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Fine-scale diet data reveal spatial variation in predator–prey interactions in Norwegian fjords
Get PDFPredator–prey interactions in time and space determine stock productivity, making them an important consideration when managing marine resources, rebuilding stocks or considering reopening a fishery.
We analysed fine-scale diet data from surveys conducted in 2009–2010 and 2018–2019 in three fjords in northern Norway with geostatistical models investigating how predation varied in space, time and between predator species. Our focus prey species was northern shrimp (Pandalus borealis), valuable both as a commercial resource and a major food source for other important species like Atlantic cod (Gadus morhua).
Diet composition of fish predators differed clearly between fjords. While predator species and size were good predictors of shrimp predation, the relationships with bathymetry, prey density and geospatial variables were complex.
Our study indicates that predation of forage species, such as shrimp, varies spatially in heterogenous fjord ecosystems. Shrimp consumption was not highest in the fjord with highest predator density, indicating a higher dependency of cod on shrimp in specific areas.
Realized predation is a complex combination of predator and prey densities and predator ecology that differed in each of the three fjords.
Synthesis and applications. Ignoring spatial variations in predator–prey interactions may lead to an inaccurate perception of stock productivity, suboptimal management and possibly unsustainable management targets. We recommend spatially explicit assessment and management for fish stocks where predator–prey interactions vary substantially in space, such as fjords and reefs.publishedVersio
Follow-up fishery survey in the Hywind Tampen offshore wind power field during construction and early operation
Get PDFThe aim of the cruise was to follow up the pre-construction studies in Hywind Tampen in 2022. In march 2023, when this cruise was carried out, seven of the eleven planned turbines were in operation. As in 2022, the experiments were based on a gradient fish capture study using bottom gillnets at pre-determined stations. The catches were sampled and analysed to obtain information about species richness, abundance, maturity stage, sex, condition and diet and how these vary with distance to the windfarm. In addition, acoustic data were collected.Follow-up fishery survey in the Hywind Tampen offshore wind power field during construction and early operationpublishedVersio
Mareanotokt 2023 leg 2 - Toktrapport 2023001009
Get PDFTokt # 2023001009 (Mareano leg 2) ble gjennomført 3. til 15. juli 2023 med FF G. O. Sars. Fire kartleggingsområder i Nordsjøen og Skagerrak ble undersøkt (Fig. 1). 43 stasjoner (inkl. 4 stasjoner for bunnprøvetaking) ble fullført i Norskerenna og 20 stasjoner (inkl. 2 stasjoner for bunnprøvetaking) i områder nærmere Skagerrak-kysten (Fig. 2). I områder vest av Utsira og i sentrale Nordsjøen ble det samlet inn bunnprøver fra syv stasjoner hvor video var tatt tidligerte på Mareano tokt # 2022118 og 2023001005. Totalt ble det observert 163 taxa med videoundersøkelse av havbunnen. Trollhummer (Munida sp.), sjøfjær (Kophobelemnon stelliferum, Funiculina quadrangularis, Virgularia mirabilis og Virgularidae indet.), og reker (Pandalidae indet og Atlantopandalus propinqvus) dominerte i Skagerrak, hvor havbunnen for det meste utgjøres av slam (mudder). Søppel ble observert på havbunnen på rundt 50 % av alle stasjoner. Mest søppel ble observert i Norskerenna hvor plast og uidentifisert søppel var vanligst. Plast ble ikke observert i grunnere områder nærmere kysten, hvor strømmen er sterkere og eksponert fjell, grus, stein og sand er mer vanlig. På større dyp skifter bunnforholdene til sandig mudder og slam.Mareanotokt 2023 leg 2 - Toktrapport 2023001009publishedVersio
Survey report for CRIMAC SFI 2023
Get PDFThis cruise report describes the objectives, methods, and preliminary results from the tasks carried out at the CRIMAC SFI survey. The survey was conducted on board RV G.O. Sars between November 15th (Tromsø) and November 21st (Tromsø); in the fjords around Tromsø, from Malangen to Kvænangen. The main objective was to test the Kongsberg Sounder capabilities, including noise testing, weather window testing and safe operations. Other tasks were broad banded calibration procedures, testing two new Kongsberg discovery transducers (18kHz and 333kHz), automated predictions from the deep vision system, and an experiment testing whether herring are affected from a whale deterring device or not (FHF project).Survey report for CRIMAC SFI 2023publishedVersio
