Stage Dependent Vertical Distribution of Haddock (Melanogrammus aeglefinus) Eggs in a Stratified Water Column: Observations and Model

Abstract

The depth distribution of four development stages of haddock (Melanogrammus aeglefinus) eggs was measured during May 1984 in a continuously stratified water column over Browns Bank. The egg profile varied with development. Early stage eggs were most concentrated near the sea surface whereas late stage eggs were distributed uniformly over depth or had a subsurface maximum. In order to explain the shape of these profiles a one-dimensional (vertical) advection–diffusion model including density stratification was used. Model egg profiles compared favourably with observed profiles and indicate that a large proportion (>30%) of haddock eggs are below the Ekman depth (δe. This proportion increases as the eggs develop. For example more than 50% of the stage III and IV eggs are below δe. Surface drift bottles and other indicators of the very near surface wind-driven transport would appear to be poor indicators of egg transport in haddock and possibly several other species, such as Atlantic cod (Gadus morhua) and mackerel (Scomber scombrus).