September 26, 2013
Crittercam Helps Identify Unique Humpback Feeding Techniques
Brett Smith for redOrbit.com - Your Universe Online
Using underwater “critter cams” and tagging techniques, a team of marine biologists from the National Oceanic and Atmospheric Administration (NOAA) was able to confirm a unique humpback whale feeding technique performed along the ocean floor, according to their report in the journal Marine Mammal Science.Based on observations of whales off the coast of Massachusetts, the report revealed that humpbacks use three distinct feeding techniques: simple side-rolls, side-roll inversions, and repetitive scooping. The methods are used to feed on sand lance, also known as sand eels, and other bottom-dwelling treats.
The new study comes just a few years after NOAA researchers described the “bubble net” method that these whales use to herd prey into a specific area. The method involves the whales using nets of air bubbles to efficiently scoop up prey in their large filter-feeding mouths. The methods are used by both individual animals and multiple whales as part of a coordinated feeding behavior.
"Tagging technology is allowing us to observe whales underwater, much as land-based biologists study animal subjects in their specific environments," said David Wiley, a research coordinator for the Stellwagen Bank National Marine Sanctuary. "The data have allowed us to detect new feeding techniques as well as nuances in those behaviors. We have determined that bottom feeding is a much more commonly used technique than the more well known bubble net behaviors."
Marine biologists had suspected that humpbacks used a bottom side-rolling feeding technique based on scars seen on the jaws of humpback whales and from earlier projects. In recent studies, researchers found that this behavior happens for long periods at or near the seafloor, usually near high concentrations of sand lance. Previous theories also found that the animals expand their ventral (throat) pleats in the process.
In the latest study, information was collected through the use of synchronous motion and acoustic recording tags (DTAGs) and the Crittercam, the National Geographic Society's underwater video and audio recording system. Information from the DTAGs allowed the NOAA team to produce a ribbon-like image in three dimensions that represents a whale’s movements using a software system called TrackPlot.
"By visualizing the data with TrackPlot, we can actually see how the whale moves underwater and this enables us to discover different kinds of foraging behaviors," said study author Colin Ware of the University of New Hampshire's Center for Coastal and Ocean Mapping.
"With these 3-D visualizations, we can follow the path of the whale from surface to seafloor along with all of the pitch, roll and heading changes while underway,” he added. “By adding Crittercam video, we now get a more complete understanding of these various bottom feeding techniques.”
In addition to providing information on humpback whale movements, Crittercam footage also showed that sand lance congregate into dense mats along the seabed during the day. The whales use their side roll feeding techniques to more efficient feed on these carpets of prey. The whales also use coordinated feeding to help cluster prey or make sure that it does not escape.
The research team concluded that humpback side rolls seen in the Atlantic resemble the feeding technique of gray whales in the Pacific.