Whale sharks are the largest fish in the ocean and an awe-inspiring sight to behold, yet very little is known about them. Listed as Vulnerable on the IUCN Red List of Threatened Species, gaining a good understanding of some of the basic life history questions about this animal are now of pressing importance.
The Galapagos Islands are one of several locations that whale sharks are known to visit at certain times of year, typically visiting the northern islands of Wolf and Darwin between June and December. Unlike aggregations in the Indian Ocean, which are largely made up of small immature males, the majority of sharks sighted in the Galapagos Marine Reserve (GMR) are large mature females, a high proportion of which (over 90%) appear to be pregnant. Given the lack of knowledge in the breeding ecology of whale sharks and the apparent frequency that pregnant females are seen in the GMR, an exciting research opportunity exists.
What we have learned so far
In 2011 the Galapagos Whale Shark Project research team satellite tagged 24 whale sharks, the majority of which were pregnant females. The type of tag used recorded the position of the shark each time the tag broke the water’s surface, allowing for their horizontal migration to be tracked.
Sharks tagged at the beginning of the season appeared to move in a westerly direction for hundreds of kilometres, then returned east later in the season, often passing close to Darwin Island again, before continuing on towards the continental shelf. Sharks tagged later in the season moved to the continental shelf and remained along the shelf break for extended periods. Despite none of the tagged sharks remaining within the GMR for more than a few days, their predictable annual appearance suggests that the Galapagos is still an important location within their migratory pattern and further research into why pregnant females are using the area could be highly insightful.
Field Season reports
In the summers of 2014 and 2015, the team returned to Darwin and Wolf to conduct further research. The trips, which GCT funded, resulted in a further 23 sharks being tagged with at least one tag (some were tagged with two different types of tags). They were also able to fine-tune blood sampling and photo identification methods that will allow them to collect ground-breaking data on whale shark pregnancies and migration.
To view the field reports from the trip, select one of the options below:
Read the latest news from the Galapagos Whale Shark Project in our 2016 update blog.
The overall aims of the Galapagos Whale Shark Project are clear: To improve our understanding of the GMR’s significance with respect to whale shark migratory pattern; to increase our knowledge of whale shark migration patterns; and to educate local authorities and communities so they can devise effective management strategies for whale sharks in the GMR.
This will be achieved by continuing to satellite tag individual sharks across multiple seasons, photo-identifying all whale sharks that are encountered, taking tissue samples for population genetic research, confirming pregnancy in at least one female shark, and attaching “Daily Diary” tags to individuals to assess their use of the magnetic field.
Wildlife tourism is a booming industry around the world, and whale sharks are no exception. Conserving these gentle giants is key for the continuing success of marine-based tourism in Galapagos, which benefits both animals and local communities. With your support, we can continue to fund this crucial project.