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Konstantinos Ganias - One of the best experts on this subject based on the ideXlab platform.
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the use of hepatic and somatic indices and histological information to characterize the reproductive dynamics of atlantic sardine Sardina pilchardus from the portuguese coast
Marine and Coastal Fisheries: Dynamics Management and Ecosystem Science, 2011Co-Authors: Cristina Nunes, Alexandra Silva, Eduardo Soares, Konstantinos GaniasAbstract:Abstract Samples of Atlantic sardine Sardina pilchardus (also known as European pilchard) were collected bimonthly from 2004 to 2008 off the central west coast of Portugal to describe the reproductive activity of this indeterminate batch-spawning species; compare the seasonality of somatic growth, condition, and feeding; and evaluate differences between sexes. Monthly assessments of individual biological information for both males and females were complemented by histological analysis of ovaries during 1 year and liver tissues (both sexes) at different times of the reproductive cycle. The temporal patterns of the gonadosomatic index and various histological indices (most advanced oocyte stage, atresia incidence and prevalence, and spawning activity) indicated that Atlantic sardine were reproductively active mainly from October to March and that residual activity occurred in the remaining months. For both sexes, condition indices (hepatosomatic index, relative weight, and amount of fat stored) increased ma...
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Ephemeral spawning aggregations in the Mediterranean sardine, Sardina pilchardus: a comparison with other multiple-spawning clupeoids
Marine Biology, 2008Co-Authors: Konstantinos GaniasAbstract:Using previously published histological data on multiple, monthly samples of Sardina pilchardus collected in the central Aegean and Ionian Seas (September 1999–August 2000, and November 2000–February 2001), the Mediterranean sardine was treated as a case study to investigate the biological characteristics of ephemeral spawning aggregations in multiple-spawning clupeoids. Actively spawning (Day0) females in the Mediterranean sardine, i.e., the daily class of spawners caught a few hours prior, during, or after the spawning act, were shown to separate spatially from late (Day1+) spawners and non-spawning females, taking with them a large proportion of conspecific males which were also in advanced spawning condition and in better somatic condition compared to the remaining population. In addition, information from 28 stocks of multiple-spawning clupeoids from a wide range of geographic locations, belonging to 14 species and 2 families (Engraulidae and Clupeidae), was reviewed and analyzed pertinent to the formation of ephemeral spawning aggregations. Results from the latter analysis indicated similar patterns of spatial segregation of Day0 spawners in the reviewed clupeoid stocks as in the Mediterranean Sardine, which strongly suggested that the formation of ephemeral spawning aggregations is a common behavioral trait among multiple-spawning clupeoids.
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Ephemeral spawning aggregations in the Mediterranean sardine, Sardina pilchardus: a comparison with other multiple-spawning clupeoids
Marine Biology, 2008Co-Authors: Konstantinos GaniasAbstract:Using previously published histological data on multiple, monthly samples of Sardina pilchardus collected in the central Aegean and Ionian Seas (September 1999–August 2000, and November 2000–February 2001), the Mediterranean sardine was treated as a case study to investigate the biological characteristics of ephemeral spawning aggregations in multiple-spawning clupeoids. Actively spawning (Day0) females in the Mediterranean sardine, i.e., the daily class of spawners caught a few hours prior, during, or after the spawning act, were shown to separate spatially from late (Day1+) spawners and non-spawning females, taking with them a large proportion of conspecific males which were also in advanced spawning condition and in better somatic condition compared to the remaining population. In addition, information from 28 stocks of multiple-spawning clupeoids from a wide range of geographic locations, belonging to 14 species and 2 families (Engraulidae and Clupeidae), was reviewed and analyzed pertinent to the formation of ephemeral spawning aggregations. Results from the latter analysis indicated similar patterns of spatial segregation of Day0 spawners in the reviewed clupeoid stocks as in the Mediterranean Sardine, which strongly suggested that the formation of ephemeral spawning aggregations is a common behavioral trait among multiple-spawning clupeoids.
