Sharks surf the slope: Current updrafts reduce energy expenditure for aggregating marine predators

Abstract

1. An animal's energy landscape considers the power requirements associated with residing in or moving through habitats. Within marine environments, these landscapes can be dynamic as water currents will influence animal power requirements and can change rapidly over diel and tidal cycles.

Swimming performance of sharks and rays under climate change

“…Finally, more studies should be conducted to understand the effect of climate change on swimming in larger elasmobranchs. These species are typically more difficult to study in laboratory settings but technological advances in field equipment paired with laboratory testing (Whitney et al 2007;Lawson et al 2019;Papastamatiou et al 2021) can allow us to understand how sharks and rays may exploit the variation in their environment to save energy during locomotion.…”

“…Predictions of future responses to climate change often include shifts in geographic ranges, while small scale alterations in habitat use have received less attention. Elasmobranchs can utilize the diel abiotic and geographical variability in their environment to decrease costs of locomotion (Papastamatiou et al 2021). Sharks and rays are known to exploit the thermal heterogeneity in their environment by selecting different temperatures throughout the day, a behavior known as thermotaxis (Fangue and Bennett 2003; Wallman and Bennett 2006;DiGirolamo et al 2012;Speed et al 2012).…”

Swimming kinematics of the Caribbean reef shark, Carcharhinus perezi

“…Another explanation for the lack of correlation between tailbeat frequency and velocity might be that the sharks were encountering different ambient current flow velocities. Sharks swimming with the prevailing current could achieve a greater groundspeed with a lower tailbeat frequency than sharks swimming against the flow (Papastamatiou et al ., 2021). We were unable to assess current velocity from the video and were thus unable to determine how much it contributed to the high variability seen in the data.…”

Certainty and integration of options in animal movement

“…[8,9] and of currents by aquatic species [10,11], to the avoidance of steep slopes, dense vegetation, and costly substrate types (e.g., snow cover) for terrestrial species [12][13][14][15]. Some species have even evolved to harvest and store this energy, such as the use of thermal and slope updrafts by soaring birds (Box 1) [16,17] and of underwater updrafts by negatively buoyant sharks [18], where potential energy is stored in height (altitude or shallower depth) and spent (by dropping/gliding) to cover distance while minimising the use of energy-expensive types of locomotion. Using an optimality approach, animals must make cost-efficient movement decisions and move through their physical energy landscape in ways that maximise efficiency over all timescales [7,19] namely exploiting physical energy while putting in the least amount of effort per unit time (comparative with intake rate in foraging efficiency).…”

“…For a soaring bird to exploit an updraft it must adopt a specific bank angle and turning radius which, along with the bird's own vertical speed and according to the laws of physics, reflect the strength (vertical velocity) of the underlying updraft [26,27]. Importantly, these active and passive behaviours cannot be false or dishonest because movement can only ever be the combined result of locomotion and the environmentfor instance, 'soaring' animals (birds or aquatic species exploiting underwater updrafts) would otherwise drop in altitude or depth if they displayed soaring behaviour but without the support of an updraft [18,28].…”