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A long-term study to track the movements of commercially valuable fish species might have been a waste of time, thanks to crafty seals. Several years ago, fisheries scientists attached acoustic tags to a sample of salmon and lingcod, and used the signals to track the movements of fish schools in the North Atlantic. The trouble was, they weren’t the only ones listening.

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Hungry seals quickly learned the meaning of the signals and tracked down the signal to finds the schools of fish. For the seals, the research was a shortcut to a feast, and as a result the data from the entire study might be unreliable. In retrospect, maybe nobody should be surprised. Seals and sea lions have a long history of exploiting others for personal gain.

Seals and sea lions and have excellent hearing but where they truly excel is in using others to extend their own abilities. Sea lions are fully capable of catching fish, but they need to find them first, and to this end sea lions range far and wide along the California coast while foraging.

However, sea lions in Santa Monica Bay have learned to use dolphins as a shortcut, according to a 2006 study. Dolphins, with their echolocation ability, can find schools of fish more easily in the open ocean than sea lions can. Sea lions, for their part, may find fish to be a challenge but can easily find pods of noisy, chattering dolphins.

Accordingly, it appears that sea lions simply track the dolphins rather than the more difficult and costly work of tracking the fish directly. Sea lions were found far more in association with dolphins than without, and according to the study’s authors the sea lions were the ones deciding whether to hang with the dolphins that day or not. Unable to hear the ultrasonic echolocation clicks, the sea lions simply stuck their heads out of the water to visually track the leaping dolphins, a behavior known as spy hopping.

Whether listening for the signals of research tags, shadowing dolphins, or stealing fish from nets, seals and sea lions really know how to leverage their available resources.


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Journal of Mammalogy, Vol. 87, No. 3 (Jun., 2006), pp. 606-617
American Society of Mammalogists