And yet, for all this,

the dolphin has no organ of hearing discernible. Furthermore, when
engaged in their craft, fishermen are particularly careful to make
no noise with oar or net; and after they have spied a shoal, they
let down their nets at a spot so far off that they count upon no noise
being likely to reach the shoal, occasioned either by oar or by the
surging of their boats through the water; and the crews are strictly
enjoined to preserve silence until the shoal has been surrounded. And,
at times, when they want the fish to crowd together, they adopt the
stratagem of the dolphin-hunter; in other words they clatter stones
together, that the fish may, in their fright, gather close into one
spot, and so they envelop them within their nets.