Relations between morphology, buoyancy and energetics of requiem sharks

Abstract

Sharks have a distinctive shape that remained practically unchanged through hundreds of millions of years of evolution. Nonetheless, there are variations of this shape that vary between and within species. We attempt to explain these variations by examining the partial derivatives of the cost of transport of a generic shark with respect to buoyancy, span and chord of its pectoral fins, length, girth and body temperature. Our analysis predicts an intricate relation between these parameters, suggesting that ectothermic species residing in cooler temperatures must either have longer pectoral fins and/or be more buoyant in order to maintain swimming performance. It also suggests that, in general, the buoyancy must increase with size, and therefore, there must be ontogenetic changes within a species, with individuals getting more buoyant as they grow. Pelagic species seem to have near optimally sized fins (which minimize the cost of transport), but the majority of reef sharks could have reduced the cost of transport by increasing the size of their fins. The fact that they do not implies negative selection, probably owing to decreased manoeuvrability in confined spaces (e.g. foraging on a reef).

Physical trade-offs shape the evolution of buoyancy control in sharks

“…Similarly, Fu et al [49] found the heads of juvenile tiger sharks to be more conical than their adult counterparts, suggesting streamlining for the sake of faster and more agile swimming to be increasingly less important during ontogeny. Moreover, increasing the length of the pectoral fins may also reduce the cost of transport in concert with the effects of increased buoyancy [57].…”

Combining abundance and performance data reveals how temperature regulates coastal occurrences and activity of a roaming apex predator

“…The ultimate cause of the elevated activity levels near 22°C for this species is uncertain; tiger sharks are ectotherms whose maximum power outputs, speeds minimizing cost of transport and minimum cruising speeds will all be influenced by temperature (Iosilevskii & Papastamatiou, 2016), but they are also predators that are likely to be more-active in prey-rich environments. Several other recent studies have measured temperature's influence on growth and activity of wild fishes and found close links with geographical range limits (Neuheimer, Thresher, Lyle, & Semmens, 2011;Payne et al, 2016).…”

“…The y-axis in (b) represents the relative amount of time spent in coastal areas of Hawaii for the corresponding body temperatures [Colour figure can be viewed at wileyonlinelibrary.com] cruising speeds will all be influenced by temperature (Iosilevskii & Papastamatiou, 2016), but they are also predators that are likely to be more-active in prey-rich environments. (a) Temperature's influence on swimming activity (overall dynamic body acceleration; ODBA) for five freeranging tiger sharks swimming off the eastern coast of Oahu, Hawaii, for an average of~3 days per shark.…”

Effect of weight and frontal area of external telemetry packages on the kinematics, activity levels and swimming performance of small‐bodied sharks

“…While the majority of tag validation studies to date have cited tag mass as a key determinant of tag suitability, studies ought to move away from this paradigm and provide systematic assessments of hydrodynamic drag and alterations to buoyancy, which are arguably more relevant to aquatic animals. Furthermore, buoyancy control represents a substantial energetic investment for elasmobranchs, including juveniles that are typically less buoyant than adults (Gleiss et al, 2015;Iosilevskii & Papastamatiou, 2016). Therefore, small juvenile N. brevirostris experienced alterations in activity levels, swimming kinematics and swimming performance by carrying external telemetry packages.…”