Makarchouk, Andrei and Hinrichsen, Hans-Harald (1998) The vertical distribution of ichthyoplankton in relation to the hydrographic conditions in the Eastern Baltic. [Paper] In: ICES Council Meeting 1998. , 16.-19.09.1998, Cascais, Portugal . ICES Council Meeting Papers, R: 11 .

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Abstract

The vertical distribution of eggs and larvae of cod (Gadus marhua cal/arias), sprat (Sprattus sprattus balticus) and four-bearded rockling (Onas cimbrius) has been investigated in the Gdansk Deep and the Gotland Basin in May - June and July - August 1996 and 1997. Sprat eggs occurred in the wide range of depth, but cod eggs were restricted to a tiny water layer. Mean depth of cod eggs was 95 - 87 m in the Gdansk Deep and 112 -95 m in the Gotland Basin. More cod eggs than expected were found at low salinity in the period of most intensive spawning: up to 5% at 9 psu and 22 % at 10 psu in July 1996 and 8% at 10 psu in July 1997. Mean depths of sprat eggs diminished from 81 m in spring to 58 m in summer in the Gdansk Deep and from 94 m to 65 m in the Gotland Basin. At the same time sizes of sprat eggs also decreased Most of the eggs were found at the depth of the pycnocline. No significant differences in mean depths of eggs of sprat at different stages of development were discovered. Reduction in mean diameters of sprat eggs with depth and density was observed. In contrast, sizes of cod eggs showed no clear tendencies to change either from spring to summer or with changes in water density.

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