Rheotaxis by epaulette sharks, Hemiscyllium ocellatum (Chondrichthyes : Hemiscylliidae), on a coral reef flat

Abstract

Rheotaxis (orientation to water currents) is commonly observed in fishes. Facing upstream is thought to be an element of shark behaviour during prey search and station-holding, but quantitative studies of rheotaxis by sharks in the wild are lacking. In this study, rheotaxis by the epaulette shark, Hemiscyllium ocellatum, was investigated on a coral reef flat at Heron Island, Great Barrier Reef, Australia. The orientation of 78 individuals in open areas (on sand or on top of coral heads, directly exposed to the prevailing current) was analysed with respect to current direction and velocity. H. ocellatum showed a significant (P < 0.05) preference for facing upstream (mean angle 1�, where the current origin was taken to be 0/360�) while resting on the substrate (n = 23), but showed no evidence of a preferred direction while swimming (n = 50). Observations of foraging were few (n = 5) but there was no indication of a preferred direction by these sharks. Resting H. ocellatum faced significantly more upstream at faster current velocities (P < 0.05), suggesting that rheotaxis may function in station-holding. There was no apparent relationship between rheotaxis and current velocity for swimming H. ocellatum.

A review of the biology, fisheries and conservation of the whale shark Rhincodon typus

“…Rhincodon typus possess a mechano‐sensory lateral line system similar to all sharks, but its capabilities in this species are largely unknown. The lateral line enables sharks to react to water currents (rheotaxis), as has been documented for a number of pelagic species (Hodgson & Mathewson, 1971; Kleerekoper, 1978) and in some bottom‐dwelling sharks (Peach, 2002). A similar response to currents has been seen in R. typus tracked with satellite tags from the Seychelles (Rowat & Gore, 2007) and Taiwan (Hsu et al , 2007), although it is not known to what extent this sense is developed.…”

“…Chang et al, 1997;2 Nishida, 2001;3 Kitafuji & Yamamoto, 1998;4 Uchida et al, 2000;5 Wintner, 2000;6 Graham & Roberts, 2007;7 Riley et al, 2010. Growth rates and the age at first sexual maturity have a major bearing on the life history of a species and its role within its ecosystem. Based on information for many shark species, Pauly (1997) suggested a gradual slowing of growth to maturity; using these data the FishBase R. typus maturity table (http://www.fishbase.org/ Reproduction/MaturityList.php?ID=2081&GenusName=Rhincodon&SpeciesName= typus&fc=6) calculated a length at first sexual maturity of 5·58 m L T at an age of 8·9 years for R. typus. Fowler (2000) suggested an amendment to the maximum size using the 20 m L T specimen reported by Chen et al (1997); the amended table calculated a theoretical length at first maturity of 7·69 m L T at an age of 21·4 years.…”

Regional scale horizontal and local scale vertical movements of whale sharks in the Indian Ocean off Seychelles

“…In the latter studies, it was shown that these sharks could respond to a current of only 1.08 km/h and it was postulated that this ability might assist in feeding. Peach (2002) found that the epaulette shark (Hemiscyllium ocellatum) showed a significant preference for facing upstream while resting on the substrate, but could find no evidence of a preferred direction while swimming.…”

The ecology, behaviour and physiology of fishes on coral reef flats, and the potential impacts of climate change

“…Foraging in moving water can also be aided by rheotaxis (orientation with respect to water currents), and H . ocellatum faces upstream when resting in order to aid station‐holding, but swimming was not correlated with water direction (Peach, ). Water movement has a less important role for species that forage in territories, where water depth appears most important.…”