Capelin Mallotus Research Articles

Stable isotope analysis reveals that humpback whales (Megaptera novaeangliae) primarily consume capelin (Mallotus villosus) in coastal Newfoundland, Canada

On the Newfoundland (Canada) foraging ground, humpback whales (Megaptera novaeangliae (Borowski, 1781)) are found associated with a dominant forage fish species, capelin (Mallotus villosus (Müller, 1776)), that experienced a population collapse in the early 1990s and has not recovered. Our primary goal was to reconstruct dietary proportions of humpback whales on their summer foraging grounds off the northeast coast of Newfoundland during July–August 2016 and 2017 using a Bayesian stable isotope mixing model (MixSiar). Modelled dietary proportions were similar in both years, with capelin comprising ∼90% of the diet. However, both δ13C and δ15N in humpback whale skin differed significantly between years, resulting in minimal isotopic niche overlap (9%). Lipid-extracted and nonlipid-extracted skin samples were used to develop a lipid normalization equation: Δ13C = –3.184 + 1.011(C:N). Overall, findings suggest that capelin is the primary prey type of humpback whales in coastal Newfoundland, despite the continued collapsed state of the capelin population. Findings also reiterate that dietary reconstruction from stable isotope analysis of cetacean skin can be misinterpreted without concurrently sampled isotopic ratios of potential prey types.

IDENTIFICATION OF CONTAMINATION OF SALMON MEAT BY DNA FROM BACTERIA OF THE PSEUDOMONAS FLUORESCENS GROUP IN THE IMPLEMENTATION OF THE DNA BARCODING OF PRODUCTS OF JAPANESE CUISINE

DNA barcoding as a tool for genetic certification and identification of taxonomic membership of organisms has recently become very popular. We have applied DNA barcoding method for taxonomic identification of fish ingredients (salmon, tuna, flying fish roe, shark) in product of Japanese cuisine. We have analyzed 27 samples from 6 retail outlets and 3 restaurants of the city of Voronezh. It was found that for products designated as containing “salmon” in all selected outlets were used as a fillet of Atlantic salmon (Salmo salar), which is considerably less valuable than Pacific salmon. Results of DNA barcoding showed that one of the samples of «salmon» was in fact, yellowfin tuna, whereas one sample of “tuna” was a fillet of Atlantic salmon. However in general, the “salmon” and “tuna” samples were substituted infrequently. Analysis of “flying fish roe” samples revealed that only one sample from 6 was really Fourwing flyingfish (Hirundichthys affinis). The remaining samples were identified as DNA of capelin (Mallotus villosus). By analyzing the “double” sequences in 2 samples, we have found that two samples of «flying fish roe» were mixtures of Fourwing flyingfish roe and capelin roe. A sample labeled “shark” was identified as Mozambique tilapia. This species is a freshwater fish. Bacterium Pseudomonas fluorescens was identified in one of the “salmon” samples. Analysis of “double” sequences of “salmon” samples revealed presence of P. fluorescens DNA. Analysis of salmon meat with the use of species-specific primers for this bacterium revealed contamination of all samples by P. fluorescens. This bacterium causes the disease in salmon and can be harmful to patients with compromised immune systems. Primers used for DNA barcoding were shown to have high homology to DNA of bacterial group P. fluorescens.

The formation of foraging aggregations in a highly social seabird, the thick-billed murre (Uria lomvia), at small and large scales

Analyzing how animals are distributed in space and time is important to understand the behavioural interactions that underlie population dynamics, especially for highly social species. Thick-billed murres (Uria lomvia) breed in some of the largest and densest colonies of any seabird. Although this bird is known to aggregate at sea, little is known about when, where, and why the birds form aggregations. We examined the spatial and temporal patterns of foraging aggregations during the breeding season through various scales via (1) measurement of the synchrony of arrivals of adults feeding their chicks at the colony, and (2) use of both GPS and camera loggers attached on the birds to examine the proximity of birds at sea. Adult arrivals at the colony were synchronised when bringing capelin (Mallotus villosus), a gregarious pelagic fish, but not when bringing sculpin (primarily Triglops spp.), a solitary benthic fish. Camera loggers revealed very close encounters of foraging conspecific (< 4 m), much closer than what was predicted by chance, despite low prey densities. GPS loggers also showed diffuse at-sea aggregations with minimal distances closer than expected by chance. However, those study birds did not typically share foraging trajectories. We suggest that, at smaller scales, murres form tight groups to increase searching efficiency underwater. At larger scales, murre aggregations are most likely a result of foraging individuals converging in the more prolific areas, either by independently encountering prey hotspots, or by cueing on other foraging birds.

Latitudinal dependence of body condition, growth rate, and stable isotopes of juvenile capelin (Mallotus villosus) in the Bering and Chukchi Seas

Capelin occupy a key trophic role and have a broad latitudinal distribution in the northeastern Pacific and Arctic Oceans. Understanding their adaptation to a range of conditions is important to predicting how they will respond to climate change. To quantify the variation in body condition in different physical environments, we measured energy density, RNA/DNA ratios, carbon and nitrogen stable isotope ratios in 62 juvenile capelin along the Western Alaskan coast from Bristol Bay to Point Barrow ranging across approximately 14° of latitude. Energy density correlated positively with latitude, whereas RNA/DNA (instantaneous growth index) was strongly correlated with sea surface temperature, indicating that optimal growth of capelin was achieved at ~9 °C, followed by rapid decreases in RNA/DNA ratios at higher temperatures. δ13C and δ15N had strong, inverse nonlinear relationships with latitude. Depletion of δ13C seen in capelin North of Bristol Bay may be related to the incorporation of allochthonous basal resources into the diets of juvenile capelin from nearby riverine inputs. Observed enrichment of δ15N North of Bristol Bay is likely to be related to incorporation of higher trophic level prey items. Given inverse relationship between δ13C and δ15N, these prey items are likely available due to the increased diversity of basal resources from increased inputs of riverine organic material.

Seasonal variation in cod feeding and growth in a changing sea

Seasonal variation in feeding and growth of 3- to 9-year-old Atlantic cod (Gadus morhua) was studied using data from joint Norwegian–Russian surveys in January–March (winter survey) and September–August (ecosystem survey) in the Barents Sea. The study encompassed the warmest period on record, with large cod stock and both low (2004–2007) and high (2008–2013) abundance of Barents Sea cod’s main prey, capelin (Mallotus villosus). Feeding on capelin was most important in winter. Energy acquisition (kJ·day−1) was higher during fall, but in years with high capelin abundance the seasonal difference was smaller. There was no difference in energy acquisition in years with high and low capelin abundance, underpinning recent findings on decoupling between capelin abundance and cod demography. Compensatory feeding on alternative prey takes place in fall, but not in winter. These findings were consistent across age groups. The results found for energy acquisition was mirrored in growth; in years with low capelin abundance, there was a seasonal difference in growth, whereas in years with high capelin abundance, the difference was absent.

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

Physical characteristics of persistent deep-water spawning sites of capelin: Importance for delimiting critical marine habitats

In coastal Newfoundland, high abundances of top predators aggregate (biological hotspots) over deep-water (demersal) spawning sites of capelin (Mallotus villosus), the focal forage fish on which most top predators rely for prey. We explore the mechanisms underlying the spatial persistence of hotspot formation by investigating physical characteristics associated with the persistent use of demersal spawning sites of capelin on the northeast Newfoundland coast from 2003 to 2010. The continued presence of suitable spawning sediment (0.5–16 mm) in permanent bathymetric depressions was a key determinant of site use persistence, whereas minimum temperature (~2°C) influenced the use of sites with suitable sediments. We suggest that biological hotspots associated with demersal spawning sites with similar physical characteristics could be used to delineate critical marine habitats for protection throughout the circumpolar distribution of this key forage fish species.

