ICES mar. Sei. Symp., 199: 40-46. 1995

Distribution and biology of commercial scallops (Chlamys) in the Northwest Pacific

V. G. Myasnikov and K. A. Zgurovsky

Myasnikov, V. G., and Zgurovsky, K. A. 1995. Distribution and biology of commer­ cial scallops (Chlamys) in the Northwest Pacific. - ICES mar. Sei. Symp., 199: 40-46.

Data on the three main commercial species of scallops (genus Chlamys) in the Northwest Pacific were collected from 1980 to 1988. Chlamys behringianus forms local concentrations in the Olyutorsky Gulf and off Karaginsky Island (Bering Sea), while C. albidus forms the densest concentrations off the northern . Some stocks of C. rosealbus were found off North Primorye. Commercial concentrations of these species occur at depths of 50 to 200 m. Densities can reach 200 individuals m 2. Underwater observations showed that scallop concentrations occur on level or slightly sloped surfaces. C. rosealbus can live as long as 28 to 30 years, with maximum increase in the linear increment occurring in 3- to 4-year-old scallops. Growth from this age is satisfactorily described by the von Bertalanffy equation. Time of spawning varies from March in the Sea of through July in the Bering Sea. Individual fecundity varies from 2000 to 164000 oocytes. The greatest portion of the stomach contents is detritus (up to 70%), but diatoms, peridineas, remnants of crustacean larvae, algal spores, and sand were also found.

V. G. Myasnikov and K. A. Zgurovsky: Pacific Research Institute of Fishery and Oceanography, 4, Shevchenko Alley, Vladivostok 690600, [fax: (+7) 257 783],

Introduction has been commercially harvested since 1973 and C. rosealbus has been exploited off the Primorye coast (the Scallops are distributed in practically all seas and Sea of Japan). This article describes the distribution and oceans. In the seas of the Russian Far East, three genera main biological features of the white scallop (C. albi­ of the Family Pectinidae occur in commercial quantities: dus), the pink scallop (C. rosealbus), and the Bering Patinopecten (Mezuhopectert) yessoensis (Jay, 1856), scallop (C. behringianus), i.e. those of most interest in Swiftopecten swifti (Bernard, 1858), and five species of the Northwest Pacific. Chlamys: C. albidus (Dali, 1906; cited in Scarlato, 1981), C. behringianus (Middendorf, 1849; cited in Scar­ lato, 1981), C. farreri (Jones and Preston, 1904; cited in Materials and methods Scarlato and Kafanov, 1988), C. rosealbus (Scarlato, 1981), and C. asiatica (Scarlato, 1981) (Scarlato and The material for this article was obtained in research Kafanov, 1988). cruises conducted between 1979 and 1989 in the P. yessoensis is not abundant and only limited fishing Okhotsk, Japan, and Bering seas and off the Kuril is carried out. No concentrations of S. swifti have been Islands. Sampling was done with bottom trawls and drag found and C. asiatica is extremely rare in this area. In nets. Analysis of the catch included determination of the contrast, C. farreri forms dense concentrations in shal­ size, weight, and sex, and identification of the species. low waters in some southern Primorye bays, but com­ Observations were made from a manned submersible mercial exploitation is difficult because of the shallow (TINRO-2) on the distribution, density, behaviour, depth at which it is distributed and its attached mode of accompanying species, and ground and bottom relief. life; it has more potential as an aquaculture species Data from trawl catches and midwater observations (Bregman, 1982). were compared and from these mollusc distribution The remainder of the Chlamys genera form dense charts were generated. When determining the relation­ concentrations in many areas of the Northwest Pacific. ship between raw mass and shell height, the equation of For example, off the northern Kuril Islands, C. albidus degree of dependence was employed: y = axb. ICES mar. Sei. Symp., 199 (1995) Distribution and biology o f scallops in the Northwest Pacific 41

A Bering Sea i m » 11111"

O

- 200 miles zones of the USSR I C. behringianus III C. albidus § C. rosealbus

Figure 1. Areas where concentrations of scallops (Chlamys) are found in the Northwest Pacific.

