Spatiotemporal variability in diet composition of Greenland halibut (Reinhardtius hippoglossoides) from the eastern Canadian Arctic

Greenland halibut (Reinhardtius hippoglossoides) sustain one of the most lucrative fisheries in the eastern Canadian Arctic and Labrador Sea. This species also plays an important role in food web connectivity and benthic–pelagic coupling. Despite the relatively rich knowledge of this species, R. hippoglossoides ecology in these specific areas remains poorly understood. The main aim of this study was to characterize the diet of this deepwater fish in the Labrador Sea and Davis and Hudson Straits and characterize the predator–prey relationship with northern shrimp (Pandalus borealis), another commercially important species in the region. Stomach contents analyses were conducted on 1199 fish captured from 2018 to 2020. Small specimens (60 cm) fed primarily on fish, indicative of size-related changes in diet composition. The relative abundance of Pandalus shrimp species in the environment was reflected in the diet. Location appeared to be the most influential variable on feeding patterns. Distinct oceanographic conditions among areas, resulting in differences in prey availability, could explain these results. Arctic cod (Boreogadus saida) and redfish (Sebastes sp.) were selected in locations where fish prey were the most abundant. These results shed light on the opportunistic nature of R. hippoglossoides and its preference for fish at large size. With the rapidly changing oceanographic conditions of Arctic waters, a distributional change in the biomass of shrimp is expected. Results suggest that an increase in abundance of predatory groundfish species in the system (e.g., Sebastes sp.) could lead to acute predation on shrimp and competition with R. hippoglossoides. By revealing key trophic links within the demersal ecosystem, this work provides valuable information on the development of ecosystem approaches to fisheries management for the region. -- Keywords : food web ; Labrador Sea ; northern shrimp ; predator–prey relationship ; stomach content ; trophic ecology

Natural background radiation at Lab 2 of Callio Lab, Pyhäsalmi mine in Finland

Abstract In operating mines, as well as in deep locations for planned scientific activities, it is essential to recognize the natural background radiation from the point of view of both occupational hazard and experimental background. Callio Lab, located in the Pyhäsalmi Mine, Finland, is one of the underground laboratories participating in the Baltic Sea Underground Innovation Network (BSUIN). The characterization of the natural background radiation was done at the Lab 2, which is the deepest located in Callio Lab. It involved in-situ gamma spectrometry, thermal neutron flux measurements, radon concentration determination, and α / β laboratory spectrometry of water and rock samples. At a depth of 1436 m (~4000 m w.e.) within the felsic volcanic bedrock occurs a volcanogenic massive sulphide deposit, wherein a thermal neutron flux of (1.73 ± 0.10) × 10−5 cm−2s−1, a gamma-ray flux of 12.7 ± 1.5 cm−2s−1, a gamma-ray dose of 0.158 ± 0.029 μ Sv/h and a radon concentration of 213.3 Bq/m³ ± 11% were determined