Data from: Olfaction contributes to pelagic navigation in a coastal shark

How animals navigate the constantly moving and visually uniform pelagic
realm, often along straight paths between distant sites, is an enduring
mystery. The mechanisms enabling pelagic navigation in cartilaginous
fishes are particularly understudied. We used shoreward navigation by
leopard sharks (Triakis semifasciata) as a model system to test whether
olfaction contributes to pelagic navigation. Leopard sharks were captured
alongshore, transported 9 km offshore, released, and acoustically tracked
for approximately 4 h each until the transmitter released. Eleven sharks
were rendered anosmic (nares occluded with cotton wool soaked in petroleum
jelly); fifteen were sham controls. Mean swimming depth was 28.7 m. On
average, tracks of control sharks ended 62.6% closer to shore, following
relatively straight paths that were significantly directed over spatial
scales exceeding 1600 m. In contrast, tracks of anosmic sharks ended 37.2%
closer to shore, following significantly more tortuous paths that
approximated correlated random walks. These results held after swimming
paths were adjusted for current drift. This is the first study to
demonstrate experimentally that olfaction contributes to pelagic
navigation in sharks, likely mediated by chemical gradients as has been
hypothesized for birds. Given the similarities between the fluid
three-dimensional chemical atmosphere and ocean, further research
comparing swimming and flying animals may lead to a unifying paradigm
explaining their extraordinary navigational abilities.