The year-class strength of the Gulf of Riga herring is strongly influenced by the severity of winter, which determines the water temperature and the abundance of zooplankton in spring. A series of mild winters since 1989 has been favourable for the reproduction of Gulf of Riga herring and resulted in a series of rich year classes for the period 1989–2010; the year classes were below average only in 1996, 2003, 2006, and 2010 after cold winters. Due to favourable reproduction conditions the SSB has been high since the beginning of the 1990s. The mean weight-at-age started to decrease in the mid-1980s and in 1997 reached the lowest values, especially in the older age groups. Afterwards the mean weight-at-age increased and since 2000 it has fluctuated without a clear trend, being still much lower than in the 1980s.

Environmental influence on the stock

The Gulf of Riga is a semi-enclosed ecosystem of the Baltic Sea characterized by low salinity that restricts the occurrence of marine species. The predation mortality by cod is likely to be low because cod is found in the Gulf of Riga only in periods when the cod stock size is very high (last time in the early 1980s).

Baltic Sea

The fisheries


The herring fishery in the Gulf of Riga is performed by Estonia and Latvia, using both trawls and trapnets. In the recent years the share of trapnets has been slightly above 30% and has been rather stable. Herring catches in the Gulf of Riga include the local Gulf of Riga herring and the open-sea herring, which enters the Gulf of Riga for spawning.

Catch distribution

Total herring landings in Gulf of Riga (2011) are 29.6 kt (69.8 % trawls and 30.2% trapnets). No discards or unallocated removals have been taking place. All landings are for human consumption.

Effects of the fisheries on the ecosystem

Pelagic trawl is the main fishing gear used in the trawl fishery. The bycatch of sprat is low (about 10% in recent years), and bycatch of other species is insignificant. The bycatches of other species in herring trapnets are also very low. Discarding in the herring fishery is not allowed and has not been observed by on-board sampling.

Management plans


No specific management objectives are known to ICES.

Figure 8.4.5.1

The estimated SSB in 2011 is 95 900 tonnes, well above the MSY B_trigger biomass of 60 000 t. Following high recruitment, SSB increased in the late 1980s and is currently estimated to be above the long-term average. The year classes of 2005, 2007, and 2009 are strong, while the 2006 and 2010 year classes are poor.

The above excerpts are from the first two pages of the ICES advice, the supporting information to this advice can be read in full at the following reference: