Victor V. Ivin, Vasily Z. Kalashnikov, Sergey I. Maslennikov and Vitaly G. Tarasov. 24.1 INTRODUCTION. Scallops are the most intensively consumed and fished ...
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Chapter 24
Scallops Fisheries and Aquaculture of Northwestern Pacific, Russian Federation Victor V. Ivin, Vasily Z. Kalashnikov, Sergey I. Maslennikov and Vitaly G. Tarasov
24.1 INTRODUCTION Scallops are the most intensively consumed and fished bivalve molluscs in Russia. There are more than ten scallop species found within the seas of the Russian Federation. The best known is the Yesso scallop, Mizuhopecten yessoensis, also referred to as the Ezo scallop, giant scallop, Japanese scallop, Russian scallop, Primorsky scallop and common scallop. For a long time these molluscs have been the focus of traditional fishing in the coastal waters of the Sea of Japan, Southern Sakhalin, and the Southern Kurile shoal. Commercial scallop beds, averaging 4,000 tons per year, can be found in the Barents Sea (Chlamys islandica), the Bering Sea (C. behringiana), the Kurile Islands and northern Primorye (C. albida and C. chosenica), and in Peter the Great and Posjet Bays of the Sea of Japan (C. farreri). This chapter reviews the biology and ecology of eight scallop species from the Russian part of the northern Pacific Ocean. Fishery statistics and typical technologies used at these commercial aquaculture farms are also presented. 24.2 TAXONOMIC STATUS According to (Kafanov 1991; Kafanov and Lutaenko 1998) there are eight species of Pectinidae in the Russian part of northern Pacific Ocean. Their taxonomic status follows: Class Bivalvia Linné, 1758 Order Pectinida H. Adams et A. Adams, 1857 Family Pectinidae Rafinesque, 1815 Genus Chlamys Röding, 1798 Chlamys (Chlamys) albida Arnold, 1906 (ex Dall, MS) Until recently, this species was confused with C. islandica (Müller, 1776) C. (C.) asiatica Scarlato, 1981 C. (C.) behringiana (Middendorff, 1849) C. (C.) chosenica Kuroda, 1932 Until recently, this species was confused with C. rosealba Scarlato, 1981 C. (Azumapecten) farreri (Jones et Preston, 1904)
1164 Until recently, this species was confused with C. farreri nipponensis Kuroda, 1932 or C. nipponensis Kuroda, 1932 C. (Swiftopecten) swifti (Bernardi, 1858) Genus Delectopecten Stewart, 1930 Delectopecten randolphi (Dall, 1897) Genus Mizuhopecten Masuda, 1963 Mizuhopecten yessoensis (Jay, 1857) 24.3 BIOLOGY AND ECOLOGY 24.3.1 Chlamys albida (Common names: white scallop and commercial scallop) Chlamys albida is a widespread, high-boreal, Pacific species (Fig. 24.1). It occurs from Middle Primorye (Lutaenko 1999) up to the northern part of the Sea of Japan (Tatar Strait), along the northern coastline of the Sea of Okhotsk, and near the Kurile (Paramushir and Iturup), Commodore and Aleut Islands. It lives in muddy-sands with pebbles at depths between 36–398 m (Scarlato 1981). Environmental ranges are typical for near-bottom waters: temperature -0.79 to 4.79°C, salinity 33.05–33.43‰ and oxygen concentrations from 5.67 to 6.40 mg L-1 (Myasnikov 1985). At Kurile, white scallops were more frequently fouled by sponges Mycale adhaerens and Myxilla parasitica and rarely inhabited by various hydrozoa, barnacles, bryozoa, algae, polychaetes, actinias and juveniles of bivalve molluscs (Myasnikov 1986). The growth rates of scallops from different regions of the Kurile Ridge differ greatly from each other (Silina and Pozdnyakova 1986) but approximately equal and high rates of linear growth (up to 13.5 mm yr-1) are observed in all regions during the first three years (Fig. 24.2; Table 24.1). After this age, the most intensive growth is observed in scallops living along the Sea of Okhotsk side of Onekotan Island, where shell growth is up to 18 mm⋅yr-1. Minimum shell growth was observed at Simushir Island (middle Kuriles) where the annual rates did not exceed 13 mm yr-1 and in Pacific Ocean waters of Onekotan Island. According to Zolotarev (1979) these molluscs have three strongly pronounced stages of linear growth: juvenile, mature and senile. For C. albida, juvenile or fast growth stage finishes when the age of puberty is reached. The next stage (mature) is limited to 10 years. 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 24.1). Scallop weights also change irregularly with age. In scallops up to 50–60 mm, weight increases by equal rates. After this size, the rate of weight increase in scallops inhabiting the Sea of Okhotsk side of Onekotan Island differs from that of scallops from Pacific Ocean waters. Maximum weight increases (up to 23 g yr-1) are observed at the age of 5 years.
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Figure 24.1. Natural habitat of the White scallop Chlamys albida Arnold, 1906 (ex Dall, MS) (by Scarlato 1981). A – map showing known commercial assemblages.
Table 24.1 Shell height (mm) and ages of commercial Chlamys scallops in the northwest Pacific, mm ± s.d. Age (years) 0.5 1.5 2.5 3.5 4.5 5.5 6.5 7.5 8.5 9.5 10.5 11.5 12.5
C. albida C. behringiana (Silina and Pozdnyakova 1991) 7.5 ± 0.6 8.6 ± 0.9 19.7 ± 1.0 19.0 ± 1.9 31.6 ± 1.4 31.3 ± 1.9 43.5 ± 1.5 44.0 ± 2.0 54.9 ± 1.5 55.9 ± 2.0 64.5 ± 1.5 65.4 ± 2.2 71.4 ± 1.5 72.5 ± 2.4 77.0 ± 1.8 76.9 ± 2.4
C. chosenica (Silina and Pozdnyakova 1990) 9.6 ± 0.5 23.5 ± 0.5 35.1 ± 0.6 45.0 ± 0.6 53.2 ± 0.6 59.2 ± 0.6 63.5 ± 0.6 66.7 ± 0.6 69.6 ± 0.6 72.0 ± 0.6 74.4 ± 0.7 76.2 ± 0.8 77.4 ± 1.2
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Figure 24.2. Growth rates of the White scallop Chlamys albida at Okhotsk Sea and Pacific sides of Onekotan Island, Kurile Islands (by data of Myasnikov, Kochnev 1988). A - Total shell height, mm. B - Annual shell growth, mm.
According to Myasnikov (1988), the size range in the population of C. albida from the northern part of the Sea of Okhotsk includes scallops with shell heights between 18– 93 mm (average of 68 mm) but individuals within the size of 70–80 mm (about 40%) were most common. The average shell height correlates with depth. As depth increases from 50 to 125 meters the average shell height increases from 41 to 73 mm. At depths of over 125 m, average shell heights decreased to 62 mm. The maximum age of these scallops does not exceed 28–30 yr. The age of sexual maturity is 3 to 5 years with shell heights between 40–70 mm. The sex ratio (male to female) changes from 0.6:1.0 to 2.0:1.0. At North Kuriles, mass spawning in population starts in June (Myasnikov and Kochnev 1988). There are four commercial concentrations of C. albida along the southern and northern coastlines of Northern Kurile Islands (Sea of Okhotsk side and Pacific Ocean side), at Simushir Island and in the Northern part of the Sea of Okhotsk (Myasnikov and Hen 1990; Myasnikov et al. 1992). 24.3.2 Chlamys asiatica (Common name: Asiatic scallop) Chlamys asiatica is a high-boreal, Asian-Pacific species (Fig. 24.3). The Asiatic scallop occurs on Kurile Island, on the eastern coast of Kamchatka Peninsula and in the
1167 Bering Sea (Anadyr Bay). It lives in sandy substrates mixed with shingle and muddy sands at depths between 80–120 m (Scarlato 1981). It was rarely found in its natural habitat. 24.3.3 Chlamys behringiana (Common name: Bering Sea’s scallop) Chlamys behringiana is a widespread, high-boreal, Pacific species (Fig. 24.4). It occurs within the Sea of Okhotsk at Sakhalin and Aniva Bays, the Strait of Laperuz, the southern and eastern waters of Kamchatka Peninsula, and the Kurile Islands (Paramushir and Shikotan). It is also found in the Bering Sea and in the Arctic Ocean at the southern part of the Chuckchee Sea and Sea of Beaufort. It is found at depths between 24–200 m in muddy sands mixed with shingle and gravel and in gravel with pebbled substrates (Scarlato 1981). Environmental ranges have been reported by Myasnikov (1985) for temperature (0.79 to 4.79°C), salinity (33.05–33.43‰) and oxygen concentrations (5.67 to 6.40 mg L-1). Bering Sea’s scallops are often inhabited by hydroids, Eunephtya sp., and ascidians, Pyaridae sp. (Myasnikov 1986). According to Buyanovsky (1999), larger scallops are observed at Karaginsky Island (size: 72.7 mm, age: 10–15 yr) and at Olyutorsky Bay (size: 83.3 mm, age: 20–25 yr). After these ages, shell height does not change. Higher growth rates in scallops from Olyutorsky Bay are probably linked to the more intensive water exchange via the main branch of Kamchatka Current.
