1 BI 3063 J. Mork H08 Genetic and biologic stock management N E A C The Northeast Arctic Cod The Northeast Arctic Codbiology stock structure exploitation management history

2 BI 3063 J. Mork H08 Genetic and biologic stock management In their chapter on NEAC, Nakken et al. (2008) summarizes and evaluate the available information on trends and fluctuations throughout the 20th century in: fisheries stock size biological characteristics They describe the development of our understanding of these fluctuations as well as the management measures which have been adviced and introduced in order to maintain the yield from the stock at a high and sustainable level.

3 BI 3063 J. Mork H08 Genetic and biologic stock management The Migrations of the NEAC ("Skrei") according to Sars (1879)

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5 BI 3063 J. Mork H08 Genetic and biologic stock management The life cycles of cod stocks which show temporal stability (i.e. at least for hundreds of generations), typically show some relation to current systems. In the northeast Atlantic, particularly along the Norwegian coast, the "Gulf stream", the Baltic rest-current, and the Norwegian coastal current all contribute in carrying pelagic organisms northwards. The eggs, larvae and small codlings are all pelagic. They are carried northwards from the spawning areas, which are typically to the south of the nursery areas. When the gonads mature prior to spawning, cod individuals are triggered to a contranatant swimming behaviour which brings them southwards along the Norwegian coast, and so compensates for the northwards transport of the pelagic stages. Hence the life cycle circle is closed. When ocean currents are stable over long time periods (like the "Gulf stream"), cod stocks may adapt genetically to a life cycle that utilizes the benefits of free transport to nursery areas.

6 BI 3063 J. Mork H08 Genetic and biologic stock management Transport by ocean currents: a simulation model (Stenevik & Sundby) (link)

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8 From Vikebø et al. Results from computer simulations of particle drift with currents along the coast of north Norway. Blue trajectories represent very light particles (high in the water coulmn) and red trajectories mark very heavy particles. Blue and red particles are proxies for "typical" eggs of NEAC and NCC, respectively. NB! ntermediate weigth particle trajectories are not shown. Genetic and biologic stock management

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