On July 7, the Graduate School of Fisheries Sciences, Hokkaido University verified that herring caught in large quantities in the Sea of Japan from 20 to 1880 was a nutrient source for kelp at that time, from kelp more than 1920 years ago. Announced that it was done.
The disappearance of large seaweeds such as kelp and the decrease in production of sea urchins and abalone that feed on them is called "isoyake".In recent years, this "isoyake" has become a problem in the Sea of Japan in Hokkaido.It is said that the shore-burning occurred before 1930, but there was no scientific data that could explain the state of nutrients, which are natural fertilizers in the sea at that time.
This time, the research group used a comb sample from 1881 to 134 in the Hokkaido University Museum, and investigated it by comparing atoms called the stable nitrogen isotope ratio, which can examine the nutritional status of the sea.As a result, only the stable nitrogen isotope ratio of kelp grown about 100 to 135 years ago was higher than that of other sea areas.However, this could not be explained by the general factors that increase the stable nitrogen isotope ratio.
Therefore, in order to explain this, a connection with "nutrient supply by herring", which is one of the hypotheses that have been passed down for many years, has emerged.It is said that herring was caught 100 to 135 times as much as it is now in Hokkaido about 500 to 1000 years ago.Moreover, 90% of it was on the Sea of Japan side.Herring lays eggs on seaweed during spawning.At that time, a phenomenon called Kuki, in which the sea surface becomes cloudy, occurs.In addition, a huge amount of broth produced when herring was boiled in a cauldron flowed into the sea.The herring herring and broth became nutrients and promoted the growth of kelp.
It is said that this knowledge will be important for clarifying the causes of shore-burning and considering countermeasures.