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degeneration of postovulatory follicles in the iberian sardine Sardina pilchardus structural changes and factors affecting resorption
2007Co-Authors: Konstantinos Ganias, Yorgos Stratoudakis, Cristina Nunes, Investigacao AgrariaAbstract:Inaccuracy in the aging of postovulatory follicles (POFs) and in estimating the effect of temperature on the resorption rate of POFs may introduce bias in the determination of the daily spawning age classes with the daily egg production method (DEPM). To explore the above two bias problems with f ield-collected European pilchard (Sardina pilchardus, known regionally as the Iberian sardine), a method was developed in which the time elapsed from spawning (POF age) was estimated from the size of POFs (i.e., from the cross-sectional area in histological sections). The potential effect of the preservative type and embedding material on POF size and the effect of ambient water temperature on POF resorption rate are taken into account with this method. A highly significant loglinear relationship was found between POF area and age; POF area shrank by approximately 50% per day. POFs were also shown to shrink faster at higher temperatures (approximately 3% per degree), but this temperature effect is unlikely to be an important source of bias in the assignment of females to daily spawning classes. The embedding material was also shown to influence the size of POFs, the latter being significantly larger in resin than in paraffin sections. In conclusion, the size of POFs provides an indirect, reliable estimation of the time elapsed from spawning and may thus be used to test both the validity of POF staging criteria for identifying daily classes of spawners and the effect of other factors (such as temperature and laboratory processing) in applications of the DEPM to S. pilchardus and other fish species.
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spawning habitat and daily egg production of sardine Sardina pilchardus in the eastern mediterranean
Fisheries Oceanography, 2006Co-Authors: Stylianos Somarakis, Konstantinos Ganias, A Machias, A Siapatis, Constantin Koutsikopoulos, Costas PapaconstantinouAbstract:Spawning habitats of two eastern Mediterranean sardine, Sardina pilchardus (Walbaum, 1792), stocks (coastal waters of central Aegean and Ionian Seas) are characterized from daily egg production method (DEPM) surveys conducted during the peak of the spawning period. The latter occurs earlier in the Aegean Sea (December) than in the less-productive Ionian Sea (February). Single-parameter quotient analysis showed that the preferred bottom depth for spawning was 40–90 m in both areas but sardine selected sites of increased zooplankton in the Aegean Sea during December and increased fluorescence in the Ionian Sea during February. Estimates of daily egg production (P) and spawning stock biomass (B) were about four times lower for the Ionian Sea (P = 7.81 eggs m−2, B = 3652 tonnes) than the Aegean Sea (P = 27.52 eggs m−2, B = 16 174 tonnes). We suggest that zooplankton biomass might not be sufficient to support sardine reproduction in the highly oligotrophic Ionian Sea where the very small sardine stock may rely on the late-winter phytoplankton bloom. Actively selecting sites with increased zooplankton or phytoplankton and feeding plasticity (the well-known switching from selective particle feeding to non-selective filter feeding in sardines) are interpreted as adaptations to grow and reproduce optimally at varying prey conditions. Despite differences in temperature and productivity regimes, reproductive performance of sardine in the Ionian Sea was very similar to that in the Aegean Sea during the peak of the spawning period. In comparing adult parameters from DEPM applications to Sardina and Sardinops stocks around the world, a highly significant linear relation emerged between mean batch fecundity (F) and mean weight of mature female (W, g) (F = 0.364W, r2 = 0.98). The latter implies that, during the peak of the spawning period, mean relative batch fecundity (eggs g−1) of sardine is fairly constant in contrasting ecosystems around the world.
Yorgos Stratoudakis - One of the best experts on this subject based on the ideXlab platform.
