Rationale for Restocking the Eastern Baltic Cod Stock

Abstract

The Danish Institute for Fisheries Research and Bornholm's Salmon Hatchery examined the potential for restocking Baltic cod (Gadus morhua callarias L.) in the eastern Baltic Sea. This cod population has adapted to the unique brackish water conditions where successful spawning depends on regular inflows of oxygenated saltwater from the North Sea. Hydrographical conditions are therefore considered to constitute the principal bottleneck for recruitment of this population. Successful recruitment is also dependent upon food availability and predation pressure from mainly herring (Clupea harengus L.) and sprat (Sprattus sprattus L.). A 2-to 3-month delay in the spawning period compared to 20–30 years ago has altered feeding conditions and predation susceptibility in a way that may have exacerbated the decline in recruitment. Producing and releasing cod larvae during spring would mimic the spawning period recorded in previous times and would coincide with the spring peak in copepod production. An evaluation of 3 different release scenarios showed that a release of 474 million first-feeding larvae over 5 months would enhance the average population of 2-year-olds by 10% and be biologically and economically the most feasible scenario.

Keywords:

• restocking
• fish releases
• Baltic cod
• recruitment

ACKNOWLEDGMENTS

This project was funded by the Directorate for Food, Fisheries and Agri Business through the EU Fisheries Sector Program, FIUF. We would like to thank Ken Leber and two anonymous reviewers for their helpful comments and language improvements to the text.

Notes

* Capital costs are specific for the hatchery on Bornholm.