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Olav Sigurd Kjesbu - One of the best experts on this subject based on the ideXlab platform.

  • Timing and determination of potential fecundity in Atlantic cod (Gadus morhua)
    Canadian Journal of Fisheries and Aquatic Sciences, 2006
    Co-Authors: Jon Egil Skjæraasen, Trygve Nilsen, Olav Sigurd Kjesbu
    Abstract:

    Studies using annual averages of lipid storage or estimated quality of the feeding season have shown that energy reserves influence egg production in Atlantic cod (Gadus morhua). However, vitellogenesis starts months before spawning. Therefore, energy reserves near the start of vitellogenesis might provide better proxies of fecundity and hence egg production than yearly averages. If so, proxies with large temporal variations (e.g., weight and lipid energy) should vary similarly in their predictive power, and females with different spawning periods should have their fecundity determined at different times. We exposed cod to two photoperiods to induce different spawning seasons. Growth be- fore spawning was monitored, and potential fecundity was measured at the onset of spawning. The date yielding the greatest explanatory power differed between photoperiods. As proxies, length varied less and had lower explanatory power than weight. Lipid energy at the onset of spawning was a poor proxy. The greatest explanatory power was found ~3-4 months before spawning around the start of vitellogenesis, indicating that potential fecundity was highly influ- enced by female energy reserves at this time. Determination of potential fecundity early in vitellogenesis may be a common feature for determinate teleost spawners. Resume : Les etudes qui tiennent compte des moyennes annuelles de stockage des lipides ou d'une autre estimation de la qualite de la saison d'alimentation montrent que les reserves energetiques influencent la production d'oeufs chez la morue franche (Gadus morhua). Cependant, la vitellogenese commence plusieurs mois avant la fraye. Les reserves

  • continuous light delays sexual maturation and increases growth of atlantic cod Gadus morhua l in sea cages
    Ices Journal of Marine Science, 2006
    Co-Authors: Geirlasse Taranger, L Aardal, Tom Hansen, Olav Sigurd Kjesbu
    Abstract:

    Taranger, G. L., Aardal, L., Hansen, T., and Kjesbu, O. S. 2006. Continuous light delays sexual maturation and increases growth of Atlantic cod (Gadus morhua L.) in sea cages. e ICES Journal of Marine Science, 63: 365e375. Prevention of early sexual maturation is essential in Atlantic cod (Gadus morhua) farming because maturity results in reduced growth, affects flesh quality, and may lead to increased mortality. In farmed cod, almost 100% of the fish mature at two years of age and often at a size of 1.5e2 kg. Two pilot experiments were conducted with cod in sea cages at a commercial fish farm in western Norway (60(N) to test the effect of additional continuous light (LL) on the timing of sexual maturation and somatic growth compared with controls under natural light (NL). In the NL groups, 100% maturation was indicated during the natural spawning period from February to April at the age of two years. By contrast, LL treatment from 27 June (15-month-old cod) or 2 September (18-month-old cod) onwards delayed gonad development by three to five months, reduced reproductive investment, and enhanced winter growth compared with the controls. Fish held at NL decreased in body weight during the spawning season (FebruaryeApril), whereas LL-exposed fish appeared to continue to grow during their spawning season (MayeAugust). LL-treated cod reached mean body weights of 2.90e3.13 kg within 28 months of hatching, whereas the controls reached 2.20e2.42 kg during the same period.

  • Apoptosis in regressing follicles from Solea solea and Gadus morhua
    Fish Physiology and Biochemistry, 2003
    Co-Authors: Peter R. Witthames, E. Andersson, L.n. Greenwood, B. Lyons, Merete Fonn, Olav Sigurd Kjesbu
    Abstract:

    Apoptosis in vitellogenic, atretic and post ovulatory follicles was studied in Solea solea and Gadus morhua by either measuring 180–200 bp oligonucleotides or by TUNEL in relation to each follicle type found in histological section. Specifically stained apoptotic nuclei were only present in the granulosa layer of recently produced cod post ovulatory follicles and 180–200 bp oligonucleotides were only found in spent sole ovaries.

