Pectoral herding: an innovative tactic for humpback whale foraging

Humpback whales (Megaptera novaeangliae) have exceptionally long pectorals (i.e. flippers) that aid in shallow water navigation, rapid acceleration and increased manoeuvrability. The use of pectorals to herd or manipulate prey has been hypothesized since the 1930s. We combined new technology and a unique viewing platform to document the additional use of pectorals to aggregate prey during foraging events. Here, we provide a description of ‘pectoral herding’ and explore the conditions that may promote this innovative foraging behaviour. Specifically, we analysed aerial videos and photographic sequences to assess the function of pectorals during feeding events near salmon hatchery release sites in Southeast Alaska (2016–2018). We observed the use of solo bubble-nets to initially corral prey, followed by calculated movements to establish a secondary boundary with the pectorals—further condensing prey and increasing foraging efficiency. We found three ways in which humpback whales use pectorals to herd prey: (i) create a physical barrier to prevent evasion, (ii) cause water motion to guide prey towards the mouth, and (iii) position the ventral side to reflect light and alter prey movement. Our findings suggest that behavioural plasticity may aid foraging in changing environments and shifts in prey availability. Further study would clarify if ‘pectoral herding’ is used as a principal foraging tool by the broader humpback whale population and the conditions that promote its use.Ye

Learning from humpback whales for improving the energy capturing performance of tidal turbine blades

This paper summarizes a project on the potential of further improving the performance of horizontal axis tidal turbines via the application of leading-edge tubercles to the turbine blades inspired by humpback whales. Within this framework, a wide variety of experimental investigations, supported by numerical studies, have been conducted. The study first focused on the design and optimisation of the leading-edge tubercles for a specific tidal turbine blade section by using numerical methods to propose an “optimum” design for the blade section. This optimum design was then applied onto a representative tidal turbine blade. This representative 3D blade demonstrated significant benefits, especially after stall. The experimental measurements were further validated and complimented by numerical simulations using commercial CFD software for the detailed flow analysis. Following that, three tidal turbine models with varying leading-edge profiles were manufactured and a model test campaign was conducted in the cavitation tunnel to evaluate their efficiency, cavitation, underwater noise, and detailed flow characteristics. Based on these experimental investigations it was confirmed that the leading-edge tubercles can improve the hydrodynamic performance in the low Tip Speed Ratio (TSR) region without lowering the maximum power coefficient; constrain the cavitation development to within the troughs between the tubercles; and, hence, mitigate the underwater noise levels