Why is the Eastern Baltic cod recovering?

About five-six years ago, the eastern Baltic cod stock was at a very low level and suffered from high fishing pressure. Suddenly fishing mortality substantially declined and reached the target of the EU long-term management plan already in 2008.  The biomass of the stock more than tripled compared to the level in mid 2000s. This positive change happened surprisingly fast, especially when compared to many other depleted cod stocks in Europe where similar positive developments have not been achieved despite of large management efforts.

The investigations by DTU-Aqua within MEECE showed that the success to reverse the negative development of Eastern Baltic cod and its rapid recovery was due to a fortunate combination of both biological and management-related factors. For a number of years in the past, underreporting of cod landings has been a large problem in the Baltic Sea. Since 2007, control and enforcement was substantially improved. In parallel to temporarily reduced fisheries removals, higher numbers of recruits (2 year old cod) have been entering the stock in recent years. The number of recruits produced per one kg of adult cod has in several recent years been the highest since the 1980s.

Simulation analyses showed that the reduction in landings, mainly due to improved compliance with total allowable catch (TAC), and increased recruitment equally contributed to achieving a reduction in fishing mortality down to management plan target in 2008. The reversal of the negative trend in biomass and rebuilding of the stock to the present level were largely driven by increased recruitment. Harvest control rules of the EU multiannual management plan for setting TACs currently maintain the fishing mortality at a low level, which allows the stock to accumulate biomass and further accelerate its recovery. Relatively strong incoming year-classes and recently better control over removals distinguish the Eastern Baltic cod from other depleted European cod stocks, which have not shown similar positive trends in recent years.

Reduction in fishing mortality of the Eastern Baltic cod was due to a combination of reduction in (mainly unallocated) landings and increased recruitment. Corresponding increase in spawner biomass was primarily due to increased recruitment production.

Review by: Martig Eero (DTU-Aqua)

Full paper:
Eero, M., Köster, F.W., Vinther, M. 2012. Why is the Eastern Baltic cod recovering? Marine Policy, 36, 235–240. doi:10.1016/j.marpol.2011.05.010 PDF