Estimation of grey seal (Halichoerus grypus) diet composition in the Baltic Sea

We examined the digestive tract contents from 145 grey seals (Halichoerus grypus) collected between 2001 and 2004 in the Baltic Sea. We compensated for biases introduced by erosion of otoliths, both by using additional hard-part structures other than otoliths, and species-specific size and numerical correction factors. In the absence of numerical correction factors based on feeding experiments for some species, we used correction factors based on a relationship between otolith recoveryrate and otolith width. A total of 24 prey taxa were identified but only a few species contributed substantially to the diet. The estimated diet composition was, independently of the prey number estimation method and diet composition estimation model used, dominated by herring (Clupea harengus), both by numbers and biomass. In addition to herring, common whitefish (Coregonus lavaretus) and sprat (Sprattus sprattus) were important prey, but cyprinids (Cyprinidae), eelpout (Zoarces viviparus), flounder (Platichtys flesus) and salmon (Salmo salar) also contributed significantly. Our results indicated dietary differences between grey seals of different age as well as between seals from the northern (Gulf of Bothnia) and the southern (Baltic Proper) Baltic Sea.

Download Full-text

Understanding the diet composition of marine mammals: grey seals (Halichoerus grypus) in the Baltic Sea

ICES Journal of Marine Science ◽

10.1093/icesjms/fsq022 ◽

2010 ◽

Vol 67 (6) ◽

pp. 1230-1239 ◽

Cited By ~ 59

Author(s):

Karl Lundström ◽

Olle Hjerne ◽

Sven-Gunnar Lunneryd ◽

Olle Karlsson

Keyword(s):

Baltic Sea ◽

Marine Mammals ◽

Diet Composition ◽

Age Groups ◽

Geographic Region ◽

Halichoerus Grypus ◽

The Baltic Sea ◽

Sampling Condition ◽

The Baltic ◽

Sampling Procedures

AbstractLundström, K., Hjerne, O., Lunneryd, S-G., and Karlsson, O. 2010. Understanding the diet composition of marine mammals: grey seals (Halichoerus grypus) in the Baltic Sea. – ICES Journal of Marine Science, 67: 1230–1239. Dietary studies are important in understanding the ecological role of marine mammals and in formulating appropriate management plans in terms of their interactions with fisheries. The validity of such studies has, however, often been compromised by unrepresentative sampling procedures, resulting in false weight being given to external factors seeming to influence diet composition. The bias caused by non-random sampling was examined, using canonical correspondence analysis to assess how the prey species composition in digestive tract samples of Baltic grey seals (Halichoerus grypus) was related to spatial, temporal, and demographic factors and to whether the samples were collected in association with fishing gear or not (“sampling condition”). Geographic region explained the largest fraction of the observed variation, followed by sampling condition, age group, and year. Season and gender were not statistically significant. Segregation of the two age categories “pups” and “juveniles–adults”, and the two geographic categories “Baltic proper” and “Gulf of Bothnia” are proposed to estimate the diet and fish consumption of the Baltic grey seal population as a whole. Atlantic herring was the most commonly recovered prey item in all areas and age groups, followed by European sprat in the south, and common whitefish in the north. Pups had eaten relatively more small non-commercial species than older seals.

Download Full-text

Diet composition of herring (Clupea harengus L.) and cod (Gadus morhua L.) in the southern Baltic Sea in 2007 and 2008

Oceanological and Hydrobiological Studies ◽

10.2478/s13545-011-0046-z ◽

2011 ◽

Vol 40 (4) ◽

Cited By ~ 6

Author(s):

Diana Dziaduch

Keyword(s):

