DCF (Data Collection Framework): Investigations on the ecology of herring larvae in the Greifswalder Bodden and the Western Baltic Sea, and delivery of a recruitment index for the herring assessment (N20)
To ensure an sustainable management of fish resources, natural mortality of a species' offspring (recruits) has to be incorporated into stock assessment methods.In the Data Collection Framework the Rügen Herring Larvae Survey monitors herring recruitment and with the annual recruitment index provides an important forecast instrument for stock dynamics of Western Baltic herring. Additionally, the survey represents an essential base line to investigate the drivers and stressors of natural mortality reflected in the recruitment index every year.
Shallow, inshore systems, such as Greifswald Bay are important spawning grounds for Western Baltic herring populations. Results of the larval herring monitoring program are nowadays established data bases for ICES stock assessments and represent the earliest means in herring ontogeny to forecast stock dynamics. The aim of this extensive monitoring programs is to receive the annual recruitment index as a scientifically sound data base for sustainable resource management. Furthermore the data of the extensive time series represent a unique base line to increase understanding of the ecological mechanisms structuring the reproduction success of herring in the Baltic Sea. Studies include e.g. investigating ecological functions of Greifswald Bay as retention area for larval herring, the impact of food availability on larval growth and the importance of spawning substrate, predator-prey interaction and extreme climate events.
Based on abundance and growth patterns of herring larvae along the season an index for reproduction success (N20) is developed. This index is set in relation with abundance of young-of-the-year juveniles sampled during hydroacoustic surveys during autumn. Together these metrics provide a fishery independent measure for the year class strength of herring offspring (recruitment index). Mechanistic research approches include hydrographic dispersal modeling as well as empirical investigations of egg development on inshore spawning beds and field- and laboratory experiments to study predator-prey relationships.
Permanent task 1.2001
Project status: ongoing