© 2005 International Council for the Exploration of the Sea
The influence of spatio-temporal egg production variability on the modelled survival of the early life history stages of mackerel (Scomber scombrus) in the eastern North Atlantic
COMMSYS Baumackerweg 9, 27607 Langen, Germany
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An individual-based model (IBM) that simulates the transport, growth, and mortality of mackerel (Scomber scombrus) eggs and larvae, is used to determine the modelled survival of mackerel post-larvae in the eastern North Atlantic. Larval and post-larval growth is modelled as a function of length, temperature, and food distribution; mortality is modelled as a function of length and absolute growth rate. Simulations have previously been carried out for the years 1998, 1999, and 2000, in all cases using the same 1998 initial egg distribution as the input field. In the present contribution, the effects of varying the input field are examined by comparing simulations for 1998 and 2001 using initial egg distributions for 1998 and 2001, respectively, and also for a 2001 simulation using the 1998 egg data as input. Results showed that, for the first two cases, the estimated number of survivors for the years 1998 and 2001 was similar, although total egg production (i.e. the magnitude of the input field) in 2001 was only 
65% of that during 1998. The higher relative survival rate in 2001 results from differences in the timing of peak production, which was 5 weeks later in 2001 than in 1998, and also from greater overall food availability in 2001. Modelling survival for 2001 using 1998 egg data as the initial input field "wrongly" increases survival by 60% compared with using actual 2001 egg data for initialization. This is mainly a function of the increased egg production in 1998 compared with 2001.
Keywords: growth, individual-based model, mackerel larvae, mortality, survival indices
Received 7 October 2004; accepted 3 April 2005.