I was schooled on shoals…

I see many groups of fish of all kinds in Cabbage Tree Bay and wondered... what is the difference between a School or Shoal?

Groups of aquatic life get classified depending on whether they are a single type or mixture of species, or whether they are fish or mammals.

SHOAL - when fish, shrimp or other aquatic creatures swim together in a loose cluster, this is typically called a  shoal . It can be a mix of different species.

SCHOOL - is a group of the same fish species swimming together in synchrony; turning, twisting and forming sweeping, glinting shapes in the water. Fish probably do this to confuse predators and to save energy (by using the ‘slipstreams’ of other fish).

How do schools of fish swim in perfect unison?
A fish decides where and how to move relative to its position in the school. If the fish behind gets too close (less than two body-lengths), then it speeds up; if the fish in front gets closer than that, then it slows down. Schooling fish watch one another and also feel the waves their neighbours make as they swim, with pressure-sensitive pores along their body called the lateral line. And each fish has its preferred spot in the school. Some are natural leaders and tend to hang at the front and guide the whole school, while others choose to follow.

Are fish in a shoal all the same age?
In general, yes. Swirling, spiralling shoals are usually made up of fish of the same species and same size, and hence age. This is partly to confuse predators. Being a similar size, shape and colour makes it difficult for a hunter – a seal, dolphin or bigger fish – to make out and target a single prey fish. Other benefits of forming shoals include swimming efficiency and finding food. Roughly half of all fish species form shoals at some point and one in four species, including sardines, herring and anchovies, live permanently in shoals and get agitated when they’re on their own.

What is a big school of fish called?
Many kinds of fish prefer to swim together in groups called shoals. Some shoals are the biggest gatherings of animals on the planet others may only contain a few individuals.

Do schools of fish have a leader?
And each fish has its preferred spot in the school. Some are natural leaders and tend to hang at the front and guide the whole school, while others choose to follow.

How big is a shoal of fish?
A larger shoal might be 7 kilometres (4 mi) long, 1.5 kilometres (1 mi) wide and 30 meters (100 ft) deep. Huge numbers of sharks, dolphins, tuna, sailfish, Cape fur seals and even killer whales congregate and follow the shoals, creating a feeding frenzy along the coastline.