Latent power of basking sharks revealed by exceptional breaching events

The fast swimming and associated breaching behaviour of endothermic mackerel sharks is well suited to the capture of agile prey. In contrast, the observed but rarely documented breaching capability of basking sharks is incongruous to their famously languid lifestyle as filter-feeding planktivores. Indeed, by analysing video footage and an animal-instrumented data logger, we found that basking sharks exhibit the same vertical velocity (approx. 5 m s−1) during breach events as the famously powerful predatory great white shark. We estimate that an 8-m, 2700-kg basking shark, recorded breaching at 5 m s−1 and accelerating at 0.4 m s−2, expended mechanical energy at a rate of 5.5 W kg−1; a mass-specific energetic cost comparable to that of the great white shark. The energy cost of such a breach is equivalent to around 1/17th of the daily standard metabolic cost for a basking shark, while the ratio is about half this for a great white shark. While breaches by basking sharks must serve a different function to white shark breaches, their similar breaching speeds questions our perception of the physiology of large filter-feeding fish

Experimental Investigation of the Influence of Permeability on Finite Wing Lift and Drag (Vollbeitrag)

An analytical approach for the correction of the influence of permeability on aerodynamic lift and drag polars of finite wings is presented. The approach is validated through wind tunnel measurements of a simple wing-body configuration. Polars for both permeable and impermeable wings were measured at varying inflow velocities. Using only measured values for permeability and porosity, the permeable polars can be mapped to the impermeable case and vice versa with good agreement

Speed limits on swimming of fishes and cetaceans

Physical limits on swimming speed of lunate tail propelled aquatic animals are proposed. A hydrodynamic analysis, applying experimental data wherever possible, is used to show that small swimmers (roughly less than a metre long) are limited by the available power, while larger swimmers at a few metres below the water surface are limited by cavitation. Depending on the caudal fin cross-section, 10–15 m s−1 is shown to be the maximum cavitation-free velocity for all swimmers at a shallow depth