Ocean News

The Bull Shark Tagging Programme – what is it about?

12th January 2009

The Bull Shark Tagging Programme aims at a better understanding of the behaviour, ecology and aspects of population biology of bull sharks in the Pacific and Atlantic Ocean using direct and indirect observation methods as well as genetic techniques. Direct observation of bull sharks provides insight into the secret life of these elusive apex predators that are not possible to obtain with other methods. Since 2003, bull sharks have been observed by SCUBA divers in their natural habitat in Shark Reef Marine Reserve in Fiji. This allows to obtain, for example, data for estimating the local population size or getting information on individual bull sharks such as markings based on which individual sharks can be recognized, pregnancy or mating scars. At the same time, tissue samples are taken regularly that help to reveal the global genetic structure of the bull shark.

In Fiji and in the Atlantic (Bahamas and Florida), small- and large-scale movement patterns of bull sharks have been investigated using acoustic and satellite telemetry methods. Pop-up satellite archival tags have been externally attached to bull sharks. These tags collect pressure, temperature, and light-intensity data. After a preset attachment interval the tags detach from the shark, float to the water surface and transmit the archived data via satellite to the researcher. These data give information on large-scale movements (over hundreds of kilometers) away from the tagging site and insight into diving patterns, and therefore allow a better definition of the ecological niche of the bull shark.

As part of the Bull Shark Tagging Programme, acoustic transmitters have been fed to, externally attached onto or surgically implanted into bull sharks. Such tagged sharks are then picked up by receivers placed on the reefs whenever they come into detection range (several to dozens of meters depending on the reef topography). This allows to track the small-scale movement patterns of bull sharks as well as monitoring the presence/absence of individual sharks within a, for example, protected area or a nursery ground. Additionally, acoustic transmitters equipped with a temperature sensor that are fed to the sharks can record stomach temperature to provide important physiological data.