Feeding ecology of capelin (Mallotus villosus Müller) in West Greenland waters

Capelin (Mallotus villosus Muller) is a key pelagic mediator of energy from lower to higher trophic levels in arctic waters. This is also the case in Greenland waters, but little is known of its feeding behaviour in this region. By analysing stable nitrogen isotopes and stomach content of capelin collected along 1500 km of the Greenland west coast, this study aims to provide knowledge on capelin feeding ecology and the role that diet composition and biomass may have in generating the observed latitudinal growth differences in Greenland capelin. In total, 572 stomachs were sampled. The most dominant prey by wet weight was euphausiids (61 %) followed by amphipods (18 %) and copepods (10 %). The most common species were Thysanoessa raschii, Themisto libulla, Calanus finmarchicus and Calanus hyperboreus. Copepods dominated in smaller capelin but were replaced by euphausiids in larger fish. A similar prey shift towards euphausiids along with an increase in prey weight (relative and absolute) was seen with increasing latitude. The spatial variation in feeding pattern was supported by stable nitrogen analyses. The mean δ15N values of capelin muscle tissue for the south (60–64°N) and north (68–72°N) were 9.54 ‰ ± 0.72 and 12.47 ‰ ± 0.38 (mean ± SD), respectively. However, when differences in isotopic baseline values (C. finmarchicus δ15N, 2.47 ‰) in the two areas were taken into account, the isotope values suggest that capelin in the northern areas fed on a slightly higher trophic level higher than in the south, as would be expected with increasing importance of euphausiids. These significant feeding differences along the Greenland west coast are likely impacting capelin growth and condition as they show parallel trends along the same gradient.

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.

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.

Effects of predation from pelagic 0-group cod (Gadus morhua) on mortality rates of capelin (Mallotus villosus) larvae in the Barents Sea

Surveys were carried out in 2002 and 2003 to test whether predation from pelagic 0-group cod (Gadus morhua) juveniles affects mortality rates of Barents Sea capelin (Mallotus villosus) larvae. In 2002, capelin larvae were observed in 17% of the cod stomachs and predation was observed at 19 of 50 stations. In 2003, capelin larvae were observed in 8% of the cod stomachs and predation was observed at 19 of 37 stations. The stomach contents and zooplankton samples were dominated by copepods and krill. The number of capelin larvae in cod stomachs increased with increasing capelin larvae abundance and cod length and decreased with increasing stomach content of copepods and prey abundance of krill. The time when capelin larvae could be recognised after ingestion in the cod stomachs was estimated experimentally and depended on predator and prey lengths. The estimated overall predation mortality rate from juvenile cod on capelin larvae was about 1.5% per day for both years and can potentially have a significant effect on the survival of capelin larvae, depending on the overlap in the different years.

Trophic ecology of Greenland halibut (Reinhardtius hippoglossoides) on the Icelandic continental shelf and slope

The feeding habits of Greenland halibut (Reinhardtius hippoglossoides) in Icelandic waters were investigated. In total, 1595 Greenland halibut were collected during the period from May 1991 to March 1992. The main prey species were capelin (Mallotus villosus), eelpouts (Lycodes spp.), northern ambereye (Hymenodora glacialis) and northern shrimp (Pandalus borealis), comprising two-thirds of the total stomach contents by weight. Small crustaceans, mainly euphausiids, were the main prey of the smallest (<20 cm) Greenland halibut, whereas capelin and shrimps dominated the diet of fish 20–59 cm in length. The largest individuals (>80 cm) mainly consumed eelpouts and other relatively large fish. This ontogenetic shift in diet was confirmed by multivariate canonical correspondence analysis (CCA), which explained 6% of the total variation in the diet composition. The CCA further revealed spatial and seasonal effects on the variation in diet. This study indicates that small and medium-sized Greenland halibut (<60 cm) off Iceland are mainly pelagic or semi-pelagic feeders, whereas the largest individuals (>80 cm) seem to feed mainly on or near the bottom.

DIET–FEATHER STABLE ISOTOPE (δ15N AND δ13C) FRACTIONATION IN COMMON MURRES AND OTHER SEABIRDS

Abstract We measured the fractionation of stable nitrogen (δ15N) and carbon (δ13C) isotopes in the breast and primary feathers of 11 Common Murres (Uria aalge) maintained on a diet of capelin (Mallotus villosus). Diet–feather δ15N fractionation from delipidated capelin muscle to murre feathers was 3.6‰ ± 0.2‰ in breast feathers and 3.7‰ ± 0.2‰ in primary feathers. Fractionation of δ13C was 2.5‰ ± 0.2‰ in breast feathers and 1.9‰ ± 0.3‰ in primary feathers. Prey–feather fractionation (for delipidated, muscle-only prey samples) for nine other species of seabirds ranged from 3.0‰ to 4.6‰ for δ15N and 0.1‰ to 2.5‰ for δ13C. Studies that did not remove lipids from prey samples showed higher δ15N and δ13C fractionation, and those that used whole prey items rather than muscle tissue alone showed higher δ15N fractionation. We suggest that: (1) prey samples be delipidated to facilitate interpretation of δ13C fractionation, (2) high interstudy and interspecific variation in δ13C makes species-specific studies essen...

