How does hunting grey seals (Halichoerus grypus) on Bothnian Bay spring ice influence the structure of seal and fish stocks?

In a traditional manner, seal hunting on Bothnian Bay spring ice in 2003-2004 (16th April - 31st May) resulted in a total of 136 grey seals being shot. From each individual killed, the hunter was obliged to deliver e.g. the alimentary tract, uterus or baculum and the under jaw (for age determination from layers in cement of the canine teeth). Of the total cull 71% were females and of these 78% more than 5 years old, which already is the age of sexual maturity. This kind of sex and age ratio in the cull fits well with a population management regime that aims to diminish only the number of seals. However, if the goal is to preserve a normal population structure such ratios are disadvantageous. If hunting quotas are to be increased in coming years, culling recommendations that include the shooting of immature seals need to be prepared. Analysis of fish otolithes and other hard particles in the alimentary tract showed clearly that the herring (Clupea harengus) was the most important item of prey. Herring was found in 103 grey seals (83.1%). The number of herring per seal varied from just 1 to 309. The average number per seal was 41.1 (± sd 62.6). Four grey seals (3.2%) had eaten 1-2 salmon/trout (Salmo salar/trutta) and two grey seals (1.6%) 1-3 whitefish (Coregonus lavaretus). Nine other fish species were found in very limited numbers. The result suggests that hunting grey seals on Bothnian Bay spring ice may have some influence on herring stock, but it does not, at least direct, help the management of salmon stocks. The paper includes brief discussion on the size classes of fish eaten by grey seals and the potential advantage of shooting young seals.