SWORDFISH TOWARDS THE ARCTIC ATLANTIC IN CLIMATE CHANGE

SUMMARY The remarkable increase in abundance of swordfishes (Xiphias gladius) along the Norwegian coast is coinciding with the recent temperature increase in the North Atlantic Ocean since the cold period during the 1960s and 1970s. This increase is mainly due to the large-scale natural climate oscillation of the Atlantic Multidecadal Oscillation (AMO). The major part of the swordfishes occurred during late summer, particularly in August when sea temperature is at maximum. The swordfishes along the Norwegian coast seem to be solitary juvenile visitors and have all been within a limited size group from 1.5 to 2.65 m in length and from 20 to 40 kg in weight most probably corresponding to ages of 3-4 years. Younger fish would probably be too small for these long excursions to the north, but it is not clear why older and larger individuals stay away from the northern fringes of the distribution area. This is a different behavior from the bluefin tuna (Thunnus thynnus) in earlier periods, particularly in the 1950’s and 60’s. RESUME