Vertical distribution and egg survival of Baltic sprat in relation to temperature and oxygen conditions - implications for stock development
2002 (English)Conference paper (Other academic)
Sprat, Sprattus sprattus, is a key species in the Baltic Sea. Besides being a target species in the Baltic mixed clupeoid fishery it is a major zooplanktivore and dominates, together with herring, one of four trophic levels in the Baltic Sea food web. Occasionally strong year classes of Baltic sprat are followed by a number of year classes below average. During the 1990s however a series of year classes above average were produced and the stock reached historically high levels with implications for the Baltic food web. Spawning stock biomass and recruitment are poorly related suggesting that environmental conditions have a great impact on the year-class strength. In the main spawning areas, i.e. the Baltic deep basins, egg development occurs at highly varying environmental conditions. In the present investigation egg specific gravity and variation in vertical egg distribution as well as egg survival in relation to temperature and oxygen conditions were studied. Incubation of eggs revealed significantly lower viable hatch at <5 degree C. Egg occurrence in relation to oxygen concentration suggested lower survival at <2 ml/l. Egg specific gravity averaged 1.00858 plus or minus 0.00116 g/cm3 during peak spawning but was significantly higher early in the season and significantly lower towards the end of the spawning period. In general, eggs kept buoyant in the deep layers at low oxygen conditions early in the season, developed at more favourable oxygen concentrations but at poor temperature conditions during peak spawning, and were distributed at both more favourable temperature and oxygen conditions towards the end of the spawning season. Using conditions at in average occurrence of eggs during peak spawning for the period 1970-2000 the relative importance of temperature and oxygen conditions was evaluated. Results suggested that variation in temperature is the most important factor affecting egg survival in the Bornholm basin (SD 25), that mainly oxygen conditions determine the survival rate in the Gotland basin (SD 28) whereas variation in both temperature and oxygen conditions influence survival in the Gdansk Deep (SD 26). In conclusion, opportunities for egg survival are influenced by both temperature conditions following mild or severe winters as well as by frequency and magnitude of saline water inflows into the Baltic Sea.
Place, publisher, year, edition, pages
International Council for the Exploration of the Sea , 2002.
, ICES CM 2002 Documents, O:08
Sprattus sprattus, Baltic Sea, vertical distribution, temperature, oxygen, egg survival
Research subject Biology
IdentifiersURN: urn:nbn:se:hgo:diva-183DOI: 10.1023/B:hydr.0000018212.88053.aaArchive number: ICES CM 2002/O:08OAI: oai:DiVA.org:hgo-183DiVA: diva2:276045