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Sex-specific vertical movements of spawning atlantic cod in coastal habitats inferred from acoustic telemetry
Get PDFFish spawning location and behaviour can be challenging to detect, especially in deep water. Here we utilise two large acoustic telemetry datasets from western and mid Norway to study the vertical movement dimension of individual Atlantic cod Gadus morhua spawning behaviour in their natural habitats. The datasets comprise ~ 6 million depth detections from 644 sexed, mature cod, collected at seven different Norwegian coastal cod spawning grounds during 2017–2021. During the spawning period, females were typically found at shallower depths compared to males, while this pattern was much less pronounced or absent outside this period. Furthermore, we identify a hitherto undescribed sex-dependent vertical movement behaviour: periodic descents, where females made deep dives, putatively associated with egg release and spawning, approximately every third day. Females not showing this behaviour tended to occupy deeper positions in the water column than the “periodic descent” females and hence may approach and retreat from spawning males more horizontally. These observed sex-specific behaviours correspond well to the lek-like description of the cod mating system and with cod reproductive physiology, where females are known to mature and release batches of eggs at intervals of several days as part of a bet-hedging strategy.publishedVersio
Organ-specific mercury stable isotopes, speciation and particle measurements reveal methylmercury detoxification processes in Atlantic Bluefin Tuna
Get PDFIdentifying metabolism and detoxification mechanisms of Hg in biota has important implications for biomonitoring, ecotoxicology, and food safety. Compared to marine mammals and waterbirds, detoxification of MeHg in fish is understudied. Here, we investigated Hg detoxification in Atlantic bluefin tuna Thunnus thynnus using organ-specific Hg and Se speciation data, stable Hg isotope signatures, and Hg and Se particle measurements in multiple tissues. Our results provide evidence for in vivo demethylation and biomineralization of HgSe particles, particularly in spleen and kidney. We observed a maximum range of 1.83‰ for δ202Hg between spleen and lean muscle, whereas Δ199Hg values were similar across all tissues. Mean percent methylmercury ranged from 8% in spleen to 90% in lean muscle. The particulate masses of Hg and Se were higher in spleen and kidney (Hg: 61% and 59%, Se: 12% and 6%, respectively) compared to muscle (Hg: 2%, Se: 0.05%). Our data supports the hypothesis of an organ-specific, two-step detoxification of methylmercury in wild marine fish, consisting of demethylation and biomineralization, like reported for waterbirds. While mass dependent fractionation signatures were highly organ specific, stable mass independent fractionation signatures across all tissues make them potential candidates for source apportionment studies of Hg using ABFT.publishedVersio
Post-mortem ‘soft flesh’ in three commercial fish species from off Atlantic Morocco associated with the myxosporean parasites Kudoa thyrsites and K. encrasicoli (Myxozoa)
Get PDFSmall pelagic fishes represent one of the most important food resources off the Northwest coast of Africa. Despite their economic significance, little is known about the infections with flesh invading myxosporean parasites of genus Kudoa (Cnidaria, Myxozoa). Heavy infections in the flesh may be associated with post-mortem myoliquefaction, commonly known as ‘soft flesh’. This condition may reduce the quality and marketability of the fish fillet, resulting in both economic losses to the fishing industry and loss of consumer confidence. In this study, we investigated Kudoa-induced ‘soft flesh’ occurrence in European anchovy Engraulis encrasicolus, European pilchard Sardina pilchardus, and Atlantic chub mackerel Scomber colias caught in 2019 off the Moroccan Atlantic coast. Five hundred specimens of each fish species were examined for ‘soft flesh’ by texture testing and visual inspection 48 h post-catch. ‘Soft flesh’ occurred in 0.2 % of the European anchovies, 1.4 % of the European pilchard, and in 4.4 % of the Atlantic chub mackerel. Microscopic examination of muscle samples revealed that ‘soft flesh’-affected fish were infected with myxospores of K. thyrsites-like morphotype. Analysis of the kudoid SSU rDNA sequence obtained from European pilchard and the Atlantic chub mackerel identified these as K. thyrsites (100 % identity), whereas analysis of the sequence from European anchovy identified the presence of K. encrasicoli (100 % identity). Even if there are no known human health consequences associated with the ingestion of these Kudoa species, the unsightly appearance of some infected fillets is a food quality issue, that can eventually lead to reduced marketability and value.publishedVersio
Genetic affiliations of miniaturized species and morphotypes within the Fucus genus (Phaeophyceae, Fucales)
Get PDFIn the North Atlantic members of the Fucus genus have an important ecological role, forming habitats in the littoral or upper sublittoral zones. A phylogeographic history with frequent hybridization and large phenotypical variation challenge a full systematic and taxonomic understanding of the genus. This study treats some miniaturized Fucus taxa; F. cottonii, F. spiralis f. nanus and F. chalonii, and aims to determine their genetic affiliations using microsatellites. Samples were from Spain and Norway, with F. chalonii only sampled in Spain and F. cottonii in Norway. For microsatellite comparison, additional samples of F. vesiculosus and F. limitaneus were collected in Spain, and of F. vesiculosus and F. spiralis in Norway. Two samples of F. chalonii were analysed, and the results suggest that one sample had a close affiliation to F. spiralis f. nanus, and the other to F. vesiculosus. Individuals of both samples were dioecious. Two samples of F. cottonii were examined, where each was a multilocus genotype with the closest affiliation to F. vesiculosus. Each had a different allelic composition. This suggests they represent two clonal populations. An overall excess of heterozygosity, and occurrence of three alleles at two loci in one of the samples, may suggest that the two clones could have triploid origins. The two samples of Fucus spiralis f. nanus (from Norway and Spain) had very high FIS values, suggesting they represent very isolated and inbred populations of F. spiralis. The sample of F. spiralis f. nanus from Norway was assigned to one of the two genetic clusters found in F. spiralis. The results allow omitting the forma nanus as a taxonomic category for F. spiralis. Both F. chalonii and F. cottonii can have multiple affiliations, and the informal taxonomic category ‘species aggregate’ is suggested for both.publishedVersio
Effect of temperature on development rate and egg production in Caligus elongatus and other sea louse species
Get PDFThe sea louse Caligus elongatus (Siphonostomatoida, Caligidae) is a generalist ectoparasite commonly found on farmed salmonids in the Atlantic Ocean. Together with the salmon louse Lepeophtheirus salmonis and the Chilean sea louse Caligus rogercresseyi, they represent a major challenge to sustainable farming of Atlantic salmon Salmo salar. Here, the development rate, egg production, and copepodid survival time of C. elongatus are described at 6, 9, 12, and 15°C, and compared to available data for L. salmonis and C. rogercresseyi in a seminal attempt to qualitatively compare how these life-history traits and epidemiological factors vary among the 3 caligid sea louse species. A development model for C. elongatus was established by applying a constant scaling factor to the published model for L. salmonis and compared to the data obtained. The model assumes that caligid sea lice with similar zones of temperature tolerance share a common basic physiology, and that their rate of development is equally affected by changing temperatures within the interval where their temperature tolerances overlap. Present data, and data from the literature, suggest that C. elongatus develops to adult at approximately 63% of the time required by L. salmonis females and, compared to L. salmonis, they produce about 1/3 of the eggs per day over the temperature interval studied. This study represents a new experimental approach for establishing caligid development models and demonstrates how important life-history parameters can be scaled by constants and used as temperature-independent measures to characterize and compare the biology and epidemiology of sea lice species.publishedVersio
A pioneering longterm experiment on mesophotic macrofouling communities in the North Atlantic
Get PDFThe mesophotic zone represents one of our planet’s largest and least explored biomes. An increasing number of studies evidence the importance of macrofouling species in marine ecosystems, but information on these communities and the factors influencing their structures at mesophotic depths remain poor. This lack of understanding limits our ability to predict anthropogenic impacts or conduct restoration operations in the mesophotic and the lower boundary of the euphotic zones. In this study, we performed a 24-month experiment in a natural environment to investigate three factors influencing the macrobenthic community structure of the mesophotic and the euphotic lower boundary: depth, substrate orientation and substrate material. Using a manned submersible, several recruitment panels of two different materials were deployed at 100, 200 and 400 meters in vertical and horizontal positions. All three factors contributed to structuring the macrofouling communities, but depth and substrate orientation displayed the strongest effects. This study not only advances our understanding of lower boundary euphotic and mesophotic macrofouling communities but also establishes a foundation for future research and restoration efforts of mesophotic environments in the Madeira archipelago, where mesophotic habitats are amongst the least studied marine habitats in the Northeast Atlantic.publishedVersio
Non-indigenous seaweeds in the Northeast Atlantic Ocean, the Mediterranean Sea and Macaronesia: a critical synthesis of diversity, spatial and temporal patterns
Get PDFEffective monitoring of non-indigenous seaweeds and combatting their effects relies on a solid confirmation of the non-indigenous status of the respective species. We critically analysed the status of presumed non-indigenous seaweed species reported from the Mediterranean Sea, the Northeast Atlantic Ocean and Macaronesia, resulting in a list of 140 species whose non-indigenous nature is undisputed. For an additional 87 species it is unclear if they are native or non-indigenous (cryptogenic species) or their identity requires confirmation (data deficient species). We discuss the factors underlying both taxonomic and biogeographic uncertainties and outline recommendations to reduce uncertainty about the non-indigenous status of seaweeds. Our dataset consisted of over 19,000 distribution records, half of which can be attributed to only five species (Sargassum muticum, Bonnemaisonia hamifera, Asparagopsis armata, Caulerpa cylindracea and Colpomenia peregrina), while 56 species (40%) are recorded no more than once or twice. In addition, our analyses revealed considerable variation in the diversity of non-indigenous species between the geographic regions. The Eastern Mediterranean Sea is home to the largest fraction of non-indigenous seaweed species, the majority of which have a Red Sea or Indo-Pacific origin and have entered the Mediterranean Sea mostly via the Suez Canal. Non-indigenous seaweeds with native ranges situated in the Northwest Pacific make up a large fraction of the total in the Western Mediterranean Sea, Lusitania and Northern Europe, followed by non-indigenous species with a presumed Australasian origin. Uncertainty remains, however, regarding the native range of a substantial fraction of non-indigenous seaweeds in the study area. In so far as analyses of first detections can serve as a proxy for the introduction rate of non-indigenous seaweeds, these do not reveal a decrease in the introduction rate, indicating that the current measures and policies are insufficient to battle the introduction and spread of non-indigenous species in the study area.publishedVersio
Previous, current and future monitoring and management of common minke whales in Norway
Get PDFAn account of the historical, current and possible future management of common minke whales in Norway is presented. The current management is based on an approach very similar to the International Whaling Commission’s Revised Management Procedure (RMP) and requires historical and current catch statistics, together with new abundance estimates with associated variance estimates every six years. The abundance estimates are based on visual sampling online-transect sighting surveys with two independent observer platforms. These surveys are no longer economically viable with the current limited commercial harvest. Alternative methods for obtaining abundance estimates are discussed, including a simpler sighting survey design and genetic mark-recapture methods. The RMP requires Implementation Reviews desirably every six years, which take into account all new information available. The associated simulation trials are very technical and complex, and few experts have the insight to run these simulation tests. Simpler alternatives to the current Implementation Reviews are discussed. The objective is to develop more economically viable methods for abundance estimation and a simpler procedure for catch limit calculation without compromising the sustainability of the harvest. Any new procedure for abundance estimation and catch limit calculations will be submitted to the International Whaling Commission Scientific Committee for discussion.Previous, current and future monitoring and management of common minke whales in NorwaypublishedVersio
Tilstandsrapport for Oslofjorden
Get PDFI 2021 la regjeringen frem en helhetlig tiltaksplan som viser regjeringens viktigste prioriteringer for å gjøre Oslofjorden ren, rik og tilgjengelig for alle fram mot 2026. Tilstandsrapport for Oslofjorden, ledet av NIVA i samarbeid med HI, NINA, NMBU og UiO, gir en oversikt over miljøtilstanden i Oslofjorden de siste 5-10 årene og utviklingen de siste 10-50 årene. Oslofjorden har opplevd negativ utvikling på grunn av blant annet forurensing, overfiske og bygging i strandnære områder. Klimaendringer forventes å forverre situasjonen ytterligere. Økologisk tilstand viser forbedring i Indre Oslofjord, men forverring i Ytre Oslofjord og Skagerrak. For miljøgifter er det ofte overskridelser av grenseverdier for kjemisk tilstand. Blåskjell, dyreplankton, sjøpattedyr, fisk og sjøfugler er viktige indikatorer på fjordens helse, men det er registret nedgang i mange arter, spesielt for torskebestanden. Utbredelse av stortareskog, sukkertareskog og ålegressenger er redusert, og det er økt forekomst av lurv. Flere arter og naturtyper er regnet som truet og rødlistet. Det er registrert flere fremmede arter, som utgjør en økologisk risiko i Oslofjorden.publishedVersio
Deciphering the pathogenesis of melanized focal changes in the white skeletal muscle of farmed Atlantic salmon (Salmo salar)
Get PDFMelanized focal changes (MFCs) in the fillet of farmed Atlantic salmon is a major quality concern. The changes are thought to initially appear as acute red focal changes (RFCs) that progress into chronic MFCs. Recent findings have indicated that hypoxia may be important in their development, possibly leading to necrosis affecting not only myocytes but also adipocytes. Thus, the aim of this study was to investigate possible hypoxic conditions in RFCs and the subsequent inflammatory responses and lesions in the adipose tissue in RFCs and MFCs. A collection of RFCs, MFCs and control muscle samples from several groups of farmed salmon was studied. Using immunohistochemistry, we found induction of the hypoxia-inducible factor 1 pathway in RFCs. Histological investigations of RFCs and MFCs revealed different stages of fat necrosis, including necrotic adipocytes, a myospherulosis-like reaction and the formation of pseudocystic spaces. Accumulations of foamy macrophages were detected in MFCs, indicating degradation and phagocytosis of lipids. Using in situ hybridization, we showed the presence of tyrosinase- and tyrosinase-related protein-1-expressing amelanotic cells in RFCs, which in turn became melanized in MFCs. In conclusion, we propose a sequence of events leading to the formation of MFCs, highlighting the pivotal role of adiposity, hypoxia and fat necrosis.publishedVersio