George A Rose - One of the best experts on this subject based on the ideXlab platform.

  • Examination of fine-scale spatial-temporal overlap and segregation between two closely related congeners Gadus morhua and Gadus ogac in coastal Newfoundland.
    Journal of Fish Biology, 2014
    Co-Authors: D. C. Knickle, George A Rose
    Abstract:

    : The spatial and temporal movement patterns of sympatric juvenile Atlantic cod Gadus morhua and Greenland cod Gadus ogac were studied using high-resolution radio-acoustic positioning in a coastal area of Newfoundland during the summers of 2009 and 2010. A total of 20 fish (10 G. ogac and 10 G. morhua) were equipped with acoustic transmitters and monitored for periods up to 23 days. Most fishes showed high site fidelity with mean residence times of 12·4 (G. morhua) and 14·4 days (G. ogac). A few individuals showed a transient use of the study area, ranging distances up to c. 4 km. Mean daily home ranges [95% kernel utilization distributions (KUDs)] and core activity areas were significantly larger for G. morhua (3·8 and 0·5 ha) than for G. ogac (2·7 and 0·3 ha). Home ranges were not related to total length (LT ) for G. morhua but showed a weak positive relationship for G. ogac. Gadus morhua occupied larger areas during the day while G. ogac occupied slightly larger areas at night. Mean rates of movement for G. ogac and G. morhua ranged from 0·83 to 1·24 and 0·76 to 1·76 LT s(-1) , respectively, and were highest during crepuscular periods. Overall, G. morhua were wider ranging, moved at faster rates and were active throughout the diel cycle compared to G. ogac of the same size. It is suggested that differential use of space and activity periods plays an important role in the successful coexistence of these two species.

  • Microhabitat Use and Vertical Habitat Partitioning of Juvenile Atlantic (Gadus morhua) and Greenland (Gadus ogac) Cod in Coastal Newfoundland
    The Open Fish Science Journal, 2014
    Co-Authors: D. Craig Knickle, George A Rose
    Abstract:

    Twenty co-occurring juvenile gadids (10 Gadus ogac and 10 Gadus morhua) were surgically implanted with ultrasonic transmitters with depth sensors and continuously monitored for up to 23 days in the summers of 2009 and 2010 to test fine-scale habitat use and vertical distribution overlap in coastal Newfoundland (>18700 positional fixes). A habitat map with 8 substrate and 3 slope classes (low ( 10°)) was generated from acoustic data and coincident video data using seabed mapping software (QTC). Fish locations were integrated with a habitat map to as- sess and quantify habitat preference. Both species avoided fine gravel/sand substrates with little vegetation and selected for large particle (cobble and boulder) substrates with moderate or dense vegetation, and spent the majority of time in < 10 m of water. Nevertheless, species differences in habitat use were evident. G. ogac typically remained in close prox- imity to the seafloor whereas G. morhua was often distributed more pelagically and showed greater variation in vertical distribution. Habitat use and vertical distribution patterns were consistent across the diel period. Our results suggest that despite high overlap in habitat use, G. morhua and G. ogac often segregate vertically in the water column, which may re- duce competitive interference. We suggest that these patterns are related to differences in diet.

  • Dietary niche partitioning in sympatric gadid species in coastal Newfoundland: evidence from stomachs and C-N isotopes
    Environmental Biology of Fishes, 2014
    Co-Authors: D. Craig Knickle, George A Rose
    Abstract:

    The feeding habits of co-occurring gadid species Atlantic cod ( Gadus morhua ) and Greenland cod ( Gadus ogac ) in coastal Newfoundland waters, examined using stable isotope ( δ ^13C and δ ^15N) and stomach content analysis, indicated little dietary niche overlap and interspecific competition for food resources despite similar trophic levels. Both species consumed a variety of invertebrates and fish but showed a preference for different prey items. Polychaetes, fish and small crustaceans dominated G. ogac stomach contents while small crustaceans, in particular hyperiid amphipods and fish, dominated those of G. morhua . In general, G. morhua consumed more pelagic prey and had a significantly more pelagic (more negative) δ ^13C signature while G. ogac consumed primarily benthic prey and had a more benthic (more positive) δ ^13C signature. δ ^15N levels were similar in these species suggesting similar trophic positions, with levels increasing with fish length in both species. Dietary overlap was not significant in both stomach and stable isotope analyses. We conclude that interspecific competition for food is low between G. ogac and G. morhua and is unlikely to be a factor in the slow rebuilding of Atlantic cod in this region.

