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Chlamys albida Arnold, 1906 (ex Dall, MS)

Common names: White scallop and Commercial scallop.

According to zonal-geographical terminology Ch. albida is a Pacific widespread high-boreal species (Fig. 1). It occurs from the Middle Primorye (Lutaenko, 1999) up to in the northern part of the Sea of Japan (Tatar Strait); along northern coastline of the Sea of Okhotsk; near Kurile Islands (Paramushir and Iturup); Commodore and Aleut Islands. It is registered at depths of 36-398 m in muddy sand with pebbles (Scarlato, 1981). This species occurs at temperature range of near-bottom waters from -0.79 to 4.79 C, salinity range of 33.05-33.43 and oxygen abundance from 5.67 to 6.40 mgl-1 (Myasnikov, 1985). At Kuriles, White scallops were more frequently inhabited by sponges Mycale adhaerens and Myxilla parasitica; and rarely by various hydrozoa, barnacles, bryozoa, algae, polychaetes, actinias and juveniles of bivalve mollusks (Myasnikov, 1986).

Fig01.jpg (3646 bytes) Figure 1. Natural habitat of the White scallop Chlamys albida Arnold, 1906 (ex Dall, MS) (by Scarlato, 1981 )
The growth rates of scallops from different regions of the Kurile ridge differ greatly from each other (Silina, Pozdnyakova, 1986). Nevertheless, approximately equal high rates of linear growth (up to 13.5 mmyr-1) are observed in all regions within the first three years (Fig. 2; Table 1). After this age, the most intensive linear growth is observed in mollusks inhabited along the Sea of Okhotsk side of Onekotan Island, where the shell grows can amount up to 18 mmyr-1. After this age, the most intensive linear growth is observed in mollusks inhabited along the Okhotsk side of Onekotan Island, where the shell growth can amount up to 18 mmyr-1. The minimum shell growth was observed at Simushir Island (middle Kuriles). The annual shell growth did not exceed 13 mmyr-1 at this region and at Pacific Ocean waters of Onekotan Island. According to V. N. Zolotarev (1979) mollusks has three strongly pronounced stages of linear growth: juvenile, mature and senile. For Ch. albida, juvenile or fast growth stage finishes when the age of puberty is reached. The next stage (mature) is limited to age 10 years. Moreover, senile stage starts at 10 years when annual shell growth does not exceed 0.5-1.5 mm. Scallops reach marketable size (60 mm) at about 5 years (Table 1).

As well as in linear parameters, the weight of mollusks during their life is changed irregularly. Up to certain sizes (50-60 mm), weight increases by equal rates. Henceforward weight increase rates in scallops inhabiting the Sea of Okhotsk side of Onekotan Island are different from those of scallops from Pacific Ocean waters. Maximum weight increases (up to 23 gyr-1) are observed at the age of 5 years.

According to Myasnikov (1988), the population of Ch. albida from the northern part of the Sea of Okhotsk is represented by mollusks with shell height within 18-93 mm, at average of 68 mm. Nevertheless, individuals with the size of 70-80 mm (about 40 %) predominated. The average shell height correlates with inhabiting depths. Depth increases from 50 to 125 meters result in the average shell height increase from 41 to 73 mm. In addition, at depths of over 125 meters shell height decelerates markedly up to 62 mm.

The maximum age of scallops does not exceed 28-30 years. The age of sexual maturity is 3-5 years at shell height of 40-70 mm. The sex ratio (male : female) changes in population from 0.6:1.0 to 2.0:1.0. At North Kuriles mass spawning in population starts in June (Myasnikov and Kochnev, 1988).

Nowadays four commercial concentrations of Ch. albida are known along southern and northern coastlines of Northern Kurile Islands (Sea of Okhotsk side and Pacific Ocean side); at Simushir Island; in the Northern part of the Sea of Okhotsk (Myasnikov and Hen, 1990; Myasnikov et al., 1992).


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