Prey partitioning between cod (Gadus morhua) and minke whale (Balaenoptera acutorostrata) in the Barents Sea

Stomach samples of minke whale (Balaenoptera acutorostrata) and cod (Gadus morhua) were collected on the northeastern parts of the Finnmark coast, northern Norway, in 1998 and 1999 to investigate prey preference, niche overlap and niche width for the two species. A survey to estimate prey abundance was also conducted. Prey preference, niche overlap and niche width were described using Manly's alpha (α), Pianka's index (Ojk) and Levin's index (B), respectively. The diet of cod consisted mainly of capelin, deep-water shrimp, gadoids and krill. The smallest cod (≤64 cm length) preferred capelin, whereas the largest cod (>64 cm length) preferred gadoid species, including cod. The minke whale diet consisted mainly of capelin (Mallotus villosus), herring (Clupea harengus) and krill, and showed a particular preference for herring and capelin. Krill were consumed in large quantities, but did not seem to be a preferred food item for either cod or minke whales. In contrast to cod, which fed very little on herring, the minke whale fed heavily on herring in some areas. The niche widths for both cod and minke whales were relatively low, and the diet overlap between minke whale and cod was low.

Stomach Contents of Breeding Common Murres Caught in Gillnets off Newfoundland

Abstract We examined the stomach contents of 64 male and 43 female Common Murres (Uria aalge) caught in gillnets during late chick rearing/early chick departure period in August 2002 near breeding colonies in Witless Bay, Newfoundland, Canada. Twenty-six percent of stomachs contained no food. All others contained exclusively fish, and Capelin (Mallotus villosus) was the only fish positively identified. Gravid female Capelin were found in 82% of murre stomachs with contents. The number of fish ingested by murres differed between the sexes, with a mean of 2.7 fish in male stomachs and 1.6 fish in female stomachs. Mean mass of stomach contents did not differ between the sexes (males: 27.0 g; females: 22.6 g). Overall, results were similar to Common Murre diets recorded in the 1980s, despite changes in Capelin distribution and biology. The sample of Common Murres collected as gillnet bycatch was male-biased (59%). Males may have been more vulnerable to being caught in gillnets, perhaps because they were engag...

Gametogenesis in capelin, Mallotus villosus (Müller), in the northwest Atlantic Ocean

Capelin (Mallotus villosus) can be regarded as the most important prey item in the northwest Atlantic Ocean. The health and availability of this species are of fundamental importance for the successful growth and reproduction of many other fishes, whales, and birds. In spite of the clear need to understand this species, the life history of the capelin, especially its reproductive biology, is not well understood. This study substantially improves our knowledge of the reproductive biology of capelin and should be of particular interest to resource managers and administrators. Capelin gonads were analysed over three successive seasons using fish collected during beach spawning (June and July 1993, July 1994, July 1995) or trawled between spawnings, with 11 separate samples (fall, winter, and spring from October 1993 to June 1995). Few immature fish were collected in the trawls; 13/130 (10%) males and 3/150 (2%) females. No recovering (postspawning) males were found in the trawls, but 8/150 (5.3%) recovering females were identified on the basis of large residual oocytes (ovulated or unovulated) and (or) (in the fall) a thicker ovarian wall. Recovering females were identified as late as 10 months post spawning on the basis of residual oocytes. The essential semelparity of males was supported by a lack of apparent spermatogonia during advanced spermatogenesis, whereas the females' capacity to spawn in a subsequent year (iteroparity) was confirmed by the presence of small nonvitellogenic oocytes when other cells were in late oogenesis, in addition to the identification of recovering fish. Oocytes were separable into four stages (potential year classes) and changes occurred in all oocyte stages throughout the cycle of oogenesis. Gametogenesis was more advanced in longer fish, indicating that larger fish spawn earlier than smaller fish.

