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H. Gjøsæter - One of the best experts on this subject based on the ideXlab platform.
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predation on early life stages is decisive for year class strength in the barents sea Capelin mallotus villosus stock
Ices Journal of Marine Science, 2016Co-Authors: H. Gjøsæter, Bjarte Bogstad, Elvar H Hallfredsson, Nina Mikkelsen, Torstein PedersenAbstract:Year-class strength of Barents Sea Capelin has been monitored closely since the early 1970s and during this � 45 years period three short periods of almost total recruitment failure leading to three stock collapses have been observed. These events triggered much attention since there was a large commercial fishery for Capelin, but also because of observed ecosystem effects attributed to the first of these collapse events. This attention motivated research to clarify mechanisms behind the recruitment failures, and many papers have been published regarding the causes of these events. Here, we review this literature and try to put the various investigations into context. Most of the research conducted gives evidence in favour of a hypothesis that was formulated after the first recruitment failure event in the mid-1980s that predation on Capelin larvae was the main cause of recruitment failure. Most studies also support the hypothesis that young herring (Clupea harengus) was the main predator on Capelin larvae, but other predators like young-of-the-year cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) probably also played a role. Investigations of the effect of predators such as haddock, red king crab (Paralithodes camtschaticus), diving birds, and Capelin on the demersal Capelin eggs have also been reviewed. Usually, these predators are found to consume Capelin eggs, but most likely not to an extent that would affect the recruitment to a noticeable degree. It is concluded that the predation on Capelin larvae is the main reason for the observed recruitment failures, although predation from the predators reviewed here can hardly be the only reason for almost total recruitment failures observed in some periods.
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polar cod boreogadus saida and Capelin mallotus villosus as key species in marine food webs of the arctic and the barents sea
Marine Biology Research, 2013Co-Authors: H. GjøsæterAbstract:Abstract 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 o...
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trophic interactions affecting a key ecosystem component a multistage analysis of the recruitment of the barents sea Capelin mallotus villosus
Canadian Journal of Fisheries and Aquatic Sciences, 2010Co-Authors: Dag Ø. Hjermann, Geir Ottersen, H. Gjøsæter, Bjarte Bogstad, Gjert Endre Dingsor, Anne Maria Eikeset, Nils Christian StensethAbstract:The Barents Sea stock of Capelin (Mallotus villosus) has suffered three major collapses (>90% reduction) since 1985 due to recruitment failures. As Capelin is a key species in the area, these population collapses have had major ecosys- tem consequences. By analysing data on spawner biomass and three recruitment stages (larvae, 0-group, and 1-year-olds), we suggest that much of the recruitment failures are caused by predation from herring (Clupea harengus) and 0-group and adult Northeast Arctic cod (Gadus morhua). Recruitment is furthermore positively correlated with sea temperatures in win- ter and spring. Harvesting of maturing Capelin on their way to the spawning grounds reduced the abundance of larvae sig- nificantly, but this reduction to a large extent is compensated for later in life, as mortality is strongly density-dependent between the larval stage and age 1. Altogether, our study indicates a very high importance of trophic interactions, consis- tent with similar findings in other high-latitude marine ecosystems. Resume´ : Le stock des capelans (Mallotus villosus) de la mer de Barents a connu trois importants effondrements (reduc- tion de >90 %) depuis 1985, a cause d'echecs du recrutement. Parce que le capelan est une espece essentielle dans la re ´- gion, ces effondrements demographiques ont eu des consequences majeures sur l'ecosysteme. Apres une analyse des donnees de biomasse des reproducteurs et de celles des trois stades du recrutement (larves, poissons d'age 0 et poissons d'un an), nous croyons qu'une partie importante de l'echec du recrutement est causee par la predation par les harengs (Clupea harengus) et par les morues (Gadus morhua) d'age 0 et adultes. Il y a, de plus, une correlation positive entre le recrutement et la temperature de la mer en hiver et au printemps. La recolte des capelans en etat de maturation durant leur migration vers les frayeres reduit le nombre de larves de maniere significative, mais cette reduction est en grande partie compensee plus tard dans le cycle parce que la mortaliteest fortement relieeala densiteentre le stade larvaire et l'age 1. Notre etude indique globalement une tres forte importance des relations trophiques, ce qui concorde avec des observations similaires faites dans d'autres ecosystemes marins de haute latitude. (Traduit par la Redaction)
