Sawara or Spanish Mackerel is considered as the best kind of Mackerel in Japan. Not only it is a big variety, but its comparatively white flesh is succulent in almost any kind of cooking!
It is known under different names such as Sagoshi and Sagochi when young and Yanagi when mature.
It is basically caught by trawling, but can be fished by line. It is, unlike other mackerels, a pretty solitary fish.
It is caught widely around Japan, off Russia, China and Korea.
The total catch has varied in recent years, but thanks to import, including 21.000 tonnes from China, it has become a feature in season from late Autumn to end of Spring.
(Kan-Sawara at Uzu, Shizuoka City)
In Winter, it is called Kan Sawara/寒鰆 (寒stands for cold, 鰆 stands for Sawara/Spring Fish) and is a sought after morsel. In Shizuoka it is sometimes caught then in Sagara bay, and I can tell you it disappears quickly form the table.
(Sawara at Uzu, Shizuoka City)
Later in Spring, it is just called Sawara and is leaner.
It can be cooked in many ways: broiled as above.
Or grilled.
(Small pic, sorry!)
Of Course, as sushi nigiri! Especially Kan Sawara!
SHIZUOKA SUSHI & SASHIMI: The other Jewels of Japan 
The Sawara in the picture , thats the Northeast Asian variety of Spanish Mackerel ( Scomberomorous spp ) family. In Indonesia and Australia, the other member Scomberomorous Commerson can be as big as 30kg.
I had seen mine taken by the Indonesian fishermen in southern Indian ocean has 25kg in gross weight !!! Unfortunately larger individual has coarser meat, so smaller ones are best.
In Eastern Indonesia, there is another subspecie called Shark Mackerel, it is an offshoot of the Spanish Mackerel family and the weird thing its meat has light ammonia smell, hence it is called shark mackerel.
Cheers, Johan!
As usual, thanks for the great information!
Best egards,
Robert-Gilles