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fishing simulation experiments for predicting the effects of purse seine capture on sardine Sardina pilchardus
Ices Journal of Marine Science, 2010Co-Authors: Ana Marcalo, Pedro Pousaoferreira, Tiago A Marques, Joao Araujo, Karim Erzini, Yorgos StratoudakisAbstract:Marcalo, A., Marques, T. A., Araujo, J., Pousao-Ferreira, P., Erzini, K., and Stratoudakis, Y. 2010. Fishing simulation experiments for predicting the effects of purse-seine capture on sardine (Sardina pilchardus). - ICES Journal of Marine Science, 67: 334-344.To study the impact of purse-seine fishing on deliberately released sardine, two laboratory experiments were performed to explore the effect of net confinement for 10, 20, 40, and 60 min at 18 and 23°C. A third experiment considered two levels of fish density while confined for 20 and 40 min at 16°C. Analysis of cortisol and haematocrit demonstrated that stress immediately after simulated fishing was milder than in commercial fishing and did not correlate with observed delayed mortality. Scale loss was related to the probability of dying (mean values of 16.3 and 2% for dead fish and survivors, respectively), and fin erosion was a long-term stress response observed in both dead and surviving fish. Time of confinement was an important stressor, with survival rates decreasing significantly with increasing periods in the net, and temperature having an additional negative effect. Density effects were less conclusive, but there was some indication that survival correlated with biological condition (heavier fish were more likely to survive). It seems that delayed mortality after release can be substantial, although death is not certain and appropriately modified fishing operations and favourable environmental conditions may enhance the probability of sardine survival.
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sardine Sardina pilchardus spawning seasonality in european waters of the northeast atlantic
Marine Biology, 2007Co-Authors: Yorgos Stratoudakis, S H Coombs, D V P Conway, N C Halliday, Ana Lago De Lanzos, G Costas, Bruno Caneco, C Franco, Begona M Santos, Alexandra SilvaAbstract:Egg data from ichthyoplankton monitoring sites in the western English Channel (1988–2003) and northern Spain (1990–2000) and macroscopic maturity data from biological samples of purse seine landings in western and southern Iberia (1980–2004) are used to describe the spawning seasonality of sardine (Sardina pilchardus) in European waters of the northeast Atlantic using generalised additive models. The fitted models reveal a double peak in spawning activity during early summer and autumn in the western Channel, a wider spring peak off northern Spain and a broad winter season in the western and southern Iberian Peninsula. At all sites, a high probability of spawning activity was observed over at least 3 months of the year, with the duration of the season increasing with both decreasing latitude and increasing fish size. Off western and southern Iberia there are indications that the spawning season has been of longer duration in recent years for all size classes (reaching in some cases 8 months of the year for large fish). These patterns are in general agreement with existing literature and theoretical expectations of sardine spawning being driven locally by the seasonal cycle of water temperature, assuming preferences for spawning at 14 –15°C and avoidance for temperatures below 12°C and above 16°C. Regional quotient plots indicated that spawning tolerance to higher temperatures increases progressively with decreasing latitude. Despite the weak evidence for geographical differences in temperature tolerance that may have some genetic origin, the degree of spatio-temporal overlap in sardine-spawning activity within Atlantic European waters is unlikely to promote any reproductive isolation in that area.
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degeneration of postovulatory follicles in the iberian sardine Sardina pilchardus structural changes and factors affecting resorption
2007Co-Authors: Konstantinos Ganias, Yorgos Stratoudakis, Cristina Nunes, Investigacao AgrariaAbstract:Inaccuracy in the aging of postovulatory follicles (POFs) and in estimating the effect of temperature on the resorption rate of POFs may introduce bias in the determination of the daily spawning age classes with the daily egg production method (DEPM). To explore the above two bias problems with f ield-collected European pilchard (Sardina pilchardus, known regionally as the Iberian sardine), a method was developed in which the time elapsed from spawning (POF age) was estimated from the size of POFs (i.e., from the cross-sectional area in histological sections). The potential effect of the preservative type and embedding material on POF size and the effect of ambient water temperature on POF resorption rate are taken into account with this method. A highly significant loglinear relationship was found between POF area and age; POF area shrank by approximately 50% per day. POFs were also shown to shrink faster at higher temperatures (approximately 3% per degree), but this temperature effect is unlikely to be an important source of bias in the assignment of females to daily spawning classes. The embedding material was also shown to influence the size of POFs, the latter being significantly larger in resin than in paraffin sections. In conclusion, the size of POFs provides an indirect, reliable estimation of the time elapsed from spawning and may thus be used to test both the validity of POF staging criteria for identifying daily classes of spawners and the effect of other factors (such as temperature and laboratory processing) in applications of the DEPM to S. pilchardus and other fish species.
