Clerkin, P.J., Arostegui, M.C., Chiang, Lin S.J., Miller C.D., and Braun C.D. 2024. First telemetry insights into the movements and vertical habitat use of megamouth shark (Megachasma pelagios) in the northwest Pacific. Deep Sea Research Part I: Oceanographic Research Papers 212. doi.org/10.1016/j.dsr.2024.104385
Mega Mystery
New tracking data is shedding light on the daily lives of one of the most mysterious sharks in the world, the megamouth shark. This species wasn’t discovered until 1976 and it was only because one accidentally became tangled in an anchor. Since then only a couple hundred other individuals have ever been documented. This has left us with many questions about its life that are not easily answered because of where it lives.
Megamouth sharks are found from the ocean surface down to the bathypelagic zone which ranges from 1,000 to 4,000 meters (3,300 to 13,100 feet) deep. To put this into perspective, most military submarines are limited to 500 to 800 meters of water. Sunlight doesn’t reach this part of the ocean, making it the midnight zone. This doesn’t bother the shark though because it’s a filter feeder. Similar to the other large filter feeder sharks (whale shark and basking shark), it eats zooplankton. These are microscopic organisms that are an important part of the base of the oceanic food chain. All the megamouth shark has to do is open its mouth and suck water in. Its mouth is designed to filter the zooplankton from the water, and as you can imagine with a name like megamouth, it does it very well.
These zooplankton perform daily migrations throughout the water column. They stay deep during the day and then rise to the surface at night before repeating the process the next day. This is known as diel vertical movement or DVM. They do this to feed on the phytoplankton at the surface that have been growing and producing energy while in the sun. This is an important process because this migration impacts many other animals, including those that feed on zooplankton.
It’s believed that megamouth sharks demonstrate DVM as well, following their food source, but this hasn’t been confirmed. Scientists in a new study tagged and released three megamouth sharks off the coast of Taiwan to understand their daily and seasonal movements.
Daily Swimming
The tags confirmed that the megamouth sharks performed diel vertical movements that matched their food. They would stay in the mesopelagic zone (200 – 1000 m) during the day, but come to the epipelagic zone (0 – 200 m) at night. This behavior had been found in another study that followed a single individual for 2 days off the coast of California back in 1997. However, there were concerns that this was not representative of the population. This study confirms this initial finding is species wide.
Diel vertical movements can also be used for thermoregulation. Like most sharks, megamouths are cold blooded. They’re dependent on external temperatures to regulate their body temperature. The mesopelagic zone happens to contain the thermocline. This is where warm surface water meets deep, cold water. The temperature changes the most along this area with a rapid decline the deeper you go. DVM may help megamouths regulate their body temperature, staying in a particular temperature range that moves up and down the water column as the sun rises and sets.
Into the Deep
Megamouth sharks continue to remain mysterious to us because of how deep they live. However, this study confirms the sharks perform diel vertical movements to feed and/or thermoregulate. This is significant to understanding how they use their habitat. We don’t know what the megamouth shark population looks like so we have no idea how many individuals there are. In this case, any new information that we can learn about them will help promote conservation efforts to protect this species.
I am a recent MSc graduate in marine biology from Bangor University, where I studied population dynamics of elasmobranchs off the coast of Wales. My interests lie in ecological data analysis to understand environmental processes and identify natural patterns. However, nothing beats being in the field and interacting directly with the marine life.
