Climate-Challenged Whale Sharks Drawn to Azores
As sea surface temperatures rise, whale sharks are flocking to waters off of the volcanic Azore islands, a new study has found.
Whale sharks tend to enjoy warmer waters between 79 and 86 degrees Fahrenheit (26-30 degrees Celsius), but even these marine titans can't stand the heat, according to the study, published in the journal PLOS ONE.
Climate change appears to be forcing these sharks to waters with more ideal, or "Goldilocks," temperatures. In recent years, fishermen have increasingly spotted these large fish around the Azores Islands, nine volcanic isles in the central North Atlantic west of Portugal.
Lead researcher Pedro Afonso of the University of the Azores and his colleagues wrote that the "occurrence of the whale shark in the wider Azores region increased drastically in 2008. Prior to this, and for a full decade, these large animals had only been sighted sporadically."
To better understand what is drawing whale sharks to the area, researchers analyzed a 16-year (1998-2013) observer data set from tuna fishermen around the region - it is known that the sharks appear during the summer at the same time as tuna schools. They also used models to investigate the movement of the sharks in relation to factors such as food, sea surface temperature and seafloor features.
The year 2008 was an exceptionally warm year, and since then whale sharks - called "pintados" by the locals - have been spotted in the Azores regularly.
Even though these island waters tend to be cooler and lie on the edge of the whale shark ocean temperature range, climate change has warmed their temperatures to most ideal conditions, now making it whale shark central.
The temperature increase in the Azores correlated with larger amounts of chlorophyll-a, a type of whale shark food, according to a press release.
The researchers also found that whale shark populations are higher in areas of increased seafloor slope and closer to seamounts - regions with large amounts of chlorophyll-a.
"Our findings underline the potential for an increase of the wider Azores region's importance as an oceanic habitat for the whale shark in the North Atlantic in years of exceptionally high water temperature, and for a concomitant shift in the whale shark distribution within the Atlantic Ocean, as predicted by global modeling studies," Afonso and his team concluded.