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growth of barents sea Capelin mallotus villosus in relation to zooplankton abundance
Journal of Materials Science, 2002Co-Authors: H. Gjøsæter, Padmini Dalpadado, Arne HasselAbstract:Gjosaeter, H., Dalpadado, P., and Hassel, A. 2002. Growth of Barents Sea Capelin (Mallotus villosus) in relation to zooplankton abundance. – ICES Journal of Marine Science, 59: 959–967. Because Capelin feed on zooplankton, the availability of the latter may be a limiting factor for Capelin growth in at least some areas and at certain times. It was therefore hypothesized that a relationship exists between Capelin growth and zooplankton biomass either in the same year or in the previous autumn. Capelin growth in a given year was more closely correlated with the estimate of zooplankton abundance in the previous autumn than with that in the present autumn. Growth of the youngest Capelin was well correlated with abundance of the smallest zooplankton, whereas growth of older Capelin was more closely correlated with abundance of the larger zooplankton forms. Various water masses were defined on the basis of hydrographic conditions, and significant differences in the zooplankton content among the water masses were detected. An inverse relationship between zooplankton abundance and Capelin biomass was found, indicating that grazing by Capelin has a negative effect on zooplankton abundance. 2002 International Council for the Exploration of the Sea. Published by Elsevier Science Ltd.
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predation by cod gadus morhua on Capelin mallotus villosus in the barents sea implications for Capelin stock assessment
Fisheries Research, 2001Co-Authors: B Bogstad, H. GjøsæterAbstract:Abstract The Barents Sea Capelin ( Mallotus villosus ) is the most important prey item for the stock of Northeast Arctic cod ( Gadus morhua ) in the Barents Sea, and cod is also the most important predator on Capelin in this area. Mainly cod larger than 25 cm consume Capelin. The Barents Sea Capelin stock is assessed using a multispecies assessment method, involving in addition to Capelin and cod, the stock of Norwegian spring-spawning herring ( Clupea harengus ). One fundamental assumption in this method is that in the period January–April, only immature cod prey on only mature Capelin. In this paper, it is found that immature Capelin makes up a significant part of the consumption of Capelin by cod during the period January–April. Also, mature cod to some extent take part in the consumption of Capelin during this period. These findings are both in contrast to what is currently assumed in Capelin assessment. The results indicate that the assessment method presently in use overestimates the consumption of mature Capelin by cod in this period.
Torstein Pedersen - One of the best experts on this subject based on the ideXlab platform.
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predation on early life stages is decisive for year class strength in the barents sea Capelin mallotus villosus stock
Ices Journal of Marine Science, 2016Co-Authors: H. Gjøsæter, Bjarte Bogstad, Elvar H Hallfredsson, Nina Mikkelsen, Torstein PedersenAbstract:Year-class strength of Barents Sea Capelin has been monitored closely since the early 1970s and during this � 45 years period three short periods of almost total recruitment failure leading to three stock collapses have been observed. These events triggered much attention since there was a large commercial fishery for Capelin, but also because of observed ecosystem effects attributed to the first of these collapse events. This attention motivated research to clarify mechanisms behind the recruitment failures, and many papers have been published regarding the causes of these events. Here, we review this literature and try to put the various investigations into context. Most of the research conducted gives evidence in favour of a hypothesis that was formulated after the first recruitment failure event in the mid-1980s that predation on Capelin larvae was the main cause of recruitment failure. Most studies also support the hypothesis that young herring (Clupea harengus) was the main predator on Capelin larvae, but other predators like young-of-the-year cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) probably also played a role. Investigations of the effect of predators such as haddock, red king crab (Paralithodes camtschaticus), diving birds, and Capelin on the demersal Capelin eggs have also been reviewed. Usually, these predators are found to consume Capelin eggs, but most likely not to an extent that would affect the recruitment to a noticeable degree. It is concluded that the predation on Capelin larvae is the main reason for the observed recruitment failures, although predation from the predators reviewed here can hardly be the only reason for almost total recruitment failures observed in some periods.
