Flokkur: Greinar

Tengiliður

Davíð Gíslason

Verkefnastjóri

davidg@matis.is

Harvest can change phenotypic traits of populations through immediate demographic consequences, evolutionary responses to harvest selection, or developmental responses by individuals. This study investigated the plastic phenotypic effects of harvest on size and age at maturity in a commercially exploited freshwater fish. We tested an individual growth and life history plasticity model using lagged correlations incorporating how harvesting of ages 2 and older fish influenced the abundance of juvenile fish, resource availability, individual growth rates, and carry-over responses in age and size at maturity. Our test used cohort data for Lake Erie yellow perch (Perca flavescens). Age and size at maturity fluctuated widely and rapidly across 23 cohorts between 1991 and 2013, suggesting phenotypic plasticity contributed strongly to maturation dynamics. The changes in maturity could not be explained by responses to harvest, as expected under the plasticity model. In Lake Erie, age and size at maturity in yellow perch appear to be responding to other drivers, such as harvest-induced dynamics of other fish stocks or ecosystem changes that are independent of harvest.

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Tengiliður

Davíð Gíslason

Verkefnastjóri

davidg@matis.is

Overexploitation and collapse of major fisheries raises important concerns about effects of harvest on fish populations. We tested for ecological and evolutionary mechanisms by which harvest could affect exploited fish populations in Lake Erie over the last four decades, over most of which intensive fisheries management was implemented. We did not detect evidence of long-term negative effects of harvest on yellow perch (Perca flavescens), walleye (Sander vitreus), white perch (Morone americana), or white bass (Morone chrysops) populations, either through recruitment success or through alteration of maturation schedules. Current fisheries management in Lake Erie has been relatively successful with respect to minimizing negative harvest effects, such that the dynamics of exploited fish populations in Lake Erie were more strongly affected by environment than harvest. Our study adds to the evidence that effective fisheries management is capable of rebuilding depleted fisheries and (or) maintaining healthy fisheries. Nevertheless, fisheries management needs to move beyond the ecological dimension to incorporate economic, social, and institutional aspects for society to be better assured of the sustainability of fisheries in rapidly changing ecosystems.

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Tengiliður

Davíð Gíslason

Verkefnastjóri

davidg@matis.is

Harvested marine fish stocks often show a rapid and substantial decline in the age and size at maturation. Such changes can arise from multiple processes including fisheries‐induced evolution, phenotypic plasticity, and responses to environmental factors other than harvest. The relative importance of these processes could differ systematically between marine and freshwater systems. We tested for temporal shifts in the mean and within‐cohort variability of age‐ and size‐based maturation probabilities of female yellow perch (Perca flavescens Mitchill) from four management units (MUs) in Lake Erie. Lake Erie yellow perch have been commercially harvested for more than a century and age and size at maturation have varied since sampling began in the 1980s. Our analysis compared probabilistic maturation reaction norms (PMRNs) for cohorts when abundance was lower and harvest higher (1993–1998) to cohorts when abundance was higher and harvest lower (2005–2010). PMRNs have been used in previous studies to detect signs of evolutionary change in response to harvest. Maturation size threshold increased between the early and late cohorts and the increases were statistically significant for the youngest age in the western MU1 and for older ages in the eastern MU3. Maturation envelope widths, a measure of the variability in maturation among individuals in a cohort, also increased between early and late cohorts in the western MUs where harvest was highest. The highest rates of change in size at maturation for a given age were as large or larger than rates reported for harvested marine fishes where declines in age and size at maturation have been observed. Contrary to the general observation of earlier maturation evolving in harvested stocks, female yellow perch in Lake Erie may be rapidly evolving delayed maturation since harvest was relaxed in the late 1990s, providing a rare example of possible evolutionary recovery. This article is protected by copyright. All rights reserved.

