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Life in the fast lane: Revisiting the fast growth—High survival paradigm during the early life stages of fishes
Get PDFEarly life survival is critical to successful replenishment of fish populations, and hypotheses developed under the Growth-Survival Paradigm (GSP) have guided investigations of controlling processes. The GSP postulates that recruitment depends on growth and mortality rates during early life stages, as well as their duration, after which the mortality declines substantially. The GSP predicts a shift in the frequency distribution of growth histories with age towards faster growth rates relative to the initial population because slow-growing individuals are subject to high mortality (via starvation and predation). However, mortality data compiled from 387 cases published in 153 studies (1971–2022) showed that the GSP was only supported in 56% of cases. Selection against slow growth occurred in two-thirds of field studies, leaving a non-negligible fraction of cases showing either an absence of or inverse growth-selective survival, suggesting the growth-survival relationship is more complex than currently considered within the GSP framework. Stochastic simulations allowed us to assess the influence of key intrinsic and extrinsic factors on the characteristics of surviving larvae and identify knowledge gaps on the drivers of variability in growth-selective survival. We suggest caution when interpreting patterns of growth selection because changes in variance and autocorrelation of individual growth rates among cohorts can invalidate fundamental GSP assumptions. We argue that breakthroughs in recruitment research require a comprehensive, population-specific characterization of the role of predation and intrinsic factors in driving variability in the distribution and autocorrelation of larval growth rates, and of the life stage corresponding to the endpoint of pre-recruited life.publishedVersio
Kartlegging av østersbestander i Rogaland i 2021 og 2023 - innsamling av data som grunnlag for bestandsforvaltning
Get PDFFlatøstersen, Ostrea edulis, er utbredt fra Marokko i syd, i Middelhavet, Svartehavet og langs kysten av Europa, nord til Vest-Norge. I det meste av utbredelsesområdet er bestandene kraftig redusert på grunn av overhøsting, ødeleggelse av østersbanker i forbindelse med høsting og dødelighet forårsaket av parasittsykdommene bonamiose og marteiliose. Det arbeides nå med å kartlegge og bevare de siste intakte bestandene i Europa, og det gjøres flere forsøk på å restaurere opprinnelige bestander. Havforskningsinstituttet og Universitetet i Agder har de siste årene kartlagt og beskrevet norske østersbestander. Formålet med arbeidet som er beskrevet i denne rapporten var å kartlegge flatøstersbestandene i Rogaland og beskrive bestandene i Hafrsfjord ved Stavanger og Haugavågen på Karmøy. Resultatene viser at noen av flatøstersbestandene i Rogaland er unike, og kan representere donorbestander som er sentrale i å opprettholde lokale flatøstersbestander og spre larver til omliggende områder. Disse lokalitetene har kanskje Europas nordligste og mest intakte, sykdomsfrie og naturlig reproduserende flatøstersbestander. Prosjektene har samlet inn data som kan bidra til å legge grunnlaget for forvaltning av bestandene og beskyttelse av disse mot overhøsting eller habitatforringelse.Kartlegging av østersbestander i Rogaland i 2021 og 2023 - innsamling av data som grunnlag for bestandsforvaltningpublishedVersio
Detecting significant retrospective patterns in state space fish stock assessment
Get PDFRetrospective patterns are commonly investigated to validate fish stock assessment models. A widely applied measure for retrospective bias is Mohn’s ρ and corresponding retrospective plots. However, retrospective patterns can be interpreted differently by experts. To make decisions regarding significant retrospective patterns less subjective, we proposed a post-sample Mohn’s ρ significance test. As case studies, we applied the state space assessment model SAM with data on Northeast Arctic cod and Norwegian coastal cod north of 67°N. We showed that the acceptance regions of Mohn’s ρ depends on both the data available and the assessment model complexity. We also assessed the test power under a range of assumption violations and conclude that Mohn’s ρ is useful for detecting violations associated with bias, but not for violations associated with variances and correlations.publishedVersio
Fish investigations in the Barents Sea Winter 2022
Get PDFAnnual catch quotas and other regulations of the Barents Sea fisheries are set through negotiations between Norway and Russia. Assessment of the state of the stocks and quota advice are based on survey results and international landings statistics. The results from the demersal fish winter surveys in the Barents Sea are an important source of information for the annual stock assessment.Fish investigations in the Barents Sea Winter 2022publishedVersio
