Smithsonian.com

Short-beaked common dolphin (credit: NOAA/NMFS Southwest Fisheries Science Center)

If you had to catch all of your food, would you go after anything and everything that came across your path? Or would you wait for the bigger payoff? Squirrels and bunnies or deer and bear?

Dolphins go for the marine version of option B, preferring to eat only high-energy fish, according to a new study in the Journal of Experimental Marine Biology and Ecology.

Short-beaked common dolphins (Delphinus delphis) are the most common cetacean species in warm Atlantic waters. Biologists in France studied these mammals’ diets by looking in the stomachs of dolphins that had been caught accidentally in tuna drift nets in the Bay of Biscay. The dolphins most frequently ate Kroyer’s lanternfish (Notoscopelus kroeyeri) and Glacier lanternfish (Benthosema glaciale), two relatively rare but high-calorie species. Although other fish, such as Bean’s sawtooth eel (Serrivomer beanii) and Boa dragonfish (Stomias boa ferox) are much more abundant, the dolphins tended not to eat these low-calorie meals.

Living in the sea requires a lot of energy—just think about how tired you get from swimming—so dolphins require high-energy fuel to keep going. They need to be discerning in their eating habits.