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Tengiliður

Davíð Gíslason

Verkefnastjóri

davidg@matis.is

Biodiversity in the oceans has dramatically declined since the beginning of the industrial era, with accelerated loss of marine biodiversity impairing the ocean’s capacity to maintain vital ecosystem services. A few organisms epitomize the damaging and long-lasting effects of anthropogenic exploitation: Some whale species, for instance, were brought to the brink of extinction, with their population sizes reduced to such low levels that may have caused a significant disruption to their reproductive dynamics and facilitated hybridization events. The incidence of hybridization is nevertheless believed to be rare, and very little information exists on its directionality. Here, using genetic markers, we show that all but one whale hybrid sample collected in Icelandic waters originated from the successful mating of male fin whale and female blue whale, thus suggesting unidirectional hybridization. We also demonstrate for the first time the existence of a second-generation adult (male) hybrid resulting from a backcross between a female hybrid and a pure male fin whale. The incidence of hybridization events between fin and blue whales is likely underestimated and the observed unidirectional hybridization (for F1 and F2 hybrids) is likely to induce a reproductive loss in blue whale, which may represent an additional challenge to its recovery in the Atlantic Ocean compared to other rorquals.

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Tengiliður

Davíð Gíslason

Verkefnastjóri

davidg@matis.is

Decreases in size at maturation in harvested fish populations can reduce productivity and resilience. Delineating the causes for these changes in maturation is challenging. We assessed harvest and large-scale ecosystem variability as causes for changes in maturation in four Lake Erie fishes. Regulated harvests of yellow perch (Perca flavescens) and walleye (Sander vitreus) are greater than unregulated harvests of white perch (Morone americana) and white bass (Morone chrysops). Our assessment considered cohort data from 1991 to 2012 for each species. We used a conceptual model of harvest-induced plasticity to show that changes in female length at 50% maturity (L ₅₀) were unrelated to harvest intensity in all species. We then demonstrated that changes in female L ₅₀ among cohorts were synchronous across species. Post hoc analysis of variables capturing year-to-year variation in climatic and lake conditions suggested L ₅₀ was larger when water levels were near the norm for the study period and smaller at low and high levels. We conclude that changes in L ₅₀ were most strongly related to ecosystem changes unrelated to harvest intensity.

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Davíð Gíslason

Verkefnastjóri

davidg@matis.is

Understanding the genetic differentiation among populations of most marine fish requires investigating the differences among spawning grounds. However, this can be challenging as spawning grounds for some species are not well known, or spawning fish are difficult to collect. An alternative is to collect juvenile fish in nursery habitats closely associated with potential spawning grounds. Greenland halibut is a deep-dwelling, commercially important species with at least two identified major offshore spawning grounds in the North Atlantic and weak genetic differentiation across the Atlantic. In this study, we sampled juveniles from three sites representing the Davis Strait spawning area in the northwest Atlantic and one site in the northeast Atlantic representing the primary spawning area along the western slope of the Barents Sea. We applied genotype by sequencing and discovered 90 genetic markers that could be used to assess genetic differentiation among the four sites. The northeast and northwest Atlantic showed major genetic differentiation, supporting the existence of the two primary spawning clusters. Additionally, we found genetic differentiation between the three northwest Atlantic samples implying the existence of more than one spawning area in the northwest.

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Tengiliður

Davíð Gíslason

Verkefnastjóri

davidg@matis.is

Capelin (Mallotus villosus) is both an important commercial and ecological resource of the North Atlantic subpolar region. Two decades ago, the stock distribution around Iceland drastically changed. During autumn, which corresponds to the main feeding period, the capelin stock was previously located between the North of Iceland and the Jan Mayen area. Since the beginning of 2000s, the feeding aggregation has been located at the east coast of Greenland, inducing slight changes in the timing and route of the capelin spawning migration along the Icelandic shelf, and therefore in the catches. Changes in the distribution of capelin around Iceland made it both more difficult and expensive to assess the distribution of the stock with current survey methods. Here, we compare environmental DNA (eDNA) data to the acoustic data collected during the autumn monitoring survey, which leads to a preliminary estimation of the stock size. eDNA samples were collected at five different depths and were analyzed both horizontally across latitudes and longitudes and vertically across depth profiles. We detected eDNA in most of the locations where acoustic data detected capelin. Generalized linear models suggested that eDNA concentrations can be used as a proxy for the detection and quantification of capelin. The horizontal distribution of eDNA observed during both years corresponds with the horizontal distribution of capelin registered with the acoustic approach, while the vertical distribution indicated both effects of oceanic currents and diel vertical migration on eDNA detection and quantification.

