Tolotti et al.: Vertical movements of oceanic whitetip sharks ( Carcharhinus longimanus ) 
393 
indicate a behavioral thermoregulation mechanism. 
In fact, the use or active avoidance of heat sources to 
regulate body temperature has been reported for oth- 
er shark species (Campana et al., 2011; Speed et a!., 
2012; Vianna et al., 2013). There is evidence support- 
ing the idea that behaviorally induced thermoregula- 
tion optimizes physiological and metabolic processes, 
reducing metabolic losses and increasing foraging ef- 
ficiency (Sims, 2003; Campana et al., 2011). Unfortu- 
nately, the relatively small sample size of our study 
hampers a more detailed analysis and discussion con- 
cerning behaviorally induced thermoregulation on oce- 
anic whitetip sharks. Although additional data are still 
required, the results presented here indicate that the 
accumulation of heat could play an important role in 
triggering vertical movements. It seems that warmer 
SST allows oceanic whitetip sharks to tolerate a great- 
er temperature range and, therefore, to temporarily ex- 
pand their vertical niche. 
Longlining is the main gear responsible for the de- 
mise of populations of oceanic whitetip shark (Rice and 
Harley 1 ). Given that the depth stratum of this fishing 
gear considerably overlaps with the vertical distribu- 
tion of this species (Tolotti et al., 2015b), it is impor- 
tant to continue our efforts to understand the behav- 
ioral patterns of sharks and the drivers behind these 
patterns. It must be noted that when dealing with 
rare, threatened animals, such as the oceanic whitetip 
shark, sample size is constrained largely by opportuni- 
ty. This study was based on only 6 individuals, but the 
observations over 538 d in the Atlantic Ocean and 100 
d in the Indian Ocean provide new information on the 
behavior of this shark. Nevertheless, the scientific com- 
munity should direct its efforts to increase the number 
of tagged individuals, including tagging across a broad- 
er geographic region. Electronic tags are resourceful, 
nonlethal instruments that can significantly improve 
our knowledge of the ecology of this threatened species 
and, consequently, can aid its conservation. 
Acknowledgments 
We thank the crews, observers, and scientists in- 
volved in the tagging of oceanic whitetip sharks. We 
also thank A. Villareal and C. Taylor for returning the 
tag that was found stranded at a beach in Texas. This 
study was financed by the Commission of the European 
Communities Framework Program 7, Theme 2, through 
the research project “Mitigating adverse ecological im- 
pacts of open ocean fisheries.” M. Tolotti received doc- 
toral grants from the Coordenagao de Aperfeigoamento 
de Pessoal de Nivel Superior and France Filiere Peche. 
Literature cited 
Abecassis, M., H. Dewar, D. Hawn, and J. Polovina. 
2012. Modeling swordfish daytime vertical habitat in the 
North Pacific Ocean from pop-up archival tags. Mar. 
Ecol. Prog. Ser. 452:219-236. 
Backus, R. H., S. Springer, and E. L. Arnold Jr. 
1956. A contribution to the natural history of the white- 
tip shark, Pterolamiops longimanus (Poey). Deep Sea 
Res. 3:178-188. 
Barker, M. J., and V. Schluessel. 
2005. Managing global shark fisheries: suggestions for 
prioritizing management strategies. Aquat. Conserv. 
15:325-347. 
Bauer, R. K., F. Forget, and J.-M. Fromentin. 
2015. Optimizing PAT data transmission: assessing the 
accuracy of temperature summary data to estimate en- 
vironmental conditions. Fish. Oceanogr. 24:533-539. 
Baum, J., E. Medina, J. A. Musick, and M. Smale. 
2015. Carcharhinus longimanus. The IUCN Red List 
Threatened Species 2015: e.T39374A85699641. 
Beerkircher, L. R., E. Cortes, and M. Shivji. 
2002. Characteristics of shark bycatch observed on pe- 
lagic longlines off the southeastern United States, 1992- 
2000. Mar. Fish. Rev. 64(4):40-49. 
Bernal, D., C. Sepulveda, M. Musyl, and R. Brill. 
2009. The eco-physiology of swimming and movement pat- 
terns of tunas, billfishes, and large pelagic sharks. In 
Fish locomotion: an etho-ecological perspective (P. Do- 
menici and D. Kapoor, eds.), p. 436-483. Science Pub- 
lishers, Enfield, New Hampshire. 
Bloomfield, P. 
2004. Fourier analysis of time series: an introduction, 288 
p. John Wiley & Sons Inc., New York. 
Bonfil, R., S. Clarke, and H. Nakano. 
2008. The biology and ecology of the oceanic whitetip 
shark, Carcharhinus longimanus. In Sharks of the open 
ocean: biology, fisheries and conservation (M. D. Camhi, 
E. K. Pikitch, E. A. Babcock, eds.), p. 128-139. Black- 
well Publishing Ltd., Oxford. 
Brunnschweiler, J. M., and D. W. Sims. 
2012. Diel oscillations in whale shark vertical movements 
associated with meso-and bathypelagic diving. Am. 
Fish. Soc. Symp. 76:457-469. 
Bustamante, C., and M. B. Bennett. 
2013. Insights into the reproductive biology and fisher- 
ies of two commercially exploited species, shortfin mako 
( Isurus oxyrinchus) and blue shark ( Prionace glauca), in 
the south-east Pacific Ocean. Fish. Res. 143:174-183. 
Camargo, S. M., R. Coelho, D. Chapman, L. Howey-Jordan, 
E. J. Brooks, D. Fernando, N. J. Mendes, F. H. V. Hazin, C. 
Oliveira, M. N. Santos, et al. 
2016. Structure and genetic variability of the oceanic 
whitetip shark, Carcharhinus longimanus, determined 
using mitochondrial DNA. PLoS ONE ll(5):e0155623. 
Campana, S. E., A. Dorey, M. Fowler, W. Joyce, Z. Wang, D. 
Wright, and I. Yashayaev. 
2011. Migration pathways, behavioural thermoregulation 
and overwintering grounds of blue sharks in the north- 
west Atlantic. PLoS ONE 6(2):el6854. 
Coelho, R., J. Fernandez-Carvalho, and M. N. Santos. 
2015. Habitat use and diel vertical migration of bigeye 
thresher shark: overlap with pelagic longline fishing 
gear. Mar. Environ. Res. 112:91-99. 
Compagno, L. J. V. 
1984. FAO species catalogue, vol . 4. Sharks of the world: 
an annotated and illustrated catalogue of shark spe- 
cies known to date. Part 1 — Hexanchiformes to Lamni- 
formes. FAO Fish. Synop. 125, 249 p. FAO, Rome. 
