Warmer Waters Bring Tuna And Jelly Fish

Thursday, 24 August 2023 07:44

Exotic marine life are becoming more regular visitors to island waters, including bluefin tuna and crystal jelly fish.

If you've been in the water recently, you may well have swum among crystal jelly fish.

They're palm sized, surprisingly dense and heavy and translucent, or white, depending on the light.

They're normally seen in the Mediterranean, but Alex Purdie, a marine biologist with the Alderney Wildlife Trust, says as the seas warm, they're seeking food and cooler waters:

"Water currents can bring the babies and the young further north. Because sea temperatures are warming, these species are starting to survive into adulthood, and we're getting blooms of species here, and they're beautiful creatures."

Alex says they're harmless to humans, although the advice is to leave them alone. He says they often appear motionless:

"That's just where they're hunting in the water column, a lot of plankton may be moving near the top, especially the phytoplankton and zoo plankton."

Anyone on a boat in local waters may have been lucky enough to see shoals of bluefin tuna. Again, Alex says the warmer waters and a ban on fishing for them is increasing their numbers:

"They're still recovering. It's important that we give them the chance to cement themselves in the ecosystem."

Bluefin tuna are being tagged off Jersey with satellite trackers, to determine their movements. The trackers are harmless and fall off within two years. Alex Purdie says seeing the tuna feed is quite a sight:

"They form a ring around a shoal of bait fish, like mackerel. Then they jet out of the water, and you'll see the whole water boiling, and these beautiful torpedo like fish jumping out of the water."