The von Bertalanffy equation was used to describe makes it difficult to identify some of them. The morpho­ growth. Age was determined from the “annullii” logical variability of the Pectinidae was noted earlier by formed by the concentrations of scales at the shell sur­ Scarlato (1981) and Woodburn (1987). face. Age determination using the sculptural marks on In all areas studied, the character of the distributions the surface of the shell was done by calculating the was similar, but densities differed. The frequency of number of dark bands on the ligament and by determin­ scallops in the trawl catches varied from 40 to 60% ing the magnesium concentration in the shell samples; between years. The bottom relief in areas where mol­ minimum levels of magnesium correspond to slow luscs occur is usually a plain with flat uprisings, and the growth in the winter, while maximum levels reflect the distribution of individuals is either random or grouped. rapid growth that occurs during the summer (Silina et An even distribution is characteristic of younger individ­ al., 1976; Silina, 1981; Myasnikov and Kochnev, 1988; uals. Fields of adult scallops contain scallop aggre­ Silina and Pozdnyakova, 1990). Spawning time was esti­ gations varying from only 3-5 individuals up to several mated from changes in gonad index. hundred or even several thousand. On the Onekotan Island shelf (northern Kuril Islands), C. albidus aggregates either as “heaps” (with Results and discussion scallops forming several layers one upon the other), “rosettes” (with individuals gathered in a hollow, touch­ The largest scallop stock discovered was C. albidus off ing each other with their shell locks), or as “brushes” the northern Kuril Islands. Concentrations were also (with the scallops positioned on the bottom with their found off the central and southern Kurils and in the apertures up and their locks close to each other) (Fig. 2). northwestern Sea of Okhotsk. The second largest In this last case, densities can reach 200 individuals m-2. scallop stock is the C. rosealbus concentration off the Maximum density for C. albidus was difficult to calcu­ Primorye coast. The most abundant stock of C. behr­ late, as the scallops in the “heaps” form layers one atop ingianus was found in the area of Karaginsky Island and the other. For C. rosealbus, maximal density was esti­ in the Olyutorsky Gulf of the Bering Sea (Fig. 1). Distri­ mated at 25 individuals m~2 and for C. behringianus at butions of these Chlamys species overlap somewhat and 10-15 individuals m~2. In areas with complex relief there are transitional forms between the species, which (base rock), only individual scallops were observed, 42 V. G. Myasnikov and K. A. Zgurovsky ICES mar. Sei. Symp., 199 (1995)

Uniform distribution "Heaps"

Figure 2. Types of distribution of the white scallop off Onekotan Island.

although large scallops are able to concentrate in non­ taken from a depth of 75 to 175 m. Off the northern Kuril stable groups, sometimes attached to rocks (usually in Islands, C. albidus is found at 50-200 m, and on the silted places). Juveniles are almost always attached to Pacific side they are found down to a depth of 250m. pieces of wood, bivalve or gastropod shells, rocks, or Scallops do migrate and we have repeatedly observed stones (Zgurovsky and Myasnikov, 1986). high scallop activity from the submersible. Migrations to In the northern Sea of Okhotsk, white scallop juven­ some extent influence their bathymetric distribution. iles occur profusely among hydroids and moss animals Thus, if the distribution of young C. behringianus and C. which are most abundant at a depth of 30-40 m. Dense albidus does not depend on depth, as the available data scallop concentrations in the Bering Sea occur in areas indicate, juveniles of C. rosealbus and C. albidus (from dominated by pebble grounds with silt; off the Primorye the northern Sea of Okhotsk) prefer depths of less than coasts, scallops concentrate on silt and silt-and-sand 50 m - although they occur at all depths. As they grow, grounds. In the Sea of Okhotsk, scallops prefer the silt- they migrate to the shelf areas at depths of 65 to 125 m, and-sand grounds with gravel and pebbles. In all these where the main concentrations of C. rosealbus and C. areas, undersea currents of 0.1-0.3m s-1 are always albidus occur. present; maximum current speed was observed off In areas of mass concentrations in the studied areas, Onekotan Island, where it reached 0.5m s-1. fairly high oxygen levels are observed (up to 4.7- Chlamys genera inhabit depths of 15 to 400 m, but C. 7.5mgl-1) and the salinity varies from 33.05 to rosealbus in the Bay of Peter the Great (Petra Velikogo 34.10ppm. The temperature range at which these scal­ Bay) (Sea of Japan) occurred at a depth of up to 2030 m lops occur is fairly broad (from —1.9 to 13.03°C), but (Scarlato, 1981). In the Sea of Japan, the main C. roseal­ maximum concentrations are observed at a temperature bus concentrations occur at depths of 50-150 m; in the of 1-3°C. Bering Sea the largest catches of C. behringianus are It may be necessary for scallops to concentrate in i c e s mar. s d . Symp., 199 (1995) Distribution and biology o f scallops in the Northwest Pacific 4 3