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Integrating spatial and temporal mortality from herring on Capelin larvae: a study in the Barents Sea
ICES Journal of Marine Science, 2009Co-Authors: O.p. Pedersen, Torstein Pedersen, Kurt S. Tande, Dag SlagstadAbstract:Pedersen, O. P., Pedersen, T., Tande, K. S., and Slagstad, D. 2009. Integrating spatial and temporal mortality from herring on Capelin larvae: a study in the Barents Sea. - ICES Journal of Marine Science, 66: 2183-2194.Barents Sea herring and Capelin are commercially very important fish stocks. We investigate the spatial and temporal mortality rate of Capelin larvae in 2001 as a function of herring predation. Our methods are based on Lagrangian modelling, field surveys, and experimental data. The impact of juvenile herring predation on Capelin recruitment is corroborated, in particular the importance of the integrated spatio-temporal overlap between the two stocks. Capelin larvae were reduced to 20-50% in two weeks in accordance with different simulation scenarios. Hamre advanced a hypothesis in 1994 that juvenile herring are important predators of Capelin larvae and a main cause of poor Capelin recruitment in years when herring are very abundant in the Barents Sea. This hypothesis is supported through the results of this work.
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Advection and retention as life trait modulators of Capelin larvae—A case study from the Norwegian coast and the Barents Sea
Fisheries Research, 2009Co-Authors: O.p. Pedersen, Torstein Pedersen, Kurt S. Tande, Dag SlagstadAbstract:Abstract The Barents Sea Capelin stock is, potentially, the largest Capelin stock in the world, with a maximum biomass in the range of 6–8 million tonne. The main spawning grounds for this Capelin stock are along the coast of northern Norway. By modeling and fieldwork, this study addresses the interaction between mesoscale physical process and newly hatched Capelin larvae. The study documents a close relationship between selected spawning location, advection, retention, mortality windows and dispersal patterns.
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Diet of 0-group stages of Capelin (Mallotus villosus), herring (Clupea harengus) and cod (Gadus morhua) during spring and summer in the Barents Sea
Marine Biology, 2008Co-Authors: Torstein Pedersen, Maria FossheimAbstract:Recruitment of Capelin in the Barents Sea fail when juvenile herring and cod are abundant and the potential for feeding competition of wild sympatric Capelin and herring larvae and small cod juveniles were investigated. The frequency of gut evacuation after capture of Capelin larvae were also studied in mesocosms. Small Capelin larvae (26 mm length). Calanus copepodites were the major food sources for contemporary herring larvae (25–35 mm length) and Calanus and euphausiids were the major prey for small juvenile herring (37–60 mm length) and cod (18–40 mm length). Capelin larvae reared in mesocosms evacuated the guts shortly after capture. Capelin larvae had a smaller mouth and fed on smaller prey than herring and cod of the same length. This implies that the small Capelin larvae, in contrast to sympatric small herring and cod, are not tightly linked to the food chain involving Calanus and euphausiids. Thus, exploitative competition between Capelin larvae and planktivorous fish that rely on Calanus and euphausiids in the Barents Sea may be relaxed.
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effects of predation from pelagic 0 group cod gadus morhua on mortality rates of Capelin mallotus villosus larvae in the barents sea
Canadian Journal of Fisheries and Aquatic Sciences, 2007Co-Authors: Elvar H Hallfredsson, Torstein PedersenAbstract: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 ef...
George A Rose - One of the best experts on this subject based on the ideXlab platform.
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bottom up limits to newfoundland Capelin mallotus villosus rebuilding the euphausiid hypothesis
Ices Journal of Marine Science, 2014Co-Authors: Shannon G Obradovich, Erin H Carruthers, George A RoseAbstract: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 ofNGB Capelinwere all lowerwhen comparedwith Capelin from the eastern Scotian Shelf (ESS), where abundance increased followingpredator declines. Forage 2–5 Capelin of both sexes, all but oneof five comparable age–sex groupswere 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 differenceswere prominent. ESS Capelin hadhigher total fullness indices (TFIs) thanNGBfish at all sizes [mean TFIESS 1⁄4 1.43 (+ 1.14), mean TFINGB 1⁄4 0.48 (+ 0.70)]. Euphausiids (especially Thysanoessa spp.) were a main dietary component on the ESS but not on the NGB. Stable isotope analyses (dN and dC) for NGB Capelin also indicated few dietary euphausiids. Trophic fractionation of d N was 4.74/00, 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.
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Capelin are good for cod: can the northern stock rebuild without them?