Figure 24.3. Natural habitat of the Asiatic scallop, Chlamys asiatica Scarlato, 1981 (Scarlato 1981).
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Figure 24.4. Natural habitat of the Bering Sea’s scallop Chlamys behringiana (Middendorff, 1849) (Scarlato 1981).
The maximum age of the Bering Sea’s scallop is 35 years old but most of the older population is 25–28 years old. The most intensive growth period is observed during the first two years and can be as high as 15 mm yr-1. Between the ages of 3–6 yrs, the shell typically grows 4.2–11.5 mm yr-1. Then, at the age of sexual maturity, growth rates decrease considerably until they reach 1.6–1.2 mm yr-1 in 10-year-old scallops (Silina and Pozdnyakova 1991). Scallops reach marketable size (60 mm) in about 6 years (Table 24.1). Scallop weights increase almost in proportion to their age (Buyanovsky 1999). 24.3.4 Chlamys chosenica (Common names: Pink scallop and White-pink scallop) Chlamys chosenica is a low-boreal, Asian Pacific species (Fig. 24.5). It occurs in the Sea of Japan along the Primorye coastline, at the western Sakhalin Island and the north western part of Hokkaido Island, in waters of the small Kurile Ridge and at Iturup Island. Pink scallops are found at depths between 13–2,030 m in muddy sands mixed with shingle and gravel and sometimes in sand or shell-rock substrates (Scarlato 1981). The pink scallop is a eurybiontic species occurring at temperatures ranging from -0.09 to 13.03°C, salinities ranging of 33.34–34.15‰ and oxygen concentrations ranging from 5.49 to 7.49 mg L-1 (Myasnikov 1985). Along the coast of Northern Primorye, pink scallops are mainly colonised by the gastropod Vetulina sp. (Myasnikov 1986).
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Figure 24.5. Natural habitat of the Pink scallop, Chlamys chosenica Kuroda, 1932 (Scarlato 1981). A – map showing known commercial populations.
According to Silina and Pozdnyakova (1990), the population from the northern Primorye is characterised by scallops with shell heights up to 90 mm. The size distribution is a uni-modal curve with most individuals measuring 68–81 mm (peak at 77– 76 mm). The maximum age of scallops is 22 years but most of the population is 11–12 years old.
1170 The most intensive time of growth is observed within the first two years and can be up to 16 mm yr-1. Between the ages of 3 to 6 years the shell grows by 5.2–10.8 mm yr-1. At the age of sexual maturity, growth rates decrease to 2.5–1.0 mm yr-1 in 10-year-old scallops. Pink scallops reach marketable size (60 mm) in about 6 years (Table 24.1). In 9 to 14 year old scallops, with an average shell height of 70–79 mm, the muscle weight ranges from 7.4–10.4 g. In four years, from 10 to 14 yr, muscle weight increases by not more than 25% and shell weight increases by least by 50%. At the same time, the muscle comprises 20–25% of the total weight of the mollusc whenever shells comprise 44–52%. The sex ratio (male to female) in these populations is approximately 1.0:1.2. The domination of females (55%) implies stable status. Spawning of the population takes place in the first half of summer (Silina and Pozdnyakova 1990). 24.3.5 Chlamys farreri (Common names: Japanese scallop, Chinese scallop, Farrer’s scallop, Akazara scallop) Chlamys farreri is a subtropical, Asian-Pacific species (Fig. 24.6). In the Sea of Japan it is widely distributed along the southern coasts. This is the northern border of its natural habitat. It also occurs at Middle Primorye and Japanese Island at depths from 0.5 to 24 m (Scarlato 1981). The scallop is mainly found in gravel and pebbled habitats. Frequently these scallops form many-tiered reefs in the rocks and oyster banks. Settlement densities can vary between 150–180 specimens m-2 (in reefs) at depths of 1.5– 2.5 m. At other depths, their density decreases to 5–10 specimens m-2. This species occurs at a temperature range of 19–22°C and a salinity range of 32–34‰. This species is a candidate for mariculture and fishery in East Asian countries (Wang and Shieh 1991). In Russia, the Japanese scallop is one of the most prominent species for commercial fishing and mariculture (Bregman 1982; Afreichuk 1992a). According to Afreichuk (1992a), the population of C. farreri from Posjet Bay includes scallops with shell heights of up to 112 mm but most individuals measure 70–80 mm. The maximum age of this species is 9 years but most of the population is three (35%) or four (27%) years old. After age 6, natural mortality increases and results in only 12% of population being older than 6 years. The most intensive growth period is observed in the first three years and can be as high as 19 mm⋅yr-1. Between the ages of 4 and 7, the shell grows by 5.8–11.5 mm yr-1. After this, growth rates decrease (Afreichuk 1992b). These scallops reach marketable size (72 mm) in about 3–4 years. At that time the muscle weighs about 5.5 g. The muscle weight of a 5-year-old scallop with average shell height of 90 mm is 11 g. In total, the muscle comprises 12–14% of the total weight of the scallop and the shells amounts to 63% (Afreichuk 1990). The age of sexual maturity is 2 years old with shell heights typically 40–45 mm (Table 24.2). The approximate sex ratio (male to female) in population is 1:1.36. At Posjet Bay spawning of the population starts at the end of June when the temperature of near-bottom waters approaches 16°C. The mass spawning (average 65 days) begins in the middle of July at temperatures of 18–20°C and ends at the end of August or early in September (Afreichuk 1992a).
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Figure 24.6. Natural habitat of the Japanese scallop, Chlamys farreri (Jones and Preston, 1904) (Scarlato 1981).
Table 24.2 Shell height (mm) of different ages of Japanese scallop Chlamys farreri at southern part of the Sea of Japan (Bregman 1982), mm ± s.d. Age (years) Shell height (mm)
1 2.70 ± 0.96
2 4.30 ± 1.50
3 5.85 ± 0.90
4 7.00 ± 0.96
5 7.80 ± 0.96
1172 At Peter the Great Bay larvae occur in plankton during the warmest months (July and August) at water temperatures between 15–20°C (Kas’yanov et al. 1980). The maximum density of larvae occurs in shallower bights between 5–7 m (Afreichuk et al. 1988). The period of settling on hard and fibrous substrate (depths up to 23 m) continues from the middle of July to early August. The optimal depth for spat collection is 5–8.5 m (Gabaev 1988). The density of juvenile settlement on collectors can reach a maximum of 229 and an average of 48 specimens m-2 (Afreichuk et al. 1988; Gabaev 1990b). The morphology of larvae and larval shell structure were described by Kulikova et al. (1981). 24.3.6 Chlamys swifti (Common name: Swift’s scallop) Chlamys swifti is a low-boreal, Asian-Pacific species (Fig. 24.7). It is distributed along the southern coasts of the Sea of Japan, in Western Sakhalin, Hokkaido and northern waters of Honshu Island. In the Okhotsk Sea Swift’s scallops have been found in southern Sakhalin (Aniva Bay) and in shallow waters of South Kurile Shoal. The scallop mainly inhabits the gravel, pebbled and shell areas at depths of 2–143 m (Scarlato 1981). This species occurs within a temperature range of 9 to 22°C and a salinity range of 32– 34‰. According to Ponurovsky (1982) and Ponurovsky and Silina (1983), the population of C. swifti from the Northern Primorye is characterised by scallops with shell heights up to 121 mm, but individuals measuring between 65–90 mm predominate. The maximum age of scallops is 13 years, but the majority of the population is five years old. Swift’s scallops grow throughout their lifetime. However, the greatest growth period is observed during the first three years after settling on the bottom and can be as high as 21–26 mm yr-1. After 4 years old, linear growth rates decline and are only 1.0 mm yr-1 in 8-year-old individuals (Ponurovsky 1977; Ponurovsky and Silina 1983). The highest growth rates were found in regions of the Sea of Japan, Petrov and Putyatin Islands, and Vostok Bay (Table 24.3). These areas are more favourable for intensive growth of Swift’s scallop (Ponurovsky 1982). The sexual maturity is reached at 3 years when shell heights are 50–70 mm. The approximate sex ratios (male to female to hermaphrodite) in the population are 1.0:0.67:0.02 (Denisova 1981). By the age of 3, males predominate (86.3%) in the population. Later, the percentage of males declines. By the age of 10, females predominate (81.2%) the population. At Peter the Great Bay and Bousse lagoon (southern Sakhalin Island) larvae are abundant in the plankton from August to September in water temperatures between 15– 20°C. The maximum density of larvae occurs in near-bottom waters at depths of 10–20 m (Kas’yanov et al. 1983). The morphology of larvae and larval shell structure were described by V. A. Kulikova with co-authors (1981). The optimal depth for spat collection is greater than 15 m (Gabaev 1988).
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Figure 24.7. Natural habitat of the Swift’s scallop, Chlamys swifti (Bernardi, 1858) (Scarlato 1981).
