A new study covering 16 years of whale sharks which was just published on July 16, 2014 in the journal Plos One, shows that as global sea temperatures have been increasing, whale sharks seem to be driven more and more to a smaller, more specific area of water: the ocean near the volcanic Azore islands. The study suggests that even though the sharks can thrive at anywhere from 26-30 degrees Celcsius, they seem to prefer even more specific cooler temperatures, which the body of water around the Azore islands provides. Researchers are calling this the "Goldilocks" temperature, because it is not too hot or too cold, but just right.
The new research study was headed by Pedro Afonso, who works at the University of Azores, and a team of colleagues who work together at the University. The Azores islands are an area in Portugal consisting of nine volcanic islands in the mid-North Atlantic. Even though this body of water is on the edge of the temperature range the sharks could live at, the study tracking shark migration patterns and water temperature over the past 16 years suggests that they prefer to live in cooler waters.
Whale sharks are the biggest living fish. They can grow up to 47,000 pounds heavy and 41.5 feet long. These sharks are filter-feeders, meaning that they are not predatory animals; instead they suck tiny fish from the sea by filtering them out through rows of teeth in their mouths. Research suggests that this large shark seasonally comes together at coastal areas. Scientists analyzed data from a 16-year period starting in 1998 and ending in 2013 which was gathered by a fishery near the Azores. They investigated the patterns of shark migration compared to features in the ocean like food availability, sea surface temperature, and features along the floor of the sea.
Analyzing the research, scientists found that the amount of whale shark sightings recorded in 2008 drastically increased, and remained to be increased for the rest of the period studied (through 2013). They speculated that this was because 2008 was an unusually warm year, so sharks sought out a cooler place. Aside from sea surface temperature, whales also seemed to be more plentiful in areas with a higher seafloor slope and that were closer to seamounts. These conditions tend to mean that the area has more chlorophyll-a, which is what whale sharks eat. The study suggested that as ocean temperatures rise, the Azores region will be critical for whale sharks because it has certain vital ocean-like features that the whales need to survive, and also has a cooler temperature which whales seem to prefer.
You can read the whole paper online for free here: http://dx.plos.org/10.1371/journal.pone.0102060