Baseline A baseline study of metals in cod (Gadus morhua) from the North Sea and coastal Norwegian waters, with focus on mercury, arsenic, cadmium and lead Kaare Julshamn a,⇑ , Arne Duinker a , Bente M. Nilsen a , Kjell Nedreaas b , Amund Maage a a National Institute of Nutrition and Seafood Research (NIFES), P.O. Box 2029 Nordnes, N-5817 Bergen, Norway b Institute of Marine Research, P.O. Box 1870 Nordnes, N-5817 Bergen, Norway article info Keywords: Arsenic Mercury Cadmium Lead Cod North Sea abstract This study is one of several baseline studies that will provide basic and reliable information about the content of undesirable substances in important species of fish caught in Norwegian waters. Concentra- tions of metals in the muscle and livers of 516 cod caught at 22 positions in the North Sea were analysed. An additional 687 cod were caught from 13 fjords and coastal areas along the coast of Norway. Three out of 1203 samples of muscle exceeded the maximum limit of 0.5 mg Hg kg À1 wet weight set by the EU for foodstuffs. The mercury concentration in cod muscle was higher and the cadmium concentration in the liver was lower in the North Sea and coastal areas in the southern part of Norway than in the Barents Sea and coastal areas in the northern part of Norway. These differences are perhaps caused by differences in the cod diet. Ó 2013 Elsevier Ltd. All rights reserved. Atlantic cod (G. morhua) is distributed in the North Atlantic Ocean and consists of several different stocks. In addition to North- east Arctic cod in the Barents Sea which is the largest cod stock in the world, North Sea cod and Norwegian fjord and coastal cod stocks are important cod stocks for the European and Norwegian fisheries. The coastline of Norway consists of numerous fjords that favour the formation of a complex system of cod subpopulations. Subpopulations of fjord and coastal cod inhabiting areas with dif- ferent environmental conditions differ from each other in their migration patterns, spawning localities, growth and maturation rates, otolith structures, genetic features etc. (Berg and Albert, 2003; Jorde et al., 2007; Link et al., 2009; Stransky et al., 2008). Cod in the North Sea are quite locally based, and it is expected that there are several local stocks within the spawning areas in the English Channel, the Dogger Bank and along the Scottish coast. There are no clear boundaries between these stocks, and spawning may occur throughout the North Sea. Over the last 30 years, spawning has markedly declined for North Sea cod (Heath, 2005; ICES, 2012). Spawning takes place from January to May, peaking first in the south, in February and March (Rogers et al., 2001). The eggs hatch after 2–3 weeks, and the main growing areas are along the Danish coast and in the German Bight, but also along the coast of Shetland. North Sea cod may already mature at an age of 2 years, but most cod become sexually mature at 3 or 4 years (ICES, 2012). Cod in the North Sea grow faster, mature earlier and have a shorter life span than cod living in colder water. Although cod live mainly on the bottom, they also migrate vertically in the water column to feed on different prey organisms. It is a predatory fish and the diet varies with age. Juvenile cod feed mainly on crustaceans, but as the cod grows, fish such as sand eels, herring and Norway pout become the most important prey (Yaragina et al., 2011). Cod also show cannibalistic behaviour and juveniles are eaten by older cod. The total landings of North Sea cod in 2011 was 27,728 tonnes and the Norwegian catch was 4870 tonnes (ICES, 2012). The North Sea is regarded as a moderately polluted sea area. Pollution is brought into this area via air, ocean currents and rivers, with air being the principal route of long-range transportation of undesirable substances (www.environment.no). In order to ensure that fish containing particularly high levels of undesirable ele- ments are not sold in the European market, the EU has set maxi- mum limits for concentrations of mercury, cadmium and lead of 0.5, 0.05 and 0.3 mg/kg wet weight (ww), respectively, in the mus- cle tissue of fish intended for human consumption (EC, 2006). The levels of undesirable substances in fish and other seafood in Nor- way have been regularly monitored since 1994. Since cod is a highly important commercial species for Norway, this species has been frequently sampled during this period (Julshamn et al., 2004; www.nifes.no/seafooddata). In order to establish reliable background data on undesirable substances, comprehensive baseline studies are needed for impor- tant species such as cod. Based on the findings it is also the inten- tion to provide authorities with recommendations on how future monitoring should be performed (e.g. frequency of sampling and number of sampling sites). The sampling frequency undertaken 0025-326X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.marpolbul.2013.04.018 ⇑ Corresponding author. Tel.: +47 99 48 77 01; fax: +47 55 90 52 99. E-mail address: kaare.julshamn@nifes.no (K. Julshamn). Marine Pollution Bulletin 72 (2013) 264–273 Contents lists available at SciVerse ScienceDirect Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul