Quantifying predation on Baltic cod early life stages

• Published in: Canadian Journal of Fisheries and Aquatic Sciences
• Main Authors: Neumann, Viola, Schaber, Matthias, Eero, Margit, Böttcher, Uwe, Köster, Friedrich-W.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2017
• Subjects: Text; article; ddc:570; Gadus morhua
• Online Access: https://doi.org/10.1139/cjfas-2016-0215; https://www.openagrar.de/receive/openagrar_mods_00033404; https://www.openagrar.de/servlets/MCRFileNodeServlet/openagrar_derivate_00008169/dn059354.pdf

Predation on cod (Gadus morhua) eggs by sprat (Sprattus sprattus) and herring (Clupea harengus) is known to be one of the processes influencing reproductive success of the eastern Baltic cod and has been reported to have contributed to lack of recovery of the stock in the 1990s. This study quantifies the predation on cod eggs in the Bornholm Basin, the major spawning area of cod in the central Baltic Sea, in the 1990s in comparison with the second half of the 2000s. The analyses involve estimating daily consumption rates of predator populations, which are then compared with corresponding daily egg production rates. As a methodological advancement compared with earlier studies, spatially resolved information on predator distribution and abundance is utilized in quantifying predator stock size. This resulted in more realistic consumption estimates in relation to overall egg production compared with earlier studies that consistently overestimated predation pressure by clupeids. Our results suggest a generally lower predation pressure on cod eggs in the mid- to late 2000s, due to a combination of reduced predator abundance and lower daily rations by individual predators. Il est établi que la prédation des oeufs de morue (Gadus morhua) par les sprats (Sprattus sprattus) et les harengs (Clupea harengus) est un des processus qui influencent le succès de reproduction de la morue de la mer Baltique orientale, et des rapports indiquent qu’elle contribuerait a` expliquer l’absence de rétablissement du stock dans les années 1990. L’étude quantifie la prédation des oeufs de morue dans le bassin de Bornholm, le principal lieu de frai des morues dans la partie centrale de la mer Baltique, dans les années 1990 comparativement a` la deuxième moitié des années 2000. Les analyses comprennent l’estimation des taux de consommation quotidiens de populations de prédateurs, qui sont ensuite comparés aux taux de production d’oeufs quotidiens correspondants. Une avancée méthodologique par rapport aux études antérieures consiste en ...