Mackerel: the fish that turns the water silver

Ask a diver where the mackerel are at Kilkee and the honest answer is: anywhere. We see them at the Diamond Rocks as much as anywhere else, but a mackerel shoal is not a feature of a dive site. It is a moving thing that happens to be passing.

The fish

Atlantic mackerel, Scomber scombrus. Steel blue on top with those dark wavy bars that no two fish wear the same way, silver-white underneath, and a body built entirely for going forward. Most of what you see off the Clare coast is somewhere between 30 and 40 centimetres.

Two things about them are genuinely unusual. They have no swim bladder, so they cannot hang motionless in the water the way a pollock does — they sink if they stop, which means they effectively never stop. And they are ram ventilators: they have to keep swimming with their mouths open to push water over their gills. A mackerel that stops moving suffocates.

Why they are here in summer and not in winter

Mackerel spend the cold months out deep along the shelf edge west of Ireland, doing very little. As the water warms they move inshore and north to feed, and that is when they arrive over the reefs and into the bays. Around Clare that generally means from early summer through to autumn, with the best of it in the warmest water — which, worth remembering, is late August and September rather than July.

They chase small fish and plankton, and they hunt as a shoal, driving bait upwards and holding it against the surface.

What to look for

From the surface, the giveaway is birds. Terns and gulls working hard over one patch of water usually means something is pushing bait up from below, and around here that is often mackerel. The water can go visibly rough over a small area, a sort of localised boil, and then flatten again as the shoal moves on.

Underwater they arrive as a wall of moving silver and then simply are not there. Divers who wait for a photograph rarely get one. The trick is to look up — a shoal passing between you and the surface is one of the better sights in Irish water, and it usually happens overhead rather than beside you.

Mackerel are not a dive site. They are a moment. Look up more often than you think you need to.

Everything else eats them

This matters more than the fish itself. Mackerel are the middle of the food chain off this coast, and where they gather, bigger animals follow. Dolphins work mackerel shoals. Minke whales feed on them. Seabirds mark them from above. If you are watching from the cliffs and you find a working shoal, stay with it — that is your best chance of seeing something larger.

They are also fished commercially in a big way, and stock advice for the northeast Atlantic has been a live argument between scientists and fishing nations for years. Worth knowing if you buy them.

If you catch one

Mackerel spoil faster than almost any fish you will land in Ireland — oily flesh, and it goes off quickly in the sun. Ice them or eat them the same day, and take only what you will actually use. A full shoal will oblige you far past the point of sense.

Sea temperature and conditions for Kilkee are live on our home page, and if you want to be in the water when the shoals are about, come and talk to us on the East Pier.