Table 24.3 Shell height (mm) of Swift’s scallop, Chlamys swifti in the northwest part of the Sea of Japan (Ponurovsky 1982), mm ± s.d. Age years 1 2 3 4 5 6 7 8 9 10 n
Region (from southern to northern) of scallops collection Furugelm Vityaz Stenin Klykov Putyatin Island Inlet Island Island Island 29.7±0.5 26.7±0.4 21.2±0.5 24.3±0.4 29.3±0.2 44.1±1.0 37.4±0.7 32.3±1.0 34.9±0.8 45.8±0.4 62.3±1.7 52.8±1.5 48.9±1.6 49.4±1.4 67.2±0.6 87.4±1.8 70.2±20.1 67.6±2.0 69.1±1.7 90.6±0.6 95.1±1.4 87.5±2.0 86.1±1.9 87.9±1.7 106.4±0.4 101.5±1.5 97.8±1.9 96.9±1.4 99.8±1.7 112.9±0.4 102.3±1.8 104.4±1.7 102.1±1.2 105.3±1.3 116.8±0.5 104.5±2.5 107.1±1.4 105.3±1.2 109.1±1.3 118.6±0.6 105.6±2.7 107.4±1.6 106.5±1.3 111.3±1.5 120.6±0.7 No data No data 107.2±1.4 112.1±1.4 121.1±1.0 22 33 30 43 243
Vostok Bay 21.3±0.2 45.8±0.6 70.3±0.7 88.9±0.7 100.3±0.7 105.7±0.8 106.7±0.9 108.7±1.1 109.0±1.5 No data 160
Melkovodnaya Inlet 24.2±0.4 40.0±0.7 60.58±0.7 81.3±0.7 94.7±0.6 98.8±0.6 102.0±0.6 104.0±0.8 105.6±0.9 106.2±1.7 51
Petrov Island 29.8±0.3 47.3±0.5 69.8±0.6 90.5±0.5 101.6±0.5 105.1±0.5 107.5±0.6 109.6±0.8 110.8±0.9 110.5±0.8 219
1174 24.3.7 Delectopecten randolphi (Common name: Randolph’s scallop) Delectopecten randolphi is a widespread North Pacific species (Fig. 24.8). It is found in the Sea of Japan at Posjet Bay, Peter the Great Bay, and the eastern coastline waters of Honshu Island (Sagami Bay). It is also found in the Okhotsk Sea along eastern and western coastlines and in the Bering Sea along the eastern coastline. The Randolph’s scallop inhabits muddy areas at depths of 418–3,080 m (Scarlato 1981). Its temperature range is 0.2–2.5°C. The largest specimen known had dimensions of 23.5 x 27.0 mm and was found in Peter the Great Bay. 24.3.8 Mizuhopecten yessoensis (Common Names: Yesso scallop, Ezo scallop, Giant scallop, Japanese scallop, Russian scallop, Primorsky scallop and Common scallop) The Yesso scallop, Mizuhopecten yessoensis, is a low-boreal, Asian-Pacific species (Fig. 24.9) with the highest commercial value of all the Pectinidae. It is found along the northern coastline of the Korean peninsula, the coastline of Primorye, near the shores of the Sakhalin islands, South Kuriles and Hokkaido and on the northern coastline of Honshu Island (Scarlato 1981).
Figure 24.8. Natural habitat of Randolph’s scallop, Delectopecten randolphi (Dall, 1897) (Scarlato 1981).
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Figure 24.9. Natural habitat of the Yesso scallop, Mizuhopecten yessoensis (Jay, 1857) (Scarlato 1981 with additions). A and B – maps show known commercial assemblages at Sakhalin and Kunashir Islands.
24.3.8.1 Total populations and biomass The most exhaustive studies of the Yesso scallop were completed along the coasts of Primorye by Razin (1934), Biryulina and Rodionov (1972), Markovskaya (1951), Bregman (1979), and Kalashnikov (1986, 1991). In 1932, an estimated 40 million scallops inhabited some of the 16,000–17,000 hectares along the coast of Primorye. Between the 1940’s-1960’s, the scallop population in most areas decreased and in some places completely disappeared. From 1932 to 1959, the scallop stocks in Peter the Great Bay had reduced thrice. In the following decade, the abundance remained almost the same at 5,703 million scallops on 906 hectares with a biomass of 1,708 tons (Biryulina and Rodionov 1972).
1176 At the same time, a significant drop in the abundance of scallops was observed in the northern areas of Peter the Great Bay (Olga Bay) where the scallop population in 1932 was four times as high as it was in 1975 (Silina and Bregman 1986). According to Skalkin (1971), the biomass in Aniva Bay (southern Sakhalin) in 1969 was twice as low as compared to 1961–1962. The scallop populations became ten times as low in Terpenie Bay (northern Sakhalin) and some areas of the Kuriles. Most investigators believe that intensive industrial fishing caused the overall drop in scallop stocks. At the present time, commercial reserves of wild Yesso scallop along the coast of Primorye are exhausted due to overfishing during the last decade. 24.3.8.2 Distribution in Primorye The Yesso scallop was widely distributed in southern and middle Primorye where it is found in bays and coves and forms aggregations at depths between 6–30 m. These scallops were an object of traditional catching until the beginning of 1970’s. The map (Fig. 24.10) shows the locations of existing and potential plantations sites for bottom cultivation of this scallop species. Commercial populations were well known in Bays of Posjet, Ussuri, Amur, Vladimir, Vostok and Strelok. The average density of settlements on bottom grounds increased from 0.05 to 1.0 specimen m-2 (average 0.1 specimen m-2). Average individual biomass was 0.2–0.4 kg. At the present time, the average density does not exceed 0.001 specimen m-2 at sites described by other authors. 24.3.8.3 Distribution over depths In the shallows, the Yesso scallop occurs between depths of 0.5–1.0 m in small inlets protected from wind and waves. Minimum depth corresponds to the winter time water level under the ice cover. Most of the scallops were found in the range of 4–10 m in closed inlets and at depths between 20–25 m in open and relatively deep-water sites of bays and inlets. According to Razin (1934) this species is typically found between 14–30 m on the open coastline of Primorye, however some specimens are found at 48 m. Most of the scallops were found along the coastline at a depth of 20–25 m near rugged shores. This is apparently due to the corresponding range of spat settlement in the region, i.e., underwater rocks are substrate carriers for attaching scallop larvae. In Peter the Great Bay, scallops were recorded at a maximum depth of 82 m (Scarlato 1981). 24.3.8.4 Age structure of scallop settlements Biologists believe that this species does not live more than an average of eleven years (Tibilova and Bregman 1975) with a typical life expectancy ranging from 7 to 9 years (Makarova 1985). The most extensively studied populations in Primorye have no 1–2 year old specimens. Eleven-to-twelve year-old scallops are frequent but older specimens are rare (see Table 24.4). In some settlements, 70 percent of the individuals range in age from 8 to 16 years. Generally, the age structure of the scallop population of various
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Figure 24.10. Locations of existing and potential plantations for bottom cultivation of the Yesso scallop M. yessoensis in Primorye.
regions reflects the randomness of replenishment and presence of abundant and nonabundant generations (Fig. 24.11). 24.3.8.5 Scallop growth Fertilised eggs (average 60–70 micrometers in diameter) develop into larvae, which settle onto substrates (shell averages 260–285 µm) in 20–40 days, depending on temperature. Definitive development of scallops terminates on the substrate. The scallop detaches from the substrate in 3–4 months when the shell height is 10–30 mm. Subsequent scallop growth rate depends on temperature, feeding, water exchange, and many other conditions on the sea floor.
1178 Table 24.4 Age composition of Yesso scallop settlements at Peter the Great Bay (Silina and Bregman 1986). Number of specimens from respective age groups. Region Vityaz Inlet Stenin Island Priboinaya Inlet Shkota Inlet Andreev Inlet Putyatin Island Lake Vtoroe Melkovodnaya Inlet Olga Bay
1–2 ----15 -18 2 --
3–4 1 1 10 2 10 22 32 13 --
5–6 8 1 30 16 14 10 101 20 1
7–8 14 5 6 6 21 4 45 11 23
9–10 10 11 1 6 1 4 7 6 16
11–12 7 7 1 6 -4 -5 7
13–14 1 5 -2 ---1 1
The scallop shell grows isometrically to retain its initial form. Makarova (1985) calculated the general equation for the linear growth rate of the Yesso scallop: Ht = (160.92 ± 18.7) ⋅ (1 - e(-0.378 ± 0.04) ⋅ t),
(1)
where Ht is the shell height in mm and t is scallops age in years. The scallop grows at temperatures ranging from -2°C to 26°C. The optimal growth temperature is 4–6°C. In Primorye, the temperature optimum occurs in May-June and in September-October (Silina and Pozdnyakova 1986). Within the initial three years, the scallop height reaches 90–110 mm and then its growth slows exponentially (Table 24.5). The largest individuals occur at depths of 20 m in populations located on silty-sandy soils with good water exchange and relatively stable temperatures. These specimens reach 190–195 mm shell height or longer at the age of 16 and older. In the South Kurile shallows, specimens older than 20 years with shell heights of 220 mm are found (Skalkin 1966). In shallow silty inlets, scallops seldom exceed 150 mm and live for not more than 10–12 years. In Posjet Bay, we recorded the largest scallop specimen, whose dimensions were as follows: shell height 222 mm, length 202 mm, and width 37 mm. Scallop weights vary proportionally to its linear dimensions (Fig. 24.12; Silina and Pozdnyakova 1986). The proportion of muscle in scallop total mass amounts to 10–18% in various settlements of Peter the Great Bay (Belogrudov 1981). 24.3.8.6 Sex structure of settlements The average (male to female) sex ratio within populations is 1.0:1.0. Hermaphrodites were rarely observed (i.e., not more than 0.3–0.4% of all cases; Bregman 1979). In these populations, males dominated in younger generations and females dominated in older ones. By age 1–3 the sex ratio was 2.0:1.0, by age 5–6 it was 1.9:1.0 and by the age of 7– 8 the sex ratio was 1.0:1.9. This could be due to either sex specific different death rates or hermaphroditism.
1179
Figure 24.11. The age structure of the Yesso scallop population of various regions of Primorye. A – dispersal settlement from deep and open region of Posjet Bay; B – Olga Bay ribbon settlement; C – settlement of closed Vladimir Bay; D – settlement under kelp farm; E – shallow-water settlement in surf bay; F – shallow-water settlement in closed inlet; G – single scallops near surf shore; H – age composition (Razin 1934).
1180
Table 24.5 Linear growth of Yesso scallop Mizuhopecten yessoensis from various regions of natural habitat (by Silina and Pozdnyakova 1986). Region
Shell height at corresponding age (in numerator) and annual shell growth (in denominator), mm (mm±s.d.) 1 2 3 4 5 6 7 8 9 10 Furugel’m 50.2±1.2 101.4±1.2 125.9±1.3 141.4±1.9 151.8±1.8 156.4±2.5 Island 50.2±1.2 51.2±0.9 24.5±1.0 15.5±1.0 10.4±0.8 4.6±0.8 --------Bol’soi Pelis 89.8±4.2 120.4±3.2 139.1±2.1 147.8±2.4 151.5±2.6 151.8±2.8 Island --no data 30.5±1.0 18.7±2.0 8.7±1.8 no data no data ------Andreev 46.9±0.8 85.8±1.0 107.0±1.0 118.8±1.1 124.7±1.3 128.3±1.1 130.4±1.5 133.5±1.7 Inlet 46.9±0.8 38.9±1.0 21.2±1.0 11.8±1.0 5.6±0.9 3.6±0.8 2.4±0.6 3.0±0.8 ----Putyatin 50.7±1.6 90.8±1.2 115.3±1.0 128.5±1.1 135.7±1.8 141.1±1.0 Island 50.7±1.6 40.2±1.4 24.5±1.2 13.2±1.1 7.3±1.2 no data --------36.6±1.1 83.2±1.4 114.6±1.4 133.8±1.0 145.4±0.9 152.0±1.1 154.5±1.1 155.4±1.5 158.8±1.7 Olga Bay 36.6±1.1 43.8±2.2 30.4±2.0 14.0±1.6 11.0±1.3 no data no data no data no data --33.6±2.6 77.4±2.8 107.8±2.4 121.8±2.8 132.8±2.8 Vladimir Bay 33.6±2.6 43.8±2.2 30.4±2.0 14.0±1.6 11.0±1.3 ----------26.1±2.4 56.2±2.1 86.9±2.0 110.9±1.42 125.5±1.6 134.2±2.1 143.6±2.2 148.4±2.3 156.2±2.3 160.8±2.5 Aniva Bay 26.1±2.0 30.1±2.0 30.7±1.8 24.0±1.6 14.6±1.4 8.7±1.0 9.4±0.8 4.8±0.6 no data no data 24.9±5.8 75.2±8.4 97.9±10.4 119.9±8.2 130.7±8.4 138.4±5.2 141.2±3.9 143.0±4.8 Izmena Strait 24.9 50.3 22.7 22.0 10.8 7.7 2.8 1.8 ----South Kuril 20.7±5.5 56.9±6.8 89.0±11.5 119.1±12.2 141.3±11.1 150.3±8.7 155.3±7.7 158.4±7.5 161.3±8.0 Strait 20.7 36.2 32.1 30.1 22.2 9.0 5.0 3.1 2.9 ---
1181
Figure 24.12. Relationship between Yesso scallop weight and shell height in various settlements in Peter the Great Bay. Numbers represent scallop age in years.
24.3.8.7 Replenishment Scallop populations replenish annually owing to spawning, subsequent development of larvae in plankton, their settling on substrate and juveniles’ transition to free life on the seabed. 24.3.8.8 Spawning Spawning in scallop populations starts at temperatures ranging from 7–9°C. (Belogrudov 1981). In the waters around Primorye, spawning begins in the middle of May and spawning ends at the end of June. Spawning begins in shallow waters of
1182 southern regions. As the seawater warms up individuals from the deeper and more northerly settlements begin to spawn. Absolute fertility varies from 25–30 to 180 million eggs (Yamamoto 1964) depending on age and size. 24.3.8.9 Larvae morphology The morphology of larvae and larval shell structure of three widespread scallops: Yesso scallop M. yessoensis, Japanese scallop C. farreri and Swift’s scallop C. swifti have been described by Kulikova et al. (1981). All of the larvae are of triangular form and the anterior end is the apex of the triangle. The larvae are inequivalve. The umbos are low, rounded and poorly defined. The taxodonte hinge has several teeth at each side of the hinge line. The central hinge area is undifferentiated. Some specific characteristics were distinguished among the scallop larvae of Peter the Great Bay. The main differences are in the shell form, umbo form, shell size, and number of teeth at each side of the hinge line (Kulikova et al. 1981). 24.3.8.10 Development in plankton The duration of larval growth in the plankton lasts from 20 to 40 days (Kas’yanov et al. 1980). Current-induced distribution disseminates larvae to create new local settlements. Plankton surveys (Belogrudov 1981) show that larvae can form dense concentrations in Posjet and Peter the Great Bays over several square kilometers. In that case, higher densities are noted at areas with abounding adult scallops. In bonanza years, larval density reached 200–300 specimens per cubic meter in the closed inlets and at the same time, it did not exceed 20–30 specimens per cubic meter in the adjacent open inlets and bays. Long-term studies in Posjet Bay show the absence of direct spatial relations between parents and new scallop generations. On the eve of scallop cultivation, the number of sexually mature specimens in Minonosok Inlet in 1972 was 70,000. Ten years later, the number has increased up to 650,000 because of sowing culture (Fig. 24.13). The number of annually collected spat showed instability of larvae settling throughout all periods. Nor was there any sign of increases in the number of spat during the year. Apparently, the parent-larvae relationship was indirect because of great dilution of larvae pool by the water mass (Kalashnikov 1986). Water exchange with adjacent bodies of water (about 10% of waters every day is replaced by tidal) disturbed the parent-larvae relationships. A comparison of the age composition (Fig. 24.13) and the results of spat collection in various bays and inlets showed that intensity of replenishment changes asynchronously. Bonanza generations in one bay do not necessarily correspond to the same in another bay. For instance in 1980, the lowest spat settling rates (2–20 specimens per collector) were noted in Posjet Bay, but in Vostok Bay the collectors recorded 400–500 specimens each. It is of interest to note that during that year, red tides were absent in Vostok Bay but observed in Posjet Bay. However, these distinctions were also noted in other bays without red tides, and this suggests that the intensity of replenishment is a local characteristic.
1183
Figure 24.13. Dynamics of spat collection (A) and size of the Yesso scallop population of Minonosok Inlet (B).