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spawning season and temperature relationships for sardine Sardina pilchardus in the eastern north atlantic
Journal of the Marine Biological Association of the United Kingdom, 2006Co-Authors: S H Coombs, Yorgos Stratoudakis, Timothy J Smyth, D V P Conway, N C Halliday, Miguel Bernal, P AlvarezAbstract:Spawning temperature preferences for sardine (Sardina pilchardus) in the eastern North Atlantic were determined from egg survey data. These were compared with climatological temperature cycles (1986 2002) derived from satellite observations, by geographical region, to predict spawning seasons. Optimum spawning temperatures were determined as 14.0-15.0°C from the English Channel to Portugal and 16.0-18.0°C for all north-west African regions. Spawning seasons were closely related to the general latitudinal trend of the annual temperature cycle, with modification by upwelling in the western Iberian and north-west African regions. Some differences between temperature-based spawning season predictions and field observations were related to variations in seasonal plankton production. Correlations in the annual time-series of favourable spawning temperatures suggested relatively strong linkages between the southern areas from Portugal to Senegal. There was no consistent relationship between annual variations in extent of temperature-predicted spawning seasons and observed field abundance of eggs.
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sardine Sardina pilchardus stress reactions to purse seine fishing
Marine Biology, 2006Co-Authors: Ana Marcalo, L Mateus, Jose Duarte Correia, Pedro Serra, Rob Fryer, Yorgos StratoudakisAbstract:Observations from the purse seine fishery off northern Portugal are used to describe the early dynamics of sardine (Sardina pilchardus) stress reactions and identify likely stressors during the commercial fishing operation. Sardine blood and muscle were sampled from the onset of fishing (school identification and encircling) to the end of fish transfer onboard (90–120 min later). The evolution of haematocrit, haemoglobin, cortisol, glucose, ionic concentrations, ATP and its catabolites were modelled using linear mixed models as a function of time spent in the net, biological (sex, reproductive state and condition) and operational variables (catch, light level and phase of fishing operation). Significant linear trends with time were detected for most stress variables and mean concentrations after 2 h in the net were similar to literature values corresponding to acute stress reactions for teleosts. Biological variables were rarely significant and explained a small proportion of variation, while operational variables were never significant. For each stress variable, levels varied considerably between trips but the temporal evolution was common across trips. Random trip effects were uncorrelated among most biochemical variables, suggesting that distinct factors affected each stress variable during the sampled trips. However, the linear trend with time spent in the net observed for most stress variables indicates that the duration of the fishing operation is an important stressor in purse seine fishing due to the progressive water volume restriction, crowding and manipulation associated to the fishing method.
S H Coombs - One of the best experts on this subject based on the ideXlab platform.
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sardine Sardina pilchardus spawning seasonality in european waters of the northeast atlantic
Marine Biology, 2007Co-Authors: Yorgos Stratoudakis, S H Coombs, D V P Conway, N C Halliday, Ana Lago De Lanzos, G Costas, Bruno Caneco, C Franco, Begona M Santos, Alexandra SilvaAbstract:Egg data from ichthyoplankton monitoring sites in the western English Channel (1988–2003) and northern Spain (1990–2000) and macroscopic maturity data from biological samples of purse seine landings in western and southern Iberia (1980–2004) are used to describe the spawning seasonality of sardine (Sardina pilchardus) in European waters of the northeast Atlantic using generalised additive models. The fitted models reveal a double peak in spawning activity during early summer and autumn in the western Channel, a wider spring peak off northern Spain and a broad winter season in the western and southern Iberian Peninsula. At all sites, a high probability of spawning activity was observed over at least 3 months of the year, with the duration of the season increasing with both decreasing latitude and increasing fish size. Off western and southern Iberia there are indications that the spawning season has been of longer duration in recent years for all size classes (reaching in some cases 8 months of the year for large fish). These patterns are in general agreement with existing literature and theoretical expectations of sardine spawning being driven locally by the seasonal cycle of water temperature, assuming preferences for spawning at 14 –15°C and avoidance for temperatures below 12°C and above 16°C. Regional quotient plots indicated that spawning tolerance to higher temperatures increases progressively with decreasing latitude. Despite the weak evidence for geographical differences in temperature tolerance that may have some genetic origin, the degree of spatio-temporal overlap in sardine-spawning activity within Atlantic European waters is unlikely to promote any reproductive isolation in that area.
