Climate-related variations in the occurrence and distribution of mackerel (Scomber scombrus) in Icelandic waters

Based on long-term investigations on sea temperature in Icelandic waters, five climatic periods are defined from the mid-1880s until today. These are a cold period between 1880 and 1920, a warm period between 1921 and 1964, a cold period between 1965 and 1971, one of intermediate conditions (alternating warm and cold) between 1972 and 1995, and finally a warm period from 1996 until today. Mackerel were first reported from Icelandic waters in 1895, were then found intermittently until 1996, and from then appeared almost every year and since 2007 in large numbers in many areas around Iceland. The occurrence of mackerel appears to be confined mainly to warm periods in the North Atlantic Ocean and around Iceland. The unprecedented occurrence and extended distribution of the species began at the onset of the recent warm period during the mid-1990s and, in recent years, 0-group and age 1 mackerel have also been observed in Icelandic waters. This expansion in distribution resulted initially in a bycatch fishery, which then developed into a direct fishery within the Icelandic Exclusive Economic Zone, increasing from similar to 1700 t in 2006 to similar to 120 000 t in 2009 and 2010.