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Related to ark shells: Arcidae, scallop shells
See: refuge
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Thus, fishing pressure on ark shells is greater in Sendai Bay than in Nanao Bay.
KEY WORDS: ark shell, Scapharca broughtonii, age, growth, variation, shell sectioning and staining, water-based marking pen
Several previous studies analyzed age and growth of the ark shell, and the methods used in these studies can be classified into the following 3 types: decomposition of size-frequency distribution into year-classes (Machida 1988), studies of age characteristics based on the shell's outer growth rings (Fisheries Agency 1977, Selin 2000, Silina 2006), and age studies based on acetate replicas of the shell's internal growth rings (Gabaev & Olifirenko 2001).
However, to date this method has been applied to Russian ark shell populations only (Gabaev & Olifirenko 2001).
For the ark shell population in Sendai Bay, Japan, the severe overlap of the size distribution makes it difficult to apply the size distribution
The ark shell population in Mutsu Bay has been seriously depleted, and the dredge fishery for this species in this locality has not been operated since 1985.
The subcrenated ark shell Scapharca kagoshimensis (Tokunaga, 1906) is an epifaunal bivalve inhabiting the intertidal to subtidal zones along the coasts of central and southern Japan, Korea, and China.
However, little attention has been paid to the biological characteristics of the subcrenated ark shell, especially in terms of the seasonal changes in gonad development and spawning patterns.
The gonad of the subcrenated ark shell is not a discrete organ bur is arranged irregularly from foot to digestive gland; it is therefore difficult to determine gonad development from external observation.
The reproductive cycle of the subcrenated ark shell was examined by histological observation of the gonadal changes.
Thus, from December to March the sex of the subcrenated ark shell was unidentifiable.
The developing stage of the subcrenated ark shell occurred from April to July (Fig.