Butter clams occur from the Aleutian Islands to northern California, and are common throughout British Columbia wherever suitable conditions occur. They live in a wide variety of soil types from pure sand to pure gravel, but the typical substrate is a porous mixture of sand, broken shell, and small gravel. They occur mainly in the lower third of the tidal zone, but are also found to a depth of 30 ft below the zero tidal level.
The butter clam, Saxidomus gigantea, was initially the targeted species of the intertidal clam fishery in British Columbia. It is a relatively large clam, attaining a length of 12 cm. The shells are heavy and solid, square to oval in shape. The external surface has prominent concentric striations and deep winter checks. Shells are yellow in colour in juveniles, changing to grey-white with age, but the colour is often affected by the type of substrate in which it lives. The internal surface is white and smooth, but not glossy. There is a strong prominent external hinge ligament and pronounced umbones.
Sexes of butter clams are separate and spawning takes place in late spring. Examination of gonad sections taken throughout the year show that spawning may occur as early as April and May, although spent gonads may be found at any time during the year.
Successful breeding is not a regular occurrence on British Columbian beaches. All age classes are not equally represented in the various populations and successful reproductive years are infrequent. There is evidence that some populations may fail to spawn in some years, and these irregular seedings result in fluctuations in adult populations.
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