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”. 

ICES Comments

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.