Return of M74 syndrome in Baltic salmon strengthens the case for spatial management of sprat

Published on August 24, 2017

Over the past year there has been a significant increase in the M74 syndrome which has blighted salmon stocks in the Baltic Sea. This reproductive disorder is known to occur more often when sprat forms too large a part of the salmon diet.

For several years, scientists at ICES have advised redirecting the sprat fishery away from areas where cod density is highest in order to provide them with more food. Now, with the additional problems for salmon caused by the distribution of sprat, the case for spatial ecosystem-based management, as outlined in the Baltic multiannual plan, has become more difficult to ignore.

Stock interactions and the effect of environmental conditions are well researched in the Baltic. Overfishing combined with eutrophication, the fertilisation of the sea and the subsequent dead zones, have severely depleted cod biomass. As such, the pelagic fish: sprat, herring and stickleback have thrived in the absence of the top predator in the ecosystem.

This stock boom has led to large quota increases but also knock on effects throughout the ecosystem. Despite the strong evidence pointing to impacts on other species, recommendations from scientists have not been acted on.

It may be that pelagic trawlers would have higher fuel bills if the sprat fishery was redirected and this could prove an impediment to managers implementing spatial management. However, the costs of the status quo are proving high for salmon, anglers, and likely the cod and their fishers.