Review and evaluation of factors that are important for smolt survival in the Gulf of Finland
IBSFC has asked ICES for “Review and evaluation of factors that are important for smolt survival in the Gulf of Finland”.
No estimate of initial smolt survival in wild salmon populations is available. However, for reared salmon released into the Gulf of Finland the initial smolt survival is low, similar to what is found elsewhere in the Baltic Sea and in the North Atlantic. Also, similar to observations elsewhere in the North Atlantic the post smolt survival has been lower in the last five years than in the early 1990s. Smolt survival in the Gulf of Finland is lower than elsewhere in the Baltic Sea. Estimates for the Baltic salmon range from 2-20% survival during the few months of sea life.
The reason for the high mortality soon after release is unknown. Seminars in Finland in December 2003 and in Estoniain February 2004 (participation from Estonia, Finland, and Russian Federation) considered changes in the Gulf of Finland ecosystem, particularly food web and predation (seals, cormorants), as possible factors affecting post smolt survival. Recently, the quality of reared smolts produced in hatcheries has also been discussed. The seminars concludedthat feeding of post smolts, impact of thermocline and halocline shifts on food organisms, and food composition of seals and predation by cormorants are all potentially important factors. However, no conclusion was reached.
At this point in time ICES is not able to provide precise information to the question. An answer needs to wait until the scientific debate has been concluded and most probably more data collected, compiled and analysed.
Published under the auspices of the following ICES Steering Group or Committee