The distribution of Baltic sprat, Sprattus sprattus L.- causes and consequences.

Stepputtis, Daniel (2006) The distribution of Baltic sprat, Sprattus sprattus L.- causes and consequences. Open Access (PhD/ Doctoral thesis), Christian-Albrechts-Universität, Kiel, Kiel, Germany, 148 pp.

[thumbnail of d1795.pdf]
Preview
Text
d1795.pdf - Published Version
Available under License German copyright act UrhG.

Download (4MB) | Preview

Abstract

This thesis shows different aspects of the distribution of adult sprat in the central Baltic Sea. The seasonal development of the horizontal distribution of sprat was investigated in 2002/2003 under the influence of a shift in the environmental regime. During the period of investigation, several inflow events of saline and well oxygenated water into the deep Basins of the Baltic Sea were observed. This includes the first major Baltic inflow (MBI) since 1993, which occurred in January/February 2003 and dramatically changed the environmental condition in the Bornholm Basin. Prior to this MBI, a ‘typical’ seasonal development of the sprat abundance in the Bornholm Sea was observed. After the MBI in 2003, relatively cold temperatures were observed in the Bornholm Basin throughout the water column. It was assumed that these unfavourable conditions lead to an avoidance migration of sprat in the more eastern areas. This was supported by an increase of the sprat abundance in the Gotland Basin. The abiotic parameters that determine the vertical distribution of sprat were investigated during several cruises, including meso-scale and small-scale investigations. Temperature and oxygen content of the water were confirmed as main driving factors for the vertical distribution of sprat, whereby the relevant thresholds were determined as 5°C and 1ml/l oxygen content. Other environmental parameters were identified to have an impact on the diel vertical migration (DVM) of sprat. Light was assumed to induce DVM of sprat, whereas the causal relationship remained unclear. Strong vertical temperature gradients can prevent DVM, if the minimum temperature, to be passed is colder than 5°C. On the other hand, cold water was crossed where the temperature gradient was relatively low. The influence of salinity and depth was found to be negligible. The results of these investigations were used to develop two models for the vertical distribution of sprat. The first model approach bases upon the calculation of the probability of occurrence, calculated for temperature and oxygen. This simple model was successfully applied to data, derived during spawning time in spring 2002, but revealed weaknesses when applied to other seasons. Furthermore, a more complex was introduced, whereas the vertical distribution of sprat was modelled as behavioural response to external stimuli. This approach was successfully applied to model the diel vertical migration of sprat. With the latter model approach a tool is delivered to include the vertical distribution into ecosystem models and is therefore an important improvement in ecosystem research in the Baltic. With regard to the consequences of the distribution patterns of Baltic sprat it was shown, that the vulnerability of key zooplankton species to predation by clupeids is highly influenced by the spatial overlap of predator and prey. Highest impact of sprat on zooplankton species was found for Pseudocalunus sp. during spring and Temora longicornis during summer.

Document Type: Thesis (PhD/ Doctoral thesis)
Thesis Advisor: Schnack, Dietrich
Keywords: Bornholmbecken, Sprotte, Hering, Ostsee, Baltic Sea, Fisch, fish, Biologie, biology, Hydroakustik, hydroacoustic
Research affiliation: OceanRep > Leibniz-Institut für Meereswissenschaften
OceanRep > GEOMAR > FB3 Marine Ecology > FB3-EV Marine Evolutionary Ecology
Refereed: No
Date Deposited: 03 Dec 2008 16:51
Last Modified: 16 Jan 2023 10:42
URI: https://oceanrep.geomar.de/id/eprint/5663

Actions (login required)

View Item View Item