Capelin Mallotus Villosus Research Articles

Linking predator diet and prey availability: common murres and capelin in the Northwest Atlantic

We examined the predator-prey interaction between an apex seabird predator, the common murre Uria aalge, and capelin Mallotus villosus, the primary forage fish in the Northwest Atlantic. Sampling of parental deliveries to murre chicks was carried out during the breeding sea- son on Funk Island, located off northeast Newfoundland, Canada. Concurrent vessel surveys were conducted throughout the murre's diving and foraging range around the colony to charac- terize the prey field. Results indicated that in years when capelin was abundant in the size range consumed by murres (suitable capelin), murres delivered large and small fish in similar propor- tions, whereas they delivered more large fish when suitable capelin abundance was low. Consid- ering the relative abundances of small and large suitable capelin, these observations suggest neg- ative prey switching by the predator. Using foraging theory, we derived a model which estimates the probability of delivering a specific prey type (large or small capelin or other prey) to the chick based on prey availabilities. This quantitative model was capable of reproducing the general pat- terns in the observations. It also allowed estimating the shape of the common murre's multispecies functional response (MSFR) which indicated that this would conform to the definition of prey switching, and could then be classified as a Type 3. From an applied perspective, our results support the use of predator diets as indicators of their food base, but also highlight the need for understanding the shape of the predator's MSFR for quantitative development of these types of applications.

Diets and Trophic Linkages of Epipelagic Fish Predators in Coastal Southeast Alaska during a Period of Warm and Cold Climate Years, 1997–2011

AbstractThis study identifies important trophic links for epipelagic marine fish predators in Southeast Alaska to improve understanding of marine ecosystem dynamics in response to climate change. Fish predators can be viewed as autonomous samplers whose diets should integrate the available prey taxa commensurate with environmental conditions. We examined fish predators from annual (1997–2011) surveys conducted in May to September by the Southeast Coastal Monitoring (SECM) project of Auke Bay Laboratories in the marine waters of Southeast Alaska. This project has emphasized long‐term monitoring of strait and coastal marine habitats used by juvenile Pacific salmon Oncorhynchus spp. and associated epipelagic fishes to understand how environmental variation affects the sustainability of salmon resources. From 1,295 surface trawl hauls, trophic links were identified for 2,473 fish representing 19 predator species, principally adult and immature salmon, immature walleye pollock Theragra chalcogramma, and spiny dogfish Squalus acanthias. The most common fish prey consumed were fish larvae, juvenile salmon, Pacific herring Clupea pallasii, capelin Mallotus villosus, walleye pollock, lanternfishes (Myctophidae), and Pacific sand lance Ammodytes hexapterus, whereas the most common invertebrate prey consumed were euphausiids, decapod larvae, pteropods, and amphipods. This study describes the degree of piscivory, incidence of juvenile salmon prey, and frequency and weight composition of prey in the diets of epipelagic fish predators, but it did not clearly detect an effect of warm‐versus‐cold climate years on the diets of key planktivorous or piscivorous predators over the 15‐year time series. Identifying the persistence of trophic links in epipelagic waters over time is important because climate‐related changes in the upper water column have the potential to impact Southeast Alaska marine ecosystem dynamics and the productivity of important regional fisheries by altering key prey resources and trophic interactions.Received December 2, 2011; accepted May 9, 2012

Ontogenetic Diet Comparison of Atlantic Cod and White Hake Occurring at Historically Low Population Abundances

AbstractAbundances of Atlantic cod Gadus morhua and white hake Urophycis tenuis have dropped to historically low levels in the southern Gulf of St. Lawrence. Stomach samples were collected during late summer 2001 and 2002 to compare ontogenetic diet patterns at a time when food presumably was not limiting. White hake had a narrow diet and showed an abrupt ontogenetic diet change: fish less than 35 cm total length (TL) consumed benthic invertebrates (sevenspine bay shrimp Crangon septemspinosa, gammarid amphipods, or polychaetes), while those at least 35 cm TL preyed mainly on Atlantic herring Clupea harengus. Atlantic cod had a broad diet initially dominated by benthic and pelagic invertebrates (Arctic argid Argis dentata, Aesop shrimp Pandalus montagui, Eualus spp., mysids, northern propeller clams Cyrtodaria siliqua, and polychaetes). Fish (mainly Atlantic herring, capelin Mallotus villosus, and small demersal species) were gradually incorporated into the Atlantic cod diet but did not comprise more than 50% of prey biomass until the cod reached a length of 50–60 cm TL. The incidence of cannibalism was low for both fishes. Diet overlap was low between all sizes of Atlantic cod and white hake but was high between adjacent size‐classes of Atlantic cod and for all size‐classes of white hake greater than 35 cm TL (where Atlantic herring comprised more than 70% of prey biomass).

