AsianScientist (Mar. 6, 2018) – Researchers have discovered that Bryde’s whales (Balaenopteridae edeni) have developed an energy-saving mode of feeding to adapt to the shallow waters of the upper Gulf of Thailand in Southeast Asia. They published their findings in Current Biology.
The upper Gulf of Thailand is an environment depleted of oxygen, except at the sea surface. This is due to an excessive supply of nutrients arising from considerable outflow of sewage-containing water from rivers into the sea. Hence, small fish tend to remain at the water surface.
In the present study, a Thai-Japanese research group led by Dr. Takashi Iwata at the Atmosphere and Ocean Research Institute at the University of Tokyo have discovered that Bryde’s whales feed on small fish at the surface using a passive method, treading water with their mouths open and waiting for the prey to enter. The researchers came to this conclusion after making visual observations and analyzing information gathered using data loggers attached to the whales.
The scientists also noticed tread-water feeding in both solitary whales and adult-calf pairs—the latter behavior implying social learning. Such tread-water feeding behavior in Bryde’s whales has so far been observed only in the upper Gulf of Thailand. This activity may therefore be a group-typical behavior pattern unique to this region, and together with the social learning aspect, a cultural behavior only found in these waters.
The energy cost of this tread-water feeding, considered passive feeding behavior, is much lower than that for lunge feeding, which involves active chasing of prey at high speeds in deeper waters. Tread-water feeding is thus considered efficient for Bryde’s whales to catch prey at the sea surface.
“In this study, we reported a new feeding style of Bryde’s whales. We indicated that rorqual whales potentially have flexible abilities to modify their foraging behavior for various environments,” said Iwata. “Bryde’s whales in the Gulf of Thailand perform not only tread-water feeding but also lunge feeding. To understand their adaptation capacity, we hope to reveal how they use these foraging behaviors according to their environment.”
The article can be found at: Iwata et al. (2017) Tread-water Feeding of Bryde’s Whales.
Source: University of Tokyo; Photo: Takashi Iwata.
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