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Master degree

Synne finishes her master thesis

Lanternfish stomachs can become an exciting MSc thesis, as Synne Myhre Sunde has shown in the thesis she defended in late December.

Synne Myhre Sunde presenting her slides
Foto/ill.:
Anne Gro Vea Salvanes

Synne successfully defended her thesis "Feeding ecology of Northern lanternfish (Benthosema glaciale) in four north Atlantic ocean basins" on the 17th December 2018. Synne studied the diet of Benthosema glaciale from the Norwegian Sea, Icelandic Sea, Irminger Sea and the Labrador Sea, and used fish and zooplankton samples from the EURO-BASIN collections from the G. O. Sars survey in May 2013.

Synne demonstrated that B. glaciale feed on a wide range of zooplankton prey from small Appendikularia, Calanus finmarchicus and Metridia spp. to larger prey such as Calanus hyperboreus, Paraeuchaeta spp. and amphipods. She reports that the diet of B. glaciale changed with body size, with small fish consuming small prey, medium-sized ones a mixture of small and large, and large fish feeding on larger prey.

The diet also varied across the four ocean basins, depending on whether B. glaciale undertook diurnal vertical migration between the euphotic and mesopelagic zone or stayed deep day and night. In the Icelandic Sea the Calanus hyperboreus, Themisto spp. and Metridia longa, which are typical prey in arctic waters, dominated the B. glaciale diet. Here the cold East Greenland Current dominates the water masses. Overall, B. glaciale were largest in the Icelandic Sea, had higher HSI, GSI, condition, stomach fullness, and no empty stomachs, this despite of being the sea with the lowest zooplankton abundance. In the other oceans the diet was more varied.

Synne reports that the Labrador and Norwegian Seas had high densities of Calanoida, and particular Calanus finmarchicus at 0–50 m depth. Here B. glaciale did short night visits into this shallow zone, probably to feed, but stayed deep most of the time. Zooplankton densities at depths where fish spent most of the time were low. Smallest individuals with lowest fat reserves (HSI) and low gonad index (GSI) were found in the Norwegian Sea. In the Labrador Sea, where zooplankton densities were the highest, B. glaciale also included Appendicularia in their diet.

The external examiner was Trine Dahle from NIVA, and the BIO examiner was Jorun Egge. The thesis has been supervised by Anne Gro Vea Salvanes from EvoFish, Dag Aksnes from TEG, and Espen Strand and Cecilie BT Broms from the Institute of Marine Research.