Climate impacts on feeding and condition of capelin Mallotus villosus in the Barents Sea: evidence and mechanisms from a 30 year data set

Capelin Mallotus villosus is one of the most abundant fish species in the Barents Sea and is a critical link between zooplankton and commercial species such as Atlantic cod. Climatic condi- tions influence the population structure, feeding, and biological condition of capelin by affecting their distribution and that of their zooplankton prey. We sampled more than 1500 stomachs of capelin from 1978, 2002, 2003, 2006, and 2007 spanning years with cold, moderate, and warm climatic conditions, and examined the distribution of their major prey items: euphausiids and Calanus copepods. Capelin distribution is broader during warmer years, especially in the north and northeast. Copepods and euphausiids dominated the diets of capelin, but hyperiid amphipods and chaetognaths were also important. Diet and stomach fullness showed significant geographic variability within the Barents Sea, and varied among years depending on whether the climatic conditions were warmer or colder than the long-term average. Abundance of inter- and intraspecific competitors appears to affect diet, feeding intensity, and fat content. Fat content is an important indicator of capelin reproductive po- tential and their food value for predators, and was highest in northeastern regions and strongly influenced by capelin diet. Analyses of these 5 years of data plus 10 more years from previously pub- lished studies indicate the importance of climate drivers for determining fat content. Mechanisms are complex, however, and many factors directly and indirectly influence condition of this critical species in the Barents Sea ecosystem.

Greenland halibut diet in the Northwest Atlantic from 1978 to 2003 as an indicator of ecosystem change

The Northwest Atlantic marine community underwent dramatic changes during the last 30 years, including the collapse of many groundfish stocks and an increase in shrimp populations. Greenland halibut Reinhardtius hippoglossoides is an important commercial species and one of the top fish predators in this system. It is a large, wide-ranging flatfish that is found at depths up to 2200 m and it has an opportunistic diet which makes it a potential candidate for an ecosystem indicator. Analysis of stomach contents of Greenland halibut between 1978 and 2003 indicates that diet composition reflects the major changes in community structure. Over the entire period there was a clear increase in the importance of invertebrates, particularly after 1992. This change was associated with a higher importance of Pandalus shrimp and Gonatus squid and a protracted reliance on zooplankton by predators under 25 cm length. Capelin Mallotus villosus was the dominant prey between 1978 and 1992 for predators in the 12–63 cm range, but its importance dropped off drastically in the mid 1990s. Levels of main prey in the diet of Greenland halibut correlated well with fishery-independent surveys. Greenland halibut sample capelin well, compared to bottom trawl surveys and acoustic surveys. Greenland halibut consumed small shrimp which are not routinely caught by surveys and may be important in deriving information on year classes and growth of shrimp. Our results suggest that Greenland halibut's diet is a useful tracker of ecosystem change.

Influence of prey behaviour and other predators on the foraging activities of a marine avian predator in a Low Arctic ecosystem

Air-breathing marine predators can expend considerable time and energy searching for patchily distributed prey and, thus, likely employ varying foraging strategies to minimize these costs. We studied the diurnal foraging patterns of the northern gannet Sula bassana along with the distrib- utional patterns of its main prey, capelin Mallotus villosus, off the NE Newfoundland coast from 1999 to 2005. We explored whether gannets minimize searching costs for near-surface ( 70% of gannet diets. Gannets aggregated in shallow areas (<30 m) where spatially and temporally persistent shoals of capelin were accessible through daylight, but were also found in deeper water where capelin were inaccessible. Gannet diving activity was only recorded during daylight, and although activity peaked at the start and end of daylight, most dives occurred when capelin had migrated to inaccessible depths. Gannets were more tightly associ- ated with whales than with near-surface capelin shoals, suggesting that they may successfully track capelin by cueing to the foraging activities of whales. A mixed strategy of memory-based and local enhancement foraging tactics appear to play important roles in minimizing the effort required to access prey.

