The shark described a circle around the shoal of fish.

这条鲨鱼围绕着鱼群游动。

《牛津词典》

So it is a comparatively simple step from locating the sea bottom to locating a shoal of fish.

所以相比较测量海底，定位鱼群是类似的步骤。

youdao

A birdwatcher can never fly with a flock of migrating birds, but a diver can loiter in a shoal of fish.

因为即便是观鸟者也无法与鸟儿一同飞翔，但潜水者却可以和鱼儿共同在水中畅游。

youdao

His job was to shout when he spotted a shoal of fish enter the cove, so the team below could trap and catch it.

BBC: Oman��s sleepy Musandam Peninsula