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spawning season and temperature relationships for sardine Sardina pilchardus in the eastern north atlantic
Journal of the Marine Biological Association of the United Kingdom, 2006Co-Authors: S H Coombs, Yorgos Stratoudakis, Timothy J Smyth, D V P Conway, N C Halliday, Miguel Bernal, P AlvarezAbstract:Spawning temperature preferences for sardine (Sardina pilchardus) in the eastern North Atlantic were determined from egg survey data. These were compared with climatological temperature cycles (1986 2002) derived from satellite observations, by geographical region, to predict spawning seasons. Optimum spawning temperatures were determined as 14.0-15.0°C from the English Channel to Portugal and 16.0-18.0°C for all north-west African regions. Spawning seasons were closely related to the general latitudinal trend of the annual temperature cycle, with modification by upwelling in the western Iberian and north-west African regions. Some differences between temperature-based spawning season predictions and field observations were related to variations in seasonal plankton production. Correlations in the annual time-series of favourable spawning temperatures suggested relatively strong linkages between the southern areas from Portugal to Senegal. There was no consistent relationship between annual variations in extent of temperature-predicted spawning seasons and observed field abundance of eggs.
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buoyancy measurements and vertical distribution of eggs of sardine Sardina pilchardus and anchovy engraulis encrasicolus
Marine Biology, 2004Co-Authors: S H Coombs, Guillermo Boyra, L D Rueda, M B Santos, Andres Uriarte, D V P Conway, N C HallidayAbstract:Measurements were made of the density and settling velocity of eggs of sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus), using a density-gradient column. These results were related to observed vertical distributions of eggs obtained from stratified vertical distribution sampling in the Bay of Biscay. Eggs of both species had slightly positive buoyancy in local seawater throughout most of their development until near hatching, when there was a marked increase in density and they became negatively buoyant. The settling velocity of anchovy eggs, which are shaped as prolate ellipsoids, was close to predictions for spherical particles of equivalent volume. An improved model was developed for prediction of the settling velocity of sardine eggs, which are spherical with a relatively large perivitelline volume; this incorporated permeability of the chorion and adjustment of the density of the perivitelline fluid to ambient seawater. Eggs of both species were located mostly in the top 20 m of the water column, in increasing abundance towards the surface. A sub-surface peak of egg abundance was sometimes observed at the pycnocline, particularly where this was pronounced and associated with a low-salinity surface layer. There was a progressive deepening of the depth distributions for successive stages of egg development. Results from this study can be applied for improved plankton sampling of sardine and anchovy eggs and in modelling studies of their vertical distribution.
