The effect of a non-volatile dust mantle on the energy balance of cometary surface layers

It is likely that large parts of a cometary surface layer consist of porous ices, which are covered by a thin layer of non-volatile debris, whose structure is also fluffy and porous. In this paper the results of model calculations are presented. The calculations show the effect of ice and dust pore sizes and of the dust mantle thickness upon the thermal behavior of such a dust-ice system, when it is irradiated by the sun. In particular, it is found that the average pore size of the ice and the dust material has a large influence both on the dust surface temperature and on the temperature at the dust-ice interface

The Human Dimensions of Recreational Anglers Targeting Freshwater Species in Coastal Ecosystems, with Implications for Management

Little is known about whether brackish coastal ecosystems attract specific angler types that are characterized by site‐specific preferences and behaviors while targeting freshwater fishes living in a low‐salinity environment. Using the lagoon (“Bodden”) fisheries in northeastern Germany, we compared the human dimensions among anglers fishing in Bodden sites, anglers fishing primarily in freshwater sites, and other, less‐setting‐specialized anglers that use both marine and freshwater fisheries. Data were generated from a 1‐year telephone–mail–diary study involving over 1,000 study participants. The general characteristics, demographics, specialization level, motives, catch orientation, and catch‐and‐release behaviors of the three angler groups were rather similar. However, when targeting specific freshwater fish (i.e., Eurasian Perch Perca fluviatilis, Northern Pike Esox lucius, and Zander [also known as Pikeperch] Sander lucioperca), the motives of anglers choosing the Bodden versus freshwater sites differed. Specifically, Bodden anglers targeting freshwater species in brackish waters were more catch oriented, trophy fish oriented, and challenge seeking compared to freshwater anglers. Bodden anglers were also more likely to fish with friends rather than alone compared to the other angler groups, and they were more likely to use motorboats and to take guides compared to freshwater anglers. Correspondingly, a revealed preference choice model showed that anglers expecting high catch outcomes and social experiences with friends and boat fishing were more likely to select the Bodden waters relative to freshwater sites. Additionally, anglers with a stronger orientation toward the noncatch, experience‐based aspects of fishing were more likely to fish in the Bodden and coastal sites compared to freshwater, suggesting that coastal sites satisfy both catch‐ and non‐catch‐related expectations. We suggest that given their specific preferences and characteristics, Bodden anglers will be particularly sensitive to constraints imposed on using motorboats and to declines in catch rates and trophy sizes in the catch, specifically for Northern Pike.EMFF and State of Mecklenburg‐Vorpommern http://dx.doi.org/10.13039/100014510Peer Reviewe

Data‐poor stock assessment of fish stocks co‐exploited by commercial and recreational fisheries: Applications to pike Esox lucius in the western Baltic Sea

Information on catch and effort of recreational angling in mixed‐use fisheries (co‐exploited by commercial and recreational fishers) is often scarce, preventing the application of data‐rich stock assessments typically performed for industrialised commercial fisheries. This study shows how data‐poor stock assessment methods developed for marine fisheries, particularly a model class labelled as “catch‐only” models (COMs), offer a possible solution. As a case study, COMs are used to assess a northern pike Esox lucius L. stock around the German Baltic island of Rügen. Multiple COMs were fitted to a time series of total pike removals, and their outputs were used as explanatory variables in ensemble models. The stock was found to be fully exploited and currently declining. This study highlights the potential for using COMs to determine status of previously unassessed coastal and freshwater stocks facing recreational fishing pressure and demonstrates how incorporating recreational removals is crucial for achieving reliable insights into the status of mixed‐use stocks.European Maritime Fisheries Fund (EMFF) of the EU and the State of Mecklenburg‐Vorpommern (Germany)Peer Reviewe

Data-poor stock assessment of fish stocks co-exploited by commercial and recreational fisheries: Applications to pike Esox lucius in the western Baltic Sea

Information on catch and effort of recreational angling in mixed-use fisheries (co-exploited by commercial and recreational fishers) is often scarce, preventing the application of data-rich stock assessments typically performed for industrialised commercial fisheries. This study shows how data-poor stock assessment methods developed for marine fisheries, particularly a model class labelled as "catch-only" models (COMs), offer a possible solution. As a case study, COMs are used to assess a northern pike Esox lucius L. stock around the German Baltic island of Rugen. Multiple COMs were fitted to a time series of total pike removals, and their outputs were used as explanatory variables in ensemble models. The stock was found to be fully exploited and currently declining. This study highlights the potential for using COMs to determine status of previously unassessed coastal and freshwater stocks facing recreational fishing pressure and demonstrates how incorporating recreational removals is crucial for achieving reliable insights into the status of mixed-use stocks

Free Collisions in a Microgravity Many-Particle Experiment. I. Dust Aggregate Sticking at Low Velocities