Growth and survival of Icelandic capelin Mallotus villosus larvae

Otolith increment analysis was used to reconstruct daily growth of 2 year-classes of capelin larvae, from hatch until 4 mo of age. Larvae were sampled on the continental shelf around Iceland during August 2001 and 2002. Mean hatch dates were not different between years, but hatching started earlier and lasted longer in 2002. Somatic growth was significantly faster in 2001 (0.4 mm d -1 ) than 2002 (0.3 mm d -1 ). Larvae shared a common otolith growth trajectory both within and between year-classes, described by 3 different growth phases: an initial latency period followed by a period of accelerating growth before reaching an asymptote. Daily otolith growth of the 2001 year-class was significantly faster in the age ranges 21 to 50 d and 61 to 100 d, with larvae having an average asymptotic growth of 2.1 µm d -1 in 2001 and 2.0 µm d -1 in 2002. Average daily otolith growth for calendar day increased from June to mid-July each year, decreased until early August, and then increased again. Average sea surface temperature on the capelin nursery ground increased from March to August, and was higher in 2001 than 2002. The decrease in growth during increasing ambi- ent temperature indicates that other environmental factors have significant effects on seasonal growth. Survival rate of larvae from hatch until August was 3 times higher in 2001 when larvae grew faster. Faster growth and higher survival during the first 4 mo of the 2001 year-class did not carry over to higher absolute recruitment at maturity.

Carbon transfer in a herbivore- and microbial loop-dominated pelagic food webs in the southern Barents Sea during spring and summer

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 398:93-107 (2010) - DOI: https://doi.org/10.3354/meps08335 Carbon transfer in a herbivore- and microbial loop-dominated pelagic food webs in the southern Barents Sea during spring and summer Frederik De Laender*, Dick Van Oevelen, Karline Soetaert, Jack J. Middelburg NIOO-KNAW, Centre for Estuarine and Marine Ecology, Korringaweg 7, PO Box 140, 4401 Yerseke, The Netherlands *Email: frederik.delaender@ugent.be ABSTRACT: We compared carbon budgets between a herbivore-dominated and a microbial loop-dominated food web and examined the implications of food web structure for fish production. We used the southern Barents Sea as a case study and inverse modelling as an analysis method. In spring, when the system was dominated by the herbivorous web, the diet of protozoa consisted of similar amounts of bacteria and phytoplankton. Copepods showed no clear preference for protozoa. Cod Gadus morhua, a predatory fish preying on copepods and on copepod-feeding capelin Mallotus villosus in spring, moderately depended on the microbial loop in spring, as only 20 to 60% of its food passed through the microbial loop. In summer, when the food web was dominated by the microbial loop, protozoa ingested 4 times more bacteria than phytoplankton and protozoa formed 80 to 90% of the copepod diet. Because of this strong link between the microbial loop and copepods (the young cod’s main prey item) young cod (<3 yr) depended more on the microbial loop than on any other food web compartment, as >60% of its food passed through the microbial loop in summer. Adult cod (≤3 yr) relied far less on the microbial loop than young cod as it preyed on strictly herbivorous krill in summer. Food web efficiency for fish production was comparable between seasons (~5 × 10–4) and 2 times higher in summer (5 × 10–2) than in spring for copepod production. KEY WORDS: Food web · Microbial loop · Protozoa · Copepods · Gadus morhua Full text in pdf format Supplementary Material PreviousNextCite this article as: De Laender F, Van Oevelen D, Soetaert K, Middelburg JJ (2010) Carbon transfer in a herbivore- and microbial loop-dominated pelagic food webs in the southern Barents Sea during spring and summer. Mar Ecol Prog Ser 398:93-107. https://doi.org/10.3354/meps08335Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 398. Online publication date: January 05, 2010 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2010 Inter-Research.

