In this study, the feeding apparatus (gill rakers, GR) and the diet composition of European sardi... more In this study, the feeding apparatus (gill rakers, GR) and the diet composition of European sardine Sardina pilchardus populations living in two contrasting environments were compared: the upwelling area off western Iberia and the comparatively less productive region of the north-western Mediterranean Sea. The importance of local adaptations in the trophic ecology of this species was estimated. Sardina pilchardus from the Atlantic Iberian coast and from the north-western Mediterranean Sea have clear differences in the feeding apparatus and diet compositions. Those from the Atlantic Iberian coast have significantly more GRs than S. pilchardus of the same size range in the Mediterranean Sea. While S. pilchardus from the Mediterranean Sea mostly depend on prey ranging between 750-1500 and 3000-4000 µm, corresponding mostly to cladocerans, decapods and copepods, those from the Atlantic depend on smaller prey (50-500 and 1000-1500 µm) that include phytoplankton and copepods, particularly...
Interdecadal variability of the diet composition of horse mackerel Trachurus trachurus was examin... more Interdecadal variability of the diet composition of horse mackerel Trachurus trachurus was examined through analysis of the stomach contents of fish collected from the north-west and south of Portugal during 1990-1992 and 2005-2006. These decades correspond to periods of high and low feeding intensity of T. trachurus. Dietary composition of adult T. trachurus was assessed by determining the frequency of occurrence and biovolume of identified prey, and these two variables were combined to estimate an index of relative importance of prey. Dietary composition differed between areas, seasons and, in particular, decades. The most important prey in 1990-1992 were euphausiids while in 2005-2006 the most important prey were fishes. Results show that periods of different feeding intensity for T. trachurus are characterized by diets with different dominant prey items, suggesting that a description of the diet of a fish species is not complete if only based on samples collected in a limited space and time period. This result has implications for the study of marine trophic food webs, since a generalist predator may easily and rapidly change its trophic niche, to adapt to different prey abundance and availability.
Mortality during the early stages is a major cause of the natural variations in the size and recr... more Mortality during the early stages is a major cause of the natural variations in the size and recruitment strength of marine fish populations. In this study, the relation between the size-at-hatch and early survival was assessed using laboratory experiments and on field-caught larvae of the European sardine (Sardina pilchardus). Larval size-at-hatch was not related to the egg size but was significantly, positively related to the diameter of the otolith-at-hatch. Otolith diameter-at-hatch was also significantly correlated with survival-at-age in fed and unfed larvae in the laboratory. For sardine larvae collected in the Bay of Biscay during the spring of 2008, otolith radius-at-hatch was also significantly related to viability. Larval mortality has frequently been related to adverse environmental conditions and intrinsic factors affecting feeding ability and vulnerability to predators. Our study offers evidence indicating that a significant portion of fish mortality occurs during the ...
This study provides the first measurements of the standard respiration rate (R(S)) and growth dyn... more This study provides the first measurements of the standard respiration rate (R(S)) and growth dynamics of European sardine Sardina pilchardus larvae reared in the laboratory. At 15° C, the relationship between RS (µl O(2) individual(-1) h(-1)) and larval dry mass (M(D), µg) was equal to: R(S) = 0·0057(±0·0007, ± s.e.)·M(D) (0·8835(±0·0268)), (8-11% M(D) day(-1)). Interindividual differences in RS were not related to interindividual differences in growth rate or somatic (Fulton's condition factor) or biochemical-based condition (RNA:DNA).
In this study, the feeding apparatus (gill rakers, GR) and the diet composition of European sardi... more In this study, the feeding apparatus (gill rakers, GR) and the diet composition of European sardine Sardina pilchardus populations living in two contrasting environments were compared: the upwelling area off western Iberia and the comparatively less productive region of the north-western Mediterranean Sea. The importance of local adaptations in the trophic ecology of this species was estimated. Sardina pilchardus from the Atlantic Iberian coast and from the north-western Mediterranean Sea have clear differences in the feeding apparatus and diet compositions. Those from the Atlantic Iberian coast have significantly more GRs than S. pilchardus of the same size range in the Mediterranean Sea. While S. pilchardus from the Mediterranean Sea mostly depend on prey ranging between 750-1500 and 3000-4000 µm, corresponding mostly to cladocerans, decapods and copepods, those from the Atlantic depend on smaller prey (50-500 and 1000-1500 µm) that include phytoplankton and copepods, particularly...
Interdecadal variability of the diet composition of horse mackerel Trachurus trachurus was examin... more Interdecadal variability of the diet composition of horse mackerel Trachurus trachurus was examined through analysis of the stomach contents of fish collected from the north-west and south of Portugal during 1990-1992 and 2005-2006. These decades correspond to periods of high and low feeding intensity of T. trachurus. Dietary composition of adult T. trachurus was assessed by determining the frequency of occurrence and biovolume of identified prey, and these two variables were combined to estimate an index of relative importance of prey. Dietary composition differed between areas, seasons and, in particular, decades. The most important prey in 1990-1992 were euphausiids while in 2005-2006 the most important prey were fishes. Results show that periods of different feeding intensity for T. trachurus are characterized by diets with different dominant prey items, suggesting that a description of the diet of a fish species is not complete if only based on samples collected in a limited space and time period. This result has implications for the study of marine trophic food webs, since a generalist predator may easily and rapidly change its trophic niche, to adapt to different prey abundance and availability.
Mortality during the early stages is a major cause of the natural variations in the size and recr... more Mortality during the early stages is a major cause of the natural variations in the size and recruitment strength of marine fish populations. In this study, the relation between the size-at-hatch and early survival was assessed using laboratory experiments and on field-caught larvae of the European sardine (Sardina pilchardus). Larval size-at-hatch was not related to the egg size but was significantly, positively related to the diameter of the otolith-at-hatch. Otolith diameter-at-hatch was also significantly correlated with survival-at-age in fed and unfed larvae in the laboratory. For sardine larvae collected in the Bay of Biscay during the spring of 2008, otolith radius-at-hatch was also significantly related to viability. Larval mortality has frequently been related to adverse environmental conditions and intrinsic factors affecting feeding ability and vulnerability to predators. Our study offers evidence indicating that a significant portion of fish mortality occurs during the ...
This study provides the first measurements of the standard respiration rate (R(S)) and growth dyn... more This study provides the first measurements of the standard respiration rate (R(S)) and growth dynamics of European sardine Sardina pilchardus larvae reared in the laboratory. At 15° C, the relationship between RS (µl O(2) individual(-1) h(-1)) and larval dry mass (M(D), µg) was equal to: R(S) = 0·0057(±0·0007, ± s.e.)·M(D) (0·8835(±0·0268)), (8-11% M(D) day(-1)). Interindividual differences in RS were not related to interindividual differences in growth rate or somatic (Fulton's condition factor) or biochemical-based condition (RNA:DNA).
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