How morphology changes with size can have profound effects on the life history and ecology of an animal. For apex predators that can impact higher level ecosystem processes, such changes may have consequences for other species. Tiger sharks (Galeocerdo cuvier) are an apex predator in tropical seas, and, as adults, are highly migratory. However, little is known about ontogenetic changes in their...

A number of captive sandtiger sharks (Carcharias taurus) in public aquaria have developed spinal deformities over the past decade, ranging in severity from mild curvature to spinal fracture and severe subluxation. To determine the frequency and etiologic basis of this disease, U.S. public aquaria participated in a two-stage epidemiologic study of resident sharks: 1) a history and husbandry surv...

Sharks and other large predators are scarce on most coral reefs, but studies of their historical ecology provide qualitative evidence that predators were once numerous in these ecosystems. Quantifying density of sharks in the absence of humans (baseline) is, however, hindered by a paucity of pertinent time-series data. Recently researchers have used underwater visual surveys, primarily of limit...

We used behavioural conditioning to demonstrate that sharks can detect changes in the geomagnetic field. Captive sharks were conditioned by pairing activation of an artificial magnetic field with presentation of food over a target. Conditioned sharks subsequently converged on the target when the artificial magnetic field was activated but no food reward was presented thereby demonstrating that ...

Accurate assessment of shark population status is essential for conservation but is often constrained by limited and unreliable data. To provide a basis for improved management of shark resources, we analyzed a long-term record of species-specific catches, sizes, and sexes of sharks collected by onboard observers in the western and central Pacific Ocean from 1995 to 2010. Using generalized line...

Lamniform sharks are apex marine predators undergoing dramatic local and regional decline worldwide, with consequences for marine ecosystems that are difficult to predict. Through their long history, lamniform sharks have faced widespread extinction, and understanding those 'natural experiments' may help constrain predictions, placing the current crisis in evolutionary context. Here we show, us...

A new acoustic transmitter for monitoring the tailbeat frequency of free-swimming ®shes and sharks is described. The transmitter is externally mounted on the ®sh's caudal peduncle and produces an acoustic pulse with every lateral movement of the tail. Field tests on obligate-swimming juvenile scalloped hammerhead sharks (Sphyrna lewini) show these transmitters accurately telemeter tailbeat de ̄e...

Prototype acoustic ‘business card’ (BC) tags were deployed on 4 free-swimming Galapagos sharks Carcharhinus galapagensis associated with a shark ecotourism operation near Haleiwa, Hawaii, USA. These transmitter/receiver tags employed mobile peer-to-peer (MP2P) technology that allowed the tagged sharks to exchange codes among each other and to detect other sharks implanted with standard one-way ...

Juvenile silky sharks Carcharhinus falciformis comprise the largest component of the incidental elasmobranch catch taken in tropical tuna purse seine fisheries. During a chartered cruise on board a tuna purse seine vessel conducting typical fishing operations we investigated the post-release survival and rates of interaction with fishing gear of incidentally captured silky sharks using a combin...

We used acoustic telemetry to describe the patterns of vertical movement, site fidelity and residency of grey reef sharks (Carcharhinus amblyrhynchos) on the outer slope of coral reefs in Palau, Micronesia, over a period of two years and nine months. We tagged 39 sharks (mostly adult females) of which 31 were detected regularly throughout the study. Sharks displayed strong inter-annual residenc...