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Guðjón Þorkelsson

Stefnumótandi sérfræðingur

gudjon.thorkelsson@matis.is

Edible seaweeds are usually sold as flakes or even powers, and morphological identification of seaweed taxa is difficult. Water-soluble polysaccharides (WSPs) in edible seaweeds are not only interesting functional food ingredients (e.g. gel-forming property, health benefits), but also useful for seaweed taxon differentiation. The current study aims to explore the utility of monosaccharide profiling of WSPs in seaweed differentiation. We developed a high-performance liquid chromatography-photodiode array detection for monosaccharide determination, and characterized monosaccharide profiles of WSPs from five edible seaweeds sold in Iceland (i.e. kombu Iceland – Laminaria hyperborea, sugar kelp – Saccharina latissima, dulse – Palmaria palmata and two types of nori labelled as Porphyra sp. and Pyropia sp.). Monosaccharide profiling data reflected both the complexity and quantitative differences of WSPs. The seaweed dulse showed the highest concentrations of total sugar (ca. 16 mM), followed by kombu (ca. 12 mM). From monosaccharide profiling of red algae, it was found that galactose (ca. 81–87% of total sugars) and xylose (ca. 65–77% of total sugars) are the dominant sugars in nori and dulse, respectively, which reflected the presence of galactans and xylans. In brown algae (i.e. kombu and sugar kelp), glucose (ca. 64–83%) and fucose (13–20%) are the main sugars, and they represent laminarins and fucoidans. The principal component analysis of sugar profiles showed the useful patterns ‘for seaweed taxon differentiation. The dendrogramresulting from hierarchical cluster analysis is congruent with phylogenetic tree, implying the chemotaxonomic value of seaweed monosaccharide profiles. This tool will be more useful in authentication of seaweed taxa when morphological and genetic identifications are not available.

Tengiliður

Margrét Geirsdóttir

Verkefnastjóri

mg@matis.is

Spirulina algae (Spirulina platensis) cultivated in geothermally powered photobioreactors is here proposed as a potentially resource efficient, zero-carbon, and nutritious alternative to conventional beef meat. Employing a standard life cycle assessment, environmental impacts of large-scale Spirulina production in this facility are calculated. The production facility is sited in Orka náttúrunnar (ON Power) Geothermal Park, Iceland, and benefits from resource streams accessible through Hellisheiði (Hellisheidi) power station, including renewable electricity for illumination and power usage, hot and cold water streams for thermal management, freshwater for cultivation, and CO₂ for biofixation. During cultivation, GHG-intensive ammonia-based fertilizers are replaced with macronutrients sourced from natural open mines. LCA results show that production of 1 kg of wet edible biomass in this facility requires 0.0378 m² non-arable land, 8.36 m³ fresh water and is carbon neutral with − 0.008 CO₂-eq GHG emissions (net zero). Compared with conventionally produced meat from beef cattle, Spirulina algae cultured in the ON Power Geothermal Park, referred to in this study as GeoSpirulina, requires less than 1% land and water and emits less than 1% GHGs. Considering food and nutritional security concerns, cultivation in a controlled environment agriculture system assures consistent nutritional profile year-round. Moreover, GeoSpirulina biomass assessed in this study contains all essential amino acids as well as essential vitamins and minerals. While keeping a balanced nutrition, for every kg beef meat replaced with one kg GeoSpirulina, the average consumer can save ~ 100 kg CO₂-eq GHGs. It is concluded that environmental impacts of GeoSpirulina production in the Hellisheidi facility are considerably lower than those of conventionally produced ruminants.