Food composition and prey selection of cod, Gadus morhua (Actinopterygii: Gadiformes: Gadidae), in the southern Baltic Sea
Background. At the end of 1980s, ecological regime shifts occurred in the Baltic. Since, the Baltic fish assemblage has been dominated by sprats, whereas before cod was the dominant fish species. The majority of previous food studies refer to the period before the shift. This raises the question, how changes in the Baltic ecosystem have affected the diet of cod. The aim of the presently reported study was to identify the differences in the food composition of cod depending on the area, depth, season, and the cod size and compare it with the findings from the 1970s and 1980s. Materials and Methods. Food composition and selection of prey size for Baltic cod was evaluated by examining the stomach contents of 556 adult cod, collected in 2006 and 2007. Fish stomachs were sampled from research catches within the Polish Exclusive Economic Zone. Results. The main component of the cod diet were the clupeids, constituting more than 67% of the total weight of the food recovered from the specimens studied. Other fishes in the diet represented Gobiidae, Ammodytidae, as well as young cod. The dominant invertebrate in the diet was the isopod Saduria entomon which accounted for 13% of the diet by weight. The weight proportion of larger fish, such as herring, Clupea harengus (L.), and cod, increased with the cod size, while the proportion of small- and medium-sized fish (sprats, gobies) decreased. The food composition of cod varied seasonally. The weight proportion of European sprat, Sprattus sprattus (L.), was much higher in winter (55%) than in fall (27%), while the proportion of cod in the diet was higher in the fall (10%) than in winter (4%). The proportion of sprat in the diet increased with depth, while that of Ammodytidae and Gobiidae showed a decreasing trend. At depths greater than 40 m, the proportion of invertebrates in cod stomachs decreased. This study demonstrated a significant area effect for sprat; year effect for sprat and Saduria entomon; a seasonal effect for young cod and S. entomon; and a depth effect for sprat, young cod, and S. entomon. The occurrences of herring and small cod increased in the stomach as the predator increased, while no significant relation was found for sprat and S. entomon. The data collected do not indicate that cod select a specific size of sprat or herring, though cod were found to use size selection for S. entomon and juvenile cod. Conclusion. The food composition of cod has undergone certain changes compared to results of Załachowski (1977, 1985), which covered the 1970s and 1980s. Currently, the proportion of clupeids in the food is approximately 67% (in weight), while during the 1977–1982 it was in the range of 25%–50% depending on cod length. In 2006 and 2007 sprat was the main cod diet component rather than herring.
- Alheit J., Möllmann C., Dutz J., Kornilovs G., Loewe P.,Mohrholz V., Wasmund N. 2005. Synchronous ecological regime shifts in the central Baltic and the North Sea in the late 1980s. ICES Journal of Marine Science 62 (7):1205–1215. DOI: 10.1016/j.icesjms.2005.04.024
- Anonymous 2012. Report of the Baltic fisheries assessment working group (WGBFAS). 12–19 April 2012, ICES Headquarters, Copenhagen. ICES CM 2012/ACOM: 10.
- Arntz W.E. 1977. The food of adult cod (Gadus morhua L.) In the western Baltic. Meeresforschung 26: 60–69.
- Chrzan F. 1962. Pokarm i odżywianie się dorsza w Zatoce Gdańskiej. [The food and feeding of cod in the Gulf of Gdańsk.] Prace MIR, seria A 11: 161–199. [In Polish, with English summary.]
- Cięgielewicz W., Załachowski W., Szypuła J., Krzykawski S.,Krzykawska I. 1972. Odżywianie się ryb przemysłowych południowego Bałtyku. [Feeding of commercial fishes of the southern Baltic.] Ekosystemy morskie 2: 363–450 [In Polish.]
- Costello M. J. 1990. Predator feeding strategy and prey importance:a new graphical analysis. Journal of Fish Biology 36 (2):261–263. DOI: 10.1111/j.1095-8649.1990.tb05601.x
- Härkönen T.J. 1986. Guide to the otoliths of the bony fishes of the northeastern Atlantic. Danbiu ApS, Hellerup, Denmark.
