Background info to Baltic Cod research

We have analyzed the recent development using existing reproduction and stock data from ICES for cod in the eastern Baltic Sea (ICES 2008). Although there are uncertainties in ICES stock assessments, these are the best available data. We have used ICES standard equations to run three different scenarios, investigating: How would the stock have developed after 2004 up to the beginning of 2009 with:

1) A continued poor reproduction and a maintained high fishing pressure?
2) A continued poor reproduction and reduced catches?
3) Good reproduction in 2003-2006 and a maintained high fishing pressure?
 
These scenarios were contrasted to the real situation, as described by ICES:
4) Reduced catches and good reproduction

- Poor reproduction was defined as the average number of individuals at age 2 between 1989-2004 in all years.

- Good reproduction was defined as the number of individuals at age 2 registered by ICES (with values above average especially in 2005 and 2007, i.e. hatched in 2003 and 2005, respectively)

- Maintained high fish catches was defined as: the average fishing mortality (F) between 1996-2004, F = 1.1 (including estimated unallocated landings and discards). This means that around 60% of all adult fish is caught annually.

- Reduced catches was defined as: the real catches used by ICES (including estimated unallocated landings and discards) and for 2008 we assume that total catches will be the decided quota plus an overfishing of 37% (average estimated overfishing 2004-2007).
 
The results are striking and illustrate the relative contributions of different factors for the registered increase in spawning stock biomass (SSB) from 80 000 to 215 000 tonnes:

1) A continued poor reproduction combined with high catches would result in a spawning stock biomass staying at a very low level, i.e. 80 000 tonnes

2) Same low reproduction as above, but with real catches would result in an increase by the beginning of 2009 to 115 000 tonnes

3) If real data on reproduction are used, but are combined with a high fishing mortality (F = 1.1), the stock would have increased to 115 000 tonnes

4) When real data for reproduction are being used and are combined with actual estimated catches, the stock increase to 215 000 tonnes

References

Citation

ICES 2008. Report of the Baltic Fisheries Assessment Working Group (WGBFAS). ICES CM 2008/ACOM:06 (available at www.ices.dk)

2015-01-22

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