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modelling the vertical distribution of eggs of anchovy engraulis encrasicolus and sardine Sardina pilchardus
Fisheries Oceanography, 2003Co-Authors: Guillermo Boyra, S H Coombs, L D Rueda, Svein Sundby, Bjorn Adlandsvik, M B Santos, Andres UriarteAbstract:Measurements were made of the density and settling velocity of eggs of sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus), using a density-gradient column. These results were related to observed vertical distributions of eggs obtained from stratified vertical distribution sampling in the Bay of Biscay. Eggs of both species had slightly positive buoyancy in local seawater throughout most of their development until near hatching, when there was a marked increase in density and they became negatively buoyant. The settling velocity of anchovy eggs, which are shaped as prolate ellipsoids, was close to predictions for spherical particles of equivalent volume. An improved model was developed for prediction of the settling velocity of sardine eggs, which are spherical with a relatively large perivitelline volume; this incorporated permeability of the chorion and adjustment of the density of the perivitelline fluid to ambient seawater. Eggs of both species were located mostly in the top 20 m of the water column, in increasing abundance towards the surface. A sub-surface peak of egg abundance was sometimes observed at the pycnocline, particularly where this was pronounced and associated with a low-salinity surface layer. There was a progressive deepening of the depth distributions for successive stages of egg development. Results from this study can be applied for improved plankton sampling of sardine and anchovy eggs and in modelling studies of their vertical distribution.
N C Halliday - One of the best experts on this subject based on the ideXlab platform.
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sardine Sardina pilchardus spawning seasonality in european waters of the northeast atlantic
Marine Biology, 2007Co-Authors: Yorgos Stratoudakis, S H Coombs, D V P Conway, N C Halliday, Ana Lago De Lanzos, G Costas, Bruno Caneco, C Franco, Begona M Santos, Alexandra SilvaAbstract:Egg data from ichthyoplankton monitoring sites in the western English Channel (1988–2003) and northern Spain (1990–2000) and macroscopic maturity data from biological samples of purse seine landings in western and southern Iberia (1980–2004) are used to describe the spawning seasonality of sardine (Sardina pilchardus) in European waters of the northeast Atlantic using generalised additive models. The fitted models reveal a double peak in spawning activity during early summer and autumn in the western Channel, a wider spring peak off northern Spain and a broad winter season in the western and southern Iberian Peninsula. At all sites, a high probability of spawning activity was observed over at least 3 months of the year, with the duration of the season increasing with both decreasing latitude and increasing fish size. Off western and southern Iberia there are indications that the spawning season has been of longer duration in recent years for all size classes (reaching in some cases 8 months of the year for large fish). These patterns are in general agreement with existing literature and theoretical expectations of sardine spawning being driven locally by the seasonal cycle of water temperature, assuming preferences for spawning at 14 –15°C and avoidance for temperatures below 12°C and above 16°C. Regional quotient plots indicated that spawning tolerance to higher temperatures increases progressively with decreasing latitude. Despite the weak evidence for geographical differences in temperature tolerance that may have some genetic origin, the degree of spatio-temporal overlap in sardine-spawning activity within Atlantic European waters is unlikely to promote any reproductive isolation in that area.
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spawning season and temperature relationships for sardine Sardina pilchardus in the eastern north atlantic
Journal of the Marine Biological Association of the United Kingdom, 2006Co-Authors: S H Coombs, Yorgos Stratoudakis, Timothy J Smyth, D V P Conway, N C Halliday, Miguel Bernal, P AlvarezAbstract:Spawning temperature preferences for sardine (Sardina pilchardus) in the eastern North Atlantic were determined from egg survey data. These were compared with climatological temperature cycles (1986 2002) derived from satellite observations, by geographical region, to predict spawning seasons. Optimum spawning temperatures were determined as 14.0-15.0°C from the English Channel to Portugal and 16.0-18.0°C for all north-west African regions. Spawning seasons were closely related to the general latitudinal trend of the annual temperature cycle, with modification by upwelling in the western Iberian and north-west African regions. Some differences between temperature-based spawning season predictions and field observations were related to variations in seasonal plankton production. Correlations in the annual time-series of favourable spawning temperatures suggested relatively strong linkages between the southern areas from Portugal to Senegal. There was no consistent relationship between annual variations in extent of temperature-predicted spawning seasons and observed field abundance of eggs.