ICES Journal of Marine Science, 2002Co-Authors: George A Rose, R. L. O'driscollAbstract:The stock of northern cod (Gadus morhua) off Newfoundland and Labrador is at its lowest level in recorded history, with no rebuilding of northern spawning aggregations since the fishing moratorium in 1992. Cod diet was historically dominated by Capelin (Mallotus villosus), which have been scarce in the northern areas since 1990. Using the study areas Hawke Channel and Trinity Bay within the historical northern cod range, and Placentia Bay (south coast), we examine growth, condition, and reproductive potential with respect to Capelin diet in 18 000 cod sampled primarily in January and June of the years 1996-2000. Overall diet weights differed among areas and seasons (Placentia=Hawke>Trinity in January; Placentia>Trinity=Hawke in June). However, just 7 of 3383 cod stomachs (0.2%) from Hawke contained Capelin (PFI=0). In contrast, 10% of cod of ages 3-7 in Placentia and Trinity Bays preyed on Capelin and overall Capelin partial fullness indices (PFI) were 0.2-0.4. Capelin PFIs were correlated with an index of availability (potential contact of Capelin within 40 km of cod) calculated from acoustic surveys. Seasonally adjusted cod liver condition was strongly associated with Capelin availability (p Trinity≫Hawke).
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Feeding of Capelin (Mallotus villosus) in Newfoundland waters
Sarsia, 2001Co-Authors: Richard L. O'driscoll, Morag J.d. Parsons, George A RoseAbstract:Abstract The diet of Capelin (Mallotus villosus Muller) from six areas off the Newfoundland and Labrador coast was compared over three seasons (January, May–June, August–September) in 1999. A total of 1247 stomachs were examined. Of these, 837 (67 %) contained food. The proportion of empty stomachs was higher in winter (55 %) than in spring (28 %) or autumn (20 %). Copepods were the major prey over all areas and seasons, occurring in 90 % of non-empty stomachs. Hyperiid amphipods, euphausiids, larvaceans and chaetognaths were also important, occurring in 30 %, 11 %, 9% and 7% of non-empty stomachs respectively. The importance of these other prey groups increased with increasing Capelin size. Larger Capelin contained larger prey. There were also spatial and temporal differences in diet. Capelin from Placentia Bay, southeastern Newfoundland, consumed smaller copepods and a higher proportion of amphipods than Capelin from other areas. Diet composition, particularly the incidence of lipid-rich Calanus species...
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Spatial Dynamics of Cod-Capelin Associations off Newfoundland
2001Co-Authors: George A RoseAbstract:Statistical analysis of large-scale (1-1,000 km) predator-prey associations between cod (Gadus morhua) and Capelin (Mallotus villosus) is difficult because the spatial distributions of both species are heterogeneous and temporally dynamic. Statistics based on Ripley’s K-function were used to describe the spatial association between cod and Capelin off Newfoundland. The number of Capelin prey around cod predators (potential contact) was computed from acoustic survey data for a range of possible cod ambits, from 5 to 100 km. Potential contact between cod and Capelin varied seasonally in Placentia Bay, southeastern Newfoundland in 1998, being highest in June and lowest in January. This seasonal difference was largely attributable to an increase in the spatial association of cod and Capelin at scales of 10-50 km in spring. A similar pattern was observed off the northeast Newfoundland shelf in 1991-1994 where postspawning cod migrated inshore in spring and encountered groups of Capelin. As a consequence of this migration pattern, spatial association and potential contact between cod and Capelin were dependent on survey timing relative to the timing of cod spawning.
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In situ acoustic target strength of juvenile Capelin
ICES Journal of Marine Science, 2001Co-Authors: Richard L. O'driscoll, George A RoseAbstract:A dispersed, monospecific aggregation of juvenile (0+) Capelin was detected acoustically in shallow (20-70 m) water in Bonavista Bay, northeastern Newfoundland in January 2000. This provided a rare opportunity to measure acoustic target strength (TS) of very small (mean length=51 mm) Capelin in situ. Mean observed TS at 38 kHz was −61.0 dB. Observed TS was similar to TS predicted by the Norwegian-Icelandic Capelin TS-length relationship (TS=19.1 log L (cm)−74), but ∼2 dB lower than predicted by the existing TS-length relationship for Capelin in Newfoundland waters at 38 and 49 kHz (TS=20 log L (cm)−73.1). Combining present data with previous 38 kHz data indicates the relationship TS=23.3 log L (cm)−77.1 (r 2 =0.95, n=6) for Capelin of lengths 5-14 cm in Newfoundland waters.
