Investigations on the feeding ecology of Baltic Sea herring (Clupea harengus L.) and sprat (Sprattus sprattus L.)

• Main Author: Bernreuther, Matthias
• Other Authors: Temming, Axel (Prof. Dr.)
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Staats- und Universitätsbibliothek Hamburg Carl von Ossietzky 2007
• Subjects: Clupeiden; Nahrungszusammensetzung; Magenleerung; Bioenergetik; Konsumtion; clupeids; diet composition; gastric evacuation; bioenergetics; consumption; 590 Tiere (Zoologie); 42.94 Meeresbiologie; ddc:590; North East Atlantic
• Online Access: http://nbn-resolving.de/urn:nbn:de:gbv:18-33346; https://ediss.sub.uni-hamburg.de/handle/ediss/1765

The general aim of this work was to investigate the feeding ecology of the main planktivorous fish species in the Baltic Sea, herring and sprat. Extensive diet analyses on herring and sprat in the Bornholm Basin from April 2002 to November 2003 revealed that diets of both dominant planktivores were quite similar, indicating strong potential competition for food resources, which was supported by the relatively low amount of stomach contents in comparison to other water bodies in the North-east Atlantic and Black Sea. Interestingly, there was no evidence that herring, a facultative filter-feeder, had a competitive advantage expressed as consumption in % BW (body weight) over sprat, a species that is an obligate particulate feeder and does not filter feed. The results of a 24 h in situ prey selectivity experiment suggested that both species actively selected adult females and males (c6) and older copepodite stages (c4-5) of mainly Temora longicornis and Pseudocalanus acuspes and additionally cladocerans (Evadne nordmanni and Podon spp). Due to the stage-resolved analyses of zooplankton caught in net samples and analysed in fish stomachs and the diel observation protocol, periods were identified during which younger copepodite stages (c1-3) were actively selected. The importance of employing stage-resolved analyses in selectivity investigations was stressed by calculating an “impact factor” to quantify the bias occurring when such analyses were not included. Pooled results (that did not include resolve to stage) underestimated the feeding impact on older copepodite stages c4 and c5 and mature adult (c6) females and males. To adequately assess the potential for top-down control, laboratory gut content analyses of herring and sprat must be combined with experiments on food consumption rates. Gaps in knowledge concerning important parameters used to derive food consumption estimates were eliminated by conducting a series of experiments that quantified: 1) the effect of temperature on metabolic rate of juvenile herring, ...