Basking shark diving patterns change with seasons, study finds
Scientists have said through a study that basking sharks exhibit variations in diving patterns based on season – during winters these sharks dive to greater depths while in summer they tend to stay near the surface.
Basking sharks are the world’s second-largest shark species. Basking sharks spend most of the summer months at the ocean’s surface, but dive to deeper depths in winter, the study found. According to researchers this change in diving patterns is likely because of environmental conditions: sharks could be exploring different areas of the ocean to deal with changes in food abundance.
Another finding of the study is that basking sharks exhibited “yo-yo” dives towards late winter and early spring. “Yo-yo” dives are rapid and repeated movements between deep and surface waters.
Whilst performing these dives, several of the studied sharks reached depths of over 1000 m, and two were tracked as far as 1500 m below the surface.
For the study, researchers attached satellite tags to 32 of these sharks. The tags collected data on depth and temperature, along with ambient light levels, which can be used to estimate the sharks’ location each day. The collected data reveal a seasonal change in diving behaviour, it also showed that basking sharks move to different depths depending on the time of day.
Moving to shallower depths during the day and diving down at night is referred to as “reverse diel vertical migration”. All three planktivorous sharks – basking sharks, whale sharks and megamouth sharks – have been shown to display this behaviour.
Scientists believe that it enables them to track their main food source, plankton. Like basking sharks, plankton can remain close to the ocean’s surface during the summer and move to deeper depths to over winter.