Diel and tidal rhythms in diving behaviour of pelagic sharks identified by signal processing of archival tagging data

Abstract

Patterns of vertical movement in pelagic predators can be highly complex, reflecting behaviours such as foraging, thermoregulatory excursions and spawning. Here we used fast Fourier analysis to identify periodicity in the vertical movements of 6 basking sharks Cetorhinus maximus from archival tagging data that totalled 595 d. We analysed quantitatively fine-scale vertical movements of basking sharks over seasonal scales (May to February) and detected predominant periodicities related to the vertical movements of the sharks' zooplankton prey. Normal and reverse diel vertical migration (DVM) represented the main periodic dive behaviour, occurring for 11 to 72% of individual track times. A tidal pattern of vertical movement, previously unreported for sharks, was also identified. A possible mechanism for this behaviour appears related to the shark exploiting tidally-induced aggregations of zooplankton prey at depth. The youngest shark tagged showed a markedly different pattern of vertical behaviour. Long-term data sets of swimming depth are becoming increasingly available for pelagic predators from pressure-sensitive data loggers. This study demonstrates the utility of signal processing techniques in objectively identifying both expected and unexpected periodicity in these continuous, high-resolution tracks.

Philopatry and migration of Pacific white sharks

“…This coincides figure S2). While this distribution includes areas with colonies of endangered monk seals (Baker et al 2007), detailed dive records from four recovered satellite tags (three females and one unsexed; three separate years) indicated that the dominant behaviour, when not transiting (Weng et al 2007), was a precise diel vertical migration, between the surface and 600 m, consistent with foraging within the deep scattering layer community (Shepard et al 2006) (electronic supplementary material, figure S3). …”

Short-term movements and diving behaviour of satellite-tracked blue sharks Prionace glauca in the northeastern Atlantic Ocean

“…Intra-individual differences have been less well documented, although it is unclear whether this is because such patterns rarely occur or whether it is only recently that animals have been tracked with sufficient spatial and temporal resolution to identify such transitions (Shepard et al 2006). Recent examples indicate significant shifts in movement patterns, diving behaviour and thermal biology in Atlantic bluefin tuna at different stages of the breeding cycle ), whilst abrupt changes were observed in the swimming behaviour of individual white sharks Carcharodon carcharias (Bruce et al 2006) and in the depth use of basking sharks Cetorhinus maximus (Shepard et al 2006).…”

“…Recent examples indicate significant shifts in movement patterns, diving behaviour and thermal biology in Atlantic bluefin tuna at different stages of the breeding cycle ), whilst abrupt changes were observed in the swimming behaviour of individual white sharks Carcharodon carcharias (Bruce et al 2006) and in the depth use of basking sharks Cetorhinus maximus (Shepard et al 2006). Knowing how individual behaviour varies across a range of spatio-temporal scales is an essential step towards understanding habitat selection processes in large marine animals (Sims et al 2006a).…”

Diel vertical migration behavior of Calanus finmarchicus and its influence on right and sei whale occurrence

“…Bost et al 2002, Hays 2003, Shepard et al 2006, Baumgartner & Fratantoni 2008. For large-bodied predators like baleen whales that need to feed on tremendous quantities of zooplankton each day (Kenney et al 1986), DVM can have a profound effect on a predator's ability to find sufficient food resources and to exploit those resources efficiently.…”