Interactions between grey seal (Halichoerus grypus), Atlantic salmon (Salmo salar), and harvest controls on the salmon fishery in the Gulf of Bothnia

Interactions between grey seal, Atlantic salmon, and harvest controls on the salmon fishery in the Gulf of Bothnia, northern Baltic Sea, were investigated for the period 1999–2003. We assessed the effects of seal-induced catch losses (fish damaged or eaten by seals in the fishing gears) and harvest restrictions (delayed sequential opening of the fishery from south to north) on the Finnish coastal salmon catch and on escapement of salmon into the Tornionjoki River, the major breeding ground of the species in the Baltic Sea. Commercial logbook data on catches and seal-induced catch losses were used in a stochastic Monte Carlo analysis, indicating that mainly because of the stricter harvest controls enforced in 1996 and 1997, the average annual spawning run abundance that approached the Finnish coastal area increased by ca. 56 700 fish between 2000 and 2002. However, these fish were caught increasingly in the northern Gulf of Bothnia (Management Areas, MAs, 3 and 4), and relatively few salmon escaped into the Tornionjoki River. The landings in MAs 3 and 4 increased by 57% and 144%, respectively, whereas in the southern Gulf of Bothnia (MA 1), landings decreased by 23%. Over the five years of the study, seal-induced catch losses in MA 1 ranged from 24% to 29% of the total catch, whereas in MAs 2, 3, and 4 it ranged from 3% to 16%. The analysis suggests, however, that in MA 1 the regulation-induced catch losses were even higher than seal-induced catch losses, indicating that the salmon fishery was being impacted by both major factors. To increase escapement into the river and potentially to increase the future wild salmon catch, the opening of the harvest in the northernmost MAs should be delayed. Seal-induced catch losses should be reduced by extensive introduction of seal-safe fishing gears and by sustainable control of the grey seal population.