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Humans play an integral role in biological invasions, from aiding introductions of alien species to experiencing their impacts and holding the ability to manage them. The importance of understanding the dynamics of stakeholders' perceptions on alien species is therefore increasingly recognized. In this study, we used anonymous online surveys to contrast recreational anglers' perceptions towards European flounder (Platichthys flesus, Linnaeus, 1758) in Iceland, where it is classified as a potentially invasive species, to the perceptions prevailing amongst recreational anglers in the species' native range. We furthermore explored potential temporal changes in the perception of Icelandic recreational anglers. Our results indicate that Icelandic recreational anglers have a highly negative perception towards the European flounder, while in its native range, recreational anglers have positive perceptions towards this species. In Iceland, we have furthermore detected a significant change towards less negative perceptions between the surveys administered in October 2019 and March 2023. Finally, we compared the results of the online surveys and novel, conservation culturomics tools to further explore stakeholder perceptions and public interest in Iceland. The comparison highlighted some limitations that should be considered when using culturomics in very small societies or for small languages. For example, the text mining approaches on newspaper articles and social media conservations detected neutral perceptions in the communication to the public and within the targeted stakeholder group via social media in contrary to the perceptions detected in the online surveys. Moreover, we detected short-term peaks in the public's interest in European flounder and potential drivers of those peaks using Wikipedia pageviews but Google Trends provided mixed and unreproducible results. Overall, our study highlights that stakeholders' perceptions towards an alien species as well as the public's interest in it vary over time and space, though the drivers of these changes are often difficult to identify. [ABSTRACT FROM AUTHOR]

Atlantic cod is a keystone species that remains among the most economically important demersal fish in the North Atlantic. Throughout its distribution range, Atlantic cod is composed of populations with varying environmental preferences and migratory propensities. This life-history variation is likely to have contributed to the niche width and large population sizes of Atlantic cod, and its relative resilience to environmental change and exploitation. The Icelandic cod stock is currently managed as a single unit, but early research indicates population variation by depth and temperature and distinct offshore and inshore spawning components. Pelagic 0-group juveniles from different spawning grounds coexist in nursery areas around Iceland, but their genetic composition or habitat partitioning had not been examined post benthic settlement. In the current study we examine the genetic composition of Atlantic cod juvenile aggregations at nearshore nursery grounds in NW-Iceland and report distinct segregation by the depth of offshore and inshore juvenile cod. The physiological mechanism of this segregation is not known, but the pattern demonstrates the need to consider population structure at nursery grounds in the application of marine spatial planning and other area-based conservation tools. [ABSTRACT FROM AUTHOR]

We use biochemical, biological, archaeological, and historical analysis to examine relationships between Atlantic cod migration, sea temperature, and shifts in the distribution and occupancy of historical fishing sites in Iceland during the last millennium. Results support the hypothesis that the cooling climate of the North Atlantic during the period commonly referred to as the Little Ice Age coincided with changes in Atlantic cod migration patterns. Historical analysis shows a concomitant increase in reports of worsening Atlantic cod fishing and a severe decrease in domestic fishing, particularly in north Iceland. We conclude thatAtlantic cod fisheries in Iceland originally thrived because of the proximity to codmigration routes. However, despite themobility of local fishers, fluctuations in fish migrations, coupled with a harsher climate and increased competition for fishing grounds, resulted in a stagnation that lasted until the eventual modernization of the fishery in the mid-nineteenth century. [ABSTRACT FROM AUTHOR]

Fifteen non-indigenous species have been recorded in Icelandic waters over the past decades, of which six have been classified as invasive or potentially invasive. One of these potentially invasive species is the European flounder (Platichthys flesus). Platichthys flesus is a recent arrival that was firstly identified in 1999 and has, since then, established a population around the whole country. In this study we evaluated if there is niche overlap between juvenile P. flesus and native juvenile European plaice (Pleuronectes platessa) on nursery grounds at three sites in west Iceland. Considering the presumed clockwise spread of P. flesus' population around the country, the southernmost site, Borgarfjörður, was treated as the site of earlier settlement of P. flesus. Similarly, the northernmost site, Önundarfjörður, was treated as the site of later settlement. We used stomach content and stable isotope analyses to examine if there was a significant niche overlap between P. flesus and P. platessa and to examine if the extent of niche overlap varied between sites. Multiple cohorts of P. flesus and native P. platessa were present at all sites and there was high niche overlap between species with no indication of trophic niche segregation nor change with time from establishment of P. flesus. The current study has shown the cooccurrence and niche overlap of non-indigenous P. flesus and native P. platessa on nursery grounds in Iceland and highlighted the establishment of P. flesus in Iceland as a rare case study to investigate colonisation processes of non-indigenous fish species in sub-arctic marine environments. [ABSTRACT FROM AUTHOR]

