In 2001 Dení Ramírez Macías, has established and maintained a research project on whale sharks in the Gulf of California, also known as the Sea of Cortez. The whale shark is known to aggregate seasonally in three main areas of the Gulf of California: Bahía de los Ángeles (BLA), Bahía de la Paz (BLP) and Banco Gorda (BG), (Figure 1). In coastal waters of Bahía de La Paz and Bahía de Los Angeles the aggregations are exclusively juvenile sharks (
The goal is to determine whale shark population size. Each shark is identified with photos of the pattern of lateral markings behind the five gills slits on the left side the pattern of spots is used as a “fingerprint” because it is unique for each individual shark and does not change because it is unique for each individual shark and does not change with time (Figure 2). The sex is determined by the presence or absence of the claspers, which are the male reproductive organs (Figure 3). Total length is measured while swimming with the shark by using a measuring tape. Total length is used as a proxy of sexual maturity based on the criteria that an adult whale shark reaches sexual maturity at a length of about 9m or almost 30 feet.
With the use of photo-ID we have documented whale shark movements between BLA and BLP. Apparently the juveniles are moving from one concentration of food to another, starting in BLA and continue to BLP. One very interesting question is where do they go after they leave BLP? Do they have a migration pattern in the Gulf of California? Are the juveniles residents of the Gulf? To answer these questions we placed two PAT satellite tags on two whale sharks on January 17 of 2009. The names of the sharks are Flavio (male of 7.5 m or 25 ft.) and Tango (male of 4.5–5 m or 16 ft.). The tags will remain on the whale sharks for 9 months. The tags will continuously record information on global location, depth, and water temperature for up to 9 months. Get involved (we invite you to adopt a whale shark, see Adoption page).
Our work in genetic analysis of mitochondrial DNA and the photo ID of whale sharks in the Gulf of California (Los Angeles Bay (BLA), La Paz Bay (BLP) and Gorda Banks (BG)), demonstrated that a single population of whale sharks occur in the Gulf area. This suggests that juveniles reside within the Gulf of California, and that there is a natal philopatry of female whale sharks prevailing or returning to where they were born to give birth (Ramírez-Macías et al., 2007).
We are also collaborating with researchers in Mozambique, Australia, Taiwan and Dijibouti to prepare a genetic analysis of whale sharks on a global scale to determine how many different whale shark populations exist, as with all widely distributed and at-risk shark species this information will help to define management areas and develop international conservation strategies.
Isotope analysis is the identification of isotopic signature, the distribution of certain stable isotopes and chemical elements within chemical compounds. This can be applied to a food web to make it possible to draw direct inferences regarding diet, trophic level, and movements.