Over the past years the processes involved in the growth of planetesimals have extensively been studied in the laboratory. Based on these experiments, a dust-aggregate collision model was developed upon which computer simulations were based to evaluate how big protoplanetary dust aggregates can grow and to analyze which kinds of collisions are relevant in the solar nebula and are worth further studies in the laboratory. The sticking threshold velocity of millimeter-sized dust aggregates is such a critical value that had so far only theoretically been derived, as the relevant velocities could not be reached in the laboratory. We developed a microgravity experiment that allows us for the first time to study free collisions of mm-sized dust aggregates down to velocities of ~0.1 cm/s to assess this part of the protoplanetary dust evolution model. Here, we present the results of 125 free collisions between dust aggregates of 0.5 to 2 mm diameter. Seven collisions with velocities between 0.2 and 3 cm/s led to sticking, suggesting a transition from perfect sticking to perfect bouncing with a certain sticking probability instead of a sharp velocity threshold. We developed a model to explain the physical processes involved in dust-aggregate sticking, derived dynamic material properties of the dust aggregates from the results of the collisions, and deduced the velocity below which aggregates always stick. For millimeter-sized porous dust aggregates this velocity is 8e-5 m/s.Comment: accepted by Icaru

Farmers adoption of the Habitats Directive in Eastern Germany what drives the optimization of grassland conservation?

The following paper provides insights in the adoption-behavior of farmers in Saxony due to the Fauna-Flora-Habitat directive (habitat-directive) of the European Union (EU). For the implementation of the habitat directive, the federal state of Saxony has introduced the instrument of managementplans in combination with agri-environmental programs. The paper shows that the combination of managementplans and agri-environmental programs can be successful for the implementation of nature-conservation measures under specific circumstances. The paper investigates the determinants of the farmers decision to optimize their farming practices towards the objective of nature conservation. The data set consists of interviews with 139 farmers between 2004 and 2011 and additionally information of 333 grassland-sites. A multinomial logit model was applied. The results show that location factors and the design of AEPs exhibit an influence on the implementation of measures of the Habitat Directive. At the plot level, we can (among other factors) observe an impact of specific (dark green) agri-environmental programs on the willingness of farmers to adopt nature conservation measures within the framework of the EU habitat directive. We also investigate the determinants of participation in light green and dark green AEPs. The findings highlight the potential of integrated policy packages to incentivize specific measures of nature conservation within the Natura 2000 framework. Acknowledgement

How catch uncertainty and harvest regulations drive anglers’ choice for pike (Esox lucius) fishing in the Baltic Sea

In the brackish lagoons located in coastal inshore areas around the German island of Rügen, pike Esox lucius is a highly sought after target species for recreational fishers. Yet, the pike stock is currently in decline, and conflicts with other user groups (specifically commercial fishers) have emerged. To inform future fisheries management, an improved understanding of the human dimensions of recreational fishers, including their preferences for catch outcomes and regulations, is relevant. Our objective was to better understand how German recreational pike fishers react to different types of harvest regulations in trade-off with risky or ambiguous catch outcomes for pike and other predators in the lagoon fishery. We conducted an online survey including choice experiments for angling experiences that differed in seven attributes. Data were analyzed using a latent class model. We found four distinct angler types differentiating resident and tourists and dependency on pike. Specifically, we identified a highly involved pike tourist (42 % average probability), a consumptive, generalist tourist angler type (18 %), a highly specialized local trophy pike angler type that readily engaged in catch-and-release (12 %), and a local generalist angler that also benefitted from the catch of other predators than pike (18 %). Despite heterogeneity in preferences, all four angler types generally accepted more restrictive regulations for pike removals than currently in place, and dispreferred low catch probabilities compared to catch ambiguity. Most angler types also revealed diminishing marginal utility returns for catch rates, where the first three pike in a day provide utility, while the marginal benefits of catch rate decrease to zero for more than three pike per day. Angler types varied more in their preferences for trophy pike, the general attractiveness of the pike as a target and the utility derived from catching fish other than pike. Particularly the more specialized angler types focused on size rather than catch rate. Despite preference heterogeneity, focusing management attention on maintaining a sufficiently high catch rate and increasing the number of trophy pike in the stock seems to satisfy the expectations of most angler types. To achieve such outcomes, the anglers of all types would overwhelmingly support implementing harvest slots of 50–85 cm that allow both small and large fish to be released (rather than the current minimum-length limit of 50 cm), and accept reductions in the daily bag limit to 1 pike per day (relative to the current of 3 pike per day). Implementing these policy measures would unlikely generate substantial conflict with anglers represented in our survey

Air pollution and food prices: evidence from China

Air pollution is one of the top environmental concerns in China. On days with severe air pollution, people (both consumers and producers) often reduce outdoor economic activities in order to avoid possible health damages. This impacts the market trade of fresh food products, at least in a short run. This empirical study sheds light on the impact of air pollution on the short run prices of three major fresh food products (Chinese cabbage, tomatoes and pork) using daily data from the largest outdoor wholesale market in Beijing. With an increase in AQI (Air Quality Index) by 100 units, prices for Chinese cabbage and tomatoes decrease by 1.19 and 0.89 per cent. With an increase in PM2.5 concentration by 100 lg/m3, prices for Chinese cabbage and tomatoes decrease by 0.64 and 0.55 per cent. Air pollution affects vegetable prices, but has no significant impact on prices of pork products