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Descriptions

The Yesso scallop (Mizuhopecten yessoensis) is a cold water marine bivalve species. The valves have a convex center with a smooth exterior shell. It is white on one side and dark brown on the other side.

Habitat

The Yesso scallop is widely distributed along the cold coast of Northern Japan. Scallop cultivation is located in the northern islands of Honshu and Hokkaido, with the Sea of Oshtok, Saroma Lake and Funka Bay in Hokkaido accounting for more than 80% of the scallop production during the period of 1991 to 2002.

Ecology and Behaviour

Temperature plays a key role in the timing of spawning and larvae settlement of the Yesso Scallop (Mizuhopecten yessoensis). Generally, the scallops spawn between May 1st to June 9th over the span of 10 days. It was found that the timing for the commencement of spawning is shifted to a later date when the surface temperature of the water remains below 0°C for a prolonged period. In addition, lower temperatures throughout April could potentially influence the onset timing of scallop spawning. Furthermore, the shortening of pre-spawning period (dates between the surface water temperature rise above zero to May 1st) may be another contributing factor to the later dates of spawning. On the other hand, the timing of scallop spat settlement is closely related to water temperature too; the colder the pre-spawning period, the later the larvae settlement. The commencement of the Yesso Scallop larvae settlement is typically between June 4th to July 5th over the period of 15 days. The upper limit for scallop development was found to be 18°C.

Development

The growth of scallops also varies with the water temperature. When the water is warm and below 18°C, the scallops tend to grow most rapidly between the age of 2 and 4. On the other hand, they often reach the peak of their growing ability between 3 to 5 years of age in colder environments. Consequently, it was established that the Japanese scallop Mizuhopecten yessoensis experiences the lowest mortality rate between the age of 2 and 5. Starting from the age of 6 to 7, the mortality rate rises dramatically.

Predation

The main predators of the Yesso scallops are the sea stars Asterias amurensis and Distolasterias nipon. The scallops are preyed on one after the other, and it was found that smaller scallops are preferred over larger ones. Scallops found in warmer waters are also more likely to be preyed upon. Due to the morphological differences between D. nipon and A. amurensis, D. nipon had a much greater influence on the predation of the Yesso scallops.

Diet

The scallops depend on sinking organic matter for food, with detritus being their main source of food. These organic matter are from rivers being drained nearby. Another source of food for the scallops are dissolved organic carbon from phytoplankton production.