Baltic Sea ◽

Diet Composition ◽

Gadus Morhua ◽

Clupea Harengus ◽

The Baltic Sea ◽

Commercial Fish ◽

Southern Baltic Sea ◽

Starting Point ◽

Southern Baltic ◽

The Baltic

AbstractDiet composition of two commercial fish species, herring and cod, were studied in some regions (mainly Gda’nsk and Bornholm Basins, and the Polish coast) of the southern Baltic Sea in 2007 and 2008. Herring is the dominant zooplanktivorous species in the ecosystem of the Baltic Sea, but apart from mesoplanktonic organisms it also eats macroplanktonic and benthic species in considerable amount. The diet of cod consists of fish and crustaceans from pelagic, hyperbenthic and benthic habitats. The feeding preferences of fish indirectly reflect changes in the whole food chain in the Baltic Sea. This research focuses specifically on these invertebrate species, which are eliminated from the environment by most of the ichthyofauna of this region. The aim of this research is to examine the role of invertebrate organisms belonging to Crustacea in the diet of herring and adult cod to supply updated results about feeding of these fish as little data have been collected since the 1990s. The present study is a preliminary survey and results can not be considered conclusive. The restricted numbers of analyzed stomachs of fish and selected seasons of the year addressed in this paper are a starting point for further studies with a larger scope. In this study, 20 to 90% of herring had empty stomachs. Mesozooplankton dominated the diets of small and large herring. Mysidacea, which were historically important prey for herring, are now scarce and have been replaced by planktonic Amphipoda. In the case of cod, consumption of Mysidacea has never been as low as in this study. As for other invertebrate prey, the benthic isopod Saduria and Crangon shrimp achieved the highest amount by number and weight. These results show distinct changes in diet when compared to previous investigations and require verification at a larger spatial scale.

Download Full-text

Emergence of the Zoonotic Biliary Trematode Pseudamphistomum truncatum in Grey Seals (Halichoerus grypus) in the Baltic Sea

PLoS ONE ◽

10.1371/journal.pone.0164782 ◽

2016 ◽

Vol 11 (10) ◽

pp. e0164782 ◽

Cited By ~ 4

Author(s):

Aleksija S. Neimanis ◽

Charlotta Moraeus ◽

Anders Bergman ◽

Anders Bignert ◽

Johan Höglund ◽

...

Keyword(s):

Baltic Sea ◽

Halichoerus Grypus ◽

The Baltic Sea ◽

The Baltic

Download Full-text

An ecosystem model of food web and fisheries interactions in the Baltic Sea

ICES Journal of Marine Science ◽

10.1016/s1054-3139(03)00098-5 ◽

2003 ◽

Vol 60 (5) ◽

pp. 939-950 ◽

Cited By ~ 89

Author(s):

Chris J Harvey ◽

Sean P Cox ◽

Timothy E Essington ◽

Sture Hansson ◽

James F Kitchell

Keyword(s):

Baltic Sea ◽

Food Web ◽

Species Interactions ◽

Gadus Morhua ◽

Population Analysis ◽

Clupea Harengus ◽

Trophic Relationships ◽

The Baltic Sea ◽

Management Actions ◽

The Baltic

Abstract Because fisheries operate within a complex array of species interactions, scientists increasingly recommend multispecies approaches to fisheries management. We created a food web model for the Baltic Sea proper, using the Ecopath with Ecosim software, to evaluate interactions between fisheries and the food web from 1974 to 2000. The model was based largely on values generated by multispecies virtual population analysis (MSVPA). Ecosim outputs closely reproduced MSVPA biomass estimates and catch data for sprat (Sprattus sprattus), herring (Clupea harengus), and cod (Gadus morhua), but only after making adjustments to cod recruitment, to vulnerability to predation of specific species, and to foraging times. Among the necessary adjustments were divergent trophic relationships between cod and clupeids: cod exhibited top-down control on sprat biomass, but had little influence on herring. Fishing, the chief source of mortality for cod and herring, and cod reproduction, as driven by oceanographic conditions as well as unexplained variability, were also key structuring forces. The model generated many hypotheses about relationships between key biota in the Baltic Sea food web and may ultimately provide a basis for estimating community responses to management actions.

Download Full-text