Journal Article

Non-predation natural mortality of Norway pout (<i>Trisopterus esmarkii</i>) in the North Sea

Henrik Sparholt, Lena I. Larsen and J. Rasmus Nielsen

in ICES Journal of Marine Science

Published on behalf of ICES/CIEM

Volume 59, issue 6, pages 1276-1284
Published in print January 2002 | ISSN: 1054-3139
Published online January 2002 | e-ISSN: 1095-9289 | DOI:
Non-predation natural mortality of Norway pout (Trisopterus esmarkii) in the North Sea

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Based on age disaggregated data on catch rates in bottom trawl surveys, commercial catches, and the number consumed by the North Sea piscivorous predators, new estimates of non-predation natural mortality, M1, are obtained for Norway pout [Trisopterus esmarkii (Nilsson)]. Simple log catch ratio analysis and rough maximum likelihood procedures are applied. The analysis focus on the year classes 1977–1981 and 1987–1991, which are represented in the extensive stomach sampling of North Sea piscivorous fish in 1981 and 1991. Although the M1 of Norway pout varied between the two periods, in both periods it increased with age and was very high for age 2 and older fish (0.10 for age 1, 1.74 for age 2, 2.58 for age 3 and 3.05 for age 4 for the 1977–1981 year classes and 0.10 for age 1, 2.03 for age 2, 3.04 for age 3 and 4.39 for age 4 for the 1987–1991 year classes). This difference between the two periods is not significant. Survey data from each quarter of the year show that the main mortality takes place between the 1st and the 2nd quarter of the year, i.e. from before to after spawning, thus pointing at spawning as the main factor.

Keywords: commercial catch; natural mortality; North Sea; Norway pout; numbers consumed; population dynamics; trawl survey; Trisopterus esmarkii

Journal Article.  0 words. 

Subjects: Environmental Science ; Marine and Estuarine Biology

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