This is one of the most common questions asked by visitors to the Bay, and you can often see fish jumping as you walk around the Bay or when out kayaking. The jumping fish are called Striped Mullet (Mugil cephalus), and they are common in the Bay. So…. why do they jump?
It is quite common for fish to jump out of the water when they are being chased by predators. When escaping predators you may see several fish jump together; they usually travel more horizontally and enter the water without much splash. This behavior doesn’t always seem to fit with what we see in the Bay but remains a possible explanation for some of the jumps.
The other common hypothesis for why the mullet jump is that they need to take in more oxygen (Hoese 1985). Mullet have an organ at the back of their throat which allows them to take in oxygen directly from the air. This is a particularly helpful strategy if you live in water with low oxygen content. If our fish are jumping for this reason, we might expect to see the fish jump more when the water is warmer and oxygen content is lower. We would also expect to see the fish jump more during the day when the are actively feeding from the muddy sediments where there is less oxygen in the water.
Scientists have also proposed that the fish might jump to try to dislodge parasites from their skin or to communicate with other fish when the water is cloudy. And one of our naturalists has another suggestion – maybe it is just fun!
As you explore the Bay, see if you can spot patterns in how and when the fish jump and let us know your ideas!
Hoese et al 1985. Jumping mullet – the internal diving bell hypothesis. Environmental Biology of Fishes 13, 309-314.
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