A non‐invasive dolphin telemetry tag: Computer design and numerical flow simulation

Abstract

The impact of devices attached to animals remains a challenge in telemetry studies of dolphins. It was hypothesized that the hydrodynamic design of a tag could provide stable attachment to the dorsal fin by means of resultant hydrodynamic force appearing when a dolphin is swimming. To verify this hypothesis the computer fluid dynamics (CFD) study of tag performance was carried out. A virtual model presenting authentic geometry of a dolphin with tag attached to the dorsal fin was constructed. The same model without tag was used as a reference object to calculate tag impact as regards drag, lift, and moments coefficients. Flow around the models was simulated for the range of velocities as well as the ranges of pitch and yaw angles. It was shown that in 33 of 35 CFD scenarios the streamlined shape of a tag generates the lift force that facilitates keeping a tag attached to the fin. Throughout the set of calculations the tag-associated drag coefficient does not exceed 4%, which indicates low impact. Data obtained present a baseline for the further development of non-invasive dolphin telemetry tags.

Effects of added drag on cetaceans : fishing gear entanglement and external tag attachment

“…A more streamlined urethane housing containing all of the tag elements (electronics, VHF and flotation) minimizes geometric disruptions in the flow around the housing, reducing drag forces. Similar to previous papers on tag design Culik et al, 1994;Hazekamp et al, 2009;McMahon et al, 2011;Pavlov and Rashad, 2012), the study by Shorter et al (2013) suggests that tag designs should: (1) minimize frontal cross-sectional areas and maintain a smooth exterior to reduce drag; (2) cover suction cups or other exposed features to reduce flow stagnation and wake generation; and (3) reduce lift by minimizing the attachment area and by adding flow channels or spoilers to reduce differences in flow speed above and below the housing, or redirect flow to counter lift.…”

“…CFD simulations assume static and uniform flow conditions across a rigid-body dolphin model (Chapter 8; Hazekamp et al, 2009;Pavlov and Rashad, 2012;Shorter et al, 2013) and therefore model passive drag forces only. Swimming dolphins interact with non-uniform and variable flow, interact with the water's surface, and generate additional (i.e., active) drag forces as they propel their bodies through the water (Lighthill, 1969;Webb, 1975b).…”

“…Both researchers and tag companies have taken active roles to work together in reducing device size Hazekamp et al, 2009;Pavlov and Rashad, 2012;Balmer et al, 2013), refining the tools on the market. For example, the transition from the DTAG2 to current DTAG3 model reduced the frontal area by~1/3, making it more suitable for deployments on smaller species ( Figure 8B; Shorter et al, 2013).…”

“…To improve environmental context, data from the tags themselves Aoki et al, 2011;Ware et al, 2016), along with estimated body parameters, have been used to estimate drag forces on free-swimming animals. In contrast with the various experimental methods described above, computational fluid dynamics (CFD) models are becoming an increasingly popular method to simulate the expected effects of instrumentation and to refine tag design (Hazekamp et al, 2009;Pavlov and Rashad, 2012;Balmer et al, 2013;Shorter et al, 2013;van der Hoop et al, 2014a).…”

Phenotypic variation in dorsal fin morphology of coastal bottlenose dolphins (Tursiops truncatus) off Mexico

“…Little empirical evidence exists, however, regarding the integrated performance 56 of dorsal fins for most cetacean species (Lang, 1966;Fish and Rohr, 1999; 57 Meagher et al, 2002; Pavlov Westgate et al, 2007;Barbieri et al, 2010;and Rashad, 2012; van 58 der Hoop et al, 2014). Estimating integrated performance is challenging since plasticity may be 59 in part regulated by the energetic cost of different swimming behaviors related to locating, 60 chasing, handling, and ingesting prey, thus maneuvering abilities may be important in feeding 61 success, and the dorsal fin may play an important role for swimming stabilization 62 Fish and Rohr, 1999).…”