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

• Published in: Marine biology Vol. 145; no. 5; pp. 959 - 970
• Main Authors: COOMBS, S. H, BOYRA, G, RUEDA, L. D, URIARTE, A, SANTOS, M, CONWAY, D. V. P, HALLIDAY, N. C
• Format: Journal Article
• Language: English
• Published: Heidelberg Springer 01-10-2004; Berlin Springer Nature B.V
• Subjects: Animal and plant ecology; Animal populations; Animal reproduction; Animal, plant and microbial ecology; Biological and medical sciences; Buoyancy; Chemical analysis; Eggs; Engraulis encrasicolus; Fish; Fundamental and applied biological sciences. Psychology; Hatching; Marine; Marine biology; Plankton; Sardina pilchardus; Sea water ecosystems; Seawater; Settling velocity; Synecology; Vertical distribution; Water analysis; Water column; Bay of Biscay; ANE, Europe, Biscay Bay; Biscay Bay; Marine environment; Vertebrata; Egg; Pisces; Vertical distribution; Buoyancy; Engraulis encrasicholus
• ISSN: 0025-3162; 1432-1793
• DOI: 10.1007/s00227-004-1389-4

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.