Mapping shark habitat

 

Mapping shark habitat

During the first months of the year, water temperatures in the Galápagos Archipelago rise and the wet season drastically changes the landscape coloration on San Cristóbal from grey brown to bright green. That’s the time when pregnant Blacktip females come into the shallow waters to give birth to an average of 6 completely independent life pups. On our trips in January and February we could reconfirm the importance of Puerto Grande bay as a nursery area due to the high abundance of newborn pups registered during our study.

Besides the extensive tracking sessions of young-of-the-year and neonate Blacktip sharks, we conducted separate field trips in order to render exact spatial information on the physical dimensions of the shark nursery. This information will help us to geo-reference and map the sharks’ habitat and thus analyze what type of habitat they prefer. Based on these maps we will determine if the pups have a preference for different water depths and substrate types and what it finally is, that makes our study site such an important environment for this threatened species.

Using a CTD (Conductivity-Temperature-Depth profiler) we measured these variables at numerous locations throughout the entire bay. Afterwards, this information is combined with high-resolution satellite images containing details on the substrate type of the bottom of the bay, using Geographic Information Systems (GIS). If the satellite images accurately represent the substrates of the real world, was previously confirmed by freediving to the seafloor at depths between 3-8 m.

Knowledge on the habitat preferences of juvenile Blacktip sharks is crucial in order to predict consequences of habitat changes and to support the designation of protected areas. This understanding can then be applied to determine other potential nurseries on this and other islands throughout the archipelago, to be included into the Galapagos Marine Reserve. Furthermore, it may serve as a guide for shark conservation research focusing on nursery areas and habitat use in other parts of the world.