1184 24.3.8.11 Migration behaviour Yesso scallops can freely move along the sea floor. The mechanism of reactive movement of freely living scallop is widely known (for example: Dautov and Karpenko 1983). Researchers have noted random movement in natural conditions or individual scallop behaviour in aquarium. These observations support the idea that the scallop is a migrating species. However, the observation that populations are present for many years in specific sites shows that ability of scallops to migrate is limited. 24.3.8.12 Risk factors 24.3.8.12.1 Abiotic factors Survival rates of pelagic larvae at metamorphosis depend on water temperature (ranges for survival is 5–20°C, with an optimum at 10–15°C), salinity (30–40‰, optimum at 33‰), density (optimum 8 specimens⋅mL-1), quantity and composition of food and on the abundance of predators (Belogrudov 1973; Bregman and Guida 1983; Chan 1989). At attachment, mortality is mainly caused by the absence of suitable substrate and intolerance to changing environments (Yamamoto 1964; Belogrudov 1973). Bregman and Guida (1983) reported that the number of attached juveniles resulted from only 5–8% of all fertilised eggs. Settling on the bottom is the next critical period in the life history of the scallop and here the mortality increases sharply. According to Yamamoto (1964), only 5– 10% or sometimes none of the settled juveniles survive. Golikov and Scarlato (1970) reported that only 4% of the settled juveniles survived as long as 6 months. Only Golikov and Scarlato (1970) have reported on the mortality of older scallops. These researchers conjectured that after 6 months the quantity of survived scallops decreased gradually. Moreover, they noted that winter was the period during which the highest mortality of scallops occurred off the north western coastline of the Sea of Japan. In contrast, in Honshu Island, the most difficult season for scallop survival is summer and early autumn when water temperature increases to above 15°C (Yamamoto 1960). Recent investigations (Silina 1996) also show the highest mortality when scallops were less than 2 years. Mortality of 2 to 5 year-old scallops is minimal. By 6–7 years of age (probably the beginning of the senile period of scallop development) and upwards to 9–10 (transition to the old-aged stage) scallops mortality increased sharply. 24.3.8.12.2 Storms Storms are another factor, which cause mass mortalities of scallops in coastal shallow settlements. Depending on local topography, storms can increase settlement dispersion over vast flat areas or make them denser at the foothills of cliffs. In either case, a considerable number of scallops are buried under moving soil. Near shallow coasts, particularly beaches, the majority of scallops die in storm debris. Even small storms deform settlements but the loss is usually compensated by annual replenishment. While the typhoons (annual frequency about 50%) are natural calamities for the benthic coastline
1185 populations, including the scallop, they destroy most of the species around open waters at 20 m deep. By counting the number of shells in the breaker zone of only one beach following typhoon “Ellis” in 1983, researchers revealed the simultaneous death of 10,000 specimens of different ages. In a similar count in 1986 after typhoon “Vera”, we discovered as many as 72,000 specimens in debris (Kalashnikov 1984). The joint effect of various factors on the sea floor populations shows perennial changes in density of artificial scallop populations, which regularly declined in all cases during the first cultivation season. The decline was greater in more open and unprotected waters (Fig. 24.14; Kalashnikov 1985). 24.3.8.12.3 Predators The first hours and days on the sea floor after the scallops become one year old (shell height about 30 mm) appeared to be the most dangerous. During this period, natural death is maximal and young scallops are preyed upon by various starfish species such as Asterias amurensis Lütken, which can grow up to 165 mm (radius) and weigh up to 450 g. Another species, Distolasterias nipon (Döderlein) is even larger growing up to 250 mm with an average weight of 1,000 g. These starfish species attack scallops of the same or younger ages. The one-time ration of one starfish increases from 1 up to 8.5 g of fish and annually amounts to 400–450 g (Biryulina 1972). In view of the great abundance of these predators (density can be up to 15 specimens m-2), the damage to scallop populations can be considerable. The death rate of young scallops located in super dense aggregations (over 100 specimens m-2) in which predators temporarily eat only scallops is especially high. When storms are so strong that they reach the sea floor scallops become weaker and readily accessible to predators. The joint effects of storms and starfishes have destroyed an artificial scallop settlement (about two hectares) with a population of over 200,000 specimens. Under stable conditions, starfish and scallops were noted to co-exist when they occupied a single habitat for several years in succession. Generally, however, the number of cultivated molluscs declines more in sites where starfish are more abundant. Sowing spat are also preyed upon by various benthic fishes such as flounders and bullheads. Other predators of sown seed and adult scallops are of lesser importance but nevertheless pose a threat to small seed and juveniles. These include the octopuses, king crabs, Paralithodes camtschatica (Tilesius), and hermit crabs (Kalashnikov 1986). Crabs predate mainly on seed scallops present in large numbers. For example, during seasonal migrations, crabs can greatly denude newly seeded grounds. Some predatory gastropod molluscs pose a threat to both juveniles and adult scallops. Belogrudov (1973) reported that the drilling Muricidae gastropod Boreotrophon candelabrum (Adams et Reeve) and Tritonia japonica (Dunker) could attack and eat the scallops. At natural population levels, 14–27% of adult scallops had drilling marks on the shells. Gabaev and Kolotukhina (1999) reported that two-year scallops (shell height up to 73 mm) in the cages are preyed upon the gastropod Nucella heyseana (Dunker).
1186
Figure 24.14. Density of Yesso scallops plantations in Posjet Bay (number m-2). 1 = closed lagoon; 2 = protected island terrace; 3–6 = sites of open waters.
1187 24.3.8.12.4 Parasites In comparison to other cultured bivalves, such as oysters and mussels, little is known about the parasites and diseases of scallops. Epizootic diseases, like those that have devastated the oyster culture industry in parts of the world, have not been encountered by the scallop culture industry. The relative lack of information on parasites and diseases in scallops may be attributed to less intensive cultures and comparatively fewer investigations. Infection of scallops by parasites is low, as the parasitic fauna is scarce and includes only a few potentially pathogenic species. Mass scallop deaths caused by parasites have never been recorded. There are only 17 parasites and commensals now associated with scallops (Kurochkin et al. 1986; Kovalenko 1990; Plyusnin 1990; Rakov 1990; Didenko 1996). Sirolpidium zoophthorum Vishniac, 1955 (Lagenidiales) This fungus was found in 1972 in juveniles at a scallop farm in Posjet Bay. Myxosporidia gen. sp. (Myxosporea) Local pestholes, which probably were caused by unknown Myxosporidia, were noted at a scallop farm in Minonosok Inlet (Posjet Bay) in April of 1996. Perkinsus sp. (Sporozoa) They were unknown until 1979 when a spherical cyst (0.2–03 mm in diameter) of Perkinsus sp. was found in 86% of discovered scallops (intensity of invasion by 1–2 cysts). Occasionally they can pose serious threats to scallop spat. Conceivably it was introduced with scallop seed from Aomori prefecture, Japan. Pectenita golikowi Jankowski, 1973 (Ciliophora) Almost all scallops are affected by this endoparasitic infusoria. Intensity of invasion is several tens of individuals within a scallop’s intestine. Pathogenic effects on the host are unknown. Trichodina pectenis Stein, 1974 (Ciliophora) See below. Trichodina sp. Stein, 1974 (Ciliophora) These two species of endoparasitic infusoria were described in the mantle of Yesso scallops. Intensity of invasion is 20–100% and by several tens of specimens. Pathogenic effects on the host are unknown but probably caused by a secondary parasite. Cliona sp. (Porifera) This drilling parasitic sponge causes extensive invasions of up to 70% on lower (right) valve and up to 10% on upper (left) one.
1188 Hirudinea gen. sp. (Hirudinea) Leeches were found in the mantle on isolated instances. Podocotype spp. (Trematoda) Approximately 1% of all scallops are affected by trematode metacercaria, which were found in various tissues (including adductor muscle). Intensity of invasion is only one specimen per scallop. Anisakidae gen. sp. (Nematoda) Larvae of these nematodes were found in the digestive system on isolated instances. Ohridiidae gen. sp. (Nematoda) Ohridiidae affects approximately 73% of scallops. Larvae of these nematodes were found in the mantle with intensity of invasion up to 17 specimens per scallop. Polydora ciliata (Johnston, 1838) (Polychaeta) This widespread and well-known drilling polychaete is responsible for loss of market quality among cultivated and natural Yesso scallops. It has a larger effect on the upper (left) valve. The burrows excavated by Polydora in scallop shells cause unsightly blisters containing compacted mud. Approximately 75% of scallops have wormholes and blisters. Since 1974 infestation of scallop shells by the boring polychaetes has increased as siltation of the bottom increases (Silina et al. 2000). Polydora websteri Hartmann, 1943 (Polychaeta) Burrows and blisters of this species are indistinguishable from ones of P. ciliata. Dodecaceria concharum Oersted (Polychaeta) These drilling polychaete have wormholes similar with ones of Polydora. They can use old holes created by other polychaetes and sponges. Herrmannella longicaudata G. Avdeev, 1975 (Copepoda) These small (maximal length up to 2.2 mm) cyclopoid copepods were found in approximately 73% of Giant Yesso and Swift scallops. Pathogenic effects on the host are unknown even in the case of great abundances. Average intensity of invasion by commensals is nine specimens in the mantle. Odostomia fujitanii Yokogawa, 1927 (Gastropoda) O. (Evalea) culta Dall et Bartsch, 1906 (Gastropoda) These small (maximal shell height up to 5 mm) littoral gastropods often prey on various bivalves as temporary parasites. Gastropods feed with using a long proboscis, which they introduce between shell valves.
1189 24.3.8.12.5 Bacterial contamination Numerous species of bacterial contaminants have been identified from cultivated scallops (Table 24.6; Avdeeva and Filipchuk 1988, Kovalenko 1989, Plyusnin 1990, Plyusnin and Cherkashin 1991, Kovalenko 1994). A total of 29 species were identified from scallop farms. Most of them are Gram-negative bacteria (22 species). Some of them (e.g., Aeromonas, Vibrio and Pseudomonas) are potentially pathogenic in situations where environmental culture conditions are poor. 24.3.8.12.6 Epibionts Natural and farmed scallops are an excellent substrate for the settlement of many other organisms (collectively called fouling communities). Marine organisms that occur on scallop shells may be competitors for space and food. Epizoans may also reduce water flow and food accessibility. 24.4 FISHING AND AQUACULTURE 24.4.1 Fishing 24.4.1.1 History Paleontological and archaeological studies reveal that the people inhabiting the coastal areas of the Far East had, from time immemorial, used marine organisms, including bivalve molluscs, to develop their national economy (Krasnov et al. 1977). A unique Yankovsky culture of shell mounds has been found in many regions (Okladnikov and Derevyanko 1973) dating from the Paleolithic age (25,000–30,000 years BC). Numerous shell concentrations suggest that the inhabitants of the coasts of Sakhalin, the Kuriles, Japan, Primorye and Korea preferred gastropods, mussels, and scallops. We still do not know how ancient people obtained the scallops. Without any suitable gear and boats they may have only been able to collect them from storm debris. The subsequent history of scallop fishing in Primorye is known from descriptions by pioneer explorers of Ussuri Region, including N. M. Przevalsky and V. K. Arseniev. Russian merchants recall that during the last century Yesso scallops were exported as seasoned meats (muscles). Scallops were fished in Vladimir Bay and sold to China. The second half of the 19th century saw further development of scallop fishery along with the settlement of the Russian Far East. This was supported by its value and by the boundless demand on the local market. By the 1920’s, the price for Yesso scallop in Vladivostok was as high as 10 rubles per 100 molluscs. During that time, they fished scallops in shallow bights using one-or-two-pronged lances and scoop nets (while watching it from the surface through a glass-bottom box), primitive dredges and cords (Razin 1934).
1190 Table 24.6 Known bacteria of Yesso scallop Mizuhopecten yessoensis cultivated in Peter the Great Bay at cages and bottom ground (compiled from Avdeeva and Filipchuk 1988; Kovalenko 1989; Plyusnin 1990; Avdeeva et al. 1991; Plyusnin and Cherkashin 1991; Kovalenko 1994) Cg = Cages; Gr = Ground
Species Gram-negative Pseudomonas sp. P. putida Yersinia ruckeri Vibrio sp. V. anguillarium V. parahaemolyticus Aeromonas hydrophila A. punctata A. salmonicida A. s. achromogenes A. s. masoucida A. dourgesii Aeromonas sp. Plesiomonas sp. Bacteroides sp. Moraxella sp. Acinetobacter sp. Alcaligenes sp. Chromobacterium sp. Flavobacterium breve F. halmephilum Enterobacteriaceae g. sp. Gram-positive Micrococcus sp. Leuconosfoe sp. Streptococcus sp. Listeria sp. Corynebacterium sp. Artrobacter sp. Lactobacter sp.
1987 C
1988 Gr Cg
1989 Gr Cg
1990 Gr Cg
1991 Gr Cg
+ --+ --+ -----+ + + --+ -+ + +
+ --+ -----+ --+ + + -+ + + + ---
--+ + -----+ --+ ----+ -+ ---
+ -+ + -+ --+ + + + + ----+ + + -+
+ + + + -----+ + + + + ---------
+ --+ -+ + --+ -+ + -+ + -+ -+ ---
+ --+ -+ ------+ ----+ -----
-+ + -+ + + + ---+ -+ ---+ -+ ---
---+ -+ + ----+ -----+ -+ ---
----+ + --
+ + + + ----
+ + -+ ----
+ -+ --+ +
--+ + + ---
+ + + + -+ --
+ --+ ----
-+ --+ + --
+ -------
1191 24.4.1.2 Fishing gear Dip-nets were used to fish Yesso scallops in clear water and quiet weather. The pole was 8 m long and the average haul was 50–60 specimens per day, though it could be much higher in shallower waters with excellent weather. Following rain storms the turbid water made this virtually impossible. Initially only simple dredges (about 75 cm wide) were used for fishing scallops. They were towed by small sampans, whose prototypes were brought by members of an expedition led by N. N. Muraviev-Amursky, the first governor-general of the Ussuri Territory, together with boats from neighbouring countries. Their displacement was 1–1.5 t, and they used sails or one oar, the so-called “yula”. Industrial fishing by means of cords was unique at that time. It was performed in the following way: an anchored buoy was placed in the centre of the catching site and a cord was attached to it. The cord had length of 200 m and was 1–3 mm in diameter. The small lead loads (11–15 g each) were fixed to the cord at intervals of every 2 m. The catcher would sail in a boat to drag the cord and start making circles near the buoy. When the cord was trapped by the open scallop valves, the molluscs would abruptly close them and affix themselves. The more often the catcher would pull the cord, the tighter the bivalves would grip the gear. On even ground, a good catcher would haul several thousand scallops. In 1919–1920, Yesso scallop in Ussuri Territory was fished by professional women-divers with the ability to stay underwater for long periods of time even in the cold autumn months. At the end of 1920’s when diving gear and motorboats equipped with dredges were introduced, greater scallop hauls were caught. When the Association for Exploiting Marine Resources was especially active the stocks rapidly diminished. After World War II industrial fishing was resumed for a short period of time but then totally banned in 1960. Yesso scallops and commercial scallops (C. albida, C. behringiana and C. chosenica) were fished using small seiners (about 300 tons displacement) on the coasts of northern Primorye, southern Sakhalin, Kurile Islands and the Bering Sea. This involves a steel dredge, which is 1.5–3.0 m wide. The dredge is towed for 5–30 min. In Kuriles, one such haul would yield 0.39–1.28 tons of shells (Kochnev 1987). In Peter the Great Bay, divers use free diving down to 5 m and SCUBA diving down to 30 m to gather Yesso scallops. 24.4.1.3 Yesso scallop landings Scallops are the most intensively consumed and fished bivalve molluscs. The best known is the Yesso scallop, M. yessoensis. For a long time these molluscs were an object of traditional catching (Tables 24.7 and 24.8). 24.4.1.3.1 Primorsky territory Yesso scallop landings in southern Primorye were apparently not recorded for a long period of time. Starting in 1919, when diver boats were introduced, scallop hauls reached the impressive figure of 400 tons. By 1920, industrial fishing grew threefold, but in subsequent years, it sharply declined and then almost stopped. A Trust for Marine
1192 Fisheries was organised in 1933 in Vladivostok with a network of enterprises all over the Soviet Far East. The new outfit resumed industrial fishing of the Yesso scallop to raise the average hauls for 1933–1937 up to 900 tons (Table 24.7). In subsequent years, the scallop was not fished and only 160 tons were landed in 1948–1949. 24.4.1.3.2 Sakhalin-Kurile region In addition to the fishing areas in southern Primorye, the Yesso scallop was harvested in Sakhalin-Kurile areas. The commercial fishing of Yesso scallops at Sakhalin and Kurile Islands by Japanese fishers occurred from the 1930’s to 1945. The main fishing area at that time was Aniva Bay. Between 1933 and 1943, annual yield was 1,000–2,300 tons. At Southern Kuriles values for landings were significantly greater (Skalkin 1966). Commercial exploitation of scallop populations after World War II was founded by Russian fishers in 1961. The scallops were only fished with dredges from small seiners (Kochnev 1993). One year later in 1962 the catch of molluscs peaked at 5,230 tons. In the four following years, because of excessive catching, the annual yields in Aniva Bay decreased to only 30 tons (Table 24.8). Although it was a stable but poorly maintained population of scallops, the commercial stock of this population was evaluated at about 3,600 t. The reason for such a decrease was the dredging method of catching scallops and in 1967 catching of scallops in Aniva Bay was banned. In 2000, after a long prohibition, commercial catching using dredging was reinstated again in Aniva Bay (Shpakova 2001b). Several years later commercial catching was banned at Southern Kuriles. At Terpenie Bay scallop landings endured for only one more year. As in Aniva Bay, annual yields were decreased because of excessive and irrational catching (Table 24.8). Between 1976 and 1984, commercial catching was reinstated and the annual yields were 9.5–282.9 tons. From 1985 to the present catching of scallops has been banned (Kochnev 1993) in Southern Kuriles. 24.4.1.4 Yesso scallop commercial stock 24.4.1.4.1 Primorsky territory The commercial reserves of natural Yesso scallops along the coast of Primorye are presently exhausted after the last decade of irrational catching and poaching. 24.4.1.4.2 Sakhalin-Kurile region Commercial populations of Yesso scallops along the coast of Sakhalin Island at Aniva and Terpenie Bays are shown on the map (Fig. 24.9). Commercial stocks at Tartar Strait have not been estimated.
1193 Table 24.7 Annual catch (metric tons*) of Yesso scallop in Primorsky Territory in 1919–1937 (Belogrudov 1981). Years 1919 1920 1923–1926 1933–1937 1948–1949 Catch 400 1,200 35 900 160 * To remove the confusion originated with using out-of-date units in first edition (Kalashnikov 1991) we shall use metrical ones.
Table 24.8 Annual catch (metric tons) of Yesso scallop at Sakhalin and Kurile Islands in 1961–1985 (by Kochnev 1993).
