was influenced by the density and behaviour of their main prey fish, capelin Mallotus villosus, at spawning sites on the northeast Newfoundland coast during July, 2009-2012. From ~720 h of video, we analyzed 99 events where capelin and murres were observed together, ranging from 1-20 s, and 952 events where murres were observed alone, ranging from 1-14 s. Although 91% of all video footage of capelin was in high density schools, 69% of active foraging behaviour of murres (i.e. attempted contacts, approaches) was exhibited on individual capelin, compared to 24% on low density shoals and 7% on high density schools. Similarly, more murres were observed turning, a proxy of area-restricted search behaviour, when solitary and low density capelin shoals persisted for longer durations relative to when schools persisted for longer. When murres made contact with capelin (n = 16), ~70% (n = 11) were deemed successful (i.e. resulted in ingestion or ascent with fish in bill). Unsuccessful contacts resulted from fish escaping during beak manipulations to orient the fish head-first. Capelin were 7-11 times more likely to accelerate when murres displayed active versus passive (i.e. search, travel) foraging behaviours and 5-6 times more likely to accelerate in response to murre presence when in schools relative to low density shoals or solitary individuals. Overall, these results suggest that murres may increase their foraging success within areas of high prey density by preferentially searching for and targeting solitary fish that are less responsive to predators. KEY WORDS: Seabird · Common murre · Capelin · Foraging behaviour · Schooling · Antipredator · Predator–prey Full text in pdf format PreviousNextCite this article as: Crook KA, Davoren GK (2014) Underwater behaviour of common murres foraging on capelin: influences of prey density and antipredator behaviour. Mar Ecol Prog Ser 501:279-290. https://doi.org/10.3354/meps10696 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 501. Online publication date: March 31, 2014 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2014 Inter-Research.

Bottom-Up Regulation of Capelin, a Keystone Forage Species

The Northwest Atlantic marine ecosystem off Newfoundland and Labrador, Canada, has been commercially exploited for centuries. Although periodic declines in various important commercial fish stocks have been observed in this ecosystem, the most drastic changes took place in the early 1990s when the ecosystem structure changed abruptly and has not returned to its previous configuration. In the Northwest Atlantic, food web dynamics are determined largely by capelin (Mallotus villosus), the focal forage species which links primary and secondary producers with the higher trophic levels. Notwithstanding the importance of capelin, the factors that influence its population dynamics have remained elusive. We found that a regime shift and ocean climate, acting via food availability, have discernible impacts on the regulation of this population. Capelin biomass and timing of spawning were well explained by a regime shift and seasonal sea ice dynamics, a key determinant of the pelagic spring bloom. Our findings are important for the development of ecosystem approaches to fisheries management and raise questions on the potential impacts of climate change on the structure and productivity of this marine ecosystem.

LA‐ICP‐MS Analysis of Small Samples: Carbonate Reference Materials and Larval Fish Otoliths

This article proposes a methodology to analyse the composition of very small carbonate samples such as larval fish otoliths. The chemical composition of otoliths, which are carbonate structures in the inner ear, is often used to explore population dynamics in fishes. Recent advances in laser ablation‐inductively coupled plasma‐mass spectrometry have suggested its potential application to this field. In this study, analyses were performed using a 193 nm ArF Resonetics LA system, coupled to an Agilent 7700X‐ICP‐MS, with the following ablation parameters: a beam diameter of 5 μm, energy of 3 mJ, 2.7 J cm−2, laser repetition rate of 10 Hz and translation speed of 2.5 μm s−1. NIST SRM 610 glass was used as the primary calibration material. Performing this protocol, characterisation of a USGS GP‐4 reference material was achieved with suitable precision and accuracy, but the USGS MACS‐3 reference material appeared more heterogeneous under the ablation conditions tested. Calibration was performed using two different beam diameters (5 and 11 μm). Capelin (Mallotus villosus) otoliths measuring between 10 and 20 μm in diameter were tested. Even though a smaller beam diameter and lower energy were used compared with those normally employed to analyse larger otoliths, the method was successful.

