Extensive use of mesopelagic waters by a Scalloped hammerhead shark (Sphyrna lewini) in the Red Sea

Abstract

Background: Despite being frequently landed in fish markets along the Saudi Arabian Red Sea coast, information regarding fundamental biology of the Scalloped hammerhead shark (Sphyrna lewini) in this region is scarce. Satellite telemetry studies can generate important data on life history, describe critical habitats, and ultimately redefine management strategies for sharks. To better understand the horizontal and vertical habitat use of S. lewini in the Red Sea and to aid with potential future development of zoning and management plans for key habitats, we deployed a pop-up satellite archival transmitting tag to track a single female specimen (240 cm total length) for a tracking period of 182 days. Results:The tag was physically recovered after a deployment period of 6 months, thus providing the complete archived dataset of more than one million depth and temperature records. Based on a reconstructed, most probable track, the shark travelled a circular distance of approximately 1000 km from the central Saudi Arabian Red Sea southeastward into Sudanese waters, returning to the tagging location toward the end of the tracking period. Mesopelagic excursions to depths between 650 and 971 m occurred on 174 of the 182 days of the tracking period. Intervals between such excursions were characterized by constant oscillatory diving in the upper 100 m of the water column. Conclusions:This study provides evidence that mesopelagic habitats might be more commonly used by S. lewini than previously suggested. We identified deep diving behavior throughout the 24-h cycle over the entire 6-month tracking period. In addition to expected nightly vertical habitat use, the shark exhibited frequent mesopelagic excursions during daytime. Deep diving throughout the diel cycle has not been reported before and, while dive functionality remains unconfirmed, our study suggests that mesopelagic excursions may represent foraging events within and below deep scattering layers. Additional research aimed at resolving potential ecological, physiological and behavioral mechanisms underpinning vertical movement patterns of S. lewini will help to determine if the single individual reported here is representative of S. lewini populations in the Red Sea.

Seasonal Movements and Habitat Use of Juvenile Smooth Hammerhead Sharks in the Western North Atlantic Ocean and Significance for Management

“…Francis (2016) also reported diel differences in depth distribution of another juvenile smooth hammerhead tracked with a popup satellite transmitter, with a shallower distribution at night compared to daylight hours. In contrast, scalloped hammerhead sharks have been observed to remain in shallow waters during the day and dive at night presumably to forage (Klimley and Nelson, 1984;Hoffmayer et al, 2013), or show continuous deep diving behavior throughout the 24 h cycle (Spaet et al, 2017). Similarly, Santos and Coelho (2018) found that similarly sized smooth hammerheads to those in this study [T-test; T (6 .…”

Movement, Behavior, and Habitat Use of a Marine Apex Predator, the Scalloped Hammerhead

“…The scalloped hammerhead (Sphyrna lewini) is a circumglobal shark species that lives in warm temperate and tropical seas (Compagno, 1984). This species is highly mobile, capable of extensive migrations, and is generally found across a mosaic of ecosystems including bays and estuaries, continental shelves, and offshore pelagic waters (Compagno, 1984;Spaet et al, 2017). Current concerns over the population status of scalloped hammerheads include temporal declines in abundance (Baum and Blanchard, 2010;Powers et al, 2013) and high atvessel mortality rates (Morgan and Burgess, 2007).…”

“…Evidence suggests substantial genetic heterogeneity for a large marine predator on a global scale and multiple subpopulations and cryptic speciation in the western North Atlantic Ocean (Quattro et al, 2006;Chapman et al, 2009). Tagging studies demonstrate that scalloped hammerheads have the capacity to travel distances exceeding 1,000 km (Kohler and Turner, 2001;Bessudo et al, 2011;Spaet et al, 2017). However, several studies have found that scalloped hammerheads have relatively small home ranges and display aggregative behaviors around bathymetric features, such as seamounts, potentially due to enhanced prey availability, geomagnetic associations from gradients in the seafloor, or simply short durations of tagged individuals (Klimley, 1993;Hearn et al, 2010).…”

Spatiotemporal distribution patterns of immature Australasian white sharks (Carcharodon carcharias)

“…For wide ranging species, long-term monitoring of a representative proportion of a population [2][3][4][5][6] is crucial for interpreting whether the apparent measures of abundance or rates of encounter are related to abundance changes or shifts in spatial distribution 7,8 . For marine species, large scale satellite and acoustic telemetry studies have provided many insights into the spatial resolution of movements and long-distance migrations of predators, often challenging our existing understanding of a species' spatial distribution and habitat use 9,10 . White sharks (Carcharodon carcharias, Linnaeus, 1758) are an exemplar species in this sense.…”