Anadromous Arctic charr Salvelinus alpinus and sea trout Salmo trutta are commonly found in marine, estuarine and freshwater habitats across the Northern Hemisphere. The marine phase varies between populations but often involves summer foraging in nearshore waters while spawning and overwintering occur in freshwater. The dependence of anadromous salmonids on nearshore habitats makes them vulnerable to increased industrial activity, such as aquaculture developments, that may increase the risk of salmon lice Lepeophtheirus salmonis, infection. Lice infection in wild salmonids depends on farmed fish density but can also be correlated to environmental factors, including foraging ecology. In the current paper we examine niche use and trophic variation of co-occurring Arctic charr and sea trout in northwest Iceland, using stomach contents and stable isotope values of δ13C, δ15N and δ34S. We then test if these factors correlated to salmon lice infection. The salmonid species differed in niche use, for example, in time of marine foraging, with Arctic charr having a longer marine phase than was expected, and in the level of piscivory between both species. Moreover, we show that both environmental factors and individual trophic use are related to salmon lice infection in sea trout. This information may be useful in evaluating the risk and spatial management of sea farming. [ABSTRACT FROM AUTHOR]

Seasonal migrations of marine fish between shallow summer feeding habitats and deep overwintering grounds are driven by fluctuations in the biotic and abiotic environment as well as by changes in the internal state. Ontogenetic shifts in physiology and metabolism affect the response to environmental drivers and may lead to changes in migration timing and propensity. In this study, we investigated the effect of temperature and body size on migration timing and depth distribution in acoustically tagged Atlantic cod, Gadus morhua, and saithe, Pollachius virens, during the period of seasonal migration from shallow summer habitats. The results from our study revealed a wide range of horizontal and vertical distribution of age 1 and 2 G. morhua within the fjord. Larger G. morhua inhabited deeper, cooler waters than smaller juveniles, likely reflecting size‐dependent thermal preferences and predation pressure. Conversely, juvenile P. virens occupied primarily shallow waters close to land. The variation in depth distribution of G. morhua was mainly explained by body size and not, against our predictions, by water temperature. Conversely, the dispersal from the in‐fjord habitats occurred when water temperatures were high, suggesting that seasonal temperature fluctuations can trigger the migration timing of P. virens and larger G. morhua from summer habitats. Partial migration of small juvenile G. morhua from in‐fjord foraging grounds, likely influenced by individual body condition, suggested seasonal migration as a flexible strategy that individuals may use to reduce predation and energetic expenditure. Predation mortality rates of tagged juveniles were higher than previously suggested and are the first robust predation mortality rates for juvenile G. morhua and P. virens estimated based on acoustic transmitters with acidity sensors. The results have relevance for climate‐informed marine spatial planning as under the scenario of increasing ocean temperatures, increasing summer temperatures may reduce the juveniles' resource utilization in the shallow summer nurseries, resulting in lower growth rates, increased predation pressure, and lower chances of juvenile winter survival. [ABSTRACT FROM AUTHOR]

A correction to the article "Historical DNA reveals the demographic history of Atlantic cod (Gadus morhua) in medieval and early modern Iceland" that was published in the 2014 issue is presented.

Stable isotope analyses of zooarchaeological material can be used to examine ecological variability in exploited species at centennial to millennial scales. Climate change is a notable driver of marine ecosystem change, although historical fishing is also likely to have impacted past marine systems. Fishing removes the oldest and largest individuals and may thereby result in shorter trophic pathways and reduced niche width of predatory fish species. In the current study we examine the trophic niche of Atlantic cod, haddock and Atlantic wolffish, in the last millennium using δ 13 C and δ 15 N values of bone collagen. We report a lower trophic level of Atlantic cod and haddock but higher level of wolffish in present times, following centuries at consistent and higher trophic levels of Atlantic cod. This results in a concurrent converging trophic niche of the demersal fish. We suggest that the current data set provides a valuable historical baseline facilitating interpretation of current variability in the trophic ecology of northern demersal fish.

Atlantic cod (Gadus morhua) vertebrae from archaeological sites were used to study the history of the Icelandic Atlantic cod population in the time period of 1500-1990. Specifically, we used coalescence modelling to estimate population size and fluctuations from the sequence diversity at the cytochrome b (cytb) and Pantophysin I (PanI) loci. The models are consistent with an expanding population during the warm medieval period, large historical effective population size (NE), a marked bottleneck event at 1400-1500 and a decrease in NE in early modern times. The model results are corroborated by the reduction of haplotype and nucleotide variation over time and pairwise population distance as a significant portion of nucleotide variation partitioned across the 1550 time mark. The mean age of the historical fished stock is high in medieval times with a truncation in age in early modern times. The population size crash coincides with a period of known cooling in the North Atlantic, and we conclude that the collapse may be related to climate or climate-induced ecosystem change.