The code of the long-term biomass cycles in the Barents Sea

Abstract Barents Sea capelin (Mallotus villosus), Norwegian spring-spawning herring (Cluea harengus), and Northeast Arctic cod (Gadus morhua) have been associated with large fluctuations of biomass growth. The cause of these large fluctuations has been poorly understood and led to problems in biomass management. The identification of a deterministic cause would provide the possibility of forecasting future biomass fluctuations. In this investigation, the Kola Section sea temperature and the biomasses of capelin, herring, and cod have been analyzed by a wavelet transform to identify the source of the long-term cycles. The wavelet analysis shows that the Kola Section temperature has dominant cycles at the lunar-nodal tide cycles of 3×18.6=55.8, 18.5 and 18.6/3 = 6.2 years. The recruitment of Barents Sea capelin, Norwegian spring-spawning herring, and Northeast Arctic cod has adopted an optimal recruitment cycle close to the stationary 6.2 years Kola temperature cycle. Long-term biomass growth is correlated to the phase relation between the biomass eigen-frequency cycle and the Kola temperature cycles. The biomasses of capelin, herring and cod have long-term growth when the 6.2 and 18.6 years Kola temperature cycles are positive at the same time. There is a long-term biomass reduction when the temperature cycles are not positive at the same time, and a biomass collapse when the temperature cycles are negative at the same time. The deterministic property of the 18.6 years lunar-nodal tide provides a new way of long-term biomass forecasting over periods of 50–80 years or more.

Juvenile capelin (Mallotus villosus) off Newfoundland and Labrador in the 1990s

Anderson, J. T., Dalley, E. L., and O'Driscoll, R. L. 2002. Juvenile capelin (Mallotus villosus )o ff Newfoundland and Labrador in the 1990s. - ICES Journal of Marine Science, 59: 917-928. Juvenile capelin, Mallotus villosus (Muller), were distributed primarily on the northern Grand Banks and secondarily along the northeast coast of Newfoundland during late summer, 1994-1999. In some years, distributions extended to coastal Labrador. Capelin were seldom observed over deep water of the northeast Newfoundland Shelf or in shallow water of the southern Grand Banks. There were large areas encompassing wide ranges of capelin densities measured by the IYGPT trawl where the acoustic system did not detect capelin. Mean growth rate of capelin from 0- to 2-group was represented by length (mm)=90.9 age (years) 0.57 (r 2 =99%). The 1-group capelin formed discrete schools that varied significantly in fish length from 65 to 110 mm (p<0.05). Spatially, the different size groups occurred at scales of <55 km and possibly <3 km in some cases. The geographic distribution of age groups was not a simple function of cohort abundance. Capelin were distributed primarily in the middle ranges of temperature (5-8C) and zooplankton biomass (2-4 g dry weight m 2 ) sampled during the surveys. It is possible that interspecific competition limits the distributions of juvenile capelin, where juvenile Arctic cod (Boreogadus saida )a nd sandlance (Ammodytes sp.) were abundant to the north and south respectively. 2002 International Council for the Exploration of the Sea. Published by Elsevier Science Ltd.

Estimating the relative roles of dispersion and predation in generating regional differences in mortality rates of larval radiated shanny (Ulvaria subbifurcata)

We followed three patches of larval radiated shanny (Ulvaria subbifurcata) using drogued drifters to assess regional differences in growth and mortality rates. We estimate dispersive losses directly using local surveys of surface currents corrected for the tidally induced divergence caused by the lack of synopticity of our surveys. We also monitored the abundance of juvenile capelin (Mallotus villosus), the major planktivore in the region, using hydroacoustic integration. The pattern of divergence–convergence showed considerable temporal and spatial variability, which resulted in substantial changes in the inferred biological mortality rates. The net mortality rates appeared to be directly proportional to the local abundance of pelagic fish. As with other patch studies, we are limited in the number of observations we obtained, but the results of this multidisciplinary study do suggest a strong potential for prey–predator interactions between larvae and adult planktivorous fish.