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Migration of Hammerheads in the Gulf of Mexico |
Bonnethead-hammerhead sharks (Sphyrna tiburo) prefer to live in coastal areas where they are also fished. In order to protect this shark species it is very important to know if losses in one area can be compensated by the immigration of animals from another, less intensively fished area.
© SeaPics / Shark Foundation
Illustration: A bonnethead-hammerhead shark (Sphyrna tiburo).
A masters thesis by Markus Ruch in the Zoological Museum of Zurich University deals with this theme.
Using molecular-biological parentage analysis of various bonnethead-hammerhead populations in the Gulf of Mexico it could already be determined that certain populations in this area trade individuals to different degrees. The less trading of individuals, the more sensitive do these groups react to overfishing.
© Shark Foundation
Illustration: Genetic exchange with bonnethead-hammerhead sharks in the Gulf of Mexico.
Black arrows: thin = minimum exchange, thick = high exchange
The masters thesis was submitted in January 2001 and accepted. Additional tissue samples from the area of Panama (Mexico) are currently being examined for publication in a scientific journal.
Publication:  Masters thesis on Bonnethead-hammerhead sharks
The Foundation is entrusted with scientific supervision (Manager Dr. Gaston D. Guex). It also procured the tissue samples from various regions and partially financed the project (currently totalling about CHF 5,000).
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Fiji: Bull shark migrations near Fiji |
We lack biological data for practically all shark species, especially on their precise geographical distribution areas, their migration behavior or reliable population numbers. This also applies to widely distributed species living in coastal areas, e.g. the bull shark (Carcharhinus leucas).
© Klaus Jost / Shark Foundation
Illustration: Bull sharks (Carcharhinus leucas).
In areas where bull sharks can be seen regularly, observations over past years have shown that grown individuals leave these areas in the spring for two to four months and return in the summer. Where they migrate to during this time is not yet known, but presumably they visit their reproduction regions/nurseries during this time period.
Early in 2003 an international research team launched a bull shark tagging program in the Bahamian waters. The purpose of this program is to find the bull shark nurseries and their migration routes, and in a second step to establish concepts for the protection of these areas.
The experiences and results of the Bahama pilot project led to the initiation of a study on the migratory behavior of bull sharks near Fiji in 2004. Various bull sharks were tagged with satellite transmitters for this research program. At a fixed time, the transmitters come off the sharks and transmit data on the migratory routes, depth, temperatures etc. to satellites. The data is then evaluated using computer programs designed specifically for the project.
In a first phase three bull sharks were equipped with satellite transmitters programmed to release themselves from the sharks at the end of 2004 and then float to the water surface. In the course of 2004 additional bull sharks were tagged with such transmitters. At the end of 2004 the first data arrived and is ready for evaluation in 2005.
 
© Klaus Jost / Shark Foundation
Illustration: Preparing the highly complex transmitter.
Simultaneous to the fastening of the transmitters, initial steps are taken to implement protection provisions. Small reef sections where bull sharks are seen regularly are no longer allowed to be accessed by the fishing industry Fiji Shark Reef
Project Manager: Jürg Brunnschweiler
In 2004 the Foundation partially financed the project by sponsoring two satellite transmitters worth approx. CHF 10,000.
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