Distribution and abundance of Norwegian spring-spawning herring during the spawning season in 2023
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Algal oil gives control of long-chain omega-3 levels in full-cycle production of Atlantic salmon, without detriment to zootechnical performance and sensory characteristics
Get PDFThe levels of eicosapentaenoic (EPA) and docosahexaenoic (DHA) in salmon fillets have decreased because of the progressive replacement of fish oil (FO). This study contributes to enabling the sustainable growth of aquaculture by confirming the effects of partially or fully replacing FO with microalgal oil (AO) on growth, muscle fatty acid profiles, and muscle quality of farmed Atlantic salmon. Crucially, this is now done throughout the entire post-smolt production cycle and up to a harvest weight of 3 kg. Three experiments were performed using fish ranging from 145 g to 3 kg and testing different diets, replacing FO up to 100%. Zootechnical performance was similar among treatments in all experiments. Changing the lipid source in the diet resulted in EPA and DHA digestibility of greater than 96%. Sensory characteristics of raw fish fillets were similar among treatments, supporting a similar sensorial experience with the replacement of FO with no impact on consumers. Overall, results confirm that the AO tested here enables the sustainable growth of Atlantic salmon aquaculture by helping to maintain a level of EPA and DHA in the fish fillets, without detriment to zootechnical performance and sensory characteristics, while simultaneously contributing to a reduced marine footprint for aquafeeds.publishedVersio
Why do regional biogeochemical models produce contrasting future projections of primary production in the Barents Sea?
Get PDFProjected future changes in primary production in the Barents Sea vary among different regional biogeochemical models, with some showing an increase, some a decrease, and some no change. This variability has been attributed to differences in the underlying physics, but little effort has been spent to understand the primary causal processes. In this study, we compare two extreme projections: one model (NORWECOM.E2E) projects a 36% increase and another model (SINMOD) projects a 9% decrease in primary production in a future warmer Barents Sea. Using structural equation modeling, we identify the direct and indirect effects of the major environmental variables on primary production. The results show that the two biogeochemical models agree on the directions of impacts, and that differences in the physical environment, specifically the factors controlling nutrient availability, are the main cause of the disparities. Both models agree that decreasing ice-coverage leads to increased primary production. However, the projection with a decrease in primary production was characterized by a decrease in winter nitrate concentrations and stronger temperature-induced stratification. By contrast, the projection with an increase in primary production was characterized by an increase in winter nitrate concentrations and weaker stratification due to a relatively smaller temperature increase which was offset by increasing wind stress. The results emphasize the need for accurate descriptions of the physical environments and inform discussions about the future of the Barents Sea ecosystem and the potential for Arctic blue growth.publishedVersio
Three decades of change in the Skagerrak coastal ecosystem, shaped by eutrophication and coastal darkening
Get PDFGlobal coastal ecosystems are under accelerating pressure from human activities and climate change. In this study we explore a long-term time series (mostly 1990–2016) from major Norwegian rivers, together with coastal time series from the Norwegian Skagerrak coast. The aims are to: 1) analyse long-term trends in riverine loadings to Skagerrak, changes in coastal water quality and pelagic and benthic species composition, and 2) to describe the relationships between human drivers (eutrophication and coastal darkening) and community structure of benthic communities. Riverine discharge and transport increased by 23–85% over the time period, corresponding to a 40–78% increase in concentrations of suspended particulate material in coastal waters and reduced surface salinity, connected to the reported coastal darkening of coastal waters. There was a worsening in ecological status for hard-bottom benthic communities (0–30 m) and a reduction in the lower growth depth limit of several macroalgae species. A structural shift in the community composition from macroalgae towards increased abundance of animals was found to be related to coastal darkening and reduced eutrophication. The concentration of coastal inorganic nutrients (DIN, PO4) declined by 27–36%, in response to management efforts to reduce eutrophication in European regional seas. Results indicate that reduced eutrophication was related to increased ecological status of the deep soft-bottom community (350 m), with a reduction in opportunistic polychaetes and an increase in filter feeding bivalves. This work highlights how climate change and other human-induced changes in a boreal ecosystem intensifies land-ocean interactions, and calls for more adaptive monitoring, where traditional water quality programs and policies need to evolve iteratively as new information emerges and the major drivers of the systems change.publishedVersio