- Helgason T., Gislason H. 1979. VPA analysis with species interactions due to predation. International Council for the Exploration of the Sea, Demersal Fish Committee, G:52.
- Horbowy J. 1996. The dynamics of Baltic fish stocks on the basis of a multispecies stock-production model. Canadian Journal of Fisheries and Aquatic Sciences 53 (9):2115–2125. DOI: 10.1139/f96-128
- Nelder J.A., Wedderburn R.W.M. 1972. Generalized lineał models. Journal of the Royal Statistical Society, Series A (General) 135 (3): 370–384.
- Neuenfeldt S., Beyer J.E. 2003. Oxygen and salinity characteristics of predator–prey distributional overlaps shown by predatory Baltic cod during spawning. Journal of Fish Biology 62 (1): 168–183. DOI: 10.1046/j.1095-8649.2003.00013.x
- Neuenfeldt S., Beyer J.E. 2006. Environmentally driven predator–prey overlaps determine the aggregate diet of the cod Gadus morhua in the Baltic Sea. Marine Ecology Progress Series 310: 151–163. DOI: 10.3354/meps310151
- Reimann Z. 1955. Odżywianie się i pokarm młodocianego dorsza (Gadus callarias) południowego Bałtyku. [Nutrition and food of young cod (Gadus callarias) of the southern Baltic.] Prace MIR 8: 171–186. [In Polish, with English summary.]
- Strzyżewska K. 1959. Odżywianie się i pokarm dorsza bałtyckiego.[Nutrition and food of Baltic cod.] Pp. 45–59. In:Mańkowski W. (ed.) Dorsz bałtycki: jego połowy i technologia.[Balitic cod: ts catches and processing technology.]Gdańskie Towarzystwo Naukowe, Gdańsk, Poland.[In Polish.]
- Strzyżewska K. 1962. Odżywianie się i pokarm dorsza Bałtyku Południowego. [Nourishment and food of southern Balic cod]. Prace MIR, seria A 11: 387–419. [In Polish, with English summary.]
- Uzars D. 1985. Food composition in the Eastern Baltic cod for the 1963–1984 period. ICES CM 1985/J3.
- Uzars D., Baranova T., Yula E. 2000. Variation in environmental conditions, feeding and growth of cod in the Ekstern Baltic. ICES CM 2000/Q10.
- Uzars D., Plikshs M. 2000. Cod (Gadus morhua L.) cannibalism in the Central Baltic: interannual variability and influence of recruit abundance and distribution. ICES Journal of Marine Science 57 (2): 324–329. DOI: 10.1006/jmsc.1999.0527
- Załachowski W., Szypuła J., Krzykawski S., Krzykawska I.1975. Feeding of some commercial fishes in the Southern Region of Baltic Sea – in 1971 and 1972. Polskie Archiwum Hydrobiologii 22 (3): 429–448.
- Załachowski W. 1977. Ilościowa i ekologiczna analiza pokarmu użytkowanego przez populację dorsza w południowym Bałtyku w latach 1972–1974. [Quantitative and ecological analysis of food consumed by southern Baltic cod population in the years 1972–1974.] Rozprawy, Akademia Rolnicza w Szczecinie, Szczecin, Poland No. 53: 1–109.[In Polish, with English summary.]
- Załachowski W. 1985. Amount and composition of food of cod (Gadus morhua) in the southern Baltic in 1977–1982. Acta Ichthyologica et Piscatoria 15 (2): 95–118.
- Załachowski W. 1986. An attempt to estimate food biomass eliminated annually by the cod (Gadus morhua L.) population in the Baltic, based on studies in 1977–1982. Acta Ichthyologica et Piscatoria 16 (1): 3–23.
- Załachowski W. 1992. Odżywianie się dorsza (Gadus morhua) w południowym Bałtyku w latach 1986–1989. [Feeding of cod in the southern Baltic within 1986–1989.] Zeszyty Naukowe Akademii Rolniczej w Szczecinie 19 (150): 59–66. [In Polish, with English summary.]
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