Ecology of small neritic fishes in the western Gulf of Alaska. I. Geographic distribution in relation to prey density and the physical 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 392:223-237 (2009) - DOI: https://doi.org/10.3354/meps08160 Ecology of small neritic fishes in the western Gulf of Alaska. I. Geographic distribution in relation to prey density and the physical environment Matthew T. Wilson* Alaska Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, 7600 Sand Point Way NE, Seattle, Washington 98115, USA *Email: matt.wilson@noaa.gov ABSTRACT: Physical heterogeneity affects the geographic structure of coastal ocean ecosystems by influencing the spatial distribution of zooplankton and their nektonic predators. This was examined in the western Gulf of Alaska (GOA) during late summer (2000, 2001, and 2003) when seasonal increases in the Alaska Coastal Current flow and additions of Age-0 fishes to the nektonic community of small neritic fishes coincided with declining zooplankton abundance. The 48-site sampling grid was divided into 5 meso-scale areas based on physical condition (temperature, salinity, net current velocity). Larval crabs and fishes, and krill were the only zooplankton taxa for which the population density consistently differed by area regardless of diel period (day, night) or year. Larval crabs and fishes concentrated near shore in warm, low-salinity water. Krill concentrated in high-flow areas, which, over the shelf, were associated with sea valleys. Dominant fishes were walleye pollock Theragra chalcogramma, capelin Mallotus villosus, and eulachon Thaleichthys pacificus. Few fish occurred beyond the shelf in the cold, swift-flowing Alaskan Stream boundary current. Over the shelf, Age-1+ walleye pollock and eulachon aggregated with krill in high-flow areas. Smaller fishes (Age-0 walleye pollock and capelin) were more variably distributed, and were not well associated with taxon-specific zooplankton densities. Thus, relatively high flow in proximity to sea valleys was associated with concentrations of krill and fishes that presumably were able to efficiently forage on krill in high-flow areas. The year-to-year consistency in patterns is a noteworthy indication that geographic structure in the coastal GOA ecosystem may resist climate forcing. KEY WORDS: Walleye pollock · Capelin · Eulachon · Zooplankton · Population density · Body size Full text in pdf format PreviousNextCite this article as: Wilson MT (2009) Ecology of small neritic fishes in the western Gulf of Alaska. I. Geographic distribution in relation to prey density and the physical environment. Mar Ecol Prog Ser 392:223-237. https://doi.org/10.3354/meps08160Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 392. Online publication date: October 19, 2009 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2009 Inter-Research.

Ecology of small neritic fishes in the western Gulf of Alaska. II. Consumption of krill in relation to krill standing stock and the physical environment

Krill (Euphausiacea) is a patchily distributed taxon whose availability may limit neritic fishes in temperate oceans. In the western Gulf of Alaska, krill-fish aggregations were associated with high-flow areas over the shelf. We examined fish impacts on krill standing stocks in areas of dif- ferent temperature, salinity, and net current velocity. Samples were collected during September 2000, 2001, and 2003 over a 48-site grid within a known walleye pollock nursery. Krill were a dietary staple of the dominant fishes: walleye pollock Theragra chalcogramma, capelin Mallotus villosus, and eulachon Thaleichthys pacificus, but their proportion in diets varied by predator species and predator length. Predators daily consumed ≤12% of standing stocks; thus, krill appeared to be amply available. However, the krill consumed by eulachon and large (>120 mm) walleye pollock were, on average, large compared to krill in plankton samples; therefore, standing stock sizes might have been overestimated by including small krill. A compensatory response in consumption occurred dur- ing 2001 in proximity to the Shelikof sea valley due to increased per capita predation rates and local concentration of Age-1+ walleye pollock and eulachon. High abundance of krill in 2001 was associ- ated with high ocean current flow. No compensatory response was observed where local standing stocks were dominated by small krill. Thus, apparent bottom-up influences of ocean currents on krill abundance in neritic areas can be partly compensated by localized top-down predation from nek- tonic fishes having prey size preferences that match available prey sizes.