Gail K. Davoren - One of the best experts on this subject based on the ideXlab platform.
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Diet of Capelin (Mallotus villosus) in the Eastern Canadian Arctic inferred from stomach contents and stable isotopes
Polar Biology, 2020Co-Authors: Wesley R. Ogloff, Steve H. Ferguson, Ross F. Tallman, Gail K. DavorenAbstract:Capelin ( Mallotus villosus ), a sub-Arctic forage fish, has become abundant in the Canadian Arctic in recent decades, with consistent spawning documented; however, the trophic role of Capelin in these systems is unknown. We investigated the diets of small, immature (70–129 mm), medium, mature (130–174 mm), and large, mature (175–219 mm) Capelin in Pangnirtung Fjord, Nunavut during and prior to spawning in June–July, 2015–2016 using stomach contents and stable isotopes, respectively. Ontogenetic niche shifts were observed in both cases. Small, immature Capelin consumed predominantly small copepods (primarily Clausocalanidae) and had a narrow isotopic niche (SEA_C: 0.11 ‰^2). In contrast, medium-sized, mature Capelin consumed a mix of Calanus copepods, amphipods, and mysids and had a broad isotopic niche (SEA_C range: 0.23–0.51 ‰^2), while large, mature Capelin consumed higher proportions of large prey types (primarily Calanus hyperboreus and amphipods) and had a narrower isotopic niche (SEA_C range: 0.09–0.26 ‰^2). A higher percentage (by dry biomass) of Capelin eggs (73–100%) were consumed by mature Capelin in 2016, when ice cover in the fjord delayed the initiation of sampling by ~ 10 days after spawning had begun, relative to 2015 (0–9%). Non-egg prey types primarily consisted of amphipods (77–100% by dry biomass, mostly ice-associated Apherusa glacialis ) in 2016 and primarily pelagic Calanus copepods (64–99%) in 2015. As Capelin diet was broadly similar to other Arctic forage fishes, such as polar cod ( Boreogadus saida ), high dietary overlap may occur. Findings provide baseline data to examine future changes in Capelin diet as well as their trophic interactions in the Canadian Arctic.
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Capelin (Mallotus villosus) availability influences the inshore summer diet of Atlantic cod (Gadus morhua) in coastal Newfoundland
Environmental Biology of Fishes, 2020Co-Authors: Marissa T. Berard, Gail K. DavorenAbstract:In the early 1990s, the Atlantic cod ( Gadus morhua ) population on the Newfoundland and Labrador shelf declined dramatically, leading to a fishing moratorium in 1992. The Northern cod population has not fully recovered, possibly due to the simultaneous population collapse of an important prey type, Capelin ( Mallotus villosus ), which migrates from the continental shelf into coastal Newfoundland to spawn every summer. Our objective was to test whether Capelin availability influenced short-term dietary shifts of cod while inshore on the northeast Newfoundland coast. We quantify the dietary composition and relative abundance and biomass of prey types in cod stomachs sampled weekly or bi-weekly throughout July-August 2017 and 2018. Survey-based acoustic estimates of Capelin biomass and the timing of spawning in the study area revealed that peak Capelin biomass was five times higher (0.239 g/m^2) and two weeks earlier (July 28) during 2018 relative to 2017 (0.048 g/m^2, August 9). Cod stomachs were ~ 10 times more likely to contain Capelin during 2018 relative to 2017. As Capelin availability increased throughout each summer, cod shifted from a high diversity diet of lower-quality invertebrate prey (e.g., shrimp, crab) to a low diversity, Capelin-dominated diet, whereby Capelin presence, abundance and biomass increased. These findings indicate that Capelin remains a primary prey type of cod in inshore waters during their summer growing season, but dietary proportions of Capelin vary with their availability. As low dietary proportions of Capelin are associated with reduced body condition and reproductive potential in cod, findings support the need for an integrated Capelin-cod management approach.
