Hokkaido is the northernmost island of Japanese archipelago. It has a long shoreline extending about 2,700 km, which corresponds to about 10% of the Japanese coastline. The island is surrounded by three different seas-the Japan Sea, the Pacific Ocean, and the Okhotsk Sea. The coastline of Hokkaido is influenced by two warm currents, the Tsushima and the Kuroshio, and one cold current, the Oyashio (Fig. 1). The seasonal fluctuations of these warm and cola currents considerably influence the oceanographic conditions in each local region. Therefore, Hokkaido has many specific ecological features as a result of these oceanographic, as well as topographic, conditions.
The Japan Sea coast of Hokkaido can be divided into two regions by the Shakotan Peninsula: The northernegion is characterized by simple sandy beaches, while the southern region, including the Shakotan Peninsula, is characterized by a rough, rocky shoreline. Along this coast, the warm Tsushima Current flows northward. In addition, some upwelling of cold water-masses from the lower layers of the Japan Sea occurs both in the offshore waters and the inshore area of the Tsushima Current. This intermingling of warm and cold water-masses complicates the oceanographic conditions of the area. Moreover, strong northwest winds bring stormy weather conditions to this region during the winter. Therefore, because of the oceanographic conditions, stormy winters, and open topography, it is very difficult to establish and maintain artificial equipment (rafts, longlines, etc.) for marine cultivation.
The Pacific coast can also be divided into two regions by Cape Erimo. In the eastern region, there are many small bays or inlets in the Akkeshi area, but the largest embayment, Uchiura Bay, is found in the western region. The whole coastline of the Pacific region, except in the area of Tsugaru Strait, where wide, rocky shores are found, is made up of simple, sandy beaches. The fundamental water system of this region consists of two warm currents, the Kuroshio and the Tsugaru, and one cold current, the Oyashio. In the western region, the warm Tsugaru Current and the cold Oyashio Current interchange alternatively by seasons; therefore, the oceanographic conditions of this region are quite variable. On the other hand, in the eastern region, the coastal area is affected entirely by the cold Oyashio Current throughout the entire year. Dense sea fogs often occur during the summer (June to August), especially in the eastern part. There are, on the average, 58 foggy days per year.
The Okhotsk Sea coast can be divided into two regions by the Shiretoko Peninsula: The northern region is characterized by a flat sandy beach; in the southern region, a big embayment is formed between the Shiretoko Peninsula and the Nemuro Peninsula. In addition, some of the Kurile Islands are located in the entrance of this embayment. The channel lying between Hokkaido and Kunashiri Island is called the Nemuro Strait. This region is characterized by many large and small brackish lakes along the coast. The warm Soya Current (a branch of the Tsushima Current) flows southward along the Okhotsk Sea coast and a cold East Sakhalin Current runs along the outside and parallel with the Soya Current. Considerable freezing of seawater, especially in lakes and inlets, and drifting ice occur from December to April in this region. Because of these icy conditions, fishing activities as well as maintaining artificial equipment for marine cultivation are greatly restricted during this period.
The major species which are artificially cultivated and propagated in Hokkaido are restricted in numbers because of environmental conditions of this region. Almost all are northern forms which have their major distributional range in Hokkaido (Table 1). Recently, the cultivation of fishes and other marine organisms has become of major interest in Hokkaido, and it has become necessary to establish seed production systems for some of the most important northern forms. The species listed in this article are presently being cultivated in Hokkaido.
The present status of some important invertebrates and seaweeds is as follows:
Scallop (Patinopecten yesoenssis)
Sea scallops are distributed along the whole coast of Hokkaido. However, in recent years, the major areas of production have been limited to the Okhotsk Sea region, especially in the southern half of the northern region and the Nemuro Strait area in the southern region. Scallop production in Hokkaido reached its peak in 1934, when 78,674 tons were harvested. Since then, production has been declining, with accompanying wide annual fluctuations. A low of 3,843 tons was recorded in 1968. However, in 1969, production rose to 8,618 tons. This increase may be due to the gradual development of the artificial cultivation and the use of underwater off-bottom techniques in Lake Saloma and Uchiura Bay, and the stocking of seed scallops along the Okhotsk Sea coast. It is not clear whether the remarkable reduction in production was caused by overfishing or by a decrease in the amount of scallop setting as a result of some adverse oceanographic conditions.
Japanese surf clam (Mactra sachaliensis)
This clam is found along the entire Hokkaido coast. Major areas of production are the Pacific coast region and the Nemuro Strait. In Hokkaido, the annual production of surf clams is nearly 5,000 tons. Commercial-sized clams range in age composition from 4 to 10 yr old, and it is doubtful that the resource would recover if overfished. At present, the clam resource is being carefully managed by regulating the size of the catch, fishing seasons, fishing grounds, and minimum shell size. Transplanting of juvenile clams has been attempted for the purpose of preserving this resource.