Table 1. Parameters of the von Bertalanffy growth equation for scallops (Chlamys) in the Northwest Pacific. 1+ 3 Species H„„ ± m K ± m 0

C. rosealbus 112.5 ± 3.2638 0.0912 ± 0.0087 -0.9326 ± 0.3746 C. behringianus 94.2 ± 1.1095 0.1275 ± 0.0064 -0.1385 ±0.0215 C. albidus Onekotan Island Okhotsk Sea coast 109.0 ± 3.2678 0.2220 ± 0.0206 0.6242 ± 0.0446 Pacific coast 84.9 ± 1.6288 0.1995 ±0.0186 0.1483 ± 0.2358 C. albidus Northern Okhotsk Sea 79.3 ± 0.6952 0.2010 ± 0.0089 -0.0433 ± 0.1178

order to spawn successfully. It has been suggested that decreases in catches of Placopecten magellanicus are 110 related to a reduction in the number of juveniles caused by intensive fishing of the adult population (Gaudet and

Belanger, 1987). E E The life span of the species we have studied is 28 to 30 70 j z o> years (Myasnikov and Kochnev, 1988), considerably CD I higher than reported for Chlamys in other areas. In Q) Broom’s review (1976), the maximum age of Atlantic scallops was cited as 2-6 years, and according to Denisenko (1979) the life span of C. islandicus off the eastern Murmansk coasts (Barents Sea) does not exceed 15 or 16 years. Other members of the Pectinidae family frequently reach 20-25 years or more (Hennick, 1970; Gruffydd, 1974; MacDonald, 1986). 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 Scallop growth, starting from the age of 2 or 3 years, is Years well described by the von Bertalanffy equation. In Table Figure 3. Growth curves of scallops in areas of the Northwest 1, the calculated coefficients of the von Bertalanffy Pacific. 1 = C. albidus off the Okhotsk Sea coast of Onekotan equations are given. As noted earlier, growth rates in Island; 2 = C. albidus off the oceanic coast of Onekotan Island; 3 = C. behringianus in Olyutorsky Bay in the Bering Sea; 4 = C. the white scallop differ not only between populations, rosealbus in the Sea of Japan; 5 = C. albidus, the northern part but also among habitats and year classes (Myasnikov of the Sea of Okhotsk. and Kochnev, 1988). Figure 3 shows scallop growth curves in some areas of the Northwest Pacific. Because of different rates of growth at different life stages, three stages of linear growth were distinguished: juvenile, The highest growth rate (linear increments up to mature, and senile, as has been used with other bivalves 18 mm yr” 1) among the far eastern scallops is observed (Zolotaryov and Selin, 1983; Zolotaryov, 1989). The in C. albidus from the Sea of Okhotsk coast of Onekotan variation in annual linear increments is clearly seen in Island. The smallest increments in this species (up to Figure 4. Scallop growth is greatest from approximately 12 mm yr-1) are found in scallops off Island the third through the fifth year, after which there is a (the central Kurils) (Myasnikov and Kochnev, 1988). decrease in linear increment. After reaching about 10 The relationship between body weight and shell height years of age, the increment remains almost constant and and the parameters of the growth equations for the does not exceed 0.5-1.5mm yr_1. Thus, growth in shell Chlamys scallops in the Northwest Pacific are given in height practically stops; there is continued thickening of Figure 5 and Table 2. The dependence character for the the shell’s edge, making the shell more convex. These majority of species is similar. Only C. behringianus is features are characteristic of the presence of the senile any different, having an unusually high regression coef­ stage. This change in the shape of the shell of the white ficient (3.75). scallop takes place at 6-18 years of age (average of 10 In most areas, it is usual for large adults to dominate years of age), at a shell size of 70-100mm (average the catch (Fig. 6). This is partially related to the poor about 90 mm). Both valves are affected, so the shells of catchability of juveniles with the fishing gear that is used. those individuals are quite protuberant. This senile stage However, it may also be indicative of weak recruitment. represents 23% of the entire catch of C. albidus off The large number of dead scallops found in areas with­ Onekotan Island (Myasnikov and Kochnev, 1988). out live individuals testifies to uneven recruitment. 44 V. G. Myasnikov and. K. A. Zgurovsky ICES mar. Sei. Symp., 199 (1995)