Years
Aniva Bay 1961 200 1962 1,800 1963 260 1964 150 1965 110 1966 30 1967 banned 1968 --1969 --1970 --1971 --1972 --1973 --1974 --1975 --1976 56 1977 70 1978 67 1979 169 1980 114 1981 117 1982 64 1983 3 1984 28 1985 banned *Experimental fishing
Regions South Kuriles Terpenie Bay ----1,230 2,200 2,010 --5,070 100 2,460 banned 1,400 --1,220 --1,410 --1,200 --600 --banned ------------------141 --102 --99 --97 16.9* 12 --12 0.5 36 --6.5 --11 --banned banned
Total catch 200 5,230 2,270 5,320 2,570 1,430 1,220 1,410 1,200 600 banned --------197 172 166 282.9 126 129.5 100 9.5 39 ---
1194 24.4.1.4.2.1 Aniva Bay In Aniva Bay, Yesso scallops are found along western and north eastern coasts at depths of 8–30 meters. Their distribution has an irregular and mosaic pattern. The total stock in Aniva Bay is estimated at 16,030 t (79.37 million scallops) with 4,970 t (15.63 million scallops) of them being of commercial stock (Shpakova 2001a). Settlement densities on bottom grounds in the bathymetric range of 7–21 meters average 4.33 specimens m-2 with an average biomass up to 0.3 kg m-2. Average shell height of the commercial molluscs (14–99%) is between 139–156 mm (Shpakova 2001a, b). 24.4.1.4.2.2 Terpenie Bay In Terpenie Bay, Yesso scallops are distributed along the north eastern coast in waters 11–20 m deep. Total stock in Terpenie Bay is estimated at 1,300 tons (2.1 million scallops) but only 600 tons of them are of commercial stock. Settlement densities on bottom grounds average 0.03 specimens m-2 with an average biomass of 0.008 kg m-2. Average shell height of the commercial molluscs is about 167.1 ± 6.9 mm at individual biomass of 518.7 ± 9.8 g. Mean age of population is about 6.9 years. 24.4.1.4.2.3 Kuriles In Kuriles, commercial assemblages of Yesso scallop are known in shallow waters of Kunashir Island and on the South Kuriles Shoal (Fig. 24.9). Total stock is specified as 40,000 t (200–300 million scallops) with about 18,000 tons of commercial stock (Ponurovsky et al. 2000; Ponurovsky and Brykov 2001). Settlement densities on bottom grounds in the bathymetric range of 5–20 m average 0.5 specimens m-2. Average shell height of the commercial molluscs (44.8% of total population) is 126.8 ± 1.1 mm. Mean age of population is 3.5 years with the maximum lifetime of 12 yr. 24.4.1.5 Commercial Chlamys scallops In addition to M. yessoensis, some scallops from the genus Chlamys have trade significance. These are less known because of their smaller size and their occurrence at depths greater than 50 m. The most abundant of them in north western Pacific are white scallops, C. albida, pink scallops, C. chosenica, and Bering Sea’s scallops, C. behringiana. The Asiatic scallops, C. asiatica, rarely occur here. 24.4.1.5.1 Primorye In Primorye, Chlamys scallops, mainly C. chosenica, form concentrations at depths between 25–250 m. Myasnikov (1982) reported three large populations of pink scallops along the northern coast of Primorye (stretching from Cape Povorotnyj to Cape Zolotoj). The highest density of settlements reaches up to 25 specimens m-2 with an average of five specimens m-2. Total stock of scallops is estimated at 420,000 tons (10.6 million scallops)
1195 located at depths of 90–100 m. Since 1990 these reserves have provided annual yields of 1,000 t (Myasnikov and Hen 1990). 24.4.1.5.2 Kurile Islands On the Kurile Islands, commercial fishing of Chlamys scallops by Japanese fishers occurred from the 1930’s to World War II (Skalkin 1975). After 1972, there was a renewal of commercial fishing. From 1972 to 1975 annual yields did not exceed 140– 1,170 t. After 1976 annual yields increased up to 1,500–3,050 t with an average of 1,990 tons. Major scallop landings (about 75% of annual yield) are derived from the Sea of Okhotsk side of Onekotan Island at depths between 50–200 m (Kochnev 1987). It is now the most stable scallop fishery in the Russian Far East region (Myasnikov et al. 1992). Two species (C. albida and C. chosenica) occur in mixed settlements. Due to an intense fishing increase the annual yields was 3,462–7,198 t with an average of 4,693 t (Table 24.9). Populations of Chlamys scallops on Onekotan Island are found on both the Sea of Okhotsk side and at pacific side of the island. On the Sea of Okhotsk side of the island scallops are distributed over depths of 40–140 m. Density of settlements on the bottom grounds are 90.0 specimens m-2 with a biomass of 6.0 kg m-2. Average density and average biomass are 2.7 specimens m-2 and 0.25 kg m-2, respectfully. On the pacific side of the island, the largest density of scallops was found between 40–100 m. Densities of settlements on bottom grounds on this side are as high as 175 specimens m-2. Total stock of Chlamys scallops in the region is estimated at 64,400 t (730.5 million scallops) with about 42,000 t of commercial stock.
Table 24.9 Annual catch (metric tons) of Chlamys scallops near Onekotan Island (Kurile Islands) in 1976–1997 (by Kochnev 1993). Year 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986
Catch 1,601 3,050 2,392 2,317 1,501 1,625 1,543 2,101 1,413 2,370 2,945
Year 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997
Catch 2,700 2,000 2,898 1,754 1,494 2,400 3,462 7,198 3,574 4,963 4,269
1196 24.4.1.5.3 In Bering Sea In the Bering Sea commercial concentrations of Bering Sea’s scallop C. behringiana are found (Myasnikov 1992). Commercial stock of scallops is estimated at 3,000 t within bathymetric range of 110–120 m. 24.4.1.6 Other Chlamys species Along with the commercial importance of Chlamys species described above there are other potential species such as the Japanese scallop, C. farreri, and the Swift’s scallop, C. swifti. 24.4.1.6.1 Chlamys farreri The Japanese scallop, C. farreri, is the most thermophilic scallop in Russian waters. It only occurs in southern Primorye (Fig. 24.6). Afreichuk (1992b) reported concentrations in Posjet Bay. The total stock is estimated at several thousand tons located at depths between 3–5 m. Commercial stock has not been estimated. This species is an object for mariculture and fishery in East Asian countries (Wang and Shieh 1991). In Russia, mainly in southern Primorye, the Japanese scallop is one of most promising species for fishery and mariculture (Bregman 1982; Afreichuk 1992a). 24.4.1.6.2 Chlamys swifti Stocks of Swift’s scallop, C. swifti, in Primorye have not been evaluated. In Aniva Bay, Swift scallops are found between 2–19 m. Average density of settlements on bottom grounds ranges from 0.04 to 5.50 specimen m-2 with an average of 0.17 specimen m-2. Biomass ranges from 3.8 to 498.8 g m-2, with an average of less than 16 g m-2. Shell height ranges between 32–114 mm with an average of 86.8 mm. Individual biomass ranges from 24 to 208 g with an average of 94.1 g. Although this species is widespread in the bay it does not form commercial aggregations because of its low density. 24.4.2 Aquaculture The Yesso scallop, M. yessoensis, is the only scallop species cultured in Russia. It is cultured in the coastal waters of Primorye in the north western part of the Sea of Japan. 24.4.2.1 History After the ban on scallop fishing in Primorye in 1962 stocks were replenished very slowly. The first steps in the mariculture of Yesso scallops in the Russian Far East occurred after 1968. In 1971, after several years of research, the first scallop farm was organised in Posjet Bay (southern Primorye). This industry reached its greatest development in Primorye in the 1980’s. In addition to the farm in southern Primorye,
1197 experimental work for spat collection was attempted in the 1970’s in Sakhalin in Bousse lagoon but further cultivation was discontinued. Mariculture at this time had financial assistance from the largest fishing enterprises of region, such as “Dal’ryba” and “Primorrybprom” and from Ministry of Fishery of the USSR. By the mid-1980’s production reached over 10 million spat a year and at least 40 million one-year-olds were settled in various sites within Posjet Bay. Since 1977, in addition to its own plantations, the Posjet farm transferred 2–10 million young scallops from other bays to other marine farms. Starting in 1983, scallop cultivators in Posjet Bay collected 30 million spat, while industrial production was only 20–50 tons. It was not until 1989 that production output exceeded 100 t (Table 24.10). In the 1990’s, during the crash of the socialist system and the disintegration of the USSR, all the created farms were bankrupted or crisis-ridden. Since the end of the 1990’s with the formation of the exchange relations in the Russian Federation, a new period in mariculture development has started. After the economic depression in 1997 the interest in mariculture has increased and a new period of economic expansion has started. 24.4.2.2 Present situation The number of scallop farms in Primorye is quickly growing (Table 24.10). There are now 20 Yesso scallop farms with a total area of more than 700 hectares of single-crop area. There are 125 hectares of hanging culture and about 600 hectares under sowing culture. The development of mariculture in the Sakhalin region has been completely terminated.
