Spatial distribution of ciliates, copepod nauplii and eggs, Engraulis japonicus post-larvae and microzooplankton herbivorous activity in the Yellow Sea, China

The abundance of anchovy Engraulis japonicus larvae, >20 mum ciliates, copepod eggs and nauplii, and microzooplankton herbivorous activity were studied in the Yellow Sea in June 2000. Anchovy juveniles and larvae were found in only 6 of the 19 stations sampled. The ciliate communities were dominated by 2 species: Laboea strobila and Strombidium compressum. In the surface waters, the abundance of L. strobila ranged between 0 and 560 ind. l(-1). S. compressum only appeared at Stns 15 to 18 (20 to 3300 ind. l(-1)). L. strobila was found mainly in the top 20 m. The abundance of L. strobila was less than 50 ind, l(-1) in waters deeper than 25 m. S, compressum showed subsurface abundance peaks at the salinity abnormality. Tintinnids occurred occasionally with abundance lower than 100 ind. l(-1), The total ciliate abundance fell in the range of 40 to 3420 ind. l(-1). The ciliate biomass in the surface water and the water column ranged between 0,15 and 6.76 mug C l(-1) and 0.4 and 134.4 mg C m(-2), respectively, In the surface waters, the abundance of copepod eggs and nauplii ranged from 0,3 to 3.1 and 1,1 to 15.6 ind, l(-1), respectively. The average abundance of copepod eggs and nauplii in 4 depth (0, 5, 10 and 20 m) fell in the range of 0.2 to 2.8 and 1.0 to 29.4 ind. l(-1), respectively. As a food item of the E. japonicus post-larvae, the abundance of copepod nauplii and eggs appeared to be low. The abundance peaks of ciliate and E, japonicus post-larvae coincided. Although not found in the gut of E, japonicus post-larvae, aloricate ciliates might be ingested by first-feeding anchovy larvae, preventing initial starvation and prolonging the time to irreversible starvation. On the basis of dilution experiments with positive microzooplankton grazing rates, microzooplankton grazed at rates of 0 to 0.61 d(-1). Grazing pressure of microzooplankton on chlorophyll a standing stock (P-i) and potential chlorophyll a primary production (P-p) were 17 to 46% and 35 to 109% d(-1), respectively.

Wind mixing, food availability and mortality of anchovy larvae Engraulis encrasicolus in the northern Adriatic Sea

A study was carried out in June/July 1996 in the River Po outflow in the northern Adriatic to investigate spawning of anchovy Engraulis encrasicolus and survival of larvae in relation to food availability and wind mixing. Hydrographic- and bongo net sampling was carried out on 2 grid surveys; one after a period of low winds and settled weather, and the other after an intervening period of strong winds, which resulted in a decrease in water column stratification. The spawning areas of anchovy and the larval distributions were associated with the river outflow plume (most clearly on the second survey grid, after the period of higher winds). Potential food particles for anchovy larvae, primarily copepod nauplii and copepodite stages, were also concentrated in the area influenced by the river outflow. Although there was a nearly 50% reduction in the mean water column abundance of potential food particles between the 2 survey grids, mostly due to a decline in abundance outside the immediate river plume area, there was no significant change in mortality of anchovy larvae between the 2 grids; the exponential decline in numbers of eggs and larvae to 10 mm in length being equivalent to overall mortality rates of 43.2%/d on the first survey and 44.7%/d on the second. The resilience of larval survival under potentially less favourable feeding conditions, following the period of wind mixing, was ascribed, in part, to the maintenance of local water column stratification by the superficial low salinity input from the River Po. This stratification in the immediate outflow area was associated with the presence of concentrated layers of potential food particles (typically >50 particles/L and 1.5 to 2.8 times the mean water column abundance) in the upper 10 m of the water column, coincident with peak numbers of anchovy larvae. However, since there was no evidence for lower larval survival in areas, less influenced by the immediate river outflow plume, a simple direct relationship between enhanced water column stability, improved feeding conditions and larval survival was not supported.

Modelling the vertical distribution of eggs of anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus)

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.

Buoyancy measurements and vertical distribution of eggs of sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus)

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.