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buoyancy measurements and vertical distribution of eggs of sardine Sardina pilchardus and anchovy engraulis encrasicolus
Marine Biology, 2004Co-Authors: S H Coombs, Guillermo Boyra, L D Rueda, M B Santos, Andres Uriarte, D V P Conway, N C HallidayAbstract:Measurements were made of the density and settling velocity of eggs of sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus), using a density-gradient column. These results were related to observed vertical distributions of eggs obtained from stratified vertical distribution sampling in the Bay of Biscay. Eggs of both species had slightly positive buoyancy in local seawater throughout most of their development until near hatching, when there was a marked increase in density and they became negatively buoyant. The settling velocity of anchovy eggs, which are shaped as prolate ellipsoids, was close to predictions for spherical particles of equivalent volume. An improved model was developed for prediction of the settling velocity of sardine eggs, which are spherical with a relatively large perivitelline volume; this incorporated permeability of the chorion and adjustment of the density of the perivitelline fluid to ambient seawater. Eggs of both species were located mostly in the top 20 m of the water column, in increasing abundance towards the surface. A sub-surface peak of egg abundance was sometimes observed at the pycnocline, particularly where this was pronounced and associated with a low-salinity surface layer. There was a progressive deepening of the depth distributions for successive stages of egg development. Results from this study can be applied for improved plankton sampling of sardine and anchovy eggs and in modelling studies of their vertical distribution.
Stylianos Somarakis - One of the best experts on this subject based on the ideXlab platform.
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diel feeding intensity and daily ration of the sardine Sardina pilchardus
Marine Ecology Progress Series, 2011Co-Authors: Nikolaos Nikolioudakis, Isabel Palomera, A Machias, Stylianos SomarakisAbstract:The diel variation in feeding intensity and daily ration of the sardine Sardina pilchardus (Walbaum, 1792) was investigated based on 50 pelagic trawl hauls carried out during the period of thermal stratification (July 2007 and July 2008) and mixing (December 2007 and Feb- ruary 2009) in a coastal area of the North Aegean Sea (eastern Mediterranean). Concurrently col- lected hydrographic (temperature and salinity), plankton (chlorophyll a, microzooplankton and mesozooplankton) and fish parameters (somatic condition, sexual maturity and catch per unit effort of sardine, CPUE) were used to explain seasonal and inter-annual variability in feeding peri- odicity and daily ration. A piecewise regression fitted to the weight-length data indicated a signif- icant inflexion point at a length of ~100 mm that was used to split the fish sample into adults and juveniles. The stomach fullness index (stomach content mass/fish mass) was strongly dependent on size, and a generalized linear model was used instead to standardize stomach content mass. During summer, sardine fed consistently during daytime with a prominent peak at around sunset. In winter, high feeding rates were recorded in the early night (first 6 h after sunset) but not in the second half of the night. Field estimates of gastric evacuation rate (R) ranged from 0.101 to 0.225 h �1 and were strongly related to temperature (T) (R = 0.075e 0.038T , r 2 = 0.785). Daily rations were estimated by applying the Elliott-Persson and the Eggers models and varied from 2.02 to 3.67% total weight (TW) in adults and 4.18 to 5.36% TW in juveniles. A significant positive rela- tionship emerged when daily ration was regressed against the ratio of mesozooplankton biomass to sardine CPUE, implying a density-dependent rate of food consumption.
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assessment of the sardine Sardina pilchardus walbaum 1792 fishery in the eastern mediterranean basin north aegean sea
Mediterranean Marine Science, 2011Co-Authors: K Antonakakis, Marianna Giannoulaki, Stylianos Somarakis, A Machias, S Sanchez, Leire Ibaibarriaga, Andres UriarteAbstract:The aim of this study was to describe the biometric characteristics of the European sardine ( Sardina pilchardus ) catches and assess the current status of sardine stock in North Aegean Sea based on population characteristics and abundance trends. The stock was dominated by age groups 1 and 2, not exceeding age group 4. The sardine stock in this area was assessed through an Integrated Catch-at-Age model which implements a separable Virtual Population Analysis on catch at age data with weighted tuning indices. Sardine landings data derived from the commercial purse seine fishery over the period 2000-2008 were combined with the age structure of the stock as resulted from fisheries independent acoustic surveys. Sensitivity analysis of the impact of natural mortality values on stock assessment results was applied. Additionally forecast of the sardine population parameters and catches under different exploitation scenarios was implemented in a medium term basis. Results indicated that the North Aegean Sea sardine stock is considered fully exploited with the fishery operating close but over the empirical exploitation level for sustainability. Finally, the status of the sardine stock in N. Aegean Sea is discussed in relation to the sardine stocks from the western and the central Mediterranean basin.
