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Astthorsson, O. S., Valdimarsson, H., Gudmundsdottir, A., and Óskarsson, G. J. 2012. Climate-related variations in the occurrence and distribution of mackerel (Scomber scombrus) in Icelandic waters. – ICES Journal of Marine Science, 69: . 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 ∼1700 t in 2006 to ∼120 000 t in 2009 and 2010.

Valdimarsson, H., Astthorsson, O. S., and Palsson, J. 2012. Hydrographic variability in Icelandic waters during recent decades and related changes in distribution of some fish species. – ICES Journal of Marine Science, 69: 816–825. Seasonal time-series of temperature and salinity around Iceland have been collected, with repeat observations at stations, since the start of the 1970s. After fairly cold years during the early 1990s, a reversal occurred during the mid-1990s and the period from 1996 to 2010 was one with warmer, more saline water in shelf seas around Iceland. Temperatures and salinities have been frequently above the long-term mean in the waters to the south and west of the country, and these conditions have also influenced the shelf area north of the country. Marked changes have also been observed in the distribution of many fish species during this warm period. Southern commercial species have extended farther north (e.g. haddock, monkfish, mackerel), a northern species is retreating (capelin), rare species and vagrants have been observed more frequently (e.g. greater fork beard, blue antimora, snake pipefish, sea lamprey, Ray's bream), and 31 species, from both shelf and oceanic waters, have been recorded for the first time since 1996. The most obvious explanation for these changes in the ecosystem has to be the warming of 1–2°C in the waters south and west of Iceland during the past 15 years.

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Abstract. The seasonal abundance, distribution, maturity, growth and population dynamics of the euphausiids Thysanoessa raschi (M. Sars, 1864), T. inermis (Kroyer, 1846) and Meganyctiphanes norvegica (M. Sars, 1857) were studied in Isafjord-deep, a fjord in northwest Iceland, from February 1987 to February 1988 Sampling was made at nine stations along the length of the f~ord at approximately monthly intervals, along with hydrographic measurements and water sampling for nutrient analysis and measurements of chlorophyll a concentrations. Spring warming of the water began in late May and maximum temperatures (8 ° to 10 °C) were observed in late July-September. The phytoplankton spring-bloom started in early April, and the highest chlorophyll a levels were measured in early May (7.0 mg m-3). A small increase was observed in the chlorophyll a content in August. The greatest abundance of juveniles and males and females of all three species was observed during January and February 1988, during which period the euphausiids were concentrated in the middle and inner parts of the fjord. Euphausiid eggs were first recorded in the plankton in mid-May, and the greatest abundance of Thysanoessa spp. larvae occurred at the end of May. Larvae of M. norvegica were not observed in [saljord-deep, indicating that recruitment of this species was occurring from outside the fjord. T. raschi and T. inerrnis had a life span of just over 2 yr; the life span of M. norvegica was more difficult to determine. Almost all female T. raschi were mature at the age of 1 yr, while most T. inermis females appeared not to mature until 2 yr of age. Most males of both species took part in breeding at 1 yr of age. The maximum carapace length of T. raschi and T. inerrnis was 8 to 9 and 9 to 10 ram, respectively. The largest M. norvegica had a carapace length of 9 to 10 ram. The spawning of the euphausiids in Isafjord-deep appeared to be closely related to the phytoplankton spring bloom; water temperature appeared to have no influence on spawning.

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