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This study aimed to assess possible shifts in distributional patterns of cetaceans residing in the Norwegian Sea, and to relate the distribution to their feeding ecology during the summer seasons of 2009, 2010, and 2012. During this same period, historically large abundances in the order of 15 million tonnes pelagic planktivorous fish such as Norwegian spring-spawning herring (Clupea harengus), northeast Atlantic mackerel (Scomber scombrus) and blue whiting (Micromesistius poutassou), have been reported feeding in the Norwegian Sea during the summer. There is also observed elevated average surface temperatures and a reduction in zooplankton biomass during the last two decades. Such changes might influence species composition, distribution patterns and feeding preferences of cetaceans residing the region. Our results show higher densities of toothed whales, killer whales (Orcinus orca) and pilot whales (Globicephala melas), than the previous norm for these waters. Baleen whales, such as minke whales (Balaenoptera acutorostrata) and fin whales (Balaenoptera physalus), which are often associated with macro-zooplankton, displayed a distribution overlap with pelagic fish abundances. Humpback whales (Megaptera novaeangliae) were observed in low numbers, indicating a shift in habitat preference, compared to sighting data collected only few years earlier. Our study illustrate that both small and large cetaceans that reside in the Norwegian Sea have the capability to rapidly perform shifts in distribution and abundance patterns strongly associated with adaptive search behavior in relation to both changing levels of abundance in their prey and elevated sea-surface temperatures. This study provides new evidence on high ecological plasticity in response to changing predator-prey trophic relationships and elevated sea-surface temperatures.

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Krill and salps are important for carbon flux in the Southern Ocean, but the extent of their contribution and the consequences of shifts in dominance from krill to salps remain unclear. We present a direct comparison of the contribution of krill and salp faecal pellets (FP) to vertical carbon flux at the Antarctic Peninsula using a combination of sediment traps, FP production, carbon content, microbial degradation, and krill and salp abundances. Salps produce 4-fold more FP carbon than krill, but the FP from both species contribute equally to the carbon flux at 300 m, accounting for 75% of total carbon. Krill FP are exported to 72% to 300 m, while 80% of salp FP are retained in the mixed layer due to fragmentation. Thus, declining krill abundances could lead to decreased carbon flux, indicating that the Antarctic Peninsula could become a less efficient carbon sink for anthropogenic CO2 in future.

Active acoustic techniques can be used to detect whales. The ability to detect whales from a moving vessel or stationary buoy could reduce conflicts between hazardous human activities and whales, enabling implementation of mitigation procedures. In order to identify acoustic targets correctly as whales, knowledge of whale target strength (TS) is required. Active acoustic detections of fin whales (Balaenoptera physalus) were made in the Norwegian Sea; acoustic data were collected using calibrated omnidirectional sonar, operating at a discrete frequency of 110 kHz. Three fin whales of similar size (estimated between 16 and 18 m total length) had an overall average TS for all insonified body aspects of −11.4 dB [95% CI −12.05, −10.8] at 110 kHz, with a total spread of nearly 14 dB. As expected, the received signals were stronger when the fin whales were insonified at broadside (−5.6 dB). Individual fin whale TS varied by approximately 12 dB, probably due to variation in lung volume with breathing, and to dynamic swimming kinematics. Our TS values are consistent with values reported previously for other large whales. All data together pave the way for development of automated acoustic whale detection protocols that could aid whale conservation.