Rapid faunal colonization and recovery of biodiversityand functional diversity following eelgrass restoration
Get PDFSeagrass meadows and their associated biodiverse assemblages have declined globally due to environmental and anthropogenic stressors. Restoration of these critical habitats has the potential to reverse coastal biodiversity loss. Here, we tested the role of patch size (which can affect recruitment, food availability, and/or predation) in driving faunal colonization in an eelgrass (Zostera marina) restoration trial in Sweden. Eelgrass shoots were transplanted in plots with different configurations (continuous vs. checkerboard patterns with three patch sizes), and we followed invertebrate colonization (biodiversity and functional diversity) during the first two growing seasons. We found rapid faunal colonization following the transplantation of eelgrass shoots in all plots with invertebrate densities reaching 50–80% of the reference meadow after only one growing season (3 months). After two growing seasons (15 months), the faunal density, biodiversity, and functional diversity were similar to the reference meadow, despite eelgrass density and biomass still being lower than the reference meadow. Biodiversity, functional diversity, and community structure were similar among the different planted plots, that is, there was no indication that patch size influenced faunal colonization. We therefore consider that smaller patches embedded within larger restoration plots can be as effective for promoting biodiversity as continuous patches, with reduced costs and fewer shoots required. We also noted high natural variability between years both in the reference meadow and planted plots, showing the dynamic nature of seagrass ecosystems, and the importance of a well-planned monitoring scheme that considers the reference area and restored area within the same temporal scale.publishedVersio
Major fine-scale spatial heterogeneity in accumulation of gelatinous carbon fluxes on the deep seabed
Get PDFAbyssal plain communities rely on the overlying water column for a settling flux of organic matter. The origin and rate of this flux as well as the controls on its fine-scale spatial distribution following seafloor settlement are largely unquantified. This is particularly true across regions where anthropogenically-induced seafloor disturbance has occurred. Here, we observed, quantified and mapped a mass deposition event of gelatinous zooplankton carcasses (pyrosomes) in July-September 2015 across one such physically disturbed region in the Peru Basin polymetallic nodule province (4150 m). Seafloor in this area was disturbed with a plough harrow in 1989 (as part of the DISCOL experiment) causing troughs in the sediment. Other parts were disturbed with an epibenthic sled (EBS) during a cruise in 2015 resulting in steep-walled, U-shaped troughs. We investigated two hypotheses: a) gelatinous food falls contribute significantly to the abyssal plain carbon pump and b) physical seafloor disturbance influences abyssal distribution of organic matter. We combined optical and bathymetric seafloor observations, to analyze pyrosome distribution on seabeds with different levels of disturbance. 2954 pyrosome colonies and associated taxa were detected in > 14,000 seafloor images. The mean regional carbon (C) deposition associated with pyrosome carcasses was significant compared to the flux of particulate organic C (182 to 1543%), and the total respired benthic C flux in the DISCOL Experimental Area (39 to 184%). EBS-disturbed seafloor tracks contained 72 times more pyrosome-associated C than an undisturbed reference site, and up to 4 times more than an area disturbed in 1989. Deposited pyrosomes collected had a higher proportion of labile fatty acids compared to the sediment. We document the temporal and spatial extent of an abyssal food fall event with unprecedented detail and show that physical seafloor disturbance results in the accumulation of detrital material. Such accumulation may reduce oxygen availability and alter benthic community structure. Understanding both the relevance of large food falls and the fine scale topography of the seafloor, is necessary for impact assessment of technologies altering seafloor integrity (e.g. as a result of bottom-trawling or deep seabed mining) and may improve their management on a global scale.publishedVersio