How should fishing mortality be distributed under balanced harvesting?

Zhou and Smith (2017) investigate different multi-species harvesting scenarios using a simple Holling-Tanner model. Among these scenarios are two methods for implementing balanced harvesting, where fishing is distributed across trophic levels in accordance with their productivity. This note examines the effects of a different quantitative implementation of balanced harvesting, where the fishing mortality rate is proportional to the total production rate of each trophic level. The results show that setting fishing mortality rate to be proportional to total production rate, rather than to productivity per unit biomass, better preserves trophic structure and provides a crucial safeguard for rare and threatened ecological groups. This is a key ingredient of balanced harvesting if it is to meet its objective of preserving biodiversity

Tunable magnetism on the lateral mesoscale by post-processing of Co/Pt heterostructures

Controlling magnetic properties on the nm-scale is essential for basic research in micro-magnetism and spin-dependent transport, as well as for various applications such as magnetic recording, imaging and sensing. This has been accomplished to a very high degree by means of layered heterostructures in the vertical dimension. Here we present a complementary approach that allows for a controlled tuning of the magnetic properties of Co/Pt heterostructures on the lateral mesoscale. By means of in-situ post-processing of Pt- and Co-based nano-stripes prepared by focused electron beam induced deposition (FEBID) we are able to locally tune their coercive field and remanent magnetization. Whereas single Co-FEBID nano-stripes show no hysteresis, we find hard-magnetic behavior for post-processed Co/Pt nano-stripes with coercive fields up to 850 Oe. We attribute the observed effects to the locally controlled formation of the CoPt L1$_{0}$ phase, whose presence has been revealed by transmission electron microscopy.Comment: Accepted for publication in Beilstein J. Nanotechno

Balanced exploitation and coexistence of interacting, size-structured, fish species

This paper examines some effects of exploitation on a simple ecosystem containing two interacting fish species, with life histories similar to mackerel (Scomber scombrus) and cod (Gadus morhua), using a dynamic, size-spectrum model. Such models internalize body growth and mortality from predation, allowing bookkeeping of biomass at a detailed level of individual predation and growth and enabling scaling up to the mass balance of the ecosystem. Exploitation set independently for each species with knife-edge, size-at-entry fishing can lead to collapse of cod. Exploitation to achieve a fixed ratio of yield to productivity across species can also lead to collapse of cod. However, harvesting balanced to the overall productivity of species in the exploited ecosystem exerts a strong force countering such collapse. If balancing across species is applied to a fishery with knife-edge selection, size distributions are truncated, changing the structure of the system and reducing its resilience to perturbations. If balancing is applied on the basis of productivity at each body size as well as across species, there is less disruption to size-structure, resilience is increased, and substantially greater biomass yields are possible. We note an identity between the body size at which productivity is maximized and the age at which cohort biomass is maximized. In our numerical results based on detailed bookkeeping of biomass, cohort biomass reaches its maximum at body masse

Use of the forest canopy by bats in temperate forests of Central Europe

Mithilfe von parallelen Aufnahmen von Fledermausrufen wurde der bodennahe mit dem Baumkronenbereich verglichen, um die vertikale Stratifizierung von Fledermäusen in den gemäßigten Wäldern Zentraleuropas zu untersuchen. Im Zuge von 48 Nächten wurden 16 Untersuchungsflächen während des Jahres 2010 dreimalig beprobt. Dabei konnten insgesamt 2170 Rufsequenzen aufgenommen werden, wovon 40 % auf den Baumkronenbereich entfielen. Insgesamt wurden dabei 16 Fledermausarten nachgewiesen. Während im bodennahen Bereich 13 Arten nachgewiesen werden konnten, waren im Baumkronenbereich 14 Fledermausarten aktiv. Mithilfe von GLMMs wurden acht Arten, welche eine ausreichende Datenlage boten, auf die Parameter Stratum, zeitliche Periode, Temperatur und Habitatstruktur analysiert. Dabei zeigte sich für vier Arten eine klare Bevorzugung des bodennahen Bereichs. Myotis bechsteinii war die einzige Art, welche über alle drei Perioden hinweg eine signifikant höhere Aktivität im Baumkronenbereich hatte. Weiter drei Arten zeigten in mindestens einer Periode eine signifikante Präferenz für den Baumkronenbereich. Aufgrund dessen sollte die Untersuchung des oberen Stratums des Waldes für bestimmte Arten in Betracht gezogen werden. Für Naturschutzmaßnahmen und Monitoringprogramme muss die Bedeutung des Baumkronenbereichs berücksichtigt werden. Besondere Zielarten würden durch eine Betrachtung mit reinen Bodenaufnahmen unterschätzt werden.In this study parallel ground and canopy recordings of bat calls were compared in order to analyze the vertical stratification in a temperate forest in Central Europe. The recording effort was 48 nights, by sampling 16 sites three times during the year 2010. During this study, 2170 sequences were recorded with 40 % of these in the canopy level. Overall 16 bat species could be determined. On the ground level 13 species where recorded, compared to 14 species in the canopy. By calculating GLMMs for eight species with sufficient data, the effect of stratum, time period, temperature, and habitat structure on the bat activity was analyzed. The A clear preference for the ground level was proven for four bat species. Myotis bechsteinii was the only species, which had a significant preference for the canopy level in all three periods, whereas three further species showed a clear canopy preference in at least one period. Therefore, canopy sampling should be taken into account for certain species. For conservation measures and monitoring efforts it must be considered, that the canopy stratum of the forest is very important. Some target species will be underestimated by ground measurements alone