(mm) . 3

250 -

200

-j? 150

£ çn a) ^ 100 Years Figure 4. Curves (1, 2) of individual growth and linear increments of C. albidus off Onekotan Island. Arrows show time and size when variation in the curve of the shells takes place. 50

When examining the age structure of the catch, it was 10 also found that mature individuals dominated. In C. rosealbus concentrations off the Primorye coast (Sea of Japan), 7- to 12-year-olds prevailed. Off Onekotan Height (mm) Island, where C. albidus is distributed, 2- to 10-year-olds Figure 5. Relationship between body weight and height of are dominant, probably because of the removal of the shell. 1 = C. albidus off the Okhotsk Sea coast of Onekotan adults in the commercial fishery. The proportion of the Island; 2 = C. albidus off the oceanic coast of Onekotan Island; animals older than 15 years in all populations is insignifi­ 3 = C. behringianus in Olyutorsky Bay in the Bering Sea; 4 = C. rosealbus in the Sea of Japan. cant (Fig. 7). The sex ratio in the populations of C. albidus varies considerably - from 0.6:1.0 to 2.0:1.0 (females to males). In C. behringianus and C. rosealbus, the ratio is benthos is poor compared to other areas of the shelf. close to 1.0:1.0. Sexual maturity in these scallops occurs The scallops normally dominate, but Ophiactidae, by the age of 3-5 years at a shell height of 30-70mm. Ophiolepididae, Gorgonocephalidae, and sea urchins of Spawning in C. rosealbus takes place in March and the genus Strongylocentrotus also occur. Off the Pri­ April. C. albidus spawns in June off the northern Kurils morye coast, the pink scallop is common in the areas and C. behringianus spawns in late June and July. The almost completely occupied by Brachiopoda, whose fecundity of this latter species (from 2000 to 164000 density is an order of magnitude higher. Molluscs occur oocytes) is considerably lower than that of P. yessoensis, less often with sea lilies (Heliometra sp.), sponges, star­ whose gonads contain an average of 100-170 million fishes, holothurias, and hydroids. In the Bering Sea and oocytes (Yamamoto, 1964). Average individual fe­ off the Kuril Islands, in the zone of scallop concen­ cundity is greatest for C. rosealbus (47500 oocytes) trations, large cup sponges frequently occur, as well as and smallest for C. behringianus (32 300 oocytes). holothurians and starfishes of the Asteriidae, Astropec- An examination of stomach contents revealed mostly tinidae, and Solasteridae families. detritus (up to 70% of the contents); Diatomea and The fauna of the organisms encrusting the scallops is Peridinea also occur frequently, but remnants of crus­ also diverse, with the sponges Mycale adhaereus and tacean larvae, seaweed spores, and sand were less Myxilla parasitica being the most common; hydroids, common. barnacles, moss animals, seaweeds, Actinias, bivalves, Underwater surveys showed that in areas of dense and gastropods are rarer. The organisms living both on scallop habitation the specific composition of the macro- and near the scallops compete not only for space, but for i c e s mar. Sei. Symp., 199 (1995) Distribution and biology of scallops in the Northwest Pacific 4 5

Table 2. Parameters of the dependence equation of body weight on shell height for scallops (Chlamys) in the Northwest Pacific.