Economic impacts on key Barents Sea fisheries arising from changes in the strength of the Atlantic thermohaline circulation

A bioeconomic model of key fisheries of the Barents Sea is run with scenarios generated by an earth system model of intermediate complexity to assess how the Barents Sea fisheries of cod (Gadus morhua) and capelin (Mallotus villosus) are affected by changes in the Atlantic thermohaline circulation (THC) arising from anthropogenic climate change. Changes in hydrographic conditions have an impact on recruitment success and survival rates, which constitute a lasting effect on the stocks. The economic development of the fisheries is determined for the 21st century, considering a purely stock size based and a coupled stock size-hydrography based harvesting strategy. Results show that a substantial weakening of the THC leads to impaired cod stock development, causing the associated fishery to become unprofitable in the long run. Simultaneous improvements in capelin stock development help the capelin fishery, but are insufficient to offset the losses incurred by the cod fishery. A comparison of harvest strategies reveals that in times of high variability in stock development, coupled stock size-hydrography based management leads to more stable economic results of these fisheries than the stock size based fishing strategy.

Temperature and salinity conditions in a sub-Arctic intertidal spawning habitat for capelin

Temperature and salinity were logged every 35 min during 52 days in April and May at a well-known spawning beach for capelin (Mallotus villosus) in Balsfjord, northern Norway. Two loggers were located either on or within the gravel of the spawning ground, whereas a reference logger was deployed 1 m below the lowest astronomical tide (LAT). The temperature on the gravel ranged from −5.3 to 26.7°C with an overall mean of 6.2±3.6°C. The diurnal temperature fluctuations (i.e. the difference between the daily maximum and minimum temperature, ▵T) varied between 3.9 and 20.8°C. Sub-zero temperatures were registered neither within the gravel nor at the reference site and the overall temperature for these loggers fluctuated considerably less than on the gravel. The salinity on the surface of the gravel fluctuated markedly (5.2–28.6 psu) and contrasted the salinities registered within the gravel (1.8–6.3 psu) and below LAT (14.0–30.0 psu). The results suggest that beach-spawned capelin eggs have evolved an array of biological adaptations to survive the unpredictable physical conditions of an intertidal habitat.

The foraging decisions of a central place foraging seabird in response to fluctuations in local prey conditions

AbstractDuring reproduction, seabirds need to balance the demands of self‐ and offspring‐provisioning within the constraints imposed by central place foraging. To assess behavioral adjustments and tolerances to these constraints, we studied the feeding tactics and reproductive success of common murres (also known as common guillemots) Uria aalge, at their largest and most offshore colony (Funk Island) where parents travel long distances to deliver a single capelin Mallotus villosus to their chicks. We assessed changes in the distance murres traveled from the colony, their proximate foraging locations and prey size choice during two successive years in which capelin exhibited an order of magnitude decrease in density and a shift from aggregated (2004) to dispersed (2005) distributions. When capelin availability was low (2005), parental murres increased their maximum foraging distances by 35% (60 to 81 km) and delivered significantly larger capelin to chicks, as predicted by central place foraging theory. Murres preferred large (&gt;140 mm) relative to small capelin (100–140 mm) in both years, but unexpectedly this preference increased as the relative density of large capelin decreased. We conclude that single prey‐loading murres target larger capelin during long foraging trips as parents are ‘forced’ to select the best prey for their offspring. Low fledgling masses suggest also that increased foraging time when capelin is scarce may come at a cost to the chicks (i.e. fewer meals per day). Murres at this colony may be functioning near physiological limits above which further or sustained adjustments in foraging effort could compromise the life‐time reproductive success of this long‐lived seabird.

Can Kittiwakes smell? Experimental evidence in a Larid species

Birds have long been thought to have a poor sense ofsmell, although they have the proper anatomical andneurological structures for detecting olfactory cues(Roper 1999). However, in the past decade several birdspecies have been shown to use smell in various contexts,such as foraging (Nevitt et al. 1995), navigation (Wallraff2004), selection of nest materials (Petit et al. 2002,Gwinner & Berger 2008), nest location (Bonadonna B Banana group, n = 27), meltwater fromfrozen Capelin Mallotus villosus (Fish group, n = 26), orfresh water (Control group, n = 27). This experimentwas carried out during the second half of the incubationperiod (14–20 June).Leaves were used as the method of odour deliverybecause being common on Middleton they were lesslikely to elicit a reaction relative to an entirely novelobject. Cotton swabs used to spread the scent on leaves

Flexible foraging tactics by a large opportunistic seabird preying on forage- and large pelagic fishes