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Dietary Niche Shifts of Multiple Marine Predators under Varying Prey Availability on the Northeast Newfoundland Coast
Frontiers Media S.A., 2017Co-Authors: Julia Gulka, Paloma C. Carvalho, Edward Jenkins, Kelsey Johnson, Laurie Maynard, Gail K. DavorenAbstract:Understanding species interactions among top marine predators and interactions with their prey can provide important insight into community-level responses to changing prey availability and the role of apex predators as indicators of ecosystem change. On the northeast Newfoundland coast, marine predators rely on Capelin (Mallotus villosus), a dominant forage fish, as a food source. Capelin migrate into coastal regions to spawn during July, essentially transforming the food supply from low during early summer (i.e., pre-spawning) to high later in the summer (i.e., spawning). During July-August, 2016, we used stable isotopic ratios of nitrogen (δ15N) and carbon (δ13C) to investigate shifts in dietary niche metrics at the predator group-level (trophic position, dietary niche breadth) and community-level (niche overlap, trophic diversity) for multiple marine predators under varying Capelin availability. Predator groups included non-breeding shearwaters (great shearwater Ardenna gravis, sooty shearwater A. grisea), humpback whales (Megaptera novaeangliae), and gull chicks (herring gull Larus argentatus, great black-backed gull Larus marinus). We also tested the sensitivity of community-level dietary metrics to a variety of published trophic discrimination factors. Tissue samples from shearwaters (blood cellular component), gull chicks (whole blood), and whales (skin), representing average diets over 2–3 weeks, were collected during three periods (early, mid, late) corresponding to increasing Capelin availability. Isotopic niche breadth (Standard Ellipse Area, SEAb) narrowed and trophic position shifted toward higher δ15N for all predator groups as Capelin availability increased, suggesting a higher reliance on Capelin. Trophic diversity (distance to centroid) decreased with increased Capelin availability, while pairwise niche overlap between predator groups was highly variable and sensitive to trophic discrimination factors. Findings suggest that although Capelin is the dominant forage fish during the summer, predators rely on Capelin as prey to varying degrees. Combining species- and community-level metrics of dietary niche and trophic diversity may provide a more complete picture of predator responses to prey availability and, thus, may be important monitoring tools to indicate changes in the food supply of marine predators
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crepuscular foraging by a pursuit diving seabird tactics of common murres in response to the diel vertical migration of Capelin
Marine Ecology Progress Series, 2010Co-Authors: Paul M. Regular, Gail K. Davoren, April Hedd, William A. MontevecchiAbstract:The spatial and temporal distribution of prey directly influences the foraging and feed- ing behaviour of predators. To investigate predator-prey interactions through the diel cycle, we examined continuous records of diving activity by a pursuit-diving seabird, the common murre Uria aalge, in conjunction with fine-scale data on the vertical distribution of their main prey, Capelin Mal- lotus villosus, off the northeast Newfoundland coast, Canada. Diurnal patterns in the diving activities of murres closely reflected changes in the vertical distribution and movements of Capelin. During daylight hours, 43% of murre dives were deep (≥50 m), bringing murres into sub-0°C water in the Cold Intermediate Layer (CIL; ~40 to 240 m), when 82% of Capelin biomass was located within or below the CIL. At night, murres concentrated diving activity at shallower depths (94% of dives were <50 m) when 86% of Capelin biomass was in the upper water column. Capelin migrated through the water column during twilight periods, moving up at dusk and down at dawn. In response, murres' diving frequency increased and diving depths were graduated, becoming shallower through dusk and deeper through dawn. Crepuscular habits indicate that Capelin are more accessible during twi- light periods. In summary, though murres are constrained by commuting costs, they show exceptional behavioural flexibility in their efforts to access Capelin throughout their diel vertical migration (DVM). The various trade-offs involved in such predator-prey interactions are discussed, as are the ecological consequences of the DVM pattern across trophic levels.
