They can grow to 15 metres in length and 40 tonnes in weight. They provide a spectacular sight when they turn up to feed in work-ups.
The whales can detect the splashing and underwater sound waves as fish like kingfish and kahawai smash into concentrations of pilchards and anchovies, while gannets wheel and dive into the frenzy.
Not all work-ups will have snapper under them, as sometimes the school of pilchards will be demolished before there is time for snapper to be attracted. Canny boaties will continue fishing after the activity has died away as they know there will probably still be a lot of snapper down current from the work-up.
Some people drive their boats right through the centre of activity, which can drive the fish away and also increases the chances of accidentally hitting a dolphin or bird. It is better to approach slowly and fish around the edges.
The whitebait season finishes today, and recent reports indicate some good catches on the Waikato River and Bay of Plenty rivers, but in Northland the season has been slow.
The tributary streams and rivers in the Rotorua and Taupo districts open to fishing tomorrow. At Taupo the upper Tongariro is the main water which attracts anglers, after it has been closed all winter to allow trout to spawn.
Around Rotorua the upper sections of the Ngongotaha Stream above SH5, the Waiteti Stream above Hamurana Road and the Utuhina Stream between Devon and Pukehangi Roads all open to fishing.
Lake Rotorua has excellent spawning streams and does not need hatchery-raised trout to supplement the population, although a few are liberated for monitoring purposes.
Tip of the week
Take a pair of binoculars when looking for work-ups, and look for white dots circling in the distance. These will be gannets over a work-up, or if gannets are travelling head in the same direction. More fishing action can be found at GTTackle.co.nz.
• Bite times
Bite times are 8.15am and 8.40pm tomorrow and 9am and 9.30pm on Sunday.