Generalist and opportunistic marine predators use flexible foraging behaviour to exploit prey bases that change in diversity and spatial and temporal distributions. Behavioural flexibility is constrained by characteristics such as individual cognitive and physical capabilities, age, reproduc- tive condition and central place foraging. To assess flexibility in the foraging tactics of a marine bird, we investigated the diets and foraging behaviour of the largest seabird predator in the North Atlantic Ocean. Northern gannets Sula bassana exploit a broad spectrum of pelagic prey that range in mass by more than 2 orders of magnitude. We investigated their foraging activity at their largest offshore colony in the western Atlantic Ocean during 1998 to 2002, when they preyed primarily on shoals of spawning and post-spawning capelin Mallotus villosus, a small forage fish (~15 g), and also on a much larger pelagic fish, post-smolt Atlantic salmon Salmo salar (~200 g). Inter-annual dietary varia- tion is associated with gannet and prey fish distributions. Landings of capelin at the colony by gan- nets were correlated with returns of larger foraging flocks from inshore, whereas landings of Atlantic salmon were associated with smaller flocks returning from offshore. Maximum foraging trip dis- tances ranged from 20 to 200 km and averaged 57 ± 12 (SE) km, consistent with distances to inshore capelin aggregations. When capelin abundance was low (in 2002), more gannets foraged offshore, preyed on large pelagic fishes (mostly Atlantic salmon) and exhibited the greatest dietary diversity. Though the outbound portions of foraging trips were more sinuous than inbound routes, individual gannets exhibited general fidelity to foraging sites. These large avian predators used flexible forag- ing tactics to adjust to changing prey conditions and generate longer-term strategies to take advan- tage of diverse trophic interactions over a range of ocean ecosystems.

Going deep: common murres dive into frigid water for aggregated, persistent and slow-moving capelin

Owing to the necessity of delivering food to offspring at colonies, breeding seabirds are highly constrained in their foraging options. To minimize constraints imposed by central-place foraging and to optimize foraging behavior, many species exhibit flexible foraging tactics. Here we document the behavioral flexibility of pursuit-diving common murres Uria aalge when foraging on female capelin Mallotus villosus in the northwest Atlantic. Quite unexpectedly, being visual foragers, we found that common murres dived throughout the day and night. Twenty-one percent of recorded dives (n = 272 of 1,308 dives) were deep (≥50 m; maximum depth = 152 m, maximum duration = 212 s), bringing murres into sub-0°C water in the Cold Intermediate Layer (CIL; 40–180 m) of the Labrador Current. Deep dives occurred almost exclusively during the day when murres would have encountered spatially predictable aggregations of capelin between 100 and 150 m in the water column. Temperatures within the CIL shaped trophic interactions and involved trade-offs for both predators and prey. Sub-0°C temperatures limit a fish’s ability to escape from endothermic predators by reducing burst/escape speeds and also lengthening the time needed to recover from burst-type activity. Thus, while deep diving may be energetically costly, it likely increases certainty of prey capture. Decreased murre foraging efficiency at night (indicated by an increase in the number of dives per bout) reflects both lower light conditions and changing prey behavior, as capelin migrate to warmer surface waters at night where their potential to escape from avian predators could increase.

Winter diets of auks in Icelandic coastal waters

Recent studies suggest that a substantial proportion of the large Icelandic breeding populations of Razorbills Alca torda and Common Guillemots Uria aalge overwinter locally. Winter diets of these two auk species and Brünnich's Guillemots U. lomvia were studied during 1982–1983 in coastal waters in northern and south-western Iceland. Razorbills and Common Guillemots were usually found together in both areas. Brünnich's Guillemots were available from northern Iceland in late winter. A mixture of 0-group and older sandeel Ammodytes marinus dominated diets of Razorbills and Common Guillemots in south-west Iceland, with 0-group herring Clupea harengus of some importance to Razorbills in mid-winter. In northern Iceland diets consisted mainly of 0-group capelin Mallotus villosus and euphausiids for Razorbills, 0-group capelin and 0-group and second winter herring for Common Guillemots, and euphausiids and amphipods for Brünnich's Guillemots. The results thus indicate a geographical difference in diets between areas. Diets of Razorbills and Common Guillemots were similar but differed from that of Brünnich's Guillemots. Seasonal changes in auk diets were slight, with the notable exception of euphausiids replacing fish in late winter in the north. The results concur with studies on summer diets of these species where it was found that sandeel dominated auk diets off southern Iceland and capelin off the north coast.

