A Numerical Model for the Analysis of the Locomotion of a Cownose Ray

Among all aquatic species, mantas and rays swim by flapping their pectoral fins; this motion is similar to other fishes in terms of efficiency, but it gives better maneuverability and agility in turning. The fin motion is featured by a traveling wave going opposite to the forward motion, producing a force thanks to momentum conservation. This article aims at understanding the swimming dynamics of rays, focusing on energy efficiency. A CFD model of the swimming motion of a cownose ray has been implemented in OpenFOAM, simulating the acceleration of the fish from still to the steady-state velocity using an overset mesh. In this analysis, the 1-DOF dynamics of forward swimming is solved together with the fluid velocity and pressure. The effect of frequency and wavelength of fin motion on thrust, power, and velocity has been investigated and an analysis of the vortices in the wake showed has been performed. The energy efficiency of a self-propelled body has been defined in a novel way and it has been calculated for different motion conditions. The results showed that batoid fishes swim with high energy efficiency and that they are a promising source of inspiration for biomimetic autonomous underwater vehicles.

CAPTURE AND HANDLING STRESS IN INCIDENTALLY CAPTURED RAYS FROM SMALL-SCALE FISHING: A PHYSIOLOGICAL APPROACH

Incidental capture is the most common threat to rays worldwide, by both artisanal and industrial fishing. To better understand this threat, we evaluated the capture and handling stress in three incidentally captured benthopelagic ray species: American cownose ray (Rhinoptera bonasus), Brazilian cownose ray (Rhinoptera brasiliensis), spotted eagle ray (Aetobatus narinari), and one benthic species, the longnose stingray (Hypanus guttatus). Through analyzing secondary stress physiological variables (plasma lactate and glucose), our results revealed a similar physiological stress response in benthopelagic rays, suggesting they are resilient to capture using beach seine fishing. We also demonstrated that handling for research can increase the stress in both American cownose and spotted eagle rays, suggesting that more stringent handling protocols for research should be required. Findings from this study expands on the number of ray species for which stress to capture and handling has been evaluated, providing recommendations for appropriate research and management.

Bio-Inspired Design of An Underwater Robot Exploiting Fin Undulation Propulsion

Interest in autonomous underwater vehicles is constantly increasing following the emerging needs of underwater exploration and military purposes. Thus, several new propulsion mechanisms are studied and developed. Fish swimming is a promising source of inspiration because they outperform conventional propellers in terms of energy efficiency and maneuvrability. Their advantages are not only due to the streamlined shape and their low-drag skin but also, above all, due to the particular fin motion, which makes thrust generation possible with small energy dissipation. This paper analyses the motion of batoid fishes that are considered highly efficient by biologists. Their motion is reproduced by different linkage mechanisms optimized to fit underwater robots. A bioinspired robot mimicking cownose ray locomotion is, then, designed and built. Numerical analysis of its dynamics allows us to measure the size of actuators and to estimate the robot behavior. Finally, the control algorithm that maintains the mechanism synchronization according to different strategies is described and some experimental results are presented.

Genetic diversity assessment for the vulnerable migratory cownose ray Rhinoptera bonasus (Myliobatiformes: Rhinopteridae) from the southwestern Atlantic Ocean

ABSTRACT Rhinoptera bonasus is a bento-pelagic and highly migratory species occurring from southern United States to northern Argentina. Due to overfishing effects, R. bonasus is currently at risk, classified by the IUCN Red List as vulnerable. Considering the lack of molecular data available for R. bonasus, this study aimed to describe the genetic variability and population structure of specimens sampled from three Brazilian coast ecoregions (Amazon ecoregion, Pará; Northeastern ecoregion, Pernambuco and Southeastern ecoregion, Rio de Janeiro, São Paulo and Santa Catarina), through five polymorphic microsatellite markers. Here testing the panmixia hypothesis for Brazilian ecoregions and test natal philopathy. A total of 69 analyzed specimens revealed individual and significant genetic differentiation between the sampled locations. Φ ST (0.12), PCA, DAPC and Bayesian analyses of the genetic population structure revealed at least two distinct genetic R. bonasus groupings. IBD tests were significant, indicating a correlation between genetic and geographical distance among populations, which can be explained by reproductive philopatric behavior. Philopatric behavior associated with R. bonasus mobility may influence the differentiation values observed for all loci in the investigated samples.