Blue whiting (Micromesistius poutassou): behaviour and distribution in Greenland waters

As a result of climate variations, organisms are in a constant race for adapting to environmental changes, and for many species, the geographical distribution follows the climate. Climate changes have accelerated in recent decades, and particularly in Arctic and subarctic areas. These regions are further projected to undergo some of the largest climate and ecosystem changes on Earth.

Changes in the occurrence and distribution of important commercial species are among the ongoing and expected future changes. This has consequences for fisheries and communities that depend on them. Fluctuations in the abundance and distribution of fish between territorial waters may prevent nations from maintaining the exploitation of the resources, whereas it may allow for others to access them.

This has already resulted in some countries experiencing a decline in traditional fisheries, while others have embarked on new ones, such as seen with the pelagic fishery in Greenland. Blue whiting is one of the species that the Greenlandic fishing industry have observed with great anticipation, as numbers have increased among bycatches.

This thesis depicts my work describing the biology and distribution of the small gadoid fish blue whiting (Micromesistius poutassou, Risso) in Greenland waters. The work resulted in three papers, of which two have been published in scientific journals, while the third is in review. So far, there has been no significant fishing for blue whiting in Greenland (due to lack of profitability in the fishery), which otherwise has been strongly desired by both the fishing industry and local managers.

Knowledge about blue whiting in the region is limited, and this challenges the advice and management of a potential new fishery. The purpose of the thesis was, therefore, to investigate fundamental biological questions about blue whiting in Greenland waters, including mapping distribution and describing demographic migration patterns (paper I), describing environmental factors that drive fluctuations in abundance (paper II), and examining diet composition and feeding behaviour in the region (paper III).

By combining different types of data from scientific fisheries surveys and commercial fishing, it was identified where in Greenland, the different life stages of blue whiting mainly occur. At the same time, I formulated a hypothesis about the migration route to and from Greenland waters. By describing the trend in blue whiting abundance (along with other boreal fish species) and testing its correlation with variations in oceanography, I demonstrate relationships between blue whiting abundance and specific oceanographic circulation patterns, as well as increased abundance during periods of warmer ocean temperatures.

By analysing stomach content and zooplankton samples from a designed field study, a distinct diel feeding cycle and important food items in the Irminger Sea were identified. Through the work of the thesis, we have gained a better understanding of the blue whiting. This knowledge is necessary to provide sound advice about the fishery to managers in Greenland and in other countries exploiting this shared resource.