Species lna ± m b ± m r n

C. rosealbus -9.6051 ± 0.0024 3.19 ± 0.0005 1.000 1107 C. behringianus -11.6542 + 0.0680 3.75 ± 0.0162 0.999 197 C. albidus Onekotan Island Okhotsk Sea coast -9.2805 ± 0.2953 3.14 ± 0.0679 0.978 100 Pacific coast -8.6632 ±0.1645 2.97 ± 0.0395 0.992 100 C. albidus Northern part of the Okhotsk Sea -10.8024 ± 0.0200 3.37 ± 0.0490 0.999 150

crabs, benthophagous fishes, starfishes, octopuses, and 50 gastropods. In other areas of the world, the scallops’ enemies include crabs, starfishes, and flatfishes (Mar- chall, 1960, cited in Broom 1976; Naidu, 1987; Paul et 30 al., 1987). In intertidal waters, many scallops are de­ stroyed by seagulls (Gutsell, 1930, cited in Broom, :r~‘ 1976). 10 Commercial stocks of all types of Chlamys scallops have been found only near the northern and north­ 10 30 50 70 90 110 western coasts of the far eastern seas, where there are Shell Height (mm) similar environmental conditions: cold currents, water Figure 6. Size structure of some scallop populations. 1 = C. dynamics, a cold intermediate layer at depths of 50- albidus off the Okhotsk Sea coast of Onekotan Island; 2 = 200 m, similar grounds, etc. C. albidus off the oceanic coast of Onekotan Island; 3 = C. The distribution of the molluscs is characterized by a behringianus in Olyutorsky Bay in the Bering Sea; 4 = C. rosealbus in the Sea of Japan; 5 = C. albidus in the northern high degree of aggregation or by more random types of part of the Sea of Okhotsk. distribution. Scallops are found in aggregations ranging from 3-5 to several thousands of individuals. Growth of molluscs from the age of 2-3 years is well described by the von Bertalanffy equation. As the rate

26 of growth of different stages of ontogenesis changes, three stages of linear growth can be separated: juvenile (up to 3-5 years of age), mature (until 10 years of age), and senile (over 10 years of age). a - 14 Thus, fairly slow growth and low fecundity are charac­ teristic of the Chlamys scallops of the Northwest Pacific. 8 In spite of the high scallop concentrations in some parts of the far eastern seas, it is vital to approach the prob­ 2 lems of commercial harvesting with special care. In our 2 4 6 8 10 12 14 16 18 20 22 24 26 28 opinion, for each population, the volume of the catch Years and the periods when the areas are fished should be Figure 7. Age structure of scallops in some areas of the North­ west Pacific. 1 = C. rosealbus concentrations of the Primorye determined. We recommend that fishing be barred from coast (Sea of Japan); 2 = C. albidus off the oceanic coast of designated areas, so that the populations can be con­ Onekotan Island; 3 - C. behringianus from Olyutorsky Bay in trolled. the Bering Sea.

food as well. However, encrusting organisms can also increase local turbulence, which seems to increase the References flow of food. Ophiopholis aculeata in some areas of the Bernardi, M. 1858. Descriptions d’espèces nouvelles. J. northern Kurils covers the scallops (C. albidus) and Conch., T. 7, pp. 90-94, pl. 1, 2. the ground creating a “net” with its rays. Among the Bregman, Yu. E. 1982. Biology and cultivation of scallop most serious competitors of Chlamys opercularis for Chlamys farreri nipponensis. Biologiya shelfovykh zon Miro- vogo okeana. Tez. dokl. II Vses. konf. po morskpy biologii. space are the Ophiurianidae (Askew et al., cited in Vladivostok, 3: 58-60 (in Russian). Broom, 1976). Among the scallop predators in the far Broom, M. J. 1976. Synopsis of biological data in scallops eastern seas, the most significant are the paralithodes Chlamys (Aequipecten) opercularis (Linnaeus), Agropecten 46 V. G. Myasnikov and K. A. Zgurovsky ICES mar. Sei. Symp., 199 (1995)

