Author: hilduryr@matis.is

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Davíð Gíslason

Project Manager

davidg@matis.is

Harvested marine fish stocks often show a rapid and substantial decline in age and size at maturity. 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 fish 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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Davíð Gíslason

Project Manager

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 whales, which may represent an additional challenge to its recovery in the Atlantic Ocean compared to other rorquals.

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Davíð Gíslason

Project Manager

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 vitreous) 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 females 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

Project Manager

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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Contact

Davíð Gíslason

Project Manager

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 estimate 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 indicates both effects of oceanic currents and diel vertical migration on eDNA detection and quantification.

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News about climate change hits us every day, so it's clear that it's time to take action. But what is the best way to teach children and young people about such difficult issues so that they are encouraged to take action? It will be them and their descendants who will be affected by climate change, and it is therefore important that they receive education and increased knowledge of what may lie ahead. The need for quality education on the issue, which also does not promote climate anxiety, is becoming more and more inevitable. The answer may lie in innovation. These students will take over the board one day, so it is important that students receive quality education about innovation and entrepreneurship from a young age. Objectives Green Entrepreneurs of the Future (GFF) was tackling this challenge by giving students in rural areas the opportunity for innovative education and getting them interested in climate and environmental issues. Matís is responsible for the project and it took place in three elementary schools in the countryside. A number of participants came to the project, including FabLab workshops and fishing companies in the local area, N4 TV station and others. The project was financed by the Climate Fund and was originally planned for one year.

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External conditions can drive biological rates in ectotherms by directly influencing body temperatures. While estimating the temperature dependence of performance traits such as growth and development rate is feasible under controlled laboratory settings, predictions in nature are difficult. One major challenge lies in translating performance under constant conditions to fluctuating environments. Using the butterfly Pieris napi as a model system, we show that development rate, an important fitness trait, can be accurately predicted in the field using models parameterized under constant laboratory temperatures. Additionally, using a factorial design, we show that accurate predictions can be made across microhabitats but critically hinge on adequate consideration of non-linearity in reaction norms, spatial heterogeneity in microclimate and temporal variation in temperature. Our empirical results are also supported by a comparison of published and simulated data. Conclusively, our combined results suggest that, discounting direct effects of temperature, insect development rates are generally unaffected by thermal fluctuations.

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Seasons impose different selection pressures on organisms through contrasting environmental conditions. How such seasonal evolutionary conflict is resolved in organisms whose lives span across seasons remains underexplored. Through field experiments, laboratory work, and citizen science data analyses, we investigate this question using two closely related butterflies (Pieris rapae and P. napi). Superficially, the two butterflies appear highly ecologically similar. Yet, the citizen science data reveal that their fitness is partitioned differently across seasons. Pieris rapae have higher population growth during the summer season but lower overwintering success than do P. napi. We show that these differences correspond to the physiology and behavior of the butterflies. Pieris rapae outperform P. napi at high temperatures in several growth season traits, reflected in microclimate choice by ovipositing wild females. Instead, P. rapae have higher winter mortality than do P. napi. We conclude that the difference in population dynamics between the two butterflies is driven by seasonal specialization, manifested as strategies that maximize gains during growth seasons and minimize harm during adverse seasons, respectively.

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