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Modeling trophic interactions between parental common murres and Capelin off the northeast Newfoundland coast
2006Co-Authors: Gail K. Davoren, Mariano Koen-alonso, William A. Montevecchi, T John, Oceans Canada, Alejandro D. BurenAbstract:This presentation focuses on trophic interactions between Capelin ( Mallotus villosus ) and its primary avian predator, the common murre ( Uria aalge ) on Funk Island during the breeding season. Diet is evaluated through parental deliveries to the chicks and prey availability is estimated from pelagic trawl data within the murre’s foraging range. Diet composition is assessed using percentage by number (%N), with its confidence limits obtained by bootstrapping. Since the common murre is a Capelin specialist and feeds on Capelin larger than 100mm (suitable Capelin), three prey categories were considered: small Capelin (100-140mm total length), large Capelin (>140mm total length) and “others” (prey species other than Capelin). Considering the densities of these prey groups as explanatory variables and assuming a multinomial probability distribution for the individual prey deliveries, the common murre’s diet is being modeled in two different ways. One is purely statistical and uses a standard multicategory logit model. The second one, derived from ecological theory, estimates the probabilities of consuming different prey categories from a generalized form of the multispecies Holling functional response. Both models describe well the observed diets, but the model with ecological roots has a better fit than the purely statistical one. Furthermore, in years when the abundance of suitable Capelin was high the proportions of large and small Capelin consumed were not significantly different, while they were in years of low suitable Capelin abundance.
William A. Montevecchi - One of the best experts on this subject based on the ideXlab platform.
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crepuscular foraging by a pursuit diving seabird tactics of common murres in response to the diel vertical migration of Capelin
Marine Ecology Progress Series, 2010Co-Authors: Paul M. Regular, Gail K. Davoren, April Hedd, William A. MontevecchiAbstract:The spatial and temporal distribution of prey directly influences the foraging and feed- ing behaviour of predators. To investigate predator-prey interactions through the diel cycle, we examined continuous records of diving activity by a pursuit-diving seabird, the common murre Uria aalge, in conjunction with fine-scale data on the vertical distribution of their main prey, Capelin Mal- lotus villosus, off the northeast Newfoundland coast, Canada. Diurnal patterns in the diving activities of murres closely reflected changes in the vertical distribution and movements of Capelin. During daylight hours, 43% of murre dives were deep (≥50 m), bringing murres into sub-0°C water in the Cold Intermediate Layer (CIL; ~40 to 240 m), when 82% of Capelin biomass was located within or below the CIL. At night, murres concentrated diving activity at shallower depths (94% of dives were <50 m) when 86% of Capelin biomass was in the upper water column. Capelin migrated through the water column during twilight periods, moving up at dusk and down at dawn. In response, murres' diving frequency increased and diving depths were graduated, becoming shallower through dusk and deeper through dawn. Crepuscular habits indicate that Capelin are more accessible during twi- light periods. In summary, though murres are constrained by commuting costs, they show exceptional behavioural flexibility in their efforts to access Capelin throughout their diel vertical migration (DVM). The various trade-offs involved in such predator-prey interactions are discussed, as are the ecological consequences of the DVM pattern across trophic levels.
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Murres, Capelin and ocean climate: inter-annual associations across a decadal shift
Environmental Monitoring and Assessment, 2008Co-Authors: Paul M. Regular, John F. Piatt, William A. Montevecchi, F. Shuhood, T. Power, Gregory J. Robertson, D. Ballam, B. NakashimaAbstract:To ensure energy demands for reproduction are met, it is essential that marine birds breed during periods of peak food availability. We examined associations of the breeding chronology of common murres (Uria aalge) with the timing of the inshore arrival of their primary prey, Capelin (Mallotus villosus) from 1980 to 2006 across a period of pervasive change in the Northwest Atlantic ecosystem. We also assessed the influence of ocean temperature and the North Atlantic Oscillation (NAO; an index of winter climate and oceanography) on these interactions. We found a lagged linear relationship between variations in murre breeding chronology and the timing of Capelin arrival in the previous year. On a decadal level, we found a non-linear threshold relationship between ocean temperature and the timing of Capelin arrival and murre breeding. Centennially anomalous cold water temperatures in 1991 generated a marked shift in the timing of Capelin spawning inshore and murre breeding, delaying both by more than 2 weeks. By the mid-1990s, ocean temperatures returned to pre-perturbation levels, whereas the temporal breeding responses of Capelin and murres were delayed for a decade or more. Oceanographic conditions (temperature, NAO) were poor predictors of the timing of Capelin arrival inshore in the current year compared to the previous one. Our findings suggest that knowledge of the timing of Capelin availability in the previous year provides a robust cue for the long-lived murres, allowing them to achieve temporal overlap between breeding and peak Capelin availability.
