The Experts below are selected from a list of 288 Experts worldwide ranked by ideXlab platform
Anne Gro Vea Salvanes - One of the best experts on this subject based on the ideXlab platform.
-
pollack Pollachius Pollachius stock size development and potential influence on cod gadus morhua mariculture in a west norwegian fjord
Fisheries Research, 1995Co-Authors: Anne Gro Vea SalvanesAbstract:Abstract This study examines density-dependent mortality of pollack, a major cod predator, and cod, before and after juvenile cod were released on a large scale in Masfjorden, western Norway. The development in stock size, mortality by age group and diet are emphasised, and results for pollack and cod are compared. Population parameters for pollack are estimated using a combination of the catch per unit effort (CPUE) method and a general cohort analysis technique. The estimates for cod originate from a combination of the CPUE method and tag-release-recapture experiments and have been published earlier. The diet studies are based on pollack and cod subdivided into predator size groups for four seasons at a period before large-scale juvenile cod releases. During this period, but also after releases, the mortality patterns, stomach analysis and the progression in prey (1-group) and predator (2 + -group) abundance demonstrate cannibalism as well as that pollack and cod were feeding on each other's juveniles in Masfjorden. Density-dependent predation mortality and growth seem to be an important regulatory mechanism for pollack and cod stocks in Masfjorden. This may explain the unsuccessful cod mariculture in this fjord.
-
Dominating sublittoral fish species in a west Norwegian fjord and their trophic links to cod (Gadus morhua L.)
Sarsia, 1993Co-Authors: Anne Gro Vea Salvanes, Jarle Tryti NordeideAbstract:Abstract The fish fauna in the sublittoral habitat of Masfjorden, western Norway, has been studied in order to reveal survival and growth prospects of released juvenile cod in a large-scale stock enhancement experiment. Seasonal changes in abundance of dominating fish species and in the diet of potential competitors and predators to juvenile cod were emphasized. A total of 44 species from 17 families of Teleostei and 4 families of Chondrichthyes were recorded at 5–20 m depth of the sublittoral of Masfjorden. Gadids were dominating (50.2 % by numbers, 10 species) and saithe (Pollachius virens), pollack (P. Pollachius), poor-cod (Trisopterus minutus) and cod (Gadus morhua) were most numerous. Labrids form a second dominating family (44.7 % by numbers, 5 species) of which Centrolabrus exoletus, Ctenolabrus rupestris, Labrus bimaculatus and L. bergylta were the most abundant. Pollack and saithe had highest abundance during summer and autumn. The labrids and poor-cod had maximum abundance in summer. All labrid...
Nils Are Øritsland - One of the best experts on this subject based on the ideXlab platform.
-
Stomach content analysis of minke whales Balaenoptera acutorostrata from the Lofoten and Vesterålen areas, Norway
Ecography, 1991Co-Authors: Christian Lydersen, Jan Marcin Węsławski, Nils Are ØritslandAbstract:Stomach contents from 15 minke whales Balaenoptera acutorostrata collected in the Lofoten and Vesteralen areas of Norway, August 1988, were analysed. All stomachs contained identifiable remains and constituted of fish only. Herring Clupea harengus was the dominant prey species found in all whale stomachs and constituted 92% of the total prey volume. Cod Gadus morhua was the second most abundant prey. In addition pollock Pollachius virens, haddock Melanogrammus aeglefinus, and great silver smelt Argentina silus were found in single whale stomachs. All fish species found in the whale stomachs in our investigations are of commercial importance, and the sizes of the herrings and cods in minke whale stomachs are of interest for commercial exploitation.
Loic Quemener - One of the best experts on this subject based on the ideXlab platform.
-
Effects of temperature on the growth of pollack (Pollachius Pollachius) juveniles
Aquaculture, 2005Co-Authors: J. Person-le Ruyet, Vincent Buchet, Benoit Vincent, H. Le Delliou, Loic QuemenerAbstract:Abstract Growth of juvenile pollack was assessed at five constant temperatures (9, 12, 15, 18 and 21 °C) in an 84-day trial. Duplicate groups of 75 fish (initial weight 143 ± 2 g) were held in O 2 saturated water (102–103% saturation) and fed to apparent satiation. Growth increased as temperature increased from 9 °C up to a plateau at 12–15 °C (NS differences between 12 and 15 °C) followed by a decrease from 18 °C. No growth occurred at 21 °C. For the overall period, specific growth rates were 0.52% and 0.53% day − 1 at 12 and 15 °C compared to 0.40% day − 1 at 18 °C. Feed intake was maximum at 15–18 °C (0.68–0.69% day − 1 ) and it was significantly lower at 21 °C (0.45% day − 1 ). Apparent feed conversion ratio was significantly higher at 18 °C than at 12–15 °C (1.8 compared to 1.2–1.4). There was no significant change in fish whole body composition related to temperature. At the end of the experiment, fish growth recovery following a transfer from 18 and 21 °C to 15 °C was assessed using a 50-day challenge test. Growth rate of the previous 21 °C group was the same as in the 15 °C group (NS differences) and in the previous 18 °C group it was significantly lower. The study showed that pollack have a high capacity to recover from a prolonged period of low or no growth induced by high temperatures.
-
Effect of water temperature on individual reproductive activity of pollack (Pollachius Pollachius)
Aquaculture, 2004Co-Authors: Marc Suquet, Yvon Normant, Jean-louis Gaignon, Loic Quemener, Christian FauvelAbstract:Abstract The effects of water temperature on pollack (Pollachius Pollachius) spawning features were individually assessed. During the spawning period, nine fish sets, each composed of one female and two males (mean body weight: 2.5±1.0 kg), were placed in small-volume tanks (2 m3). Fish sets were held at 8, 10, or 12 °C (n=3 for each temperature). Three females released eggs at 8 and 10 °C, while only two spawned at 12 °C. One hundred thirty-one individual spawns were collected from the eight spawning fish sets. The number of spawns collected per female was significantly lower at 12 °C (3.0±3.6), compared to 10 °C (17.3±10.1) and 8 °C (23.3±2.5). Egg number (eggs kg−1 BW) was significantly lowered at 12 °C (26,068±35,989) compared to 10 °C (323,230±136,796) and 8 °C (599,612±249,545). The number of viable eggs (eggs kg−1 BW) was significantly lower at 12 °C (4,175±7,167) compared to 8 °C (192,034±145,870). When incubated at a common temperature of 10 °C, hatching and malformation percentages were significantly enhanced for breeders maintained at 8 °C (respectively, 35.8±8.5–7.3±1.4%) compared to 10 °C (9.8±8.0–2.3±1.8%). Then, pooling data were recorded at the three temperatures; a significant decrease of egg diameter with time was observed. The individual reproductive activity of pollack experienced by breeders was deeply affected by temperature during the spawning period. A temperature of 12 °C is suggested to be close to the temperature reproduction upper limit in this species.
-
Pollack (Pollachius Pollachius): Acquisition of biologic data in a breeding purpose
2002Co-Authors: Vincent Buchet, Marc Suquet, Bruno Petton, Yvon Normant, Marie-helene Omnes, Armelle Severe, Herve Barone, Christian Fauvel, Loic Quemener, Jean-louis GaignonAbstract:The fishing of pollack which concerns essentially, France, United Kingdom and Norway, and at a lower level Ireland and Denmark, is situated between 10 and 15000 tons a year. In 1996, France was the first producer of Pollack. Since 1980, a decrease of production is observed in Europe. In France, landing reached 3000t. in 1998 (Suquet, 2001). However, the demand remaining strong, aquaculture could be a solution to satisfy the deficit between the French production and the domestic demand.
Håkon Otterå - One of the best experts on this subject based on the ideXlab platform.
-
Timecourse of oocyte development in saithe Pollachius virens
Journal of fish biology, 2016Co-Authors: Jon Egil Skjæraasen, Jennifer A. Devine, Jane A. Godiksen, Merete Fonn, Håkon Otterå, O.s. Kjesbu, Birgitta Norberg, Øystein Langangen, Ørjan KarlsenAbstract:Wild caught North Sea saithe Pollachius virens were monitored for growth, sex steroid profiles and oocyte development pre-spawning and measured for egg size and group fecundity during the spawning season in the laboratory. Vitellogenesis commenced in late October-early November, at a leading cohort size (CL ) of c. 250 µm, after which oocytes grew rapidly in size until spawning started in February. Notably, a distinct cortical alveoli stage was virtually absent with yolk granules observed in developing oocytes at the very beginning of vitellogenesis. Little atresia was observed pre-spawning, but atretic re-absorption of remnant oocytes containing yolk granules was found in all females immediately post-spawning. As expected, concentrations of sex steroids, oestradiol-17β (females), testosterone (both sexes) and 11-ketotestosterone (both sexes), increased pre-spawning before dropping post-spawning. The present experiment provides the first validation of sex steroid levels in P. virens. Post-ovulatory follicles were visible in histological sections from female gonads 9-11 months post-spawning, but then disappeared. Spawning commenced around a CL of c. 750 µm (700-800 µm). Hydrated oocytes (eggs) measured between 1·04 and 1·31 mm (mean = 1·18 mm) with decreasing sizes towards the end of spawning. The average estimated realized fecundity was c. 0·84 million eggs (median female total length, LT = 60 cm). Spawning lasted from 13 February to 29 March.
-
Seasonal dynamics of growth and mortality suggest contrasting population structure and ecology for cod, pollack, and saithe in a Norwegian fjord
ICES Journal of Marine Science, 2012Co-Authors: Mikko Heino, Terje Svåsand, Jarle Tryti Nordeide, Håkon OtteråAbstract:We study the dynamics of Atlantic cod (Gadus morhua L.), pollack (Pollachius Pollachius L.), and saithe (Pollachius virens L.) in Masfjorden, a small fjord in western Norway. Annually, cohorts of pollack and cod grow in size and decline in abundance, as expected of closed populations, whereas saithe virtually disappear before maturity. Seasonally, in contrast, the dynamics of cod and pollack differ. Pollack shows a regular growth pattern, with most of the growth taking place in summer. Its abundance-at-age shows strong seasonal variations, with a marked increase from spring to summer followed by a decline through autumn and winter. These patterns relate partly to seasonal changes in depth distribution and catchability. Combined with the observation that spawning-stage pollack are abundant in spring, we interpret these patterns to suggest that pollack in Masfjorden represent a dynamically independent unit. Seasonal changes in abundance are less marked for cod, and seasonal changes in depth distribution seem insignificant. However, cod shows an unusual pattern in length at age, with no apparent growth in summer and fast growth in autumn. These patterns suggest that the population structure of cod may be more open than that of pollack and may involve mixing of more than one population component.
Jarle Tryti Nordeide - One of the best experts on this subject based on the ideXlab platform.
-
Seasonal dynamics of growth and mortality suggest contrasting population structure and ecology for cod, pollack, and saithe in a Norwegian fjord
ICES Journal of Marine Science, 2012Co-Authors: Mikko Heino, Terje Svåsand, Jarle Tryti Nordeide, Håkon OtteråAbstract:We study the dynamics of Atlantic cod (Gadus morhua L.), pollack (Pollachius Pollachius L.), and saithe (Pollachius virens L.) in Masfjorden, a small fjord in western Norway. Annually, cohorts of pollack and cod grow in size and decline in abundance, as expected of closed populations, whereas saithe virtually disappear before maturity. Seasonally, in contrast, the dynamics of cod and pollack differ. Pollack shows a regular growth pattern, with most of the growth taking place in summer. Its abundance-at-age shows strong seasonal variations, with a marked increase from spring to summer followed by a decline through autumn and winter. These patterns relate partly to seasonal changes in depth distribution and catchability. Combined with the observation that spawning-stage pollack are abundant in spring, we interpret these patterns to suggest that pollack in Masfjorden represent a dynamically independent unit. Seasonal changes in abundance are less marked for cod, and seasonal changes in depth distribution seem insignificant. However, cod shows an unusual pattern in length at age, with no apparent growth in summer and fast growth in autumn. These patterns suggest that the population structure of cod may be more open than that of pollack and may involve mixing of more than one population component.
-
Dominating sublittoral fish species in a west Norwegian fjord and their trophic links to cod (Gadus morhua L.)
Sarsia, 1993Co-Authors: Anne Gro Vea Salvanes, Jarle Tryti NordeideAbstract:Abstract The fish fauna in the sublittoral habitat of Masfjorden, western Norway, has been studied in order to reveal survival and growth prospects of released juvenile cod in a large-scale stock enhancement experiment. Seasonal changes in abundance of dominating fish species and in the diet of potential competitors and predators to juvenile cod were emphasized. A total of 44 species from 17 families of Teleostei and 4 families of Chondrichthyes were recorded at 5–20 m depth of the sublittoral of Masfjorden. Gadids were dominating (50.2 % by numbers, 10 species) and saithe (Pollachius virens), pollack (P. Pollachius), poor-cod (Trisopterus minutus) and cod (Gadus morhua) were most numerous. Labrids form a second dominating family (44.7 % by numbers, 5 species) of which Centrolabrus exoletus, Ctenolabrus rupestris, Labrus bimaculatus and L. bergylta were the most abundant. Pollack and saithe had highest abundance during summer and autumn. The labrids and poor-cod had maximum abundance in summer. All labrid...