Substantial kelp detritus exported beyond the continental shelf by dense shelf water transport
Get PDFKelp forests may contribute substantially to ocean carbon sequestration, mainly through transporting kelp carbon away from the coast and into the deep sea. However, it is not clear if and how kelp detritus is transported across the continental shelf. Dense shelf water transport (DSWT) is associated with offshore flows along the seabed and provides an effective mechanism for cross-shelf transport. In this study, we determine how effective DSWT is in exporting kelp detritus beyond the continental shelf edge, by considering the transport of simulated sinking kelp detritus from a region of Australia’s Great Southern Reef. We show that DSWT is the main mechanism that transports simulated kelp detritus past the continental shelf edge, and that export is negligible when DSWT does not occur. We find that 51% per year of simulated kelp detritus is transported past the continental shelf edge, or 17–29% when accounting for decomposition while in transit across the shelf. This is substantially more than initial global estimates. Because DSWT occurs in many mid-latitude locations around the world, where kelp forests are also most productive, export of kelp carbon from the coast could be considerably larger than initially expected.publishedVersio
The significance of shooting angle in seal shooting
Get PDFThe present study aimed to investigate the relationship between shooting angle to the head and animal welfare outcomes in the hunt of young harp seals (Pagophilus groenlandicus). The study population consisted of young harp seals belonging to the Greenland Sea harp seal population. A sample of 171, 2–7 weeks old, weaned harp seals of both sexes were included. The study was conducted as an open, randomised parallel group designed trial during the regular hunt. The animals were allocated into four groups, A–D, according to the observed shooting angle to the head, defined as the angle between the direction of the shot and the longitudinal axis of the animal’s head: (A) directly from the front; (B) obliquely from the front; (C) directly from the side; and (D) obliquely or directly from behind. Instantaneous death rate (IDR) and time to death (TTD) were the main variables. The mean IDR differed significantly between groups and was highest in group B (96.8%) and lowest in group C (66.7%). For all groups combined it was 84.2%. The mean TTD for seals not rendered instantaneously unconscious or dead (n = 27) differed significantly between groups and was shortest in group A (16 s) and longest in group C (85 s). However, the number of animals included in the TTD analysis was limited. In conclusion, based on the significantly higher IDR, the shooting angle obliquely from the front is recommended to help achieve the best animal welfare outcomes during the hunt of young harp seals.publishedVersio
Assessment report for northern shrimp (Pandalus borealis) in the Barents Sea (ICES Subareas 1 and 2)
Get PDFNorthern shrimp (Pandalus borealis) in the Barents Sea (ICES Subareas 1 and 2), including the Svalbard fishery protection zone (FPZ) and coastal shrimp along the Norwegian coast north of 62°N, is considered as one stock. Norwegian and Russian vessels exploit the stock in the entire area, while vessels from other nations are restricted to the Svalbard FPZ and the “loophole” area.Assessment report for northern shrimp (Pandalus borealis) in the Barents Sea (ICES Subareas 1 and 2)publishedVersio
Estimated summer abundance and krill consumption of fin whales throughout the Scotia Sea during the 2018/2019 summer season
Get PDFAmong large cetaceans in the Southern Hemisphere, fin whales were the most heavily exploited in terms of numbers taken during the period of intense industrial whaling. Recent studies suggest that, whilst some humpback whale populations in the Southern Hemisphere appears to have almost completely recovered to their estimated pre-whaling abundance, much less is known about the status of Southern Hemisphere fin whales. Circumpolar estimates in the 1990s suggest an abundance of about 5500 animals south of 60° S, while the IDCR/SOWER-2000 survey for the Scotia Sea and Antarctic Peninsula areas estimated 4670 fin whales within this region in the year 2000. More recent studies in smaller regions indicate higher densities, suggesting that previous estimates are overly conservative and/or that fin whales are undergoing a substantial increase. Here we report findings from a recent multi-vessel single-platform sightings survey carried out as part of the 2019 Area 48 Survey for Antarctic krill. While fin whales were encountered throughout the entire survey area, which covered the majority of CCAMLR Management Area 48, they were particularly