Feeding of anchovy Engraulis encrasicolus larvae in the northwestern Adriatic Sea in response to changing hydrobiological conditions

Results from depth integrated and vertically stratified plankton sampling in the northwestern Adriatic Sea were used for comparison of gut contents of larvae of European anchovy Engraulis encrasicolus with composition and concentration of potential prey in the plankton. Sampling was carried out over a grid of stations both before and after a period of increased wind mixing to investigate changes in food availability and larval feeding success. All larvae had empty guts soon after dusk, indicating daytime feeding and rapid gut clearance. With increasing larval length there was a greater percentage of specimens with empty guts, despite suitable food being available in the plankton for these larger larvae; this suggests differential gut evacuation during sampling-possibly related to the degree of gut development. Larval diet was principally the various developmental stages of copepods, especially calanoid and cyclopoid nauplii, which were preferentially selected by larvae, whereas selection was against harpacticoid nauplii. Lamellibranch larvae and Peridinium were generally abundant in the plankton, but were only present in the gut contents in any number when the preferred dietary organisms were present in the plankton at low concentrations. The number of food organisms in the gut contents increased with concentration of the preferred food organisms in the plankton up to a limit of similar to 50 organisms/l. Within the upper 18 m of the water column, there was a reduction in the proportion of larvae with food in their guts with increasing depth, irrespective of the vertical profile of food concentration. Following a period of wind mixing the composition of the plankton changed. This was reflected in the diet of anchovy larvae, which altered in parallel. There was also an overall 41% decrease in concentration of the preferred food particles of larvae in the plankton following the period of wind mixing, but larvae were still able to maintain their food intake. These results show that anchovy larvae can successfully adapt their diet to a changing prey field and suggest that in the conditions observed in the northern Adriatic, quite radical changes in the feeding environment were probably insufficient to affect overall larval mortality.

The life cycle of Engraulis encrasicolus sensu lato in the Guadiana estuary: Ecology, Ecohydrology and Biology

Tese dout., Ecologia das populações, Universidade do Algarve, 2007

Crescimento de larvas de Sardina pilchardus e Engraulis encrasicolus e dieta de Sardina pilchardus na Baía de Biscaia (NE Atlântico)

Dissertação de mest., Aquacultura e Pescas (Pescas), Faculdade de Ciências e Tecnologia, Univ. do Algarve, 2010

Descripción huevos y larvas de anchoveta peruana (Engraulis ringens J.)

Estudio en las aguas costeras entre Chimbote al Norte y Callao al Sur, muestras de plancton que contenían gran numero de larvas de peces, la mayoría evidenciaba una sola especie, identifica como Engraulis ringerns, la anchoveta peruana

Un análisis del número de vertebras de la anchoveta peruana (engraulis ringens j.)

Datos sobre recuentos vertebrales, branquiales y radios de las aletas dorsal y anal de las anchovetas peruanas. Como las variaciones del numero de vértebras son por lo general más usadas para la diferenciación de poblaciones de peces, en esta primera contribución se presenta el análisis estadísticos del número de vertebras en diferentes localidades, dejando los otros datos para un trabajo futuro.

La Anchoveta (Engraulis ringens J.): conocimiento actual sobre su biología ecología y pesquería

Describe la vida de la anchoveta que comprende reproducción, tasa de crecimiento, longevidad, nutrición y distribución de la especie en el tiempo. Fluctuaciones del stock, en base a las medidas de esfuerzo y captura.

Validez de la lectura de otolitos para determinar la edad de las anchoveta (engraulis ringens)

La validez de los métodos usados en determinar la edad y crecimiento de los peces es un problema de primordial importancia en Biología Pesquera. Actualmente la mayoría de investigadores hacen uso de métodos basados en los cambios estacionales que experimentan determinadas estructuras óseas del pez como escamas, otolitos y vértebras. En ese trabajo se ha tratado de solucionar el problema en la anchoveta usando para la determinación de la edad en método de lectura de otolitos.

Estudio sobre la variación del contenido de grasa en la anchoveta peruana (engraulis ringens J.)

Estudio de la variación estacional del contenido graso en las muestras de anchoveta analizadas en Chimbote, Callao e Ilo, observándose dos máximos: uno de otoño y otro en primavera; pero más marcadamente en otoño, en tanto, que el bajo contenido graso se presenta en verano y más intensamente en invierno.

Investigaciones adicionales de la pesquería de la anchoveta (Engraulis ringens) en el Perú

Examina las relaciones de los efectos de la población de aves guaneras y la pesquería comercial sobre la abundancia y cosecha total sostenible de la anchoveta. Ademas estudia las relaciones promedios entre esfuerzo pesquero, abundancia de la población y cosecha total aprovechando de un modelo generalizado de productividad de poblaciones de peces, afín de proporcionar algunas bases adicionales para decidir si algún otro modelo es más apropiado en este caso que la logística de Verhulst - Pearl.