  • Passive- and active-acoustic properties of a spawning Atlantic cod (Gadus morhua) aggregation
    Ices Journal of Marine Science, 2009
    Co-Authors: Susan B. Fudge, George A Rose
    Abstract:

    Fudge, S. B., and Rose, G. A. 2009. Passive- and active-acoustic properties of a spawning Atlantic cod (Gadus morhua) aggregation. - ICES Journal of Marine Science, 66: 1259-1263.A spawning aggregation of Atlantic cod (Gadus morhua) was observed at depths of 40-50 m with passive- and active-acoustic sensors at the Bar Haven grounds in Placentia Bay, Newfoundland, in April 2003. A hydrophone was positioned on the seabed beneath the aggregation, while a 38-kHz split-beam echosounder was moored at the sea surface above it for 18.5 h. Ten grunts were recorded with peak frequencies ranging from 30 to 250 Hz and durations of nearly 300 ms. These grunts are similar to the sounds recorded in the presence of captive, spawning cod from the same substock. The echogram reveals that cod exhibit diel, vertical-migratory behaviour, densely aggregating near the seabed by day and forming columns that extend approximately halfway to the surface at night. This is the first study to demonstrate that cod produce sounds and form columns while migrating vertically during night-time spawning.

  • Distribution shifts and overfishing the northern cod (Gadus morhua): a view from the ocean
    Canadian Journal of Fisheries and Aquatic Sciences, 2000
    Co-Authors: George A Rose, Brad Deyoung, D W Kulka, S. V. Goddard, Garth L. Fletcher
    Abstract:

    Research on northern cod (Gadus morhua) from 1983 to 1994 indicated that a southward shift in distribution in the early 1990s was real and not an artifact of sequentially fishing down local populat...

Arild Folkvord - One of the best experts on this subject based on the ideXlab platform.

  • comparison of size at age of larval atlantic cod Gadus morhua from different populations based on size and temperature dependent growth models
    Canadian Journal of Fisheries and Aquatic Sciences, 2005
    Co-Authors: Arild Folkvord
    Abstract:

    This study presents the first intraspecific evaluation of larval growth performance across several different experimental scales, environments, and regions of a marine fish species. Size- and temperature-dependent growth mod- els for larval and early juvenile Atlantic cod (Gadus morhua) are developed based on selected laboratory experiments with cod fed in excess. Observed sizes-at-age of cod from several experiments and stocks are compared with predic- tions from the models using initial size and ambient temperature history as inputs. Comparisons with results from other laboratory experiments reveal that the model predictions represent relatively high growth rates. Results from enclosure experiments under controlled seminatural conditions generally provide growth rates similar to those predicted from the models. The models therefore produce suitable reference growth predictions against which field-based growth estimates can be compared. These comparisons suggest that surviving cod larvae in the sea typically grow at rates close to their size- and temperature-dependent capacity. This suggests that climatic influences will strongly affect the year-to-year variations in growth of cod during their early life history owing to their markedly temperature-dependent growth potential. Resume : Cette etude presente la premiere evaluation intraspecifique de la performance de la croissance larvaire d'une espece de poisson marin sur plusieurs echelles experimentales differentes et dans divers environnements et regions. L'elaboration de modeles de croissance de larves et de tres jeunes morues franches (Gadus morhua) en fonction de la

Li Chen - One of the best experts on this subject based on the ideXlab platform.

Ingrid Undeland - One of the best experts on this subject based on the ideXlab platform.

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