Conservation of Red-Spotted Groupers that Respond to High Water Temperatures Using Shell Fish Reefs

Ocean Construction Co., Ltd.

Publication date	January 19, 2021 (Posted on September 13, 2022)
Sector	Agriculture, Forestry, Fisheries

Company Overview

Climate Change Impacts

Sea temperature is predicted to rise due to global warming, and this has already had an impact on the pacific saury; they have moved away from the sea close to Japan which resulted in record-breaking poor catches. In coastal areas, there has also been concerns about the decrease in seaweed beds, which results in the decrease of abalones, and the decrease in fish resources that prefer low water temperatures. However, fish that prefer warm water, such as groupers, have been expanding their distributions.

In this way, changes in the marine ecosystems due to climate change are unavoidable, and in the field of marine fisheries, it is essential to understand the state of the resources and to protect and manage resources in response to changes.

Adaptation Initiatives

Red-spotted grouper, Epinephelus akaara, was originally caught mainly in western Japan, and is known as a luxury fish called "akou" (Fig. 1) in the Kansai region. In the past, it was also called a "phantom fish," but in the recent years, it is no longer uncommon to see them in the fish section of supermarkets due to rising sea temperatures and efforts to release seedlings.

We have come to notice that their spread of distribution in the Sea of Japan and the Seto Inland Sea and focused on the high-price they are being traded for. We realized that we could make use of our technology cultivated through the development of shell fish reefs, for the conservation of resources.

By protecting the released seedlings and wild juvenile fish of the red-spotted grouper, it is possible to increase and protect resources more efficiently. Therefore, we have developed an artificial fish reef product (nursery reef) developed to protect the juvenile red-spotted grouper, and are working together with the JF Group, which is an organization of fishers, to spread its use (Fig. 2). The nursery reefs are constructed by using pipes lined with scallop shells for hiding places and oyster shell pipes to efficiently increase the amount of small shrimps and crabs that can be fed according to the size of the red-spotted grouper to be protected. The structure is designed to make it difficult for large fish that would eat the juvenile fish to enter by narrowing the inside.

This technology is an enhanced version in Okayama Prefecture, and is now being introduced in Ehime, Yamaguchi, and Hiroshima Prefecture. It has been used extensively including areas close to the Sea of Japan. Toyama Prefecture, where the distribution of red-spotted grouper is expanding in the recent years, has also decided on its use on a trial basis.

Effects / Expected Benefits

In Ehime, Yamaguchi, and Hiroshima Prefecture, where the nursery reefs have been introduced, diving inspection has been conducted after installing, and it has been confirmed that many liberated Epinephelus akaara seedlings and wild juvenile fish have been using the reefs as hiding places (Fig. 3).

In Ehime Prefecture, development of fisheries using nursery reefs to protect and nurture juvenile fish and the release of seedlings have been continuing for about 20 years, and this has tangible effects such as an increase in the trading volume of red-spotted grouper in the market (Fig. 4).

In this way, it is expected that sustainable use of marine resources will be possible by promoting efforts for the development of fisheries that match the ecological characteristics of the species for which distribution is predicted to expand due to the rise in sea water temperature in the future.