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

Abstract

Understanding and modelling the vertical distribution of fish eggs in the water column is a major challenge for future use of underway‐continuous egg samplers as estimators of the total egg abundance. This study presents modelling of field data of anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus) egg vertical distribution obtained from LHPR sampling in the Bay of Biscay. Starting from Sundby's model [Deep‐Sea Res.30 (1983) 645], improvements were achieved through successive modifications concerning egg buoyancy and vertical propagation of wind‐induced turbulence. In addition, measurements of egg settling velocity and buoyancy by stages were included as inputs for the model. The best model fitting was achieved through the adoption of a gradual turbulence vertical decay model (proportional to the inverse of the water density profile), a Gaussian variability of egg density and adaptability of the egg density to the surrounding water by means of permeability of the chorion. This led to improvements over the Sundby original model. The coefficient of determination (R2) of the modelled egg abundance profiles compared with the observed ones was around 80% for both sardine and anchovy. The model described successfully the vertical distribution of eggs for waters of high surface salinity (R2 of almost 90%), but less so for waters of low surface salinity (R2 of about 70%).

Changes in egg buoyancy during development and its effects on the vertical distribution of anchovy eggs

“…Coombs (1981) introduced the density gradient column (DGC) to measure the neutral buoyancy of fish eggs. Subsequently, models for many species have been developed using the DGC (Boyra et al, 2003;Coombs et al, 1985;Haug et al, 1986;Tanaka, 1990), with some limitations linked to limited biological knowledge (Goarant et al, 2007).…”

Simulating vertical turbulent dispersal with finite volumes and binned random walks

“…The results will then be comparable to the Eulerian finite-volume approach used by Ådlandsvik et al (2001) and Boyra et al (2003), and has the advantage that it can be used as a component in a wider particle-tracking or individualbased framework.…”

“…Christensen et al 2007, this Theme Section), and the vertical distribution of fish eggs (e.g. Ådlandsvik et al 2001Ådlandsvik et al , Boyra et al 2003. Such studies can be done in the Eulerian framework, which models the density of tracers as it evolves in time, or in the Lagrangian or individual-based framework, which adds single particles or individuals to a numeric model of the ocean and tracks their motion.…”

A maximum likelihood method for obtaining incubation temperature of eggs of synchronous spawning fishes

“…The LHPR is a vertical sampler that was towed at 2.5 knots in an oblique haul (Boyra et al, 2003;Coombs et al, 2004), and from which a series of samples was taken every 1-2 min. LHPR includes number of eggs per stages for a number of depths independently.…”

“…On the one hand, there is no unique modal depth for the egg vertical distribution. For instance Sundby (1983) and Boyra et al (2003) found surface peaks of egg distribution for high salinity areas, and sub-surface peaks with low salinity. On the other hand, the incubation temperature of all the eggs found at the station has likely not been constant throughout the whole development of the eggs.…”