irradians (Lamarck), Agropecten gibbus (Linnaeus). FAO Scarlato, O. A. 1981. Bivalvia molluscs of the west Pacific Fish. Synop., 114. 44 pp. moderate latitudes. M. Nauka Publishers. 462 pp. (in Denisenko, S. G. 1979. The life longevity and growth of the Russian). Iceland scallop off the west Murman coast. Biologicheskie Scarlato, O. A., and Kafanov, A. I. 1988. An addition to the problemy Severa. Tez. dokl. VIII Symp. Appatity 107-108 fauna of the bivalvia molluscs of the USSR far eastern seas. (in Russian). Zool. Zhur., 67: 937-942 (in Russian). Gaudet, M ., and Belanger, M. 1987. The giant scallop (Placo- Silina, A. V. 1981. Regulations of the sculpture marks for­ pecten magellanicus) from the lower north shore of the Gulf mation in the scallop shells of the far eastern seas. Biologi­ of St Lawrence (Quebec, Canada): biological characteristics cheskie resoursy shelfa, ih ratsionalnaya ekspluatatsiya i and aquacultural potential. ICES CM 1987/K: 3. zashchita. Tez. kokl. Vladivostok, 144-146 (in Russian). Gruffydd, U. D. 1974. An estimate of natural mortality in an Silina, A. V., Krasnov, E. V., and Yavnov, S. V. 1976. Period­ unfished population of the scallop Pecten maximus (L). J. ical character of some bivalvia molluscs’ growth in the far Cons. int. Explor. Mer, 35: 209-210. eastern seas. Biologia morya, Vladivostok 4: 32-37 (in Hennick, D. 1970. The weathervane scallop fishery of Alaska Russian). with notes on occurrence in Washington and Oregon. 22nd Silina, A. V., and Pozdnyakova, L. A. 1990. Growth of the Ann. Rep. Pacific Mar. Fish. Comm., 1969, pp. 33-34. scallop Chlamys rosealbus in the Sea of Japan. Biologiya Portland, Oregon. morya, Vladivostok, 1: 37-42 (in Russian). Jay, J. G. 1856. Report of the shells collected by the Japan Woodburn, L. 1987. Variation in Australian Pecten. The VI expedition with a list of Japan shells. Narrative of the ex­ International Pectinid Workshop, Menai Bridge, Wales, peditions of an American squadron to the China Sea and April 9-14,1987. ICES 1987/K: 3. Japan in 1852-1854, under the command of Commodore Yamamoto, G. 1964. Studies on the propagation of the scallops M. C. Perry Washington, 2. 291 pp. Patinopecten yessoensis (Jay) in Mutsu Bay. Nippon Suisan MacDonald, B. A. 1986. Production and resource partitioning shigon ho go Kuokai, Suisan Zoyashoku Sosho, 6: 1-77. in the giant scallop Placopecten magellanicus grown on the Zgurovsky, K. A., and Myasnikov, V. G. 1986. Study of the bottom and suspended culture. Mar. Ecol. Prog. Ser., 34: behavior and stock structure of the commercial invertebrates 79-86. using the “TINRO-2” submersible. Povedenie vodnykh bes- Myasnikov, V. G ., and Kochnev, Yu. R. 1988. Duration of life pozvonochnykh. Materialy IV Vsesoyuznogo Simpoziuma. cycle, growth and sex structure of the white scallop Chlamys Borok. 1983. Andropov 14—18 (in Russian). albidus off the Kuril Islands. Morskie promyslovye bespoz- Zolotaryov, V. N. 1989. Sclerochronology of the marine bival­ vonochnye. Sbornik trudov VNIRO. M., 153-156 (in via molluscs. Naukova Dumka Publishers, Kiev. 112 pp. (in Russian). Russian). Naidu, K. S. 1987. Predation of scallops by American plaice, Zolotaryov, V. N., and Selin, N. I. 1983. The age variation of Hippoglossoidesplatessoides. ICES CM 1987/K: 3. the grey mussel shell morphology. Biologiya midii Greya. M. Paul, I. D., Lake, N. C. H., Jones, M. B., and MacMillan, J. Nauka Publishers, pp. 73-82 (in Russian). 1987. Scallop predation by crabs in relation to the develop­ ment of on-bottom cultivation. ICES CM 1987/K: 3.