Most people call them yellowtail, but the correct term is jack mackerel. In Japan, they are known as aji and are highly regarded when filleted and boned and rolled into delicate morsels steamed with soy sauce. Commercial fishing boats hoover them up in vast schools, but they are turned into fish meal for feeding bigger fish like salmon in farms.

The humble "jack" has a symbiotic relationship with an ugly little creature called a sea louse, which hitches a ride while hanging on inside its throat and no doubt helps itself to the jack's dinner as it goes past. These loathsome, white parasites desert their host when it dies and crawl out in search of another vehicle. Jacks always seem to die with their mouth wide open.

But experienced snapper fishermen know that the yellow-brown mackerel make just about the best bait for the big ones. That is what has been happening in the Firth of Thames, out off the Whangaparaoa Peninsula and in the Bay of Islands. Kingfish love them, too, and they are often referred to as "kingfish candy".

When hoping for a snapper of five kilos or more anglers will use the whole jack as a bait. They can be hooked with a single hook inserted under the pectoral fin on one side, hook facing forward, and rolled back so the shank rests against the flank and the point sticks out with the eye of the hook facing the tail. The trace can then be looped around the tail with a couple of half-hitches to secure it for casting. If a weight is needed to pull the bait down through waves, a small ball sinker can be first pushed down against the hook so it doesn't slide up the trace during casting and create a pendulum effect. This is a top bait when stray-lining down a berley trail but also works well when dropped into 25m, like in the firth. It just needs a bigger sinker.

At popular spots like Flat Rock, Shearer's Rock and the reef south of Shearer's, where several large snapper were caught and released last week, a butterflied yellowtail is a favourite big-snapper offering. This is a jack with the backbone removed, leaving two flaps of flesh hanging from the head and leaching juices which are a magnet to the targeted quarry. It can be rigged with one hook through the bony part of the head for security, and a second hook reversed halfway down one of the fillets.

Some anglers believe the snapper is always better if there are jack mackerel in the vicinity and they are often caught on small snapper baits. But they are also easily targeted with sabiki jig flies baited with morsels of pilchard or squid.

They can be filleted and used as regular bait in chunks or strips, and such baits will resist the picking of juveniles and usually result in bigger snapper being hooked although the action will be slower than with the more common pilchard baits. Firing a big fillet of yellowtail well off the back of the boat and leaving the rod in a holder up high, with the clicker on the reel to signal action, is a good way to pick up the occasional large fish. Sharks and rays love these baits, too.

Jacks are prolific in the Bay of Islands at the moment and charter skippers like to fill the live bait tank before heading out after snapper or kingfish, and they will put down a whole or half mackerel as snapper bait, or a live bait for kingfish. When fished on the surface as a live bait, the jacks are hooked through the back just in front of the dorsal fin, but when dropped to the sea bed they are hooked through the nose so they dive through the water when dragged down, and are not pulled sideways. Of course, a live one on the bottom is just as likely to attract the attention of an old man snapper as a kingfish.

Large snapper have also been reported from the area south of Motuora Island and east of Tiritiri Matangi. In fact, the number of large fish caught and released so far this summer has surprised many people.

Further to the south, a snapper of 12.8kg was caught in 35m off Home Bay, at Great Mercury Island.

Tarakihi are also around in good numbers in 40m of water off Little Barrier Island and are in top condition. They can be targeted with small hooks and baits, fishing along the edge of weed beds or patches of foul. Hapuku are also running well off the Bay of Islands and east of Great Barrier Island but fishing at the Moko Hinau Islands has been slow.

More fishing action can be found on Rheem Outdoors with Geoff, 5pm today, and on the internet television channel, www.FishnHunt.Tv