Trophic relations of capelin Mallotus villosus and polar cod Boreogadus saida in the Barents Sea as a factor of impact on the ecosystem

Abstract The purpose of the study is to assess the role of trophic relations of the dominant pelagic fishes capelin and polar cod in the Barents Sea with regard to distribution and accessibility as prey for the Atlantic cod in warm years (2004–2005). Unlike in the previous period, during these warm years a dramatic increase of the polar cod population resulted in a northwards expansion of the feeding grounds where overlapping of polar cod and capelin concentrations was observed. This caused an increased competition for copepods, which are the main food item for young fish. In the areas dominated by polar cod the shortage of copepods forced immature capelin to switch to the chaetognath Sagitta , which affected their fatness negatively. During the warm years the feeding grounds of Atlantic cod also expanded, to a large degree caused by the shortage of their main food, the capelin. In 2004–2005 the cod formed feeding concentrations in the north and northeast Barents Sea where they fed on the capelin. In this area the consumption of polar cod by cod increased, and in some local areas the polar cod practically replaced the capelin in the diet of cod. In general polar cod in the diet of Atlantic cod were more important in the northern than in the southern part of the Barents Sea. The fatness of cod was extremely low during the whole spring–summer period (until August), and after the feeding period the fatness index of the Atlantic cod became lower than the average long-term autumn value.

Influence of environmental changes in the north-western Atlantic Ocean on a parasite, Echinorhynchus gadi (Acanthocephala) of Atlantic cod (Gadus morhua) occurring off coastal Labrador, Canada

A study was conducted to determine the influence of environmental change on an endoparasite, Echinorhynchus gadi (Acanthocephala) of Atlantic cod (Gadus morhua) over a 30-year period off the coast of Labrador in the north-western Atlantic, North Atlantic Fisheries Organization subareas 2J-3K. Cod, once an abundant fish species that had been commercially exploited for many decades, declined precipitously during the mid-1980s onwards. This decline was attributed to climatic changes that affected the entire food chain from zooplankton to fish, sea birds and marine mammals. A monitoring programme was introduced, sampling cod by otter trawling using research vessels. The fish, after capture, were frozen at - 20 degrees C, subsequently thawed and the digestive tract removed and examined for the parasite in 2006. Data from samples taken in 1976, 1980-81, 1986, 1990, 2000 and 2003 were compared statistically with those collected in 2006. The results indicate a decline in the prevalence and mean abundance of E. gadi in 1986 with a minimum in 2000 but increasing gradually in 2003 and 2006. These changes were coincident initially with a decline of oceanic temperature and the entire food web, including capelin (Mallotus villosus), a preferred prey of cod and primary source of E. gadi. The increase in prevalence and mean abundance of the parasite in 2006 were associated with an increase of oceanic temperature and the return of small schools of capelin to offshore areas. Cod older than 4 years harboured a greater abundance of E. gadi than younger fish, while no difference was observed between the sexes. The results suggest that the abundance of E. gadi can be useful as a bioindicator of environmental changes in the north-western Atlantic.

Mitochondrial DNA variation in Pacific capelin (Mallotus villosus catervarius) from the Sea of Okhotsk, inferred from PCR-RFLP analysis

Four population samples of Pacific capelin Mallotus villosus catervarius (Pennant, 1784) from geographically distant localities in the Sea of Okhotsk, Tauy Bay and the eastern coast of the Sakhalin Island, were examined using PCR-RFLP analysis of three mitochondrial DNA regions (A8/A6/COIII/ND3, ND3/ND4L/ND4, and ND5/ND6). The nucleotide divergence of mtDNA sequences among the samples, as well as the analysis of geographic heterogeneity of the haplotype frequencies and quantitative estimation of genetic differentiation performed by means of AMOVA, showed that the samples examined belonged to one panmictic population. Genealogic analysis of the mtDNA variation structure was carried out. It was demonstrated that the high level of haplotype diversity (0.9639 +/- 0.00015) along with the low level of nucleotide diversity (0.003818 +/- 0.0000003) pointed to the exponential rate of population growth of the capelin from the Sea of Okhotsk, which rather recently in its evolutionary history faced the bottleneck effect.