Every three years an international North Sea survey is carried out by two European institutes, Institute for Marine Research (IMR) from Norway and Institute for Marine Resources and Ecosystem Studies (IMARES) from the Netherlands, to monitor the spatial and seasonal distribution of North Sea mackerel. In 2011 the North Sea mackerel egg survey was performed. The entire spawning area was sampled by IMR, Norway and IMARES, The Netherlands. The whole spawning area was sampled three times. IMARES covered the complete sampling area in the first period, in the second period IMR covered the northern part and IMARES the southern part of the spawning area. The third period the whole spawning area was covered by IMR. In total 190 ichthyoplankton samples were taken with a Gulf VII plankton torpedo with a Seabird CTD mounted on top. Additionally, adult fish samples for the estimation of fecundity and atresia were taken using a pelagic trawl. The survey was successful and IMARES managed to sample all but 3 of the planned stations. Numbers of mackerel eggs found in the samples were comparable to 2008. Total mackerel egg production in 2011 was 116*1012 and Spawning Stock Biomass (SSB) was estimated at 165*103 tons, which is slightly higher compared to 2008. Highest egg production was found in the first sampling week and it is possible that the beginning of mackerel spawning is missed.
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