Is recovery of northern cod limited by poor feeding? The capelin hypothesis revisited

AbstractThe slow recovery of the “northern” Atlantic cod (Gadus morhua) stock off Newfoundland and Labrador has been ascribed to many factors. One hypothesis is poor feeding and condition as a consequence of a decline in capelin (Mallotus villosus), their former main prey. We compared the growth and condition of cod from known inshore (Smith Sound) and offshore (Bonavista Corridor) centres of rebuilding in wild subjects versus captive subjects fed an unlimited diet of oily rich fish. Wild fish in these areas have had different diets and population performance trends since stock declines in the early 1990s. Captive cod from both areas grew at the same rates and achieved equivalent prime condition, while their wild counterparts differed, with smaller sizes, lower condition in small fish, and elevated mortality levels in the offshore centre. Environmental temperature conditions did not account for the differences in performance of wild fish. Our results suggest that fish growth and condition, and hence rebuilding in the formerly large offshore spawning components of the northern cod, have been limited by a lack of capelin in their diet. Furthermore, we suggest that these groups are unlikely to rebuild until a recovery in capelin occurs.

PFAAs in fish and other seafood products from Icelandic waters.

Perfluorinatedalkyl acids (PFAAs) are of growing concern due to possible health effects on humans. Exposure assessments indicate that fish consumption is one of the major sources of perfluorooctane sulfonate (PFOS) exposure to humans, one of the major PFASs, whereas concerns of overestimation of this exposure source have been raised. Therefore, PFAAs concentrations in fish from the North Atlantic (Icelandic fishing grounds) in the flesh of different fish species were investigated along with more detailed analyses of tissue concentrations in cod (Gadus morhua) and lumpfish (Cyclopterus lumpus). Further, fish feed was investigated as a possible source of PFAAs in aquaculture by examining fish meal as feed ingredient. No PFAAs were detected in the edible part of all fish samples, except for PFOS in pollock (Pollachius virens, 0,05 ng/g wet weight). PFOS was the only PFAA detected in the fish meal samples with the exception of PFOSA in blue whiting (Micromesistius poutassou) meal (0,45 ng/g dry weight (d.w.)), where the PFOS concentration was 1,3–13 ng/g d.w. in the capelin (Mallotus villosus) and mackerel (Scomber scombrus) meal samples. The conclusions of the study are that fish commonly consumed from the Icelandic fishing grounds are unlikely to be an important source of PFAAs exposure.

First Records of the Night Smelt,Spirinchus starksi, in the Salish Sea, Washington

Ten species of smelts (Osmeridae), including 1 introduced species, have been found in the eastern North Pacific (Love and others 2005). Of these 10 species, 5 have been recorded from the inland marine waters of the Salish Sea, including Puget Sound and the Straits of Juan de Fuca and Georgia (Hart 1973): Whitebait Smelt (Allosmerus elongatus), Surf Smelt (Hypomesus pretiosus), Capelin (Mallotus villosus), Longfin Smelt (Spirinchus thaleichthys), and Eulachon (Thaleichthys pacificus). Results from a study using molecular markers to distinguish smelt remains found in the stomach contents of fishes (Paquin and others 2014) indicated that a specimen collected from Discovery Bay, Washington, an embayment at the eastern terminus of the Strait of Juan de Fuca, was misidentified as S. thaleichthys in the online Barcode of Life Database (BOLD; Ratnasingham and Hebert 2007). Subsequent examination of the preserved specimen has confirmed its identity as Night Smelt (Spirinchus starksi) and constitutes a new record for this species in the Salish Sea. Since this discovery, additional specimens of S. starksi have been collected in the area for inclusion in this study. To confirm the identification of the Discovery Bay specimen, both morphological and nucleotide sequence data from S. starksi were compared with data from the closely related species S. thaleichthys. Whole specimens and tissue samples (frozen or preserved in ethanol) from 11 S. starksi and 5 S. thaleichthys were obtained from the Northwest Fisheries Science Center (NWFSC) and the University of Washington Fish Collection (UW). Specimens of S. starksi were collected from Discovery Bay, Washington (n 5 1), Green Point, Washington (n 5 5), and north of Monterey Bay off the California coast (n 5 5). Specimens of S. thaleichthys were collected from the Gulf of Alaska (n 5 1), San Juan Islands (n 5 1), and Puget Sound (n 5 3) (Table 1). DNA extractions were performed on fin clips using a QIAGEN DNeasy kit (QIAGEN, Valencia, CA) and the manufacturer’s animal tissue protocol. A 750 base-pair region of the mitochondrial genome, cytochrome c oxidase I (COI), was amplified using PCR with universal fish primer cocktail C_FishF1t1-C_FishR1t1 (Ivanova and others 2007). The COI gene region has been used as the barcode for biodiversity to distinguish among species, whether they are distantly related species such as mammals and insects, or closely related congenerics (Ward and others 2005, 2009; Holloway 2006; Ward and others 2009). Nucleotide sequence data were collected for 16 samples (including the misidentified specimen of S. starksi from Discovery Bay) in both forward and reverse directions with Big Dye chemistry using EXOSAP purified PCR products. Sequences were read using an ABI 3730 automated sequencer

Bottom-up limits to Newfoundland capelin (Mallotus villosus) rebuilding: the euphausiid hypothesis

Abstract Capelin (Mallotus villosus) is the key forage fish species in the Newfoundland and Labrador Shelf ecosystem. Capelin stocks collapsed in the early 1990s, concurrent with declines in “northern” Atlantic cod, Gadus morhua. Neither has fully recovered yet. Changes in growth, condition, and behaviour accompanied capelin declines on the northern Grand Banks (NGB), and remain two decades later. Feeding, growth, and condition of NGB capelin were all lower when compared with capelin from the eastern Scotian Shelf (ESS), where abundance increased following predator declines. For age 2–5 capelin of both sexes, all but one of five comparable age–sex groups were significantly larger on the ESS (e.g. age 3 females average 169 mm on the ESS and 151 mm on the NGB). Neither temperature nor density-dependence explain these differences. However, dietary differences were prominent. ESS capelin had higher total fullness indices (TFIs) than NGB fish at all sizes [mean TFIESS = 1.43 (± 1.14), mean TFINGB = 0.48 (± 0.70)]. Euphausiids (especially Thysanoessa spp.) were a main dietary component on the ESS but not on the NGB. Stable isotope analyses (δ15N and δ13C) for NGB capelin also indicated few dietary euphausiids. Trophic fractionation of δ 15N was 4.740/00, suggesting NGB capelin were food limited. Capelin recovery on the Newfoundland and Labrador Shelf appears limited by bottom-up forcing, in particular lack of euphausiid prey.

Organohalogen contaminants and total mercury in forage fish preyed upon by thick-billed murres in northern Hudson Bay

Twelve marine fish species collected from a thick-billed murre (Uria lomvia) breeding colony in northern Hudson Bay in the Canadian Arctic during 2007–2009 were analyzed for legacy organochlorines (e.g. PCBs, DDT), polybrominated diphenyl ethers (PBDEs), perfluorinated carboxylates (PFCAs) and sulfonates (PFSAs), and total mercury (Hg). No one species of prey fish had the highest levels across all contaminant groups analyzed. For the two pelagic fish species sampled, concentrations of the major organochlorine groups (e.g. Σ21PCB, ΣDDT, ΣCHL, ΣCBz), ΣPBDE, ΣPFCA and Hg were consistently higher in Arctic cod (Boreogadus saida) than in capelin (Mallotus villosus). Biomagnification factors from whole fish to thick-billed murre liver across all species were generally higher for Σ21PCB and ΣDDT. ΣPBDE did not biomagnify.

Polar cod (Boreogadus saida) and capelin (Mallotus villosus) as key species in marine food webs of the Arctic and the Barents Sea

Polar cod and capelin are key species in Arctic and sub-Arctic marine food webs, respectively, and the objective of this study is to compare and contrast the two species. Their distributions are dependent on water masses, with polar cod being associated with cold, sub-zero Arctic water, whereas capelin is distributed further south into Atlantic water masses. The distribution of polar cod is more static than that of capelin, whose distribution extends further north in warm years and fluctuates greatly based on predator–prey relationships. The species occur sympatrically in the Barents Sea, with large standing biomasses (0.5–1.5×106 t polar cod versus 3–4×106 t capelin). They overlap in distribution in the southern and eastern Barents Sea, whereas polar cod are most abundant in the icy waters of the Arctic. Both species aggregate in large schools and utilize zooplankton food sources, such as calanoid copepods. Polar cod also feed to a larger extent on amphipods, whereas capelin feed predominately on krill. Both species represent high-energy prey (lipids) for upper trophic levels. Global warming, with reduction in sea ice and increase in temperature, is expected to affect these two species differently. Polar cod will likely lose the sympagic (ice-associated) part of its life cycle and become more restricted in pelagic distribution during summer, whereas the capelin stock may expand to the north and east, although with considerable interannual fluctuations.