Filter-foraging strategies of captive American paddlefish (Polyodon spathula) in relation to food type, density and distribution in the water column

The American paddlefish (Polyodon spathula) uses ram filter-feeding to forage for (mainly) zooplankton throughout the water column. It makes an ontogenetic transition from buccal pumping to ram ventilation feeding in the first year. In wild conditions, plankton is often distributed unevenly in time and space; however, this does not always apply to captive conditions. In the present study, two paddlefish were fed on a range of diets and supply methods to investigate the effect on foraging strategy. Insight into influencing foraging strategies could be beneficial for zoos and aquaria for display purposes or for improving welfare conditions. The paddlefish were studied during foraging, and foraging strategy, bout length and usage of the aquarium space were recorded. Three foraging strategies can be distinguished: foraging while swimming in straight lines, foraging while swimming in circulatory paths and particulate foraging. Although these strategies appear to not have a fixed switch-point, a significant difference was found between the foraging strategies for start and end points of certain strategies in relation to food density (P</p

Biomimetic Design of Turbine Blades for Ocean Current Power Generation

The enhancement of energy technology and innovation play a crucial role in order to meet the challenges related to global warming in the coming decades. Inspired by bird wings, the performance of a bio-inspired blade assembled to a marine turbine model, is examined. Following a biomimetic pathway, the aerodynamic performance of the bird wings of the species Common Guillemot (Uria aalge) was tested in a wind tunnel laboratory. Based on our results, we derived a bio-inspired blade model by following a laser scanning method. Lastly, the bio-inspired blades were assembled to a marine turbine model and tested in a large flow tank facility. We found efficiencies (Cp) up to 0.3 which is around 53% of the maximum power that can be expected from the turbine model according to the Betz approach. Our findings are analyzed in the discussion section as well as considerations for future research

Modulation of yaw by the caudal fin in the yellow boxfish (<i>Ostracion cubicus</i>)

Boxfishes (Ostraciidae; Tetraodontiformes) have a rigid carapace which restricts body undulation. Swimming movements can only be generated by the fins which protrude from the carapace. Nevertheless, these fishes are highly manoeuvrable and manage to swim with remarkably dynamic stability. However, the rigid carapace of boxfishes shows an inherently unstable response in yaw caused by course-disturbing flows. Hence, any net stabilising effect should come from the fishes’ fins. Here, we aim to determine the effect of the surface area and orientation of the caudal fin on the yaw torque exerted on the square cross-sectional shaped yellow boxfish (Ostracion cubicus). Yaw torques were quantified in a flow tank using a 3D printed physical yellow boxfish model with an attachable closed or open caudal fin. The model was positioned at different body and tail angles and exposed to different water flow speeds. We show that the caudal fin is crucial for yaw control. These flow tank results were confirmed by computational fluid dynamics simulations. The caudal fin acts as both a course-stabiliser and rudder for the naturally unstable rigid carapace with regard to yaw. By using physical models and computer simulations, we quantitatively show that actively changing the shape and orientation of the caudal fin plays an important role in controlling yaw torque in yellow boxfish. Further study is needed to unravel how all components of the boxfishes’ locomotor apparatus function together, from a dynamic perspective, during lateral gust flows and turning

Design optimization and wind tunnel investigation of a flapping system based on the flapping wing trajectories of a beetle's hindwings

To design a flapping-wing micro air vehicle (FWMAV), the hovering flight action of a beetle species (Protaetia brevitarsis) was captured, and various parameters, such as the hindwing flapping frequency, flapping amplitude, angle of attack, rotation angle, and stroke plane angle, were obtained. The wing tip trajectories of the hindwings were recorded and analyzed, and the flapping kinematics were assessed. Based on the wing tip trajectory functions, bioinspired wings and a linkage mechanism flapping system were designed. The critical parameters for the aerodynamic characteristics were investigated and optimized by means of wind tunnel tests, and the artificial flapping system with the best wing parameters was compared with the natural beetle. This work provides insight into how natural flyers execute flight by experimentally duplicating beetle hindwing kinematics and paves the way for the future development of beetle-mimicking FWMAVs

Coasting in live-bearing fish: The drag penalty of being pregnant

Swimming performance of pregnant live-bearing fish is presumably constrained by the additional drag associated with the reproductive burden. Yet, it is still unclear how and to what extent the reproductive investment affects body drag of the females. We examined the effect of different levels of reproductive investment on body drag. The biggest measured increase in body volume due to pregnancy was about 43%, linked to a wetted area increase of about 16% and 69% for the frontal area. We printed three-dimensional models of live-bearing fish in a straight body posture representing different reproductive allocation (RA) levels. We measured the drag and visualized the flow around these models in a flow tunnel at different speeds. Drag grew in a power fashion with speed and exponentially with the increase of RA, thus drag penalty for becoming thicker was relatively low for low speeds compared to high ones. We show that the drag increase with increasing RA was most probably due to bigger regions of flow separation behind the enlarged belly. We suggest that the rising drag penalty with an increasing RA, possibly together with pregnancy-related negative effects on muscle- and abdominal bending performance, will reduce the maximum swimming speed