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Modeling trophic interactions between parental common murres and Capelin off the northeast Newfoundland coast
2006Co-Authors: Gail K. Davoren, Mariano Koen-alonso, William A. Montevecchi, T John, Oceans Canada, Alejandro D. BurenAbstract:This presentation focuses on trophic interactions between Capelin ( Mallotus villosus ) and its primary avian predator, the common murre ( Uria aalge ) on Funk Island during the breeding season. Diet is evaluated through parental deliveries to the chicks and prey availability is estimated from pelagic trawl data within the murre’s foraging range. Diet composition is assessed using percentage by number (%N), with its confidence limits obtained by bootstrapping. Since the common murre is a Capelin specialist and feeds on Capelin larger than 100mm (suitable Capelin), three prey categories were considered: small Capelin (100-140mm total length), large Capelin (>140mm total length) and “others” (prey species other than Capelin). Considering the densities of these prey groups as explanatory variables and assuming a multinomial probability distribution for the individual prey deliveries, the common murre’s diet is being modeled in two different ways. One is purely statistical and uses a standard multicategory logit model. The second one, derived from ecological theory, estimates the probabilities of consuming different prey categories from a generalized form of the multispecies Holling functional response. Both models describe well the observed diets, but the model with ecological roots has a better fit than the purely statistical one. Furthermore, in years when the abundance of suitable Capelin was high the proportions of large and small Capelin consumed were not significantly different, while they were in years of low suitable Capelin abundance.
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Signals from seabirds indicate changing biology of Capelin stocks
Marine Ecology Progress Series, 2003Co-Authors: Gail K. Davoren, William A. MontevecchiAbstract:Key forage species lie at the core of complex marine food webs, providing essential link- ages among trophic levels. We examined the interactions of an important forage and commercial fish, Capelin Mallotus villosus, and its primary avian predator, the common murre Uria aalge, in the NW Atlantic. Murres are Capelin specialists and robust samplers of Capelin biology. During the 1990s, the coldest surface-water event in the past 50 to 100 yr occurred in the NW Atlantic (1991), and the east- ern Canadian ground-fishery was closed (1992). Concordantly, the biology and behaviour of Capelin has undergone very substantial changes. We examined parental food deliveries and production at the world's largest common murre colony on Funk Island off the northeast coast of Newfoundland throughout the 1990s. Murres delayed breeding and delivered smaller and lower quality Capelin to their chicks. These changes, corroborated with independent fisheries data, resulted in poor condition of murre chicks, indicating significant effects of changing Capelin demographics at higher trophic levels. The diets of the murre chicks indicate that the composition of the Capelin population has shifted from high size diversity to mainly smaller Capelin. We hypothesize that this change resulted from the elimination of the larger-sized and earlier-spawning genotype and that the NW Atlantic Capelin population is exhibiting signs of reduced reproductive potential that likely reflects lower spawning biomass.
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trophic relationships among Capelin mallotus villosus and seabirds in a changing ecosystem
Journal of Materials Science, 2002Co-Authors: James E. Carscadden, William A. Montevecchi, G K Davoren, B S NakashimaAbstract:Trophic interactions among seabirds and Capelin (Mallotus villosus), a key forage species off Newfoundland and Labrador, are examined. During the 1990s, estimates of relative year-class strength of Capelin were similar to estimates in the 1980s, Capelin spawned later and matured younger, mean fish size was smaller, and there were large-scale distributional shifts of Capelin. Most of these changes were linked to below-normal sea temperatures during the early 1990s, but the changes have persisted even though temperatures have returned to normal. Seabirds bred later in the 1990s and changed diets and foraging strategies. Off eastern Newfoundland, the breeding success of black-legged kittiwakes declined during the early 1990s owing to a suite of factors, including their inability to dive to capture Capelin, the late arrival of Capelin inshore and predation by gulls. Common murres and puffins did not suffer breeding failures because they could dive and catch Capelin at depth. Off Labrador, black-legged kittiwakes experienced breeding failures because of the lack of Capelin while common murres were able to find alternate prey and bred successfully. The diets of gannets in the 1990s contained a higher proportion of cold-water prey than in earlier periods when warm-water prey predominated. The population sizes of all seabird species remained stable or increased, with the exception of gulls. Increasing populations of seabirds are related in part to their lessened mortality from gillnets since the closures of the eastern Canadian groundfishery in 1992, whereas declining populations of gulls can be related to reduced food availability from fishery discards and offal. This food limitation has led gulls to switch much of their foraging effort from scavenging to predation on seabird adults and chicks before Capelin arrive inshore.
