Whale Shark Expedition 2009 to Djibouti.
The Whale Shark Expedition is a project undertaken by Danilo Rezzolla, a researcher at the Milan Aquarium and members of the Italian Shark Research Group. The project is supported by Cousteau and is one of several initiatives in the Red Sea and Gulf of Aden that are tied to the Cousteau program Divers Aware of Sharks. Danilo Rezzolla takes amateur divers to participate in research activities on a two-week expedition, exploring marine diversity in a new way!
The goal of the Whale Shark Expedition is to observe and capture identification photographs of individual whale sharks (Rhincodon typus) in the Gulf of Tadjourah at Djibouti It was conceived in 2006 as the first European research initiative targeting just these very special cartilaginous fish.
It has long been known that whale sharks are found at Djibouti between November and the end of January, located mainly in Arta Bay. This was why Danilo Rezzolla organized the first research trip to Djibouti in 2007. In one week, Rezzolla and his team photo-identified 36 individual whale sharks; the data and photographs were entered into the EcOcean database where an Australian research group that has been managing the Whale Shark Photo-identification Library since 1994.
The team’s work allowed nine new individuals to be characterized and entered into the global database. The results of the 2007 Italian expedition were very important, given that, in 14 years, the database had accumulated only 16 catalogued specimens from this region of the Red Sea. EcOcean emphasized its satisfaction with the 50% increase in just one year.
Rezzolla’s team went back to Djibouti again to study whale sharks in January 2009. Rezzolla had already taken part in the Cousteau program Divers Aware of Sharks and expanded his data collection by adding weather conditions at sea, atmospheric conditions and GPS coordinates to the observation records. The team also took samples of plankton, the basic food of whale sharks.
Under Rezzolla’s scientific supervision, the team started every day by collecting data on air (temperature, wind direction, rain or clouds) and sea conditions (surface temperature, currents, etc.). Then came the day’s first dive to look for the presence of whale sharks at depth and to record the topographic characteristics of the Gulf of Tadjourah.
Photo-identification activities began around ten o’clock in the morning: the team boarded small boats to look for sharks in Arta Bay. When a shark was spotted, Rezzolla would enter the water and swim beside the shark, taking photographs, determining the sex and morphometric characteristics, noting the presence of markings and recording its spots pattern.
The spots are white dots on the shark’s skin. Their size changes over the life of the fish but the position and distance between spots stays the same. The pattern formed by the spots is unique to the individual shark, allowing it to be identified throughout its entire life. The photographs that Rezzolla takes of spot patterns are analyzed by a computer program to identify the different sharks.
The evening of January 23 was an especially exciting moment for the researchers when they were able to observe two whale sharks at night swimming peacefully beside the boat.
During the 2009 week of research, nine new sharks were identified and reported to the EcOcean database with the codes DJ-033 to DJ-042. Ninety percent of the individuals observed were young males between 3.5 m and 4.5 m. The sharks that were photographed had never been observed elsewhere.
The 2009 expedition collected great quantities of data on the presence of whale sharks in the waters of Djibouti that will be fully presented in a scientific paper that will be published at the end of the year. Preliminary analysis of the collected data indicates that Djibouti is a feeding site for young male whale sharks in the course of their migration.
There are still many unanswered questions. Where do the whale sharks go when they leave these waters? Why is it primarily young males that are seen? Is the number of individuals rising or decreasing?
All these questions arising from the two Whale Shark Expeditions to Djibouti led by Danilo Rezzolla certainly require the research team to return in the coming years to the Gulf of Tadjourah. They also need Cousteau to establish a program, now under study, specifically to continue photo-identification of whale sharks and other research on the feeding behavior and migration routes of these magnificent giants of the sea.
Italian Shark Research Group
Aquarium de Milan