ICES Journal of Marine Science: Journal du Conseil Advance Access originally published online on May 1, 2008
ICES Journal of Marine Science: Journal du Conseil 2008 65(6):937-945; doi:10.1093/icesjms/fsn068
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Reliability of trawl surveys on cod in Norwegian fjords
1 PO Box 1870 Nordnes, N-5817, Bergen, Norway
2 Department of Biology, University of Bergen, PO Box 7800, N-5020, Bergen, Norway
Correspondence to T. M. Lunde: Faculty of Medicine, Center for International Health, PO Box 7804, N-5020 Bergen, Norway. tel: +47 454 28 780; fax: +47 55 97 49 79; e-mail torleif.lunde{at}cih.uib.no.
Lunde, T. M., Godø, O. R., and Rosland, R. 2008. Reliability of trawl surveys on cod in Norwegian fjords. – ICES Journal of Marine Science, 65: 937–945.According to ICES, the International Council for the Exploration of the Sea, populations of coastal cod (CC) in Norway north of 62°N have been declining since 1994. The estimates are based on analytical assessment in which the most recent estimates are tuned with survey information. We evaluate the quality of bottom-trawl surveys conducted in four North Norwegian fjords during autumn of the years 1995–2004. Surveys tended to be carried out later in autumn in the more recent years than in the earlier years. Consequently, there was a significant decrease in sun's altitude from 1995 to 2004 at the time the surveys were carried out. Further inconsistency among years dominated when comparing catch per unit effort (cpue) by year class and age over time. Often, the observed cpue at age a + 1 in year y + 1 was greater than in year y at age a. Spearman’s rank correlation of cpue vs. year also demonstrated inconsistencies in the data. The problems related to separating CC and northeast Arctic cod are discussed.
Keywords: coastal cod, fjords, Norway, survey methodology, trawl survey
Received 20 September 2007; accepted 24 March 2008; advance access publication 1 May 2008.