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spawning habitat and daily egg production of sardine Sardina pilchardus in the eastern mediterranean
Fisheries Oceanography, 2006Co-Authors: Stylianos Somarakis, Konstantinos Ganias, A Machias, A Siapatis, Constantin Koutsikopoulos, Costas PapaconstantinouAbstract:Spawning habitats of two eastern Mediterranean sardine, Sardina pilchardus (Walbaum, 1792), stocks (coastal waters of central Aegean and Ionian Seas) are characterized from daily egg production method (DEPM) surveys conducted during the peak of the spawning period. The latter occurs earlier in the Aegean Sea (December) than in the less-productive Ionian Sea (February). Single-parameter quotient analysis showed that the preferred bottom depth for spawning was 40–90 m in both areas but sardine selected sites of increased zooplankton in the Aegean Sea during December and increased fluorescence in the Ionian Sea during February. Estimates of daily egg production (P) and spawning stock biomass (B) were about four times lower for the Ionian Sea (P = 7.81 eggs m−2, B = 3652 tonnes) than the Aegean Sea (P = 27.52 eggs m−2, B = 16 174 tonnes). We suggest that zooplankton biomass might not be sufficient to support sardine reproduction in the highly oligotrophic Ionian Sea where the very small sardine stock may rely on the late-winter phytoplankton bloom. Actively selecting sites with increased zooplankton or phytoplankton and feeding plasticity (the well-known switching from selective particle feeding to non-selective filter feeding in sardines) are interpreted as adaptations to grow and reproduce optimally at varying prey conditions. Despite differences in temperature and productivity regimes, reproductive performance of sardine in the Ionian Sea was very similar to that in the Aegean Sea during the peak of the spawning period. In comparing adult parameters from DEPM applications to Sardina and Sardinops stocks around the world, a highly significant linear relation emerged between mean batch fecundity (F) and mean weight of mature female (W, g) (F = 0.364W, r2 = 0.98). The latter implies that, during the peak of the spawning period, mean relative batch fecundity (eggs g−1) of sardine is fairly constant in contrasting ecosystems around the world.
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evaluation of spawning frequency in a mediterranean sardine population Sardina pilchardus Sardina
Marine Biology, 2003Co-Authors: Konstantinos Ganias, Athanassios Machias, Stylianos Somarakis, A TheodorouAbstract:The postovulatory follicle method was used to assess the frequency of spawning of sardine (Sardina pilchardus Sardina) in the Central Aegean Sea (eastern Mediterranean) in November–December 1999 and 2000. A field-based aging key for postovulatory follicles (POFs) was developed, and preliminary evidence is presented of a temperature influence on the degeneration of POFs. Bias in the fraction of day-0 spawners (females that had, were, or would spawn the night of sampling) with respect to sampling time was identified and attributed to spawning behavior. An appraisal of consistency in spawners' fractions and sex ratio, based on four sets of sequential trawl hauls, showed a considerably high small-scale variability, which suggested that spawning schools are structures limited in space and/or ephemeral in time. Sampling gear, i.e. commercial purse seines and research pelagic trawls, did not differ significantly with respect to spawners' fractions. The fractions of day-1 and day-2 females were the same during both years, and their combination resulted in more precise, composite estimates of spawning frequency. In both years, the Mediterranean sardine spawned every 11–12 days. The incidence of spawning increased significantly with fish size. When compared to all estimates available for other sardine genera, species and subspecies, the spawning frequency of the Mediterranean sardine was lower; this was attributed to the synergetic effect of oligotrophy and smaller body sizes in the Mediterranean.