In the Minamikayabe district of Hakodate, thinning work is in full swing for ma-kombu kelp force-cultivated to grow in one year. The sight of fishermen leaning out over the top of their boats and thinning out the kelp by hand is a seasonal tradition heralding the arrival of spring in this major production area of deluxe-class kelp.

Naturally cultivated ma-kombu kelp grows for two years from planting in autumn, but force-cultivated ma-kombu kelp is harvested the summer of year after planting. About 50 to 60 kelp leaves grow on each stalk attached to the roping strung out at the cultivation area, and thinning is necessary to make sure nutrients in the ocean can sufficiently permeate all of the kelp. First the number is reduced to around ten healthily growing kelp leaves per stalk in the winter, and then subsequent new growth is thinned in the spring.

Early in the morning on April 11, a fisherman thinned the kelp at the approximately one-kilometer-long cultivation area situated off Port Ofune. Pulling on the roping, approximately four-meter-long kelp emerges from the water. The fisherman cut and pulled the short new growth cropping up from the same stalk. His judgement was, “The kelp is coming in nicely this year. It should grow about another two meters.”

The thinned kelp is reportedly tender, and some fishermen ship it as an ingredient for dishes like oden stew.