Table 24.10 Twenty years (1981–2000) annual trend in number of organisations involved in Yesso scallop culture and total production (metric tons) in Primorsky Territory. Figures have been compiled from reports of fishery organisations. Years 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990
Number of farms 3 3 3 3 4 4 4 4 5 5
Yield 9.0 4.5 18.1 38.0 10.4 48.8 62.3 64.0 196.0 122.5
Years 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000
Number of farms 5 5 5 5 6 8 9 10 18 20
Yield 153.0 150.0 155.0 110.0 113.0 22.0 60.0 131.0 99.6 91.2
1198 24.4.2.3 Marketing Almost all of scallop production from scallop farms is unprocessed. Unprocessed Yesso scallops are frozen as packed meats and a very small percentage of scallops (within 1%) are cooled in the shells. As for commercial scallops (Chlamys spp.), in most cases they are processed by canning. In Vladivostok fish stores and supermarkets, frozen meat may be sold for 280–340 rubles per kilogram (equivalent of $9.3–11.3). Cooled whole scallops are sold for 20 rubles per shell (equivalent of $0.7). For comparison, the cost of frozen beef is equivalent to $2.5–3.0 (75–90 rubles) per kg. Canned scallops (in sauce, oil and smoked) are sold for the equivalent of $2.0–4.0 (30–60 rubles) per 8 oz. In other Russian regions prices are a little bit higher. It is profitable to cultivate scallops at this price. In Vladivostok, several dozen tons are sold every year, which is highly insufficient even for the small local market. Frozen scallop meat is in high demand in spite of a high price. Yet, the scales of cultivation do not match the levels of need. 24.4.2.4 The culture methods All the methods used in the cultivation of Yesso scallops can be assigned to one of two categories: off-bottom cultivation or on-bottom cultivation. Experiments were conducted to harvest spat in closed and running controlled systems involving artificial spawning and larvae feeding. This technique is not popular because it is too complicated and expensive. Attempts were also made to create commercial scallop concentrations by using artificial reefs. The results concluded that this was an inefficient process. There are two main Japanese methods for commercial cultivation: hanging culture (cultivation of the scallop in cages) and sowing culture (cultivation on the bottom substrates of bays and inlets; Ventilla 1982). 24.4.2.4.1 Spat collection Long-line structures with plates or bags as collectors are commonly used for spat collection in Primorye. Long-lines are a series of floats (Ø 240–300 mm) connected together by horizontal lines (Ø 19–22 mm) that supports a large number of vertical ropes with attached collectors. There are two types of collectors: 1 - Conical plates of perforated plastic (Ø 250 mm) covered by mesh stockings (7–12 mm). Twenty-five collector plates are strung onto the rope (Ø 6–8 mm) as garland up to 2.5 m long. 2 - Commercial onion bags with mesh or monofilament filling (capron or polyethylene). The bags are attached in sets of ten to the rope (Ø 6–8 mm) as garland up to 5 m long. Prepared garlands of collectors are placed at depths between 5–10 m in semi-closed bays and inlets and at depths between 15–20 m in open waters. Mass scallop spawning in southern Primorye starts in mid-May. In order not to miss the settling peak, collectors are
1199 hung deep in the water for 15–20 days in early June, so the substrates would be covered with a bacterial-algal film. This is used to promote spat attachment prior to larvae settling (Belogrudov 1986). In southern Primorye settlement occurs in mid-June, 22–30 days after spawning begins. The size range of settling larvae is 250–275 µm. By the beginning of August, the spat average 3 mm in size and have growth rates of 3–4 mm per month. There is a direct relationship between larval concentrations in the plankton and spat abundance found on the collectors. At larval concentrations in the range of 20–30 larvae m-3 spatfall is about 100–400 spat per collector and at 50–100 larvae m-3 it is up to 500– 1,500 spat per collector. The long-term maximal larval concentration in plankton is 600 larvae m-3 (Belogrudov 1981). One month after settling spat size averages 10 mm. At least 200 spat have to settle in the collector in order for the result to be considered commercially profitable. In bonanza years 400–600, and even as many as 1,000 larvae can settle in a collector. In lean years, settling numbers from several to several dozen spat will make processing commercially unprofitable. 24.4.2.4.2 Intermediate culture The long-line for intermediate culture is set up similar to that of spat collector lines. Horizontal lines support a large number of vertical garlands of cages. In autumn, the collected spat (200–250 samples) are manually removed to hanging multi-tier cages (0.12 m-2). Spat are collected and directly placed in cages from a raft above the plantation. The collectors are lifted from the water to remove the substrate and spat are scraped off into vats filled with water. All foreign organisms (mostly mussels) and empty shells are removed during the transfer process. The necessary numbers of scallops are poured into cages and instantly placed back into the water. When performing this work, the scallop farmer will put a tent over the raft to protect the scallops from desiccation and the sun. In wintertime, the floating structures on which the cages are hung are placed under ice to protect them from destruction by moving ice floes. All structures are preferentially placed under the water to protect from heavy waves. By April and May, scallops grown in these cages average 25–30 mm in height. When cultivation is performed correctly the survival rate is approximately 90%. Most mortality occurs at the beginning and is due to the stress of the transfer and to the fragility of the thin shell. The viability of these scallops is dozens of times higher than in the autumn, and several methods are used to subsequently cultivate them to marketable size. At 30 mm the juveniles can be sowed in open waters. About 70% are used for sowing culture and the rest are used for hanging culture in lower density cages. 24.4.2.4.3 Transport of scallop seed When scallop seed are sold to other farms, or delivered for sowing on the bottom, they are packed up in boxes (volume 20–60 L) with perforated walls and bottoms. The boxes are put under the canvas on board a transport deck and should be instantly filled with molluscs in layers of 20–30 cm. Scallop seed should be covered with moist algae or
1200 seaweed leaves after being taken out of the water. During transportation, the boxes are replenished by outboard water every 30 minutes. Transportation is preferable when the water and air temperatures are approximately the same (about 5–10°C). In this manner, the scallops can survive for 24 hours (Table 24.11). 24.4.2.4.4 Sowing or on-bottom culture Sowing cultivation is based on the principle of transferring scallop juveniles from areas where they settled in great abundance, to bottom grounds, where they can be spread at lower density in order to obtain better growth rates and weights. Sowing culture is practised more widely in Primorye. Scallops are usually transferred after intermediate culture to bottom grounds in May and June when they are about one year old. Specific sites should be pre-selected before the sowing on sandy-silty sediments or on shingle-shell mixtures and should be without starfish (or at most 0.5 specimens m-2). The content of finely dispersed silt (particles smaller than 130 µm) shall not exceed 30%. Bottom grounds shall be at least 3 m deep in inlets protected from wave action. They should be over 10 m deep in open waters, partially protected from prevailing winds and over 20 m deep at bays opened to all winds, so that storms will not ruin the benthic habitat. Areas with natural scallop accumulations (past or present) are preferable for sowing culture. The selected sites should be established by taking bearings on shore to reference marks and then mapped. Prior to sowing the water space should be marked with buoys. The vessel should sail between the buoys at low speeds, and the one-year-old scallops will be evenly scattered all along the bottom grounds with a density of 10–20 specimens m-2. Sowed scallops usually weigh less and are 10–15 mm smaller in shell height than native scallops (Silina 1994). This difference usually continues throughout the lifetime of scallops. It is thought that the slower growth of sowed scallops from collectors or cages unfavourably affects the growth during winter and spring when the densities are high. Additionally, some of the growth inhibition results from shell breakage during transportation and sowing on the bottom. Growth of sowed scallops is further reduced while the animals adapt to their new habitat and generate new shell at the ventral margins. Depending on the temperature and other ground conditions, the scallops will grow to marketable sizes in two to four years. Survival on the sea floor will depend on predation and wave intensity and may vary from 5 to 20% within the same grounds during different cultivation cycles. In two to four years after sowing, SCUBA divers collect marketable scallops. Their productivity on shallow grounds (3–5 m deep) with densities over 10 samples m-2 amounts to 1,500–3,000 scallops hr-1. In cases of lower densities or larger depths and in turbid waters divers’ productivity will progressively decline down to only 300 scallops hr-1. 24.4.2.4.5 Hanging or off-bottom culture Hanging cultivation adds a third dimension to the essentially two-dimensional sowing culture. The crop is spread over and can utilise a much greater proportion of the water column. The long-line for intermediate culture is set up in the same manner as that for the
1201 Table 24.11 Survival rates (%) of Yesso scallops juveniles during transportation depending on temperature (Bregman 1987). Duration of transportation, h 3 5 10 15 20 25
5 98 97 95 93 92 90
10 98 96 94 92 91 88
Temperature °C 15 95 93 91 85 83 80
20 90 88 85 80 75 70
intermediate culture. They are usually set deep (5–15 m from the surface) to escape wave action and the thermocline in the summer months. There are two schemes for hanging culture: Young scallops with shell heights of 10–15 mm are placed into cages of 200–250 specimens. One-year old scallops (20–30 mm) are transferred into cages of 20–25 individuals and two-year-olds (50–70 mm) scallops of 5–7 individuals. In three years the scallops will reach the marketable size of 100 mm in height. Young scallops with shell heights of 10–15 mm are placed into cages of 20–30 individuals and in 1.5 years are transferred to cages of 5–7 specimens. The number of transfers in the second case is smaller, but there is strong fouling on cages due to the longer period of time between operations. Fouling has a negative effect on scallop growth and survival. All scallop transfer operations are performed in the spring and autumn at relatively low temperatures (about 10°C). When the work is performed correctly, survival rates average 90%. Most mortality occurs at the beginning since it is due to the stress of the transfer and to the fragility of the thin shell. Harvesting methods require lifting of cages and collecting the scallops of marketable size. Manual harvesting is time-consuming and labour intensive. It is assisted by mechanical winches for lifting lines. 24.4.2.4.6 Obstacles to mariculture development There are several obstacles to the development of mariculture in Russia: • Financial problems of protracted payback periods in mariculture and the necessity of a huge investment in equipment. Lump-sum investments for the creation of mariculture farms exceed $200,000. It is often very difficult to find investors for such a long-term project. • Ethnic and gastronomic problems because shellfish are not a traditional nourishment of the Russian people.
1202 • •
Legal problems arise from the absence of the laws regulating sea farming. Socio-economic problems concerned with undeveloped infrastructure of inshore population centres.
24.4.2.4.7 Ecological constraints associated with cultivation 24.4.2.4.7.1 Predation As mentioned earlier, young scallops are often preyed upon by various starfish species. In mariculture, when their bipinnaria larvae reach concentrations of 20 specimens m-3 in plankton or when inside collectors they develop twice as fast as the scallop spat they may cause 100% mortality (Belogrudov 1981; Gabaev 1981). During settling starfish larvae attach to the same collectors as the scallop juveniles. The average abundance of starfishes and scallops on spat collectors is shown in table 24.12. The relationship between the abundance dynamics of scallops and starfishes can be described by following equation (Gabaev 1990b): Ascallops = 128.7 + 39.4⋅Astarfishes (r = 0.82; p