Abalone (Haliotis discus)
Abalone are limited to the Japan Sea coast, the Tsugaru Strait, and Uchiura Bay; it has never been found in other areas. This restriction in its geographical range may be attributed mainly to the low seawater temperatures during the winter season. The number of abalone per unit of area is considerable in Hokkaido. Because of cold waters, the growth rate is slower than in the southern part of Japan. Accordingly, Hokkaido has played an important role as a source of seed abalone for southern Japan. Growth rates vary considerably along the Hokkaido coast and successful transplants have been made from poor growing grounds to good growing grounds.
Sea urchin (Strongylocentrotus intermedius and S. nudus)
Hokkaido's species of the sea urchins differ from those of the southern part of Japan. They are of commercial importance in Hokkaido and are found along all coasts. Recently, effective management of sea urchin populations has been carried out and, as a result, the annual catch has shown a rising tendency. In managing the populations, severe regulations have been established on the fishing grounds, designated fishing seasons, and minimum carapace size. Also, young individuals (those with immature ovaries) have been transplanted to productive grounds rich in seaweeds.
Kelp (Laminaria spp.)
Laminaria growing along the coast of Hokkaido are classified into several species, namely L. japonica, L. religiosa, L. ochotensis, L. diabolica, L. angustata, and L. angustata var. longissima. The classification is based on their morphological characters. However, from the taxonomical as well as distributional viewpoints, it is appropriate to divide the above-mentioned Laminaria into two major groups-Laminaria japonica group (including L. japonica, L. ochotensis, and L. diabolica) and Laminaria angustata group (including L. angustata and L. angustata var. longissima). The former group is found in Uchiura Bay, the Tsugaru Strait, the Japan Sea, the northern part of Okhotsk Sea region, and along the coast of Shiretoko Peninsula. The latter group grows along the coast of the Pacific Ocean. Since 1955, the annual production of Laminaria in Hokkaido has fluctuated between 100,000 and 150,000 tons in fresh weight. The most abundant harvests were recorded, based on a 5-yr cycle, in 1957, 1962, and 1967. Since the 19th century, various attempts have been made to increase Laminaria production. These include the planting of stones and rocks and the blasting of rocky reefs. In the recent years, cultivation of Laminaria, especially forced cultivation, by a longline type or rope-curtain type, was popularized, as in Undaria in southern Hokkaido.
Brown algae (Undaria pinnatifida)
The distributional range of Undaria in Hokkaido is generally the same as that of abalone. In recent times, the annual production of Undaria in Hokkaido has been constant at about 10,000 tons in fresh weight.
Red algae (Porphyra spp., mainly Porphyra yezoensis)
Hokkaido is still an underdeveloped area for the cultivation of Porphyra because there are many obstacles hindering its growth, such as heavy windstorms along the Japan Sea coast, freezing of sea waters, and floating drift ice in the inlets along the eastern part of the Pacific coast and the Okhotsk coast. However, since 1953, the cultivation of Porphyra has increased gradually in Uchiura Bay, Akkeshi Bay, and the northern part of the Japan Sea coast. In the former two places, the algae are not damaged by the above obstacles, while in the latter place, they are protected by special breakwater fences.
As in many agencies, organization, staff, budgets, and facilities are problems affecting research activities. However, these are omitted from this discussion for want of space. The problems to be solved in future studies are as follows:
All species being artificially propagated
1) Identification of food organisms and developing best methods for
their mass production.
2) Determination of an adaptive environmental condition for each species.
3) Determination of the size and the quality of seed to be stocked and places where stocking will be done.
4) Explanation of an annexing effect to the natural stocks as an important problem in the future.
1) Clarification of the major factors causing the decline in populations
on both the Japan Sea coast and the northern part of the Okhotsk Sea coast.
2) Establishment of a large-scale, dependable system for the mass production of seed (target is 800 million individuals).
Japanese surf clam
Establishment of a large-scale, dependable system for producing seed both naturally and artificially.
Abalone and sea urchin
Establishment of a technique for artificially planting seaweeds and clarification on the ability of abalone and sea urchin to propagate following planting.
1) Investigation of methods of growing high quality Laminaria
(2-yr old plants).
2) Improvement of methods for the forced cultivation of Laminaria (1-yr old plants).
3) Study how to protect the cultured Laminaria from the noxious bryozoan, Membranipora serrilamella.
1) Identification of the new local species and the breeding of Porphyra.
2) Study the adaptation of each local species to its environmental conditions.
3) Establishment of a suitable culture technique for each local condition.
1 Hokkaido Regional Fisheries Research Laboratory, Yoichi, Hokkaido. Japan.