abundant around the South Orkney Islands and the eastern Bransfield Strait. Large feeding aggregations were also encountered within the central Scotia Sea between South Orkney Islands and South Georgia. Distance sampling analyses suggest an average fin whale density throughout the Scotia Sea of 0.0256 ( ) whales per km2, which agrees well with recent density estimates reported from smaller sub-regions within the Scotia Sea. Design-based distance sampling analyses resulted in an estimated total fin whale abundance of 53,873 (CV = 0.15, 95% CI 40,233–72,138), while a density surface model resulted in a slightly lower estimate of 50,837 (CV: 0.136, 95% CI 38,966–66,324). These estimates are at least an order of magnitude greater than the previous estimate from the same region based on the IDCR/SOWER-2000 data, suggesting that fin whales are undergoing a substantial abundance increase in the South Atlantic. This may have important implications for the assessment of cetacean population trends, but also for CCAMLRs spatial overlap analysis process and efforts to implement a Feedback Management system for Antarctic krill. Our abundance estimate suggests an annual summer krill consumption by fin whales in the Antarctic Peninsula and Scotia Sea area of 7.97 (95% CI 4.94–11.91) million tonnes, which would represent around 20 times the total krill catch taken by the commercial fishery in Area 48 in the same season, or about 12.7% of the 2019 summer krill standing stock estimated from data collected during the same survey. This highlights the crucial importance of including cetacean krill predators in assessment and management efforts for living marine resources in the Southern Ocean, and particularly stresses the urgent need for a re-appraisal of abundance, distribution and ecological role of Southern Hemisphere fin whales.publishedVersio
Comparing physiological responses of acute and chronically stressed diploid and triploid Atlantic salmon (Salmo salar)
Get PDFWe compared the performance and physiological response of diploid and triploid Atlantic salmon (Salmo salar) following 21 days of either unpredictable chronic stress (UCS) or no disturbance (control). Thereafter, all four groups were challenged with a novel acute stressor consisting of crowding, netting and transfer into another tank. Growth was monitored during the 21-day period, and stress response to the novel acute stress challenge was assessed by blood chemistry parameters and pituitary gene expression. Plasma parameters were analyzed before (0) and 15, 30, 45, 60, 90, 120, 240, and 300 min after acute stress induction, whereas gene expression was analyzed at 0, 30, 60, 120, and 240 min. The results showed: a) similar growth rate and condition factor reductions from UCS in triploids and diploids, b) higher post-stress plasma Acth and cortisol levels in triploids compared with diploids, c) wider post-stress fluctuations in most of the other plasma parameters for triploids compared with diploids, particularly for glucose and lactate, d) pomca1, pomcb, crf-r1a and crf-r1b mRNA levels were more upregulated in control diploids than control triploids, and e) only minor changes in pituitary gene expression from UCS in both diploids and triploids, but with a noticeable upregulation of pomca2 and crf-r1a and crf-r1b in the triploids. Our results suggest that triploid Atlantic salmon have a higher energy cost in response to stress than diploids salmon. This can make them more sensitive to suboptimal conditions and episodes of acute and chronic stress.publishedVersio
Pelagic and demersal fish population rebuilding in response to fisheries-induced evolution in exploited China Seas
Get PDFMarine ecosystems are undergoing life-history adaptations with impacts on productivity, resilience, and economic value due to Fisheries-Induced Evolution (FIE). Long-term and often intense selective commercial harvesting has led to truncations in population structure and evolutionary changes in key life-history traits. However, the consequences for different functional groups have rarely been evaluated, especially in the context of rebuilding depleted marine stocks. This study uses an individual-based eco-genetic modeling approach to investigate the effects of FIE during shifts in fishing intensity. We focus on functional groups of three types of pelagic fish and three types of demersal fish with different life histories in the China Seas, proposing and evaluating two types of evolving trait response indicators to FIE, and assessing the influence of fishing intensity during the population rebuilding phase. Our results indicate that FIE has a more pronounced